AQA BIOLOGY A LEVEL PPQS

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Lactase is an enzyme. Lactose is a reducing sugar. Describe how you could use the biuret test to distinguish a solution of the enzyme, lactase from a solution of lactose. Explain the result you would expect with the enzyme. (2)

(Add Biuret reagent to both solutions) 1. Lactase / enzyme will give purple / lilac / mauve; OR 1. Lactose / reducing sugar will not give purple / lilac / mauve / will remain blue; 2. Lactase / enzyme is a protein;

Organelle X is a mitochondrion. What is the function of this organelle? (1)

(Aerobic) respiration;

The rise and fall in blood pressure in the aorta is greater than in the small arteries.Suggest why. (3)

(Aorta) 1. (is) close / directly linked to the heart / ventricle / pressure is higher / is very high; 2. (Aorta has) elastic tissue; 3. (Aorta has) stretch / recoil.

Give two ways in which the structure of starch is similar to cellulose. (2)

(Both) 1. Are polymers / polysaccharides / are made of monomers / of monosaccharides; 2. Contain glucose / carbon, hydrogen and oxygen; 3. Contain glycosidic bonds; 4. Have 1−4 links; 5. Hydrogen bonding (within structure).

What is an allele? (1)

(Different) form/type/version of a gene / different base sequence of a gene;

The volume of blood leaving the capillary network into the veins is less than the volume of blood entering from the arteries. Explain why. (1)

(Fluid) in tissue fluid / (fluid) in lymph.

When insulin binds to receptors on liver cells, it leads to the formation of glycogen from glucose. This lowers the concentration of glucose in liver cells. Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose concentration. (2)

(Formation of glycogen) 1. Glucose concentration in cell/liver falls; 2. Below that in blood (plasma)/ higher in blood; 3. Creates/maintains glucose concentration/diffusion gradient; 4. Glucose enters cell/leaves blood by facilitated diffusion/via carrier(protein)/channel (protein);

Describe how the Golgi apparatus is involved in the secretion of enzymes. (1)

(Golgi apparatus) modifies (protein) OR packages / put into (Golgi) vesicles OR transport to cell surface / vacuole;

What is a tissue? (1)

(Group of) similar/identical cells / cells with a common origin.

Explain what is meant by a phylogenetic group (1)

(Grouped according to) evolutionary links/history/relationships / common ancestry;

Explain what is meant by a phylogenetic group. (1)

(Grouped according to) evolutionary links / history / relationships / common ancestry;

Homologous chromosomes carry the same genes but they are not genetically identical. Explain why (1)

(Homologous chromosomes) carry different alleles;

What is selective breeding? (1)

(Humans breed) organisms with certain/chosen characteristics/alleles;

Why is the genetic code described as being universal? (1)

(In all organisms/DNA,) the same triplet codes for the same amino acid;

Different species occupy different ecological niches. Explain the advantage of species occupying different niches. (1)

(Less) competition for food/resource;

.A principle of homeostasis is the maintenance of a constant internal environment. An increase in the concentration of carbon dioxide would change the internal environment and blood pH. Explain the importance of maintaining a constant blood pH (3)

(Maintaining constant pH to avoid) 1. Named protein / enzyme (in blood) sensitive to / affected by change in pH; 2. (Resultant) change of charge / shape / tertiary structure; 3. Described effect on named protein or enzyme. e.g. less oxygen binds with haemoglobin / less transport across membranes / fewer substrates can fit active site / fewer enzyme-substrate complexes.

What is a pathogen? (1)

(Micro)organism that causes disease / harm to body / an immune response;

Efficient exchange of substances in the capillaries is linked to the rate of blood flow. Explain how (1)

(More) time for exchange of substances;

Blood flow in capillaries is slow. Give the advantage of this (1)

(More) time for exchange/diffusion (of substances);

Explain what is meant by the ecological term population. (1)

(Number of) organisms of one species in a habitat / same place;

The enzyme-catalysed reactions activated by ATR only occur if the substrates have been phosphorylated. Use your knowledge of energy changes in enzyme-catalysed reactions to suggest why (1)

(Phosphorylation/phosphate) makes substrates more reactive/raises their energy level(s)/lowers activation energy for the reaction;

The mitochondria all have very similar shapes in this cell. Explain why they appear to have different shapes in this drawing (1).

(Sections cut at) different angles / in different planes.

Name the process by which oxygen passes from an alveolus in the lungs into the blood. (1)

(Simple) diffusion;

Give two ways in which the structure of starch is different from cellulose (2).

(Starch) 1. Contains α / alpha glucose; 2. Helical / coiled / compact / branched / not straight; 3. 1,6 bonds / 1,6 branching; 4. Glucoses / monomers same way up; 5. No H-bonds between molecules; 6. No (micro / macro) fibres / fibrils.

What is the proteome of a cell? (1)

(The proteome is the full) range of / number of different proteins that a cell is able to produce (at a given time) OR (The proteome is the full) range / number of different proteins the genome / DNA is able to code for.

What is a homologous pair of chromosomes? (1)

(Two chromosomes that) carry the same genes;

What is a monomer? (1)

(a monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made;

Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the advantage of mitochondria in muscle cells having more cristae. (2)

(more cristae / larger surface area) for electron transport chain / more enzymes for ATP production / oxidative phosphorylation; muscle cells use more ATP (than skin cells)(not just more respiration);

Explain the difference between pre-mRNA and mRNA. (1)

(pre-mRNA) contains introns / mRNA contains only exons;

Describe the function of DNA helicase. (1)

(unwinding DNA) and breaking hydrogen bonds / bonds between chains / bases / strands.

Many different substances enter and leave a cell by crossing its cell surface membrane. Describe how substances can cross a cell surface membrane. (5)

1 (Simple / facilitated) diffusion from high to low concentration / down concentration gradient; 2 Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer; OR 2. Large / polar / water-soluble molecules go through proteins; 3 Water moves by osmosis / from high water potential to low water potential / from less to more negative water potential; 4 Active transport is movement from low to high concentration / against concentration gradient; 5 Active transport / facilitated diffusion involves proteins / carriers; 6 Active transport requires energy / ATP; 7 Ref. to Na+ / glucose co-transport;

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them. (5)

1 Many alveoli / alveoli walls folded provide a large surface area; 2 Many capillaries provide a large surface area; 3 (So) fast diffusion; ________________________________________________ 4 Alveoli or capillary walls / epithelium / lining are thin / short distance between alveoli and blood; 5 Flattened / squamous epithelium; 6 (So) short diffusion distance / pathway; 7 (So) fast diffusion; ________________________________________________ 8 Ventilation / circulation; 9 Maintains a diffusion / concentration gradient; 10 (So) fast diffusion;

Adding antibiotics to the food of cattle is now banned in many countries. Use your knowledge of selection to explain why adding antibiotics was banned. (2)

1. (Adding antibiotics) selects in favour of antibiotic resistance/resistant bacteria more likely to survive; 2. Increase in numbers/higher proportion of resistant bacteria; 3. May infect humans/may spread resistance to other species/ horizontal transfer;

Explain the advantage to a person with anaemia of the change shown in the oxygen dissociation curve. (curve shifted to left) (3)

1. (Anaemia curve shifted to right) haemoglobin has lower affinity for oxygen / binds less tightly; 2. releases more oxygen / oxygen is released quicker / oxygen dissociates/ unloads more readily to muscles/tissues/cells; 3. (For) respiration;

The thickness of the aorta wall changes all the time during each cardiac cycle. Explain why (3)

1. (Aorta wall) stretches because ventricle / heart contracts / systole / pressure increases; 2. (Aorta wall) recoils because ventricle relaxes / heart relaxes / diastole / pressure falls; 3. Maintain smooth flow / pressure

Scientists investigated the benefits of breast milk compared with formula milk. (a) The scientists used kittens (newborn cats) as model organisms in their laboratory investigation. Other than ethical reasons, suggest two reasons why they chose to use cats as model organisms. (2)

1. (Are mammals so) likely to have same physiology / reactions as humans; 2. Small enough to keep in laboratory / produce enough milk to extract; 3. (Can use a) large number.

Describe the processes involved in the transport of sugars in plant stems (5)

1. (At source) sucrose is actively (transported) into the phloem/sieve element/tube; 2. By companion/transfer cells; 3. Lowers water potential in phloem/sieve element/tube and water enters by osmosis; 4. (Produces) high (hydrostatic) pressure; 5. Mass flow/transport towards sink/roots/storage tissue; 6. At sink/roots sugars are removed/unloaded;

What is the function of the coronary arteries? (2)

1. (Carry) oxygen/glucose; 2. (To) heart muscle/tissue/cells/myocytes;

Scientists studied two species of North American seahorse. They thought that these two species are closely related. Describe how comparisons of biological molecules in these two species could be used to find out if they are closely related. (6)

1. (Compare) DNA; 2.Sequence of bases / nucleotides; 3. Compare same / named protein; 4. Sequence of amino acids / primary structure; 5. Inject (seahorse) protein / serum into animal; 6. (Obtain) antibodies / serum; 7. Add protein / serum / plasma from other (seahorse) species; 8. Amount of precipitate indicates relationship;

The complementary strand is made in the same way as a new complementary strand is made during semi-conservative replication of human DNA. Describe how the complementary strand of HIV DNA is made. (3)

1. (Complementary) nucleotides/bases pair OR A to T and C to G; 2. DNA polymerase; 3. Nucleotides join together (to form new strand)/phosphodiester bonds form;

Describe how altered DNA may lead to cancer. (6)

1. (DNA altered by) mutation; 2. (mutation) changes base sequence; 3. Of gene controlling cell growth / oncogene / that monitors cell division; 4. Of tumour suppressor gene; 5. Change protein structure / non-functional protein / protein not formed; 6. (Tumour suppressor genes) produce proteins that inhibit cell division; 7. Mitosis; 8. Uncontrolled / rapid / abnormal (cell division); 9. Malignant tumour;

Describe the role of two named enzymes in the process of semi-conservative replication of DNA. (3)

1. (DNA) helicase causes breaking of hydrogen/H bonds (between DNA strands); 2. DNA polymerase joins the (DNA) nucleotides; 3. Forming phosphodiester bonds;

Explain how a sports drink could provide an energy boost when running. (3)

1. (Drink) contains carbohydrates / sugars so High GI / (drink) contains carbohydrates / sugars so raises blood glucose concentration quickly; 2. Contains salt so glucose more rapidly absorbed; 3. Increases glucose to muscles for respiration; 4. More / faster respiration so more / faster energy release;

An enzyme catalyses only one reaction. Explain why (2)

1. (Enzyme has) active site; 2. Only substrate fits (the active site);

What is meant by the term phenotype? (2)

1. (Expression / appearance / characteristic due to) genetic constitution/genotype/allele(s); ] 2. (Expression / appearance / characteristic due to) environment;

Not all mutations result in a change to the amino acid sequence of the encoded polypeptide. Explain why. (1)

1. (Genetic) code degenerate; 2. Mutation in intron.

Explain the advantage to people living at high altitude of having the oxygen dissociation curve shown in the graph. (curve shifted to the right) (2)

1. (Haemoglobin) has lower affinity for oxygen / more oxygen released; 2. In/to the cells/ tissues;

At birth 98% of the haemoglobin is HbF. By the age of 6 months, the HbF has usually completely disappeared from the baby's blood and been replaced by HbA. Use Figure 5 to explain why this change is an advantage for the baby. (2)

1. (HbA has) lower affinity for O2 at low partial pressures; OR 1. (HbA has) lower affinity for oxygen at pp found in tissues; 2. Easier unloading of O2 for (aerobic) respiration;

High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries. This can lead to a build-up of tissue fluid. Explain how (2)

1. (Higher salt) results in lower water potential of tissue fluid; 2. (So) less water returns to capillary by osmosis (at venule end); OR 3. (Higher salt) results in higher blood pressure/volume; 4. (So) more fluid pushed/forced out (at arteriole end) of capillary;

In humans, substances move out of the capillaries to form tissue fluid. Describe how this tissue fluid is returned to the circulatory system. (3)

1. (Hydrostatic) pressure lower in capillary/blood / higher in tissues/tissue fluid; 2. Water (returns); 3. By osmosis; 4. Water potential lower/more negative in blood/capillary / higher/less negative water potential in tissues / via water potential gradient; 5. Due to protein (in blood); 6. (Returns) via lymph (system/vessels)

Monosaccharides and disaccharides taste sweet. The lactose-free milk made after hydrolysis with lactase tastes sweeter than the cow's milk containing lactose. Suggest why. (2)

1. (Lactose hydrolysed to) galactose and glucose; 2. (So) more sugar molecules; 3. (So) more / different receptors stimulated / sugars produced are sweeter (than lactose).

The ecologists noted that the species of birds surviving on the coldest islands had a larger body size than those surviving on warmer islands. Explain how a larger body size is an adaptation to a colder climate. (2)

1. (Larger birds have) a low(er) SA:VOL; 2. (So) less heat loss / more heat retained;

It is important that mammals maintain a constant core temperature. Explain why (3)

1. (Maintain) optimum temperature for enzymes; 2. If temperature rises (above normal/optimum), enzyme activity falls; 3. If temperature falls (below normal), then low kinetic energy/fewer enzyme-substrate collisions; 4. Maintains (high) rate of (biochemical) reactions/metabolic rate/respiration;

Human breast milk is produced and secreted by gland cells. These gland cells have adaptations that include many mitochondria and many Golgi vesicles. The milk contains a high concentration of protein. Explain the role of these cell adaptations in the production and secretion of breast milk. (2)

1. (Many mitochondria) release energy / ATP for movement of vesicles / synthesis of protein / active transport; 2. (Many Golgi) vesicles transport protein / glycoprotein / milk to cell membrane / out of cell;

For each structure you identified in part , explain how it is an adaptation to make possible the rapid absorption of glucose (Microvilli; Mitochondria; Vesicles;)

1. (Microvilli) increased / large / bigger (surface) area (for transport proteins / for diffusion); 2. (Mitochondria) to supply ATP/energy, for active transport / cotransport; 3. (Vesicles) to bring carrier proteins to membrane;

Give box two similarities in the movement of substances by diffusion and by osmosis (2)

1. (Movement) down a gradient / from high concentration to low concentration; 2. Passive / not active processes; OR 3. Do not use energy from respiration / from ATP / from metabolism; OR 4. Use energy from the solution;

Explain the importance of muscle fibres in the wall of an arteriole. (2)

1. (Muscle) contracts; 2. (Arteriole) constricts / narrows/alters size of lumen / reduces/regulates blood flow (to capillaries);

An arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries (2)

1. (Muscle) contracts; 2. (Arteriole) narrows/constricts/reduces size of lumen/vessel / vasoconstriction;

Mutation 1 leads to the production of a non-functional protein. Explain why. (3)

1. (Mutation) changes triplets/codons after that point/causes frame shift; 2. Changes amino acid sequence (after this)/codes for different amino acids (after this); 3. Affects hydrogen/ionic/sulfur bond (not peptide bond); 4. Changes tertiary structure of protein (so nonfunctional);

Use the information in the figure above to explain how tissue fluid is formed. (2)

1. (Overall) outward pressure of 3.2 kPa; 2. Forces small molecules out of capillary.

Describe how bacteria are destroyed by phagocytes (3)

1. (Phagocyte engulfs) to form vacuole / vesicle / phagosome; 2. Lysosome empties contents into vacuole / vesicle / phagosome; 3. (Releasing) enzymes that digest / hydrolyse bacteria;

The demand for increased food production has led to areas of heath being used to grow wheat. Explain the effect of this on the species diversity of animals. (2)

1. (Reduced) as less variety of food sources; 2. (Reduced) as fewer habitats/niches; 3. (Reduced) by pesticides/chemicals;

Give two ways in which pathogens can cause disease. (2)

1. (Releases) toxins; 2. Kills cells / tissues

Cells that secrete enzymes contain a lot of rough endoplasmic reticulum (RER) and a large Golgi apparatus. (i) Describe how the RER is involved in the production of enzymes. (2)

1. (Rough endoplasmic reticulum has) ribosomes; 2. To make protein (which an enzyme is);

Describe how you could use the emulsion test to show the presence of oil in a sample of fish. (3)

1. (Shake with) ethanol / alcohol; 2. Then add (to) water; 3. White / milky / cloudy (layer indicates oil).

There are large numbers of mitochondria in this cell. Explain how these organelles help the cell to absorb the products of digestion (2).

1. (Site of aerobic) respiration / ATP production / energy release; 2. Active transport / transport against the concentration gradient;

There are lots of mitochondria in this cell. Explain why. (2)

1. (Site of aerobic) respiration; 2. Release ATP / energy; 3. Active transport / transport against the concentration gradient / protein synthesis / exocytosis;

Suggest how the flow of some of the blood between the aorta and pulmonary artery could cause children to die in the first 12 months. (3)

1. (Some) oxygenated blood (from the aorta) flows into pulmonary artery; OR 1. Less oxygenated blood flows out through aorta; OR 1. Lower blood pressure in aorta; 2. Less oxygen delivered to cells / tissues / organs / named organ / via named blood vessel; 3. So less/not enough oxygen for aerobic respiration (in cell/ tissue/organ); 4. Tissue/organ doesn't grow/develop properly (causing death); OR 4. Tissue dies/organ stops working (causing death);

Explain the role of independent segregation in meiosis. (2)

1. (To provide) genetic variation; 2. (Allows) different combinations of maternal and paternal chromosomes / alleles;

Explain the role of independent segregation in meiosis (2)

1. (To provide) genetic variation; 2. (Allows) different combinations of maternal and paternal chromosomes/ alleles; 3. (To produce) haploid cells/half the chromosome number; 4. (Allows) homologous chromosomes/ homologous pairs to arrange randomly (at equator/middle of cell)/separate;

Atheroma makes it more likely that a blood clot will form. Describe how a blood clot may lead to a myocardial infarction. (3)

1. (Trapped in) coronary artery/artery supplying heart muscle/ tissue/cells; i.e. material of heart wall 2. Prevents oxygen; 3.Reaching (heart muscle/tissue); 4. (Heart muscle) dies/stops respiring;

A mutation of a tumour suppressor gene can result in the formation of a tumour. Explain how. (2)

1. (Tumour suppressor) gene inactivated / not able to control / slow down cell division; 2. Rate of cell division too fast / out of control.

Describe the induced-fit model of enzyme action (2)

1. (before reaction) active site not complementary to/does not fit substrate; 2. Shape of active site changes as substrate binds/as - complex forms; 3. Stressing/distorting/bending bonds (in substrate leading to reaction);

Blood leaving the kidney eventually returns to the kidney.Describe the pattern of blood circulation in a mammal that causes blood to return to the kidney. (6)

1. (blood flows from kidney along) renal vein to vena cava; 2. (along) vena cava to RIGHT atrium/side of heart; 3. (along) pulmonary artery to lungs; 4. (along) capillaries to pulmonary vein; 5. (along) pulmonary vein to RIGHT atrium/side of heart; 6. (along) aorta to renal artery (to kidney); 7. Blood may pass through several complete circuits before returning to kidney

Blood leaving the kidney eventually returns to the kidney. Describe the pattern of blood circulation in a mammal that causes blood to return to the kidney. (6)

1. (blood flows from kidney along) renal vein to vena cava; 2. (along) vena cava to right atrium/side of heart; 3. (along) pulmonary artery to lungs; 4. (along) capillaries to pulmonary vein; 5. (along) pulmonary vein to left atrium/side of heart; 6. (along) aorta to renal artery (to kidney); 7. Blood may pass through several complete circuits before returning to kidney;

Explain how tissue fluid is formed and how it may be returned to the circulatory system. (5)

1. (hydrostatic) pressure of blood high at arterial end; 2. Fluid / water / soluble molecules pass out ; 3. Proteins / large molecules remain; 4. This lowers the water potential / water potential becomes more negative; 5. Water moves back into venous end of capillary by osmosis / diffusion; 6. Lymph system collects any excess tissue fluid which returns to blood / circulatory system / link with veina cava / returns tissue fluid to vein;

State and explain the property of water that can help to buffer changes in temperature. (2)

1. (water has a relatively) high (specific) heat capacity; 2. Can gain / lose a lot of heat / energy without changing temperature; OR 2. Takes a lot of heat / energy to changetemperature;

The DNA of the virus is different from that of other organisms.Use Table 2 and your knowledge of DNA to suggest what this difference is. Explain your answer. (2)

1. A does not equal T / G does not equal ; 2. (So) no base pairing; 3. (So) DNA is not double stranded / is single stranded.

Explain five properties that make water important for organisms. (5)

1. A metabolite in condensation / hydrolysis / photosynthesis / respiration 2. A solvent so (metabolic) reactions can occur 3. High heat capacity so buffers change in temperature 4. Large latent heat of vaporisation so provides a cooling effect (through evaporation) 5. Cohesion (between water molecules) so supports columns of water (in plants) 6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms.

The diagram shows the structure of the cell-surface membrane of a cell. Name A and B (2)

1. A: phospholipid (layer); 2. B: pore/channel/pump/carrier/ transmembrane/intrinsic/transport protein;

Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2)

1. ATP cannot be stored / is an immediate source of energy; 2. ATP only releases a small amount of energy at a time;

Adenosine triphosphate (ATP) is a nucleotide derivative. Contrast the structures of ATP and a nucleotide found in DNA to give two differences. (2)

1. ATP has ribose and DNA nucleotide has deoxyribose; 2. ATP has 3 phosphate (groups) and DNA nucleotide has 1 phosphate (group); 3. ATP- base always adenine and in DNA nucleotide base can be different / varies;

What is the advantage to cells of having mitochondria? (2)

1. Able to respire aerobically; 2. So make (more) ATP/ release (more) energy;

Maltose is hydrolysed by the enzyme maltase. Explain why maltase catalyses only this reaction (3)

1. Active site (of enzyme) has (specific) shape / tertiary structure / active site complementary to substrate / maltose; 2. (Only) maltose can bind / fit; 3. To form enzyme substrate complex.

Describe the induced fit model of enzyme action. (2)

1. Active site / enzyme not complementary; 2. Active site changes (shape) / is flexible; 3. (Change in enzyme allows) substrate to fit / E-S complex to form;

Hexosaminidase only breaks down gangliosides. It does not break down other lipids. Explain why this enzyme only breaks down gangliosides. (3)

1. Active site; ( 2. Complementary / specific) structure / shape; 3. (Only) fits / binds to gangliosides; 4. Forms enzyme-substrate complexes; OR 1. Active site; 2. (Complementary / specific) structure / shape; 3. (Does not) fit / bind with other lipids; 4. Does not form enzyme-substrate complexes;

Endocellulases and exocellulases act at different places on cellulose molecules. Suggest why. (2)

1. Active sites are different shapes; 2. So different enzyme-substrate complexes (are formed); OR 2. So complementary to different parts of cellulose / substrate;

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope. (4)

1. Add drop of water to (glass) slide; 2. Obtain thin section (of plant tissue) and place on slide / float on drop of water; 3. Stain with / add iodine in potassium iodide. 4. Lower cover slip using mounted needle.

Describe how you would test a sample of food for the presence of starch. (2)

1. Add iodine / potassium iodide solution to the food sample; 2. Blue / black / purple indicates starch is present;

Water is used to hydrolyse ATP. Name the two products of ATP hydrolysis (1)

1. Adenosine Diphosphate 2. (Inorganic) phosphate

Some of the children in the trial developed cancer. How might the insertion of the DNA have caused cancer? (2)

1. Affects tumour suppressor gene; 2. Inactivates (tumour suppressor) gene; 3. Rate of cell division increased / tumour cells continue to divide;

When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay. (2)

1. Allow atria to empty / contract / ventricles to fill; 2. Before ventricles contract; OR 1. Delays contraction of ventricles; 2. Until after atria have contracted / ventricles have filled;

The number of species present is one way to measure biodiversity. Explain why an index of diversity may be a more useful measure of biodiversity (2)

1. Also measures number of individuals in a species / different proportions of species; 2. Some species may be present in low/high numbers;

The insertion of the DNA copy in one of the host cell's genes may cause the cell to make a non-functional protein. Explain how. (2)

1. Alters base / nucleotide sequence / causes frame shift; 2. Different sequence of amino acids in polypeptide / protein / primary structure alters the tertiary structure;

Apart from reduced elasticity, explain how changes to the lung tissue reduce the efficiency of gas exchange. (4)

1. Alveolar walls thicken; 2. Longer diffusion pathway; 3. Scarred/fibrous tissue; 4. Reduces surface area (for gaseous exchange);

The reduced elasticity of the lungs causes breathing difficulty. Explain how. (2)

1. Alveoli / lungs will not inflate /deflate fully / reduced lung capacity; 2. Breathing out particularly affected/no longer passive; 3. Concentration/diffusion gradient / rate of diffusion reduced;

Emphysema is another disease of the lungs. People with emphysema may feel weak and tired. Explain why. (5)

1. Alveoli break down / collapse / rupture / walls thicken; 2. Less surface area / increases diffusion distance / less diffusion; 3. Loss of elastin / elastic tissue / elastase involved; 4. (Alveoli / lungs) cannot recoil / spring back / have reduced elasticity / more difficult to expel air; 5. Reduced diffusion gradient / air not replenished / less air leaves lungs; 6. Less oxygen enters blood / tissues; 7. Less respiration / less energy released / less ATP produced;

Nitrates and phosphates are two of these nutrients. They provide a source of nitrogen and phosphorus for cells. Give a biological molecule that contains: (2) 1. nitrogen 2. phosphorus.

1. Amino acid/protein/enzyme/urea/nucleic acid/chlorophyll/DNA/RNA//ATP/ADP/AMP/ NAD/NADP; 2. DNA/RNA/nucleic acid/ATP/ADP/AMP/ NADP/TP /GP/ RuBP /phospholipids;

Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide. Scientists have produced a monoclonal antibody that stops this stimulation. Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour. (3)

1. Antibody has specific tertiary structure / binding site / variable region; 2. Complementary (shape / fit) to receptor protein / GF / binds to receptor protein / to GF; 3. Prevents GF binding (to receptor).

Atheroma formation increases a person's risk of dying. Explain how. (5)

1. Atheroma is fatty material/cholesterol/foam cells/plaque/calcium deposits/LDL; 2. In wall of artery; 3. (Higher risk of) aneurysm/described; 4. (Higher risk of) thrombus formation/blood clot; 5. Blocks coronary artery; 6. Less oxygen/glucose to heart muscle/cells/tissue; 7. Reduces/prevents respiration; 8. Causing myocardial infarction/heart attack; 9. Blocks artery to brain; 10. Causes stroke/stroke described;

Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta. (5)

1. Atrium has higher pressure than ventricle (due to filling/contraction); 2. Atrioventricular valve opens; 3. Ventricle has higher pressure than atrium (due to filling/contraction); 4. Atrioventricular valve closes; 5. Ventricle has higher pressure than aorta; 6. Semilunar valve opens; 7. Higher pressure in aorta than ventricle (as heart relaxes); 8. Semilunar valve closes; 9. (Muscle/atrial/ventricular) contraction causes increase in pressure;

Describe how phospholipids are arranged in a plasma membrane. (2)

1. Bilayer; 2. Hydrophobic / fatty acid / lipid (tails) to inside; 3. Polar / phosphate group / hydrophilic (head) to outside;

Describe how bacteria divide. (2)

1. Binary fission; 2. Replication of (circular) DNA; 3. Division of cytoplasm to produce 2 daughter cells; 4. Each with single copy of (circular) DNA;

Lyxose binds to the enzyme. Suggest a reason for the difference in the results shown in the graph with and without lyxose. (3)

1. Binding alters the tertiary structure of the enzyme. 2. This causes the active site to change (shape) 3. So more (successful ) E-S complexes form (per minute)

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. Explain why (2)

1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; 2. Creates / leads to / uncovers second / another binding site OR 2. Uncovers another iron / Fe / haem group to bind to;

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.Explain why (2)

1. Binding of first oxygen changes tertiary /quaternary (structure) of haemoglobin; 2. Creates / leads to / uncovers second / another binding site OR 2. Uncovers another iron / Fe / haem group to bind to

Some babies are born with a hole between the right and the left ventricles. These babies are unable to get enough oxygen to their tissues. Suggest why. (2)

1. Blood flows from left ventricle to right ventricle/ mixing of oxygenated and deoxygenated blood; 2. Lower volume of (oxygenated) blood leaves left ventricle/flows into aorta OR 2. Lower pressure in blood leaving left ventricle/flowing into aorta OR 2. Less oxygen in blood leaving left ventricle/aorta/C;

Compare and contrast the structure and properties of triglycerides and phospholipids

1. Both contain ester bonds (between glycerol and fatty acid); 2. Both contain glycerol; 3. Fatty acids on both may be saturated or unsaturated; 4. Both are insoluble in water; 5. Both contain C, H and O but phospholipids also contain P; 6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group; 7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region; 8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don't;

Compare and contrast the structure and properties of triglycerides and phospholipids (5)

The population number of both species of lizard varied at different times of the year. Suggest two reasons why. (2)

1. Breeding (of lizards); 2. Food source / prey; 3. Predator; 4. Variation in malarial infection; 5. Temperature variation; 6. Availability of water eg drought / 'rainy season'

If the DNA of the cell is damaged, a protein called p53 stops the cell cycle. Mutation in the gene for p53 could cause cancer to develop. Explain how. (3)

1. Cancer cells often have faulty / damaged DNA; 2. Protein / p53 faulty / not made; 3. Cell (with faulty / DNA) divides / completes cell cycle; 4. Uncontrolled division produces cancer;

Clearing the forests and burning the vegetation affects the carbon dioxide concentration in the atmosphere. Describe how and explain why (4)

1. Carbon dioxide concentration increases; Clearing 2. No/Less vegetation so no/less photosynthesis / photosynthetic organisms; 3. No/Less carbon dioxide removed (from the atmosphere); Burning 4. Burning/combustion releases / produces carbon dioxide;

Explain how human activities have contributed to global warming. (4)

1. Carbon dioxide is a greenhouse gas; 2. Deforestation/trees removed so less carbon dioxide removed by photosynthesis; 3. Burning/combustion releases/produces carbon dioxide; 4. Methane is a greenhouse gas; 5. Any valid reference to source of methane, e.g. rice fields, landfills, cattle;

Cigarette smoking and a diet high in saturated fat increase the risk of myocardial infarction. Explain how. (6)

1. Carbon monoxide combines with haemoglobin/causes less oxygen to be transported; 2. Decreases concentration of antioxidants in blood; 3. Increases the damage done to artery walls; 4. Blood clot may occur;* 5. Blood pressure increased* 6. Blocks flow of blood to heart/in carotid arteries;* 7. Saturated fat associated with cholesterol; 8. Cholesterol deposited in arteries; 9. Atheroma formation; 10. Blood clot may occur*; 11. Blood pressure increased* 12. Blocks flow of blood to heart/in carotid arteries*; 13. Cholesterol / blood clot causes constriction of coronary arteries; 14. Less oxygen transported to heart muscle tissue;

The scientists calculated the cardiac output of the volunteers before and after the exercise programme. In some volunteers, their cardiac output stayed the same, even though their resting heart rate decreased. Explain how their cardiac output could stay the same even when their resting heart rate had decreased. (2)

1. Cardiac output = stroke volume × heart rate; 2. (So) stroke volume increases / increased size or volume of ventricles;

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells. (5)

1. Cell homogenisation to break open cells; 2. Filter to remove (large) debris / whole cells; 3. Use isotonic solution to prevent damage to mitochondria / organelles; 4. Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation; 5. Centrifuge (at lower speed / 1000 g) to separate nuclei / cell fragments / heavy organelles; 6. Re-spin (supernatant / after nuclei / pellet removed) at higher speed to get mitochondria in pellet / at bottom.

E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why. (1)

1. Cell unable to change shape; 2. (Because) cell has a cell wall; 3. (Wall is) rigid / made of peptidoglycan / murein.

Give two structures a bacterial cell may have that a white blood cell does not have. (2)

1. Cell wall; 2. Capsule / slime layer; 3. Circular DNA; 4. Naked DNA / DNA without histones; 5. Flagellum; 6. Plasmid; 7. Pilus; 8. 70s / smaller ribosomes; 9. Mesosome;

Describe two differences between the structure of a cellulose molecule and a glycogen molecule. (2)

1. Cellulose is made up of β-glucose (monomers) and glycogen is made up of α-glucose (monomers); 2. Cellulose molecule has straight chain and glycogen is branched; 3. Cellulose molecule has straight chain and glycogen is coiled; 4. glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4- glycosidic bonds;

Explain how a change in a sequence of DNA bases could result in a non-functional enzyme. (3)

1. Change in (sequence of) amino acids/primary structure; 2. Change in hydrogen/ionic/disulfide bonds; 3. Alters tertiary structure/active site (of enzyme); 4. Substrate cannot bind / no enzyme-substrate complexes form;

Explain how a change in the DNA base sequence for a protein may result in a change in the structure of the protein (3)

1. Change in amino acid/s /primary structure; 2. Change in hydrogen/ionic/ disulfide bonds; 3. Alters tertiary structure;

The acidic pH conditions created by osteoclasts cause the inactive form of the protein osteocalcin to change into the active form of osteocalcin. Suggest how (2)

1. Change in pH changes / break ionic / hydrogen bonds. 2. Changes tertiary structure

A mutation can lead to the production of a non-functional enzyme. Explain how. (6)

1. Change/mutation in base/nucleotide sequence (of DNA/gene); 2. Change in amino acid sequence/primary structure (of enzyme); 3. Change in hydrogen/ionic/disulfide bonds; 4. Change in the TERTIARY struture/shape; 5. Change in ACTIVE SITE; 6. Substrate not complementary/cannot bind (to enzyme/active site) / no enzyme-substrate complexes form;

A mutation can lead to the production of a non-functional enzyme. Explain how (6)

1. Change/mutation in base/nucleotide sequence (of DNA/gene); 2. Change in amino acid sequence/primary structure (of enzyme); 3. Change in hydrogen/ionic/disulfide bonds; 4. Change in the tertiary structure/shape; 5. Change in active site; 6. Substrate not complementary/cannot bind (to enzyme/active site) / no enzyme-substrate complexes form;

When ATR phosphorylates other enzymes, these enzymes become able to bind their substrates. Use your knowledge of enzyme structure to suggest why. (2)

1. Changes tertiary structure of the enzyme 2. Active site formed / active site becomes complementary.

Oxygen and chloride ions can diffuse across cell-surface membranes. The diffusion of chloride ions involves a membrane protein. The diffusion of oxygen does not involve a membrane protein.Explain why the diffusion of chloride ions involves a membrane protein and the diffusion of oxygen does not. (5)

1. Chloride ions water soluble/charged/polar; 2. Cannot cross (lipid) bilayer (of membrane); 3. Chloride ions transported by facilitated diffusion OR 3. diffusion involving channel/carrier protein; 4. Oxygen not charged/non-polar; 5. (Oxygen) soluble in/can diffuse across (lipid) bilayer;

Oxygen and chloride ions can diffuse across cell-surface membranes. The diffusion of chloride ions involves a membrane protein. The diffusion of oxygen does not involve a membrane protein. Explain why the diffusion of chloride ions involves a membrane protein and the diffusion of oxygen does not. (5)

Explain one way in which a palisade cell is adapted for photosynthesis. (1)

1. Chloroplasts absorb light; 2. Large vacuole pushes chloroplasts to edge (of cell); 3. Thin/permeable (cell) wall to absorb carbon dioxide;

What is atheroma and how may it cause myocardial infarction? (5)

1. Cholesterol / plaque / lipoprotein / LDL / fatty material / cells; 2. In artery wall / under lining / endothelium of artery / blood vessel; 3. Atheroma linked to blood clot / thrombosis; 4. (Blocks) coronary artery / artery supplying heart muscle / tissue / cells; 5. Reduces oxygen / glucose supply (to heart muscle / tissues / cells); 6. (Heart muscle / tissue / cells) unable to respire / dies;

What is atheroma? (2)

1. Cholesterol/ lipoprotein/ fatty material/cells; 2. In the artery wall/under lining/endothelium of artery/blood vessel;

Describe and explain the appearance of one of the chromosmes in cell X. (3)

1. Chromosome is formed of two chromatids 2. (Because) DNA replication (has occurred) 3. (Sister) chromatids held together by centromere

In prophase of mitosis, the chromosomes become visible. Describe what happens in anaphase (2)

1. Chromosome/centromere splits / chromatids/ 'chromosomes' separate/pulled apart; 2. To (opposite) sides/poles/centrioles (of cell);

Describe what happens to chromosomes in meiosis (6)

1. Chromosomes shorten / thicken / condense; 2. Chromosomes associate in homologous / (described) pairs / formation of bivalents; 3. Crossing-over / chiasma formation; 4. Join to spindle (fibres) / moved by spindle; 5. (At) equator / middle of cell; 6. (join via) centromere / kinetochore; 7. (Homologous) chromosomes move to opposite poles / chromosomes separate / move apart; 8. (Pairs of) chromatids separated in 2nd division;

Describe the appearance and behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells. (5)

1. Chromosomes shorten / thicken / supercoiling; during prophase; 2. Chromosomes appear as two identical chromatids (sister chromatids) joined by centromere / copies (due to replication); 3. Chromosomes /chromatids move to equator / middle of the spindle / cell (line up on equator) (metaphase) 4. Attach to individual spindle fibres by their centromere; 5. Spindle fibres contract / centromeres divide / repel; 6. (sister) Chromatids / chromosomes (separate)/anaphase / move to opposite poles / ens of the spindle; 7. Each pole / end receives all genetic information / identical copies of each chromosomes; 8. Nuclear envelope forms around each group of chromosomes / chromatids / at each pole; Each chromatid uncoils and unwinds;

Other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA. (2)

1. Circular / non-linear (DNA); 2. Not (associated ) with proteins / histones; 3. No introns / no non-coding DNA.

Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some of these cells have membranes with a carrier protein called NHE3. NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell. Use your knowledge of transport across cell membranes to suggest how NHE3 does this. (3)

1. Co-transport; 2. Uses (hydrolysis of) ATP; 3. Sodium ion and proton bind to the protein; 4. Protein changes shape (to move sodium ion and/or proton across the membrane);

Give one feature of starch and explain how this feature enables it to act as a storage substance. (2)

1. Coiled / helical / spiral; 2. (So) compact / tightly packed / can fit (lots) into a small space; 3. Insoluble; 4. (So) no osmotic effect / does not leave cell / does not affect water potential; 5. Large molecule / long chain; 6. (So) does not leave cell / contains large number of glucose units; 7. Branched chains; 8. (So) easy to remove glucose;

The graph shows that the maximum initial rate of reaction (Vmax) when a competitive inhibitor was present (curve B) is different from when a non-competitive inhibitor was present (curve C). Explain this difference (4)

1. Competitive inhibitor binds to active sites of enzyme but non-competitive inhibitor binds at allosteric site. 2. Competitive inhibitor does not cause change in shape of active site but non-competitive does. 3. SO with competitive inhibitor, at high substrate concentrations, enzyme still available whereas with non-competitive inhibitor, enzymes no longer available. 4. At higher substrate concentrations, likelihood of enzyme-substrate collisions increases with competitive inhibitor but not possible with non-competitive inhibitor.

A molecule of NBPT has a similar structure to a molecule of urea. Use this information to suggest how NBPT inhibits the enzyme urease. (2)

1. Complementary to / fits / binds to active site; 2. Competitive / competes / 'prevents' enzyme-substrate complexes / 'prevents' urea attaching;

Describe how a peptide bond is formed between two amino acids to form a dipeptide (2)

1. Condensation (reaction) / loss of water; 2. Between amine / NH2 and carboxyl / COOH

Explain the role of the heart in the formation of tissue fluid. (2)

1. Contraction of ventricle(s) produces high blood / hydrostatic pressure; 2. (This) forces water (and some dissolved substances) out (of blood capillaries);

Describe what courtship behaviour is and the importance of it. (5)

1. Courtship behaviour is species specific; 2. Only members of the same species will do and respond to that courtship behaviour; 3. This prevents interbreeding; 4. Means reproduction is more successful (fertile offspring is produced); 5. Because it is so specific it gives us a way to classify organisms - more closely related, more similar their courtship; 6. Courtship allows identification of a mate that is capable of breeding; 7. Can result in the formation of a pair bond; 8. Correctly synchronises mating so it takes place when there is a maximum probability that the sperm and egg will meet;

Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)

1. Crush / grind; 2. With ethanol / alcohol; 3. Then add water / then add to water; 4. Forms emulsion / goes white / cloudy;

Contrast the structures of DNA and mRNA molecules to give three differences. (3)

1. DNA double stranded/double helix and mRNA single-stranded; 2. DNA (very) long and RNA short; 3. Thymine/T in DNA and uracil/U in RNA; 4. Deoxyribose in DNA and ribose in RNA; 5. DNA has base pairing and mRNA doesn't/ DNA has hydrogen bonding and mRNA doesn't; 6. DNA has introns/non-coding sequences and mRNA doesn't;

The arrows in Figure 2 show the direction in which each new DNA strand is being produced. Use Figure 1, Figure 2 and your knowledge of enzyme action to explain why the arrows point in opposite directions. (4)

1. DNA has antiparallel strands; 2. Shape of the nucleotides is different / nucleotides aligned differently; 3. Enzymes have active sites with specific shape; 4. Only substrates with complementary shape / only 3' end can bind with active site of enzyme / DNA Polymerase,#.

The events that take place during interphase and mitosis lead to the production of two genetically identical cells. Explain how. (4)

1. DNA replicated; 2. (Involving) specific / accurate / complementary base-pairing; 3. (Ref to) two identical / sister chromatids; 4. Each chromatid / moves / is separated to (opposite) poles / ends of cell.

The forest was cleared to make more land available for agriculture. After the forest was cleared the species diversity of insects in the area decreased. Explain why (3)

1. Decrease in variety of plants / fewer plant species; 2. Fewer habitats/niches; 3. Decrease in variety of food / fewer food sources; 4. Aspect of clearing forest (killing insects) eg machinery, pesticides;

Explain why a mutation involving the deletion of a base may have a greater effect than one involving substitution of one base for another (3)

1. Deletion causes frame shift / alters base sequence (from point of mutation); 2. Changes many amino acids / sequence of amino acids / sequence of amino acids (from this point) 3. Substitution alters one codon / triplet / one amino acid altered / code degenerate / same amino acid coded for

Two proteins have the same number and type of amino acids but different tertiary structures. Explain why.

1. Different sequence of amino acids OR 1. Different primary structure 2. Forms ionic / hydrogen / disulfide bonds in different places.

Tetracycline can enter a bacterium through protein A. This protein is found in the plasma membrane. Suggest how a change in the amino acid sequence of this protein could make a bacterium resistant to tetracycline. (2)

1. Different tertiary structure/tertiary shape; 2. (So tetracycline) does not fit/bind/ is not complementary / does not enter/pass through (protein/into cell);

Describe how you would test a piece of food for the presence of lipid. (2)

1. Dissolve in alcohol, then add water; 2. White emulsion shows presence of lipid.

The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values. (2)

1. Divide mass of each lipid by total mass of all lipids (in that type of cell); 2. Multiply answer by 100.

Suggest the advantage of producing trypsin in an inactive form inside cells in the pancreas. (2)

1. Does not digest protein inside cells; 2. So (pancreatic) cell/tissue/function not destroyed/damaged;

explain what is meant by an unsaturated fatty acid (2)

1. Double bonds (present) / some / two carbons with only one hydrogen / (double bonds) between carbon atoms / not saturated with hydrogen; 2. In (fatty acid) C / 3;

Describe a method you could use to find the surface area of a leaf. (3)

1. Draw around leaf on graph paper 2. Count squares (however described); 3. Multiply by 2 (for upper and lower leaf surface); OR 3. Draw around a leaf on paper of known mass (per unit area);

Explain the advantages of lipid droplet and micelle formation (3)

1. Droplets increase surface areas (for lipase / enzyme action); 2. (So) faster hydrolysis / digestion (of triglycerides / lipids); 3. Micelles carry fatty acids and glycerol / monoglycerides to / through membrane / to (intestinal epithelial) cell;

Describe the part played by the inner membrane of a mitochondrion in producing ATP (3)

1. Electrons transferred down electron transport chain; 2. Provide energy to take protons/H+ into space between membranes; 3. Protons/H+ pass back, through membrane/into matrix/through ATPase; 4. Energy used to combine ADP and phosphate/to produce ATP;

The scientist used the same concentration of endocellulase and exocellulase in the box mixtures. The rate of digestion of cellulose is greatest when both enzymes are present. Suggest why (2)

1. Endocellulase create more ends / increases surface area; 2. For exocellulase to act on / hydrolyse / digest;

Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own. (2)

1. Endopeptidases hydrolyse internal (peptide bonds) OR 1. Exopeptidases remove amino acids/hydrolyse (bonds) at end(s); 2. More ends or increase in surface area (for exopeptidases);

Give two ways in which the properties of ATP make it a suitable source of energy in biological processes. (2)

1. Energy released in small / suitable amounts; 2. Soluble; 3. Involves a single / simple reaction;

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate. (2)

1. Examine large number of fields of view / many cells. 2. To ensure representative sample OR 1. Repeat count 2. To ensure figures are correct OR 1. Method to deal with part cells shown at edge 2. To standardise counting.

Dead leaves contain starch. Describe how microorganisms make carbon in starch available to plants. (2)

1. Extracellular digestion / releases enzymes; 2. Starch to monosaccharides /glucose/sugars/smaller molecules ; 3. Respire product of digestion; 4. Produce carbon dioxide from respiration;

Contrast the processes of facilitated diffusion and active transport. (3)

1. Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins; 2. Facilitated diffusion does not use ATP / is passive whereas active transport uses ATP; 3. Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.

Explain the link between atheroma and the increased risk of aneurism (4)

1. Fatty material within walls of arteries; 2. Vessels narrow; 3. Blood pressure rises; 4. Weakened blood vessels may burst;

The scientists' hypothesis was that adding the inhibitor of amylase to the food would lead to a lower blood glucose concentration. Use your knowledge of digestion to suggest how the addition of the inhibitor could lead to a lower blood glucose concentration. (2)

1. Fewer E-S complexes formed; 2. (With inhibitor) less / no starch digested to maltose ; 3. (So) less / no glucose from maltose; 4. (So) less absorption of glucose (from gut);

Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution. (2)

1. Filter and dry (the precipitate) 2. Find mass / weight

Describe one method the scientists could have used to ensure that the sites were chosen without bias. (2)

1. Find coordinates (on a grid) / split area into squares / number the sites; 2. Method of generating/finding random numbers eg calculator/computer/random number generator/random numbers table;

Explain how changes in the shape of haemoglobin result in the S-shaped (sigmoid) oxyhaemoglobin dissociation curve for HbA. (2)

1. First oxygen binds (to Hb) causing change in shape; 2. (Shape change of Hb) allows more O2 to bind (easily) / greater saturation with O2 OR 2. Cooperative binding;

Cells constantly hydrolyse ATP to provide energy. Describe how ATP is resynthesised in cells. (2)

1. From ADP and phosphate 2. By ATP synthase 3. During respiration / photosynthesis

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein (4)

1. Glucose and galactose; 2. Joined by condensation (reaction); 3. Joined by glycosidic bond; 4. Added to polypeptide in Golgi (apparatus);

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached. Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein. (4)

1. Glucose and galactose; 2. Joined by condensation (reaction); 3. Joined by glycosidic bond; 4. Added to polypeptide in Golgi (apparatus);

Describe the processes invovled in the absorption of the products of starch digestion. (6)

1. Glucose moves in with sodium (into epithelial cell); 2. Via (carrier / channel) proetin / symport; 3. Sodium removed (from epithelial cell) by active transport / sodium-potassium pump; into blood; 4. Maintaing low concentration of sodium (in epithelial cell) / maintaining sodoum concentration gradient (between lumen and epithelial cell); 5. Glucose moves into blood; 6. By (facilitated) diffusion

Name the products of the hydrolysis of sucrose. (2)

1. Glucose; 2. Fructose;

Diabetic people who do not control their blood glucose concentration may become unconscious and go into a coma. A doctor may inject a diabetic person who is in a coma with glucagon. Explain how the glucagon would affect the person's blood glucose concentration. (2)

1. Glycogen to glucose/glycogenolysis; 2. By activating enzymes; 3. Gluconeogenesis;

Name one organelle that you would expect to find in large numbers in a mucus-secreting cell and describe its role in the production of mucus. (2)

1. Golgi (apparatus); 2. Package / process proteins; OR 3. Rough endoplasmic reticulum / ribosomes; 4. Make polypeptide / protein / forming peptide bonds; OR 5. Mitochondria; 6. Release of energy / make ATP; OR 7. Vesicles; 8. Secretion / transport of protein;

There are over 12 000 species of plants in Costa Rica. Explain how this has resulted in a high species diversity of animals (2)

1. Greater variety / different foods; 2. More habitats/niches;

Explain the increase in the diversity of birds as the woodland developed (3)

1. Greater variety/diversity of plants/insects / more plant/insect species; 2. More food sources / more varieties of food; 3. Greater variety/more habitats/niches;

What is a species? (2)

1. Group of similar organisms / organisms with similar features / organisms with same genes / chromosomes; 2. Reproduce / produce offspring; 3. That are fertile;

(a) This type of classification can be described as a phylogenetic hierarchy. (i) What is meant by a hierarchy? (2)

1. Groups within groups; 2. No overlap (between groups);

Mitosis is important in the life of an organism. Give two reasons why (2)

1. Growth / increase in cell number; Ignore growth of cells 2. Replace cells / repair tissue / organs / body; 3. Genetically identical cells; 4. Asexual reproduction / cloning;

Pernicious anaemia is another type of anaemia. One method of identifying pernicious anaemia is to measure the diameter of the red blood cells in a sample of blood that has been diluted with an isotonic salt solution. Explain why an isotonic salt solution is used to dilute the blood sample. (3)

1. Has same water potential; 2. No (net) water movement / osmosis; 3. Cells will not swell/burst/change size;

Explain why the percentages of bases from the middle part of the chromosome and the end part are different. (2)

1. Have different (base) sequences / combinations of (bases); 2. (Pre-mRNA) transcribed from different DNA / codes for different proteins;

Humans and grasshoppers have very similar percentages of each base in their DNA but they are very different organisms. Use your knowledge of DNA structure and function to explain how this is possible. (2)

1. Have different genes; 2. (So bases / triplets) are in a different sequence / order; 3. (So) different amino acid (sequence / coded for) / different protein / different polypeptide / different enzyme.

Name two enzymes involved in the semi-conservative replication of DNA. (2)

1. Helicase 2. DNA Polymerase

Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell. (6)

1. Helicase; 2. Breaks hydrogen bonds; 3. Only one DNA strand acts as template; 4. RNA nucleotides attracted to exposed bases; 5. (Attraction) according to base pairing rule; 6. RNA polymerase joins (RNA) nucleotides together; 7. Pre-mRNA spliced to remove introns.

High blood pressure leads to an accumulation of tissue fluid. Explain how. (3)

1. High blood pressure = high hydrostatic pressure; 2. Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary; 3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.

Name on mutagenic agent (1)

1. High energy radiation / ionising particles 1. Named particles / alpha, beta ,gamma 1. X Rays / cosmic rays 1. UV (light) 1. Carcinogen / named carcinogen 1. Mustard gas / phenols / tar (qualified)

A transmission electron microscope was used to produce the image in the figure above. Explain why. (2)

1. High resolution; 2. Can see internal structure of organelles.

Explain the advantage to the lugworm of having haemoglobin with a dissociation curve in the position shown (to the left). (2)

1. High(er) affinity for oxygen / absorbs/loads more oxygen; 2. At lower partial pressure (of oxygen) / lower pO2;

The oxygen dissociation curve of the fetus is to the left of that for its mother. Explain the advantage of this for the fetus (2)

1. Higher affinity / loads more oxygen; 2. At low/same/high partial pressure/pO2; 3. Oxygen moves from mother/to fetus;

Hydrogen bonds are important in cellulose molecules. Explain why. (2)

1. Holds chains / cellulose molecules together / forms cross links between chains / cellulose molecules / forms microfibrils, providing strength / rigidity (to cellulose / cell wall); 2. Hydrogen bonds strong in large numbers;

Describe the role of the centromere in mitosis. (2)

1. Holds chromatids together 2. Attaches chromatids to spindle 3. Allows chromatids to be separated / pulled apart

Describe the process of crossing over that occurs during meiosis. (3)

1. Homologous chromosome line up / come together / associate. 2. Chiasmata form 3. Break in non-sister chromatids 4. Complete exchange of genetic material / sections of the non-sister chromatids.

Explain how the chromosome number is halved during meiosis. (2)

1. Homologous chromosomes (pair) 2. One of each (pair) goes to each (daughter) cell / opposite poles

Describe and explain the processes that occur during meiosis that increases genetic variation. (5)

1. Homologous chromosomes pair up 2. Independent segregation 3. Maternal and paternal chromosomes are re-shuffled in any combination 4. Crossing over leads to exchange of (non-sister) chromatids / alleles between homologous chromosomes 5. (Both) create new combination of alleles.

Crossing over greatly increases genetic diversity in this species of moss. Describe the process of crossing over and explain how it increases genetic diversity (4)

1. Homologous pairs of chromosomes associate / form a bivalent 2. Chiasma(ta) form 3. (Equal) lengths of (non-sister) chromatids / alleles are exchanged. 4. Producing new combinations of alleles.

Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue. (3)

1. How to break open cells and remove debris; 2. Solution is cold / isotonic / buffered; 3. Second pellet is chloroplast.

The new antibiotic is safe to use in humans because it does not inhibit the ATP synthase found in human cells. Suggest why human ATP synthase is not inhibited and bacterial synthase is inhibited. (1)

1. Human ATP synthase has a different tertiary structure to bacterial synthase. OR 1. Human ATP synthase has different shape active site to bacterial ATP synthase OR 1. Antibiotic cannot enter human cells / mitochondria OR 1. Antibiotic not complementary (to human ATP synthase)

The secondary structure of a polypeptide is produced by bonds between amino acids. Describe how. (2)

1. Hydrogen bonds 2. Between NH (group of one amino acid) and C=O (group) OR 2. Forming beta pleated sheets / alpha helix

DNA is a polymer of nucleotides. Each nucleotide contains an organic base. Explain how the organic bases help to stabilise the structure of DNA. (2)

1. Hydrogen bonds between the base pairs holds two strands together. 2. Many hydrogen bonds provide strength.

Mammals have some cells that produce extracellular proteases. They also have cells with membrane-bound dipeptidases. Describe the action of these membrane-bound dipeptidases and explain their importance. (2)

1. Hydrolyse (peptide bonds) to release amino acids; 2. Amino acids can cross (cell) membrane; OR 2. Dipeptides cannot cross (cell) membrane; OR 2. Maintain concentration gradient of amino acids for absorption; OR 2. Ensure (nearly) maximum yield from protein breakdown;

Suggest how glycogen acts as a source of energy. Do not include transport across membranes in your answer. (2)

1. Hydrolysed (to glucose); 2. Glucose used in respiration;

What is digestion? (2)

1. Hydrolysis (of); 2. (Large / insoluble substances) to small(er) / soluble substances;

Explain why monitoring the pH of the mixture could show whether the cat's milk contained lipase. (2)

1. Hydrolysis of lipids produces fatty acids; 2. Which lower pH of mixture.

Describe how proteins are digested in the human gut (4)

1. Hydrolysis of peptide bonds; 2. Endopeptidases break polypeptides into smaller peptide chains; 3. Exopeptidases remove terminal amino acids; 4. Dipeptidases hydrolyse / break down dipeptides into amino acids.

Describe the difference between the structure of a triglyceride molecule and the structure of a phospholipid molecule. (1)

1. In phospholipid, one fatty acid replaced by a phosphate;

Explain one potential problem that can be caused by selective breeding. (2)

1. Inbreeding / breed closely related organisms; 2. (So higher probability of) mutations being passed on / recessive alleles being expressed / health problems/example given / increase in genetic disease; 3. Reduced genetic variation/diversity / smaller gene pool / less variety of alleles; 4. (So) can be killed by/susceptible to the same/a disease / reduces ability to adapt/survive (future) environmental changes / may not be beneficial to future breeding programmes;

An increase in respiration in the tissues of a mammal affects the oxygen dissociation curve of haemoglobin. Describe and explain how (2)

1. Increase in/more carbon dioxide; 2. Curve moves to the right/depressed;

Explain the results without inhibitor (curve A) shown in the graph (2)

1. Increases because more enzyme-substrate complexes form. 2. Levels off because all enzyme molecules involved in enzyme-substrate complexes (at a give time) / no free active sites / enzyme concentration is limiting factor.

Name two ways in which meiosis produces genetic variation (2)

1. Independent segregation (of homologous chromosomes) 2. Crossing over / formation of chiasmata

Sometimes trypsin can become activated inside a pancreatic cell. A competitive inhibitor in the cell then binds to the trypsin and stops it working. Explain how the competitive inhibitor stops trypsin working. (3)

1. Inhibitor is a similar shape to the substrate; 2. (Inhibitor) blocks active site/is complementary to the active site/binds to the active site (of trypsin); 3. Substrate can't bind to active site / no/fewer ES complexes formed;

Scientists have investigated the effects of competitive and non-competitive inhibitors of the enzyme maltase. Describe competitive and non-competitive inhibition of an enzyme. (5)

1. Inhibitors reduce binding of enzyme to substrate / prevent formation of ES complex; (Competitive inhibition), 2. Inhibitor similar shape (idea) to substrate; 3. (Binds) in to active site (of enzyme); 4. (Inhibition) can be overcome by more substrate; (Non-competitive inhibition), 5. Inhibitor binds to site on enzyme other than active site; 6. Prevents formation of active site / changes (shape of) active site; 7. Cannot be overcome by adding more substrate;

Starch is a carbohydrate often stored in plant cells. Describe and explain two features of starch that make it a good storage molecule. (2)

1. Insoluble (in water), so doesn't affect water potential; 2. Branched / coiled / (α-)helix, so makes molecule compact; OR 2. Branched / coiled / (α-)helix so can fit many (molecules) in small area; 3. Polymer of (α-)glucose so provides glucose for respiration; 4. Branched / more ends for fast breakdown / enzyme action; 5. Large (molecule), so can't cross the cell membrane

Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function. Explain one way in which starch molecules are adapted for their function in plant cells. (2)

1. Insoluble; 2. Don't affect water potential; OR 3. Helical; 4. Compact; OR 5. Large molecule; 6. Cannot leave cell.

What effect might mutation 2 have on the protein produced? Explain your answer. (2)

1. Intron non-coding (DNA)/only exons coding; 2. (So) not translated / no change in mRNA produced / no effect (on protein) / no effect on amino acid sequence; OR 3. Prevents/changes splicing; 4. (So) faulty mRNA formed; 5. Get different amino acid sequence;

In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of pre-mRNA. Explain why. (2)

1. Introns (in pre-mRNA) 2. Removal of sections of (pre-mRNA) / splicing

Cell fractionation - 3 properties of solution (3)

1. Isotonic - Same water potential to prevent lysis / bursting (of organelle) 2. Buffered - Buffered to prevent denaturing of enzyme / protein 3. Cold - (Ice) cold to prevent / reduce enzyme activity

Describe aseptic techniques and justify the chosen method. (6)

1. Keep lid on Petri dish / open lid of Petri dish as little as possible; 2. To prevent unwanted bacteria contaminating the dish or avoid bacteria getting out; 3. Wear gloves / mask and wash hands; 4. Or prevent spread of bacteria outside the lab; 5. Use sterile pipette or Flame the loop or the neck of the container of the culture; 6. To maintain a pure culture of bacteria; 7. Use Bunsen Burner to maintain upward movement of air; 8. Helps to prevent contamination of culture when lid is removed;

Suggest how adding antibiotics to the food of the cattle increased profit for the farmers (2)

1. Kills pathogenic/harmful bacteria/pathogens; 2. Disease less likely/improves health/animals healthier/reduces spread of infection; 3. Faster growth/more productive animals/more food converted to meat/greater survival/lower vet‟s bills/increased yield/less energy (for „fighting infection‟);

Describe and explain how centrifuging the culture allowed the scientists to obtain a cell-free liquid. (3)

1. Large / dense / heavy cells; 2. Form pellet / move to bottom of tube (when centrifuged); 3. Liquid / supernatant can be removed.

Some drugs used to reduce high ventricular blood pressure cause widening of blood vessels. Suggest how widening of blood vessels can reduce ventricular blood pressure. (2)

1. Larger lumen/volume (of blood vessels); 2. Reduces (blood) pressure (in blood vessels); 3. Less friction/resistance (in blood vessels);

The detail shown in Figure 3 would not be seen using an optical microscope. Explain why. (2)

1. Light has long(er) wavelength 2. (So) low(er) resolution

Using your knowledge of the structure of the cell-surface membrane, suggest how LDL enters the cell. (2)

1. Lipid soluble / hydrophobic 2. Enters through (phospholipid) bilayer OR 3. (Protein part of) LDL attaches to receptor 4. Goes through carrier / channel protein.

Describe how haemoglobin loads and unloads oxygen in the body. (4)

1. Loading / uptake / association of oxygen at high p.p. of O2; 2. In lungs (haemoglobin) is (almost) fully saturated / in lungs haemoglobin has a high affinity for oxygen; 3. Unloads / releases / dissociates oxygen at low p.p. of O2; 4. Unloading linked to higher carbon dioxide concentration; Bohr Shift;

Use Figure 6 to describe how haemoglobin loads and unloads oxygen in the body. (3)

1. Loading/uptake/association of oxygen at high p.O2; In lungs (haemoglobin) is (almost) fully saturated / in lungs haemoglobin has a high affinity for oxygen; 2. Unloads/releases/dissociates oxygen at low p.O2; 3. Unloading linked to higher carbon dioxide concentration;

1. Long and straight chains; 2. Become linked together by many hydrogen bonds to form fibrils; 3. Provide strength (to cell wall).

The structure of cellulose is related to its role in plant cell walls. Explain how (3)

1. Long/straight/unbranched chains (of glucose); 2. (Joined by) hydrogen bonds; 3. Form (micro)fibrils/(macro)fibrils; 4. Provide rigidity/strength/support;

After birth, fetal haemoglobin is replaced with adult haemoglobin. Use the graph to suggest the advantage of this to the baby (2)

1. Low affinity / oxygen dissociates; 2. (Oxygen) to respiring tissues/muscles/cells;

Banana growers can only grow new variety B plants from suckers. Suckers grow from cells at the base of the stem of the parent plant. Use your knowledge of cell division to explain how growing variety B on a large scale will affect the genetic diversity of bananas. (2)

1. Low genetic diversity because they are produced by mitosis; 2. Will all have the same DNA/genes/alleles/ will be genetically identical/will be clones; OR 1. Low genetic diversity because they are not produced by meiosis; 2. No crossing over/independent segregation/will not be genetically different;

Use the graph to explain why llamas are better adapted to live in high mountains than horses. (llama curve to the left) (3)

1. Low partial pressure of oxygen; 2. In lungs; 3. (Llama) haemoglobin able to load more oxygen/(llama) haemoglobin saturated (at low/particular partial pressure of oxygen); 4. Higher affinity for oxygen;

The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. Explain the advantage of this shift. (3)

1. Lower affinity for oxygen / releases more oxygen / oxygen is released quicker / oxygen dissociates / unloads more readily; 2. (To) muscles / tissues / cells 3. (For) high / rapid respiration;

Farmers clear tropical forest and grow crops instead. Explain how this causes the diversity of insects in the area to decrease. (3)

1. Lower diversity of plants/ few species of plants/less variety of plants/few plant layers; 2. Few sources/types of food/feeding sites; 3. Few habitats/ niches; 4. Fewer (species of) herbivore so few (species of) carnivores; 5. Aspect of agriculture (killing insects);

Explain how the active site of an enzyme causes a high rate of reaction (3)

1. Lowers activation energy 2. Induced fit causes active site (of enzyme) to change shape 3. (So) enzyme-substrate complex causes bond to form / break.

The absorption of glucose into the cell leads to the movement of water into the cell. Explain how.

1. Lowers the water potential (of the cell); 2. Water moves (in) by osmosis;

Although the speed of blood flow in an arteriole is greater than speed of blood flow in a capillary, blood does not accumulate in the arterioles. Explain why (1)

1. Many / more capillaries (than arterioles); 2. (Cross-sectional) area of capillaries (much) greater (than of arterioles)

Although the speed of blood flow in an arteriole is greater than speed of blood flow in a capillary, blood does not accumulate in the arterioles. Explain why. (1)

1. Many / more capillaries (than arterioles); 2. (Cross-sectional) area of capillaries (much) greater (than of arterioles).

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them. (6)

1. Many alveoli / alveoli WALLS folded provide a large surface area; 2. Many capillaries provide a large surface area; 3. (So) fast DIFFUSION; 4. Alveoli or capillary walls / epithelium / lining are thin / short distance between alveoli and blood; 5. Flattened / squamos epithelium; 6. (So) short DIFFUSION distance / pathway; 7. (So) fast DIFFUSION; 8. Ventilation / circulation; 9. Maintains a diffusion / concentration gradient; 10. (So) fast DIFFUSION;

Adaptations of the alveoli and ileum? (6)

1. Many alveoli / alveoli walls folded provide a large surface area; 2. Many capillaries provide a large surface area; 3. (So) fast diffusion; 4. Alveoli or capillary walls / epithelium / lining are thin / short distance between alveoli and blood; 5. Flattened / squamous epithelium; 6. (So) short diffusion distance / pathway; 7. (So) fast diffusion; 8. Ventilation / circulation; 9. Maintains a diffusion / concentration gradient; 10. (So) fast diffusion;

Describe how the student could use an eyepiece graticule to determine the mean diameter of stomata. (3)

1. Measure (each stoma) using eyepiece graticule; 2. Calibrate eyepiece graticule against stage micrometer / ruler / graph paper; 3. Take a number of measurements (to calculate a mean);

Describe how you would use a microscope to find the mean diameter of triglyceride droplets on a slide. (3)

1. Measure with eyepiece graticule / scale; 2.Calibrate with stage micrometer / scale on slide / object of known size; 3. Repeats and calculate the mean; OR 1. Use a ruler to estimate the field diameter under microscope; 2. How many droplets go across the field; 3. Repeats and calculate mean;

You could use an optical microscope and a slide of stained muscle tissue to find the diameter of one of the muscle fibres. Explain how. (2)

1. Measure with graticule/eyepiece scale; 2. Calibrate against something of known size: OR 3. Estimate/measure field diameter with a scale; 4. Estimate number of fibres to cover diameter;

Explain why it may be more useful to calculate the index of diversity than to record only the number of species present. (2)

1. Measures number of individuals (of each species) and number of species; 2. Some species only present in small numbers;

Suggest two reasons for the differences between the populations in 1700 and 2010. (2)

1. Medical/health care / vaccination / antibiotics / lower infant mortality; 2. Diet / nutrition / food availability; 3. Sanitation / water supply / sewage treatment; 4. Contraception / birth control; 5. Work related example / occupation / education; 6. Financial considerations of having children; 7. Government/state policy; 8. War;

Explain the significance of meiosis in living organisms. (3)

1. Meiosis causes / leads to genetic variation 2. Involves crossing over 3. Independent segregation of chromosomes in meiosis I 4. Involves independent segregation of chromatids in meiosis II 5. Which creates new combinations of alleles 6. Creates gametes which allows 2 parents to contribute to the new organism / offspring creating variety 7. Because of genetic variation / variant will have a selective advantage --> natural selection.

Suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients. (2)

1. Membrane folded so increased/large surface area; OR 1. Membrane has increased/large surface area for (fast) diffusion/facilitated diffusion/active transport/co-transport; 2. Large number of protein channels/carriers (in membrane) for facilitated diffusion; 3. Large number of protein carriers (in membrane) for active transport; 4. Large number of protein (channels/carriers in membrane) for co-transport;

Suggest how the student could have used his slide to find the number of stomata per cm2. (3)

1. Method of determining area of field of view/area seen using microscope; 2. Count number of stomata in field of view; 3. Repeats and calculation of mean;

This cell is adapted for the three functions listed below. Use the diagram to explain how this cell is adapted for each of these functions. Use a different feature in the diagram for each of your answers. - the active transport of substances from the cell into the blood (2)

1. Mitochondria respire; 2. Release energy/ produce ATP; 3. Transport against gradient; OR 4. Infolding of membrane; 5. Increases area; 6. More proteins for active transport;

How is the golgi apparatus involved in the absorption of lipids? (3)

1. Modifies / processes triglycerodes 2. Combines triglycerides with proteins 3. Packaged for release / exocytosis OR 3. Forms vesicles.

Biologists can also use protein structure to investigate the relationship between different species of crane. Explain why (2)

1. More closely related (species) have more similarities in amino acid sequence/primary structure; 2. In same protein / named protein e.g. albumin; 3. Amino acid sequence is related to (DNA) base/triplet sequence; OR 4. Similar species have a similar immune response to a protein/named protein; 5. More closely related (species) produce more 'precipitate' / antibody-antigen (complexes) / agglutination;

Some people produce a much higher ventricular blood pressure than normal. This can cause tissue fluid to build up outside the blood capillaries of these people. Explain why (2)

1. More fluid forced/filtered out of capillary/blood (due to high pressure); 2. Less return of fluid (into capillary/blood) due to pressure OR Lymph(atic) (system) cannot drain away all excess fluid;

There is less oxygen at high altitudes than at sea level. People living at high altitudes have more red blood cells than people living at sea level. Explain the advantage of this to people living at high altitude. (2)

1. More haemoglobin; 2. So can load/pick up more oxygen (in the lungs);

More cancer cells could be destroyed if the drug was given more frequently. Suggest why the drug was not given more frequently. (2)

1. More/too many healthy cells killed; 2. (So) will take time to replace/increase in number; 3. Person may die/have side effects;

Explain why all cells of the body will have this mutation (Patau syndrome - three of chromosome 13) (2)

1. Mutation / extra chromosome in gamete / egg / sperm (that formed zygote) 2. All cells derived from a single cell / zygote by mitosis OR 3. All cells derived from a single cell / zygote by mitosis 4. Mitosis produces genetically identical cells / a clone.

Differences in the primary structure of haemoglobin molecules can provide evidence of phylogenetic (evolutionary) relationships between species.Explain how. (4)

1. Mutations change base / nucleotide (sequence); 2. (Causing) change in amino acid sequence; 3. Mutations build up over time; 4. More mutations / more differences (in amino acid/ base / nucleotide sequence / primary structure)between distantly related species; OR 4. Few(er) mutations / differences (in amino acid /base / nucleotide sequence / primary structure)in closely related species; 5. Distantly related species have earlier common ancestor; OR 5. Closely related species have recent common ancestor;

Haemoglobins are chemically similar molecules found box in many different species. Differences in the primary structure of haemoglobin molecules can provide evidence of phylogenetic (evolutionary) relationships between species. Explain how. (5)

1. Mutations change base / nucleotide (sequence); 2. (Causing) change in amino acid sequence; 3. Mutations build up over time; 4. More mutations / more differences (in amino acid / base / nucleotide sequence / primary structure) between distantly related species; OR 4. Few(er) mutations / differences (in amino acid / base / nucleotide sequence / primary structure) in closely related species; 5. Distantly related species have earlier common ancestor; OR 5. Closely related species have recent common ancestor;

Glucose is absorbed from the lumen of the small intestine into epithelial cells. Explain how the transport of sodium ions is involved in the absorption of glucose by epithelial cells. (5)

1. Na+ ions leave epithelial cell and enter blood; 2. (Transport out is by) active transport / pump / via carrier protein using ATP; 3. So, Na+ conc. in cell is lower than in lumen (of gut); 4. Sodium/Na+ ions enter by FACILITATED diffusion; 5. Glucose absorbed with Na+ ions against their concentration/diffusion gradient / glucose absorbed down an electrochemical gradient;

Glucose is absorbed from the lumen of the small intestine into epithelial cells. Explain how the transport of sodium ions is involved in the absorption of glucose by epithelial cells. (5 marks)

1. Na+ ions leave epithelial cell and enter blood; 2. (Transport out is by) active transport / pump / via carrier protein using ATP; 3. So, Na+ conc. in cell is lower than in lumen (of gut); 4. Sodium/Na+ ions enter by facilitated diffusion; 5. Glucose absorbed with Na+ ions against their concentration/diffusion gradient / glucose absorbed down an electrochemical gradient;

Explain how the doctor could have recognised which cells were in interphase when looking at the tissue samples. (1)

1. No visible chromosomes/chromatids; 2. Visible nucleus

Give two pieces of information needed to calculate an index of diversity for a community. (2)

1. Number of (organisms of) each species; 2. Total number of organisms (of all species) / Total number of species;

Explain what is meant by stabilising selection and describe the circumstances under which it takes place. (5)

1. Occurs in an unchanging environment; 2. Selection against extremes / selection for the mean / mean / median / mode unaltered 3. Range / S.D is reduced 4. Increasing proportion of populations becomes well adapted to environment;

The solution that the student used to produce the chloroplast suspension had the same water potential as the chloroplasts. Explain why it was important that these water potentials were the same. (2)

1. Osmosis does not occur; 2. Chloroplast/organelle does not burst/lyse/shrivel/shrink;

Describe the role of haemoglobin in supplying oxygen to the tissues of the body. (2)

1. Oxyhaemoglobin formed/ haemoglobin is loaded/ uptakes/associates/binds with oxygen in area of higher ppO2 / in gas exchange surface/lungs/gills; 2. (oxygen) unloaded/dissociates from/released (in area of lower ppO2 / in capillaries/to cells/tissues);

Describe and explain ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue. (6)

1. Permeable capillary wall / membrane; 2. Single cell thick / thin walls, reduces diffusion distance; 3. Flattened (endothelial) cells, reduces diffusion distance; 4. Fenestrations, allows large molecules through; 5. Small diameter / narrow, gives a large surface area to volume / short diffusion distance; 6. Narrow lumen, reduces flow rate giving more time for diffusion; 7. Red blood cells in contact with wall / pass singly, gives short diffusion distance / more time for diffusion;

Destruction of phagocytes causes the lungs to be more susceptible to infections. Explain why (2)

1. Phagocytes engulf / ingest pathogens / microorganisms / bacteria/ viruses; 2. Phagocytes destroy pathogens / microorganisms / bacteria / viruses; 3. Lung diseases are caused by pathogens/microorganisms/bacteria/viruses;

The structure of a phospholipid molecule is different from that of a triglyceride. Describe how a phospholipid is different. (2)

1. Phosphate / PO4; 2. Instead of one of the fatty acids / and two fatty acids;

The movement of substances across cell membranes is affected by membrane structure. Describe how. (5)

1. Phospholipid (bilayer) allows movement / diffusion of non-polar / lipid-soluble substances 2. Phospholipid (bilayer) prevents movement / diffusion of polar / charged / lipid-insoluble substances 3. Carrier proteins allow active transport 4. Channel / carrier proteins allow facilitated diffusion / co-transport 5. Shape / charge of channel / carrier determines which substances move. 6. Number of channels / carriers determines how much movement. 7. Membrane surface area determines how much diffusion / movement. 8. Cholesterol affects fluidity / rigidity / permeability

Describe the structure or proteins. (5)

1. Polymer of amino acids; 2. Joined by peptide bonds; 3. Formed by condensation; 4. Primary structure is order of amino acids; 5. Secondary structure is folding of polypeptide chain due to hydrogen bonding; 6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds; 7. Quaternary structure is two or more polypeptide chains.

Describe the structure of glycogen. (2)

1. Polysaccharide of α-glucose; OR 1.polymer of α-glucose; 2. (Joined by) glycosidic bonds OR ] 2.Branched structure;

Some populations of animals that have never been hunted show very low levels of genetic diversity. Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity. (2)

1. Population might have been very small / genetic bottleneck; 2. Population might have started with small number of individuals / by one pregnant female / founder effect; 3. Inbreeding.

Explain why the scientists used isotonic solution during the process. (2) [fractionation]

1. Prevents osmosis / no (net) movement of water / water does not enter organelle / water does not leave organelle; 2. So organelle / named organelle is not damaged / does not burst / does not shrivel;

The antibiotic tetracycline binds to ribosomes in bacterial cells. Explain how this causes the death of bacterial cells. (2)

1. Prevents protein synthesis; 2. (So) enzymes not produced / any named process involving proteins/enzymes is inhibited;

Mikanolide is a drug that inhibits the enzyme DNA polymerase. Explain why this drug may be effective against some types of cancer. (2)

1. Prevents/slows DNA replication/doubling; 2. Prevents/slows mitosis; 3. New strand not formed / nucleotides(of new strand) not joined together / sugarphosphate bonds not formed;

The student prepared a temporary mount of the onion tissue on a glass slide. She covered the tissue with a cover slip. She was then given the following instruction. "Push down hard on the cover slip, but do not push the cover slip sideways." Explain why she was given this instruction. (2)

1. Push hard - spread / squash tissue; 2. Not push sideways - avoid rolling cells together / breaking chromosomes.

Use of a colorimeter in this investigation would improve the repeatability of the student's results. Give one reason why. (1)

1. Quantitative OR 1. (colour change is ) subjective 2. Standardises (the) method

Give three ways in which courtship behaviour increases the probability of successful mating (3)

1. Recognise / identify / attract same species 2. Stimulates / synchronises mating / production / release of gametes; 3. Recognition / attraction of mate / opposite sex; 4. Indication of (sexual) maturity / fertility / receptivity / readiness to mate; 5. Formation of a pair bond / bond between two organisms (to have / raise young).

The spotted owl is a bird. Numbers of spotted owls have decreased over the past 50 years. Explain how this decrease may affect genetic diversity (2)

1. Reduced (genetic diversity); 2. As fewer different/varied alleles/genes / reduced gene pool; 3. (Genetic) bottleneck;

The demand for increased food production has led to areas of heath being used to grow wheat. Explain the effect of this on the species diversity of plants (2)

1. Reduced as one crop/species grown / other species removed; 2. Use of herbicides/weeding/ploughing; 3. Wheat (better) competitor for named factor e.g. light/nutrients;

During a myocardial infarction, areas of heart muscle begin to die. Explain why. (3)

1. Reduced blood flow in coronary artery / coronary artery blocked; 2. Less / not enough / no oxygen; 3. Respiration drops / stops (so cells start to die);

Coeliac disease is a disease of the human digestive system. In coeliac disease, the microvilli are damaged. Although people with coeliac disease can digest proteins they have low concentrations of amino acids in their blood. Explain why they have low concentrations of amino acids in their blood. (2)

1. Reduced surface area; 2. (So) less absorption; 1. (Membrane-bound) enzymes less effective; 2. (So) proteins / polypeptides not digested; 1. Cell membranes damaged; 2. (So) Fewer / less effective carrier / channel proteins; 1. Carrier / channel proteins damaged; 2. (So) less absorption;

Formation of an enzyme-substrate complex increases the rate of reaction. Explain how. (2)

1. Reduces activation energy 2. Due to breaking bonds OR 2. Without enzyme, very few substrates have sufficient energy for reaction.

Use the figure in part (a) and your knowledge of enzyme action and DNA replication to explain why new nucleotides can only be added in a 5' to 3' direction. (1)

1. Reference to DNA polymerase; 2. (Which is) specific; 3. Only complementary with / binds to 5' end (of strand); 4. Shapes of 5' end and 3' end are different / description of how different.

Comparing the base sequence of a gene provides more information than comparing the amino acid sequence for which the gene codes. Explain why. (2)

1. Reference to base triplet/triplet code / more bases than amino acids / longer base sequence than amino acid sequence; 2. Introns/non-coding DNA; 3. Same amino acid may be coded for / DNA code is degenerate;

ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use. (2)

1. Releases relatively small amount of energy / little energy lost as heat; 2. Releases energy instantaneously; 3. Phosphorylates other compounds, making them more reactive; 4. Can be rapidly re-synthesised; 5. Is not lost from / does not leave cells.

A deletion mutation in gene 1. Describe how a deletion mutation alters the structure of a gene. (2)

1. Removal of one or more bases / nucleotides 2. Frameshift / (from point of mutation) base sequence change

Explain how microorganisms contributed to the increase in temperature during processing of organic waste (2)

1. Respiration/metabolism/ammonification; 2. (Releases/produces) heat

1. Ribosomes make proteins/ enzymes; 2. Enzymes are proteins; OR 3. Mitochrondria respire; 4. Release energy/produce ATP; 5. (Energy/ATP) for protein / enzyme synthesis;

The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN). Describe how. (5)

1. SAN initiates heartbeat / acts as a pacemaker / myogenic; 2. (SAN) sends wave of electrical activity / impulses (across atria) causing atrial contraction; 3. AVN delays (electrical activity / impulses); 4. (Allowing) atria to empty before ventricles contract / ventricles to fill before they contract; 5. (AVN) sends wave of electrical activity / impulses down Bundle of His / Purkyne fibres; 6. (Causing) ventricles to contract (from base up) / ventricular systole;

Describe how a heartbeat is initiated and coordinated (5)

1. SAN sends wave of electrical activity / impulses (across atria) causing atrial contraction; 2. Non-conducting tissue prevents immediate contraction of ventricles/prevents impulses reaching the ventricles; 3. AVN delays (impulse) whilst blood leaves atria/ventricles fill; 4. (AVN) sends wave of electrical activity / impulses down Bundle of His; 5. Causing ventricles to contract from base up;

The heart controls and coordinates the regular contraction of the atria and ventricles. (5)

1. SAN → AVN → bundle of His /Purkyne fibres; 2. Impulses / electrical activity (over atria); 3. Atria contract; 4. Non-conducting tissue (between atria and ventricles); 5. Delay (at AVN) ensures atria empty / ventricles fill before ventricles contract; 6. Ventricles contract from apex upwards;

Explain the advantage of showing the data using standard deviations rather than ranges. (2)

1. SD is spread of data around the mean; 2. (SD) reduces effect of anomalies/ outliers; 3. (SD) can be used to determine if (difference in results is) significant/not significant/due to chance /not due to chance;

Describe how the scientist could have used the temporary mounts of leaves to determine the mean number of chloroplasts in mesophyll cells of a leaf. (3)

1. Select large number of cells / select cells at random; 2. Count number of chloroplasts; 3. Divide number of chloroplasts by number of cells;

The sinoatrial node (SAN) is in the right atrium of the heart. Describe the role of the sinoatrial node. (2)

1. Sends out electrical activity/ impulses; 2. Initiates the heartbeat / acts as a pacemaker / (stimulates) contraction of atria; Q

DNA helicase is important in DNA replication. Explain why. (2)

1. Separates/unwinds/unzips strands/helix / breaks H-bonds; 2. (So) nucleotides can attach/are attracted / strands can act as templates;

Other than causing slow blood flow, explain one advantage of capillaries being narrow. (2)

1. Short pathway / short distance between blood and outside of capillary; 2. Large surface area (of blood) in contact with walls of capillaries; 3. Fast exchange / fast diffusion / fast osmosis.

Explain why it was important that the piece of the epidermis that the student removed was thin. (2)

1. Single layer of cells / few layers of cells; 2. So that light that can pass through / cells absorb light;

The pieces of leaf tissue examined were very thin. Explain why this was important. (2)

1. Single/few layer(s) of cells; 2. So light can pass through;

Describe what happens during anaphase hat results in the production of two genetically identical cells (2)

1. Sister / identical chromatids / identical chromosomes; 2. To (opposite) poles / ends / sides;

Explain how the body shape of a Weddell seal is an adaptation to living in a cold environment. (2)

1. Small SA:VOL; 2. (So) reduces heat loss / (more) heat retained;

There is a positive correlation between the size of snow geese and how far north they breed. A large size results in snow geese being adapted for breeding in colder conditions. Explain how. (2)

1. Small surface area to volume ratio / more fat; 2. Lose less heat (to the environment) / for insulation; 3. When they are sitting on eggs;

Heat from respiration helps mammals to maintain a constant body temperature. Use this information to explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins. (4)

1. Smaller mammal has greater surface area to volume ratio; 2. Smaller mammal/larger SA:Vol ratio more heat lost (per unit body mass); 3. Smaller mammal/larger SA:Vol ratio has greater rate of respiration/metabolism; 4. Oxygen required for respiration; 5. (Haemoglobin) releases more oxygen / oxygen released more readily / haemoglobin has lower affinity;

Give two risk factors associated with coronary heart disease (2)

1. Smoking; 2. High salt intake; 3. High (blood) cholesterol; 4. High blood pressure / stress; 5. Lack of exercise / obesity; 6. Heredity / genes / familial; 7. Gender; 8. Age;

Explain the purpose of: 1. boiling the agar 2. transferring the same volume of liquid culture onto each agar plate (2)

1. So no contamination/ other bacteria; 2. So same number of bacteria transferred to allow comparison;

Define each of the following terms. 1. Species 2. Species richness (2)

1. Species = (A group of) organisms that are able to produce fertile offspring; 2. Species richness = the number of (different) species in a community;

In prophase of mitosis, the chromosomes become visible. Describe what happens in metaphase (2)

1. Spindle formed / chromosome/centromere/chrom atids attaches to spindle; 2. Chromosomes/chromatids line up/move to middle/equator (of cell);

The concentration of glucose in the blood rises after eating a meal containing carbohydrates. The rise is slower if the carbohydrate is starch rather than sucrose. Explain why. (3)

1. Starch digested to maltose / by amylase; 2. Maltose digested to glucose / by maltase; 3. Digestion of sucrose is a single step / only one enzyme / sucrase;

Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above. (2)

1. Starch formed from α-glucose but cellulose formed from β-glucose; 2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.

The total number of bases in the DNA of the α-polypeptide gene is more than 423. Give two reasons why there are more than 423 bases. (2)

1. Stop/start sequences; 2. Non coding DNA (in the gene)/introns/multiple repeats/junk DNA; 3. Two chains/a non-coding strand/complementary base pairs; 4. Addition of base by mutation;

Describe how DNA is replicated (6)

1. Strands separate / Hydrogen bonds break; 2. DNA helicase (involved); 3. Both strands/each strand act(s) as (a) template(s); 4. Free nucleotides attach; 5. Complementary/specific base pairing / AT and GC; 6. DNA polymerase joins adjacent nucleotides (on new strand); 7. Hydrogen bonds reform; 8. Semi-conservative replication / new DNA molecules contain one old strand and one new strand;

The aorta has many elastic fibres in its wall. An arteriole has many muscle fibres in its wall. Explain the importance of elastic fibres in the wall of the aorta. (2)

1. Stretches/'expands' under high pressure/when ventricle contracts / systole; 2. Recoils/'springs back' under low pressure/when ventricle relaxes / diastole; 3. Smooths blood flow / maintains blood pressure / reduces pressure surges;

Name the monosaccharides of which the following disaccharides are composed. 1.Sucrose monosaccharides 2.Lactose monosaccharides (2)

1. Sucrose = Glucose and fructose; 2. Lactose = Glucose and galactose;

Explain how the structure of DNA is related to its functions. (6)

1. Sugar-phosphate (backbone) / double stranded / helix so provides strength / stability / protects bases / protects hydrogen bonds; 2. Long / large molecule so can store lots of information; 3. Helix / coiled so compact; 4. Base sequence allows information to be stored / base sequence codes for amino acids / proteins; 5. Double stranded so replication can occur semi-conservatively / strands can act as templates / complementary base pairing / A-T and C-G so accurate replication / identical copies can be made; 6. (Weak) hydrogen bonds for replication / unzipping / strand separation / many hydrogen bonds so stable / strong;

Explain how the structure of DNA is related to its functions (6)

1. Sugar-phosphate (backbone)/double stranded/helix so provides strength/stability /protects bases/protects hydrogen bonds; 2. Long/large molecule so can store lots of information; 3. Helix/coiled so compact; 4. Base sequence allows information to be stored/ base sequence codes for amino acids/protein; 5. Double stranded so replication can occur semi-conservatively/ strands can act as templates; 6. Complementary base pairing / A-T and G-C so accurate replication/identical copies can be made; 7. (Weak) hydrogen bonds for replication/ unzipping/strand separation; 8. Many hydrogen bonds so stable/strong;

The scientists set up their cultures in sterile glass bottles. Suggest one suitable method for sterilising the bottles and explain why it was necessary to sterilise them. (2)

1. Suitable method; eg in boiling water / steam / autoclave / wash in disinfectant / wash in alcohol 2. (Reason) to remove / kill other bacteria / organisms that might break down ammonia;

Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells (6)

1. TEM uses electrons and optical use light; 2. TEM allows a greater resolution; 3. (So with TEM) smaller organelles / named cell structure can be observed OR 3. greater detail in organelles / named cell structure can be observed; 4. TEM view only dead / dehydrated specimens and optical (can) view live specimens; 5. TEM does not show colour and optical (can) 6. TEM requires thinner specimens; 7. TEM requires a more complex / time consuming preparation; 8. TEM focuses using magnets and optical use (glass) lenses.

In humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temperature. Explain why maltase: • only breaks down maltose • allows this reaction to take place at normal body temperature. (5)

1. Tertiary structure / 3D shape of enzyme (means); 2. Active site complementary to maltose / substrate / maltose fits into active site / active site and substrate fit like a lock and key; 3. Description of induced fit; 4. Enzyme is a catalyst / lowers activation energy / energy required for reaction; 5. By forming enzyme-substrate complex;

In humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temperature. Explain why maltase: 1. only breaks down maltose 2. allows this reaction to take place at normal body temperature. (5)

1. Tertiary structure / 3D shape of enzyme (means); 2. Active site complementary to maltose / substrate / maltose fits into active site / active site and substrate fit like a lock and key; 3. Description of induced fit; 4. Enzyme is a catalyst; 5. Lowers activation energy / energy required for reaction; 6. By forming enzyme-substrate complex;

Describe how mRNA is produced in a plant cell. (5)

1. The DNA strands separate by breaking the H bonds; OR H bonds broken between (complementary) (DNA) bases; 2. (Only) one of the strands/template strand is used (to make mRNA/is transcribed); 3. (Complementary) base pairing so A→U, T→A, C→G, G→C; 4. (RNA) nucleotides joined by RNA polymerase; 5. pre-mRNA formed; 6. Splicing / introns removed to form mRNA;

Use information from Figure 2 to explain how the pressure in the dog's ventricle is related to the thickness of the ventricle wall. (2)

1. Thickness of wall increases because ventricle (wall) contracts; 2. Contraction causes the increase in pressure;

Describe how temporary mounts are made (2)

1. Thin slice/section; 2. Put on slide in water / solution / stain; 3. Add cover slip;

Describe two adaptations of the structure of alveoli for efficient gas exchange (2)

1. Thin walls/cells; 2. (Total) surface area is large;

Describe the path by which oxygen goes from an alveolus to the blood. (2)

1. Through alveolar epithelium; 2. Through capillary epithelium/endothelium;

The student cut thin sections of tissue to view with an optical microscope. Explain why it was important that the sections were thin. (2)

1. To allow (more) light through; 2. A single / few layer(s) of cells to be viewed.

When counting, cells that touch top or left lines are counted but cells that touch right or bottom lines are not counted.Suggest two reasons for this rule (2)

1. To avoid dealing with parts of cells; 2. To avoid counting same cells twice / more than once; 3. To be consistent / get comparable results;

Some proteases are secreted as extracellular enzymes by bacteria. Suggest one advantage to a bacterium of secreting an extracellular protease in its natural environment. Explain your answer. (2)

1. To digest protein; 2. (So) they can absorb amino acids for growth/reproduction/protein synthesis/synthesis of named cell component; OR 2. (So) they can destroy a toxic substance/protein

Give two ways in which the hydrolysis of ATP is used in cells (2).

1. To provide energy for other reasons 2. To add phosphate to other substances and make them more reactive / change their shape

The peptides released when gluten is digested cannot be absorbed by facilitated diffusion. Suggest why. (3)

1. Too big/ wrong shape; 2. To fit/ bind/ pass through(membrane/ into cell/through carrier/ channel protein); 3. Carrier / channel protein;

The diet of a person can increase the risk of coronary heart disease. Explain how. (5)

1. Too much saturated fat / cholesterol in diet; 2. Increase in LDL / cholesterol in blood; 3. Atheroma / fatty deposits / plaques in artery walls; 4. Reduces diameter of / blocks coronary arteries; 5. Less oxygen / glucose to heart muscle / tissue / cells; 6. Increase in blood pressure; 7. (Increased risk of) clot / thrombosis / embolism / aneurysm

Infection by the cholera bacterium can cause acute diarrhoea. Explain how (2)

1. Toxin (produced by bacterium) causes (chloride) ions to move into (lumen of) intestine; 2. Water potential (of intestine contents) falls / water moves by osmosis into intestine/out of cells;

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing are not required. (4)

1. Trachea and bronchi and bronchioles; 2. Down pressure gradient; 3. Down diffusion gradient; 4. Across alveolar epithelium. 5. Across capillary endothelium / epithelium.

What is a codon? (2)

1. Triplet/three bases on mRNA; 2. That code for an amino acid;

Not all mutations in the nucleotide of a gene cause a change in the structure of a polypeptide. Give two reasons why. (2)

1. Triplets code for same amino acid; 2. Occurs in introns / non-coding sequence

Describe and explain how the structure of DNA results in accurate replication. (5)

1. Two strands therefore semi-conservative replication (possible); 2. Base pairing / hydrogen bonds hold strands together; 3. Hydrogen bonds weak / easily broken, allows strands to separate; 4. Base (sequence) (exposed so) acts as template / can be copied; 5. A with T, C with G / complementary copy; 6. DNA now made of one parent strand, one new strand;

The bluebell is a flowering plant found in woodlands. Global warming has been associated with a change in the population of bluebells. Describe how you could estimate the number of bluebells in a small woodland. (5)

1. Use a grid / split area into squares/sections; 2. Method of obtaining random coordinates / numbers, e.g. calculator/computer/random numbers table/random number generator; 3. Count number/frequency of plants in a quadrat; 4. Calculate mean/average number (per quadrat/section); 5. Valid method of calculating total number of bluebells/plants. e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in wood;

Use information from Figure 2 to explain how the pressure in the dog's ventricle is related to blood flow into the aorta. (2)

1. Ventricle pressure rises then blood starts to flow into aorta; 2. (Because) pressure above that in aorta causes (aortic / semilunar) valve to open / pressure below that in aorta causes (aortic / semilunar) valve to be shut; 3. Ventricle pressure starts to fall so blood flow falls;

The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why. (3)

1. Water has left the capillary; 2. Proteins (in blood) too large to leave capillary; 3. Increasing / giving higher concentration of blood proteins (and thus wp)

Describe the cohesion-tension theory of water transport in the xylem (5)

1. Water lost from leaf because of transpiration / evaporation of water (molecules) / diffusion from mesophyll / leaf cells; OR 1. Transpiration / evaporation / diffusion of water (molecules) through stomata / from leaves; 2. Lowers water potential of mesophyll / leaf cells; 3. Water pulled up xylem (creating tension); 4. Water molecules cohere / 'stick' together by hydrogen bonds; 5. (forming continuous) water column; 6. Adhesion of water (molecules) to walls of xylem;

Kwashiorkor is a disease caused by a lack of protein in the blood. This leads to a swollen abdomen due to a build up of tissue fluid. Explain why a lack of protein in the blood causes a build up of tissue fluid (3)

1. Water potential (in capillary) not as low/is higher/less negative / water potential gradient is reduced; 2. Less/no water removed (into capillary); 3. By osmosis (into capillary);

In children, some diets may result in a low concentration of protein in fluid F. This can cause the accumulation of tissue fluid. Explain the link between a low concentration of protein in fluid F and the accumulation of tissue fluid. (3)

1. Water potential (in capillary) not as low/is higher/less negative / water potential gradient is reduced; 2. More tissue fluid formed (at arteriole end); 3. Less/no water absorbed (into blood capillary); 4. by osmosis; (into blood capillary);

Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar. Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria. (3)

1. Water potential in (bacterial) cells higher (than in honey) / water potential in honey lower (than in bacterial cells); 2. Water leaves bacteria / cells by osmosis; 3. (Loss of water) stops (metabolic) reactions

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA. (2)

1. Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip; 2. Two strands, so both can act as templates; 3. Complementary base pairing allows accurate replication;

Explain why the student used only the first 5 mm from the tip of an onion root (1)

1. Where dividing cells are found / mitosis occurs OR 1. No dividing cells / mitosis in tissue further away / more than 5 mm from tip OR 1. To get (soft) tissue that will squash OR 1. Length that will fit under the coverslip

Nitrogenase also catalyses reactions involving other substances. Explain what this suggests about the shapes of the molecules of these other substances. (2)

1. Will have similar shape/tertiary structure (as substrate) / complementary shape (to active site); 2. Fit/bind with active site / forms enzyme-substrate complex;

Give the name and function of the chloroplast and the nucleus. (2)

1. chloroplast, photosynthesis; 2.nucleus, contains DNA / chromosomes / holds genetic information of cell.

Describe and explain the link between oxygen concentration, rate of respiration and rate of uptake of potassium ions. (4)

1. greater rate of oxygen consumption / leads to greater rate of respiration and greater rate of uptake; 2. oxygen required for respiration; 3. respiration produces ATP / releases energy; 4. potassium ions taken up by active transport / against concentration gradient;

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide. Do not include descriptions of transcription and splicing in your water. (5)

1. mRNA associates with ribosome / ribosome attaches to mRNA; 2. Ribosome moves to / find the start codon / AUG 3. tRNA brings / carries (appropriate / specific) amino acid; 4. Anticodon (on tRNA complementary) to codon (on mRNA); 5. Ribosome moves along to next codon; OR 5. Ribosome 'fits' around two codons / can fit two tRNAs; 6. (Process repeated and) amino acids join by peptide bonds / condensation reaction (to form polypeptide_; OR 6. (Process repeated and) amino acids joined using (energy from) ATP (to form polypeptide);

Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer. (3)

1. mRNA binds to ribosome 2. Idea of two codons / binding sites 3. (Allows) tRNA with anticodons to bind / associate 4. (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules) 5. Moves along (mRNA to the next codon) / translocation described.

Give two structural differences between a molecule of messenger RNA (mRNA) and a molecule of transfer RNA (tRNA) (2)

1. mRNA does not have hydrogen bonds / base pairing, tRNA does. OR 1. mRNA is linear / straight chain, tRNA is cloverleaf 2. mRNA does not have an amino acid binding site, tRNA does 3. mRNA has more nucleotides 4. (Different) mRNAs have different lengths, all tRNAs are similar / same length 5. mRNA has codons, tRNA has an anticodon

Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells. (6)

1. made from β-glucose; 2. joined by condensation / removing molecule of water / glycosidic bond; 3. 1 : 4 link specified or described; 4. "flipping over" of alternate molecules; 5. hydrogen bonds linking chains / long straight chains; 6. cellulose makes cell walls strong / cellulose fibres are strong; 7. can resist turgor pressure / osmotic pressure / pulling forces; 8. bond difficult to break; 9. resists digestion / action of microorganisms / enzymes;

Explain how three features of a plasma membrane adapt it for its functions. (6)

1. phospholipid bilayer (as a barrier); 2 forms a barrier to water soluble / charged substances / allows non-polar substances to pass OR 2. maintains a different environment on each side / compartmentalisation; 3 bilayer is fluid; 4 can bend to take up different shapes for phagocytosis / form vesicles / self repair; 5 channel proteins (through the bilayer) / intrinsic protein; 6 let water soluble / charged substances through / facilitated diffusion; 7 carrier proteins (through the bilayer); 8 allow facilitated diffusion / active transport; 9 surface proteins / extrinsic proteins, glycoproteins / glycolipids; 10 cell recognition / act as antigens / receptors; 11 cholesterol; 12 regulates fluidity / increases stability;

The diagram shows part of a cellulose molecule. Name part A. Name bond B. (2)

1. β/beta Glucose; 2. Glycosidic;

Some people cannot digest lactose when they are adult. They could digest lactose when they were children. Use your knowledge of water potential to explain why these adults get diarrhoea when they drink milk. (2)

1.Low(er) water potential in lumen / intestine / gut; 2. Water enters lumen / leaves (body) cells / by osmosis;

What is meant by a gene? (2)

1.a length of DNA; 2. that codes for a single protein / polypeptide;

What is the equation which represents the reaction catalysed by ATP synthase? (1)

ADP + Pi ----> ATP + H2O

Write a simple equation to show how ATP is synthesised from ADP. (1)

ADP + Pi → ATP

Describe one way that the lock and key model is different from the induced fit model (1)

Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around substrate / (already) fits the substrate / is complementary (before binding);

Suggest how the scientists may have treated the milk to remove lactose (1)

Add lactase;

What is a gene pool? (1)

All the alleles in a population;

Describe the relationship between size and surface area to volume ratio of organisms (1)

As size increases, ratio (of surface area to volume) decreases;

Name box the process by which prokaryotic cells divide (1)

Binary fission;

What information is required in order to calculate the growth rate of a population? (2)

Birth rate and death rate = 2 marks;; OR 1. Change in population / births and deaths / population at start and end; 2. In a given time;

Explain what is meant by birth rate (1)

Births per thousand/given number of the population and per year/given period of time;

Which test could the scientists have used to identify that there are amino acids in white wine? (1)

Biuret;

Explain what is meant by codominant alleles (1)

Both alleles are expressed/shown (in the phenotype);

Explain what is meant by codominant alleles. (1)

Both alleles are expressed/shown (in the phenotype);

The scientists measured cell damage by measuring the activity of lysosomes. Give one function of lysosomes. (1)

Break down cells / cell parts / toxins.

Explain why the scientists homogenised the tissue (1) [fractionation]

Breaks open cells / disrupts cell membrane / releases cell contents / releases organelles / break up cells;

Some substances can cross the cell-surface membrane of a cell by simple diffusion through the phospholipid bilayer. Describe other ways by which substances cross this membrane. (5)

By osmosis (no mark) 1. From a high water potential to a low water potential/down a water potential gradient; 2. Through aquaporins/water channels; By facilitated diffusion (no mark) 3. Channel/carrier protein; 4. Down concentration gradient; By active transport (no mark) 5. Carrier protein/protein pumps; 6. Against concentration gradient; 7. Using ATP/energy (from respiration); By phagocytosis/endocytosis (no mark) 8. Engulfing by cell surface membrane to form vesicle/vacuole; By exocytosis/role of Golgi vesicles (no mark) 9. Fusion of vesicle with cell surface membrane;

Give two advantages of ATP as an energy-storage molecule within a cell. (2)

Cannot pass out of cell; Quickly / easily broken down (hydrolysed) / broken down in a on-step reaction / immediate source of energy; Stores / releases small amounts of energy;

Cholera bacteria are prokaryotic cells. Give three structures found in prokaryotic cells but not in eukaryotic cells. (3)

Capsule / glycocalyx / slime layer; Circular / ring of / non-linear DNA / DNA without histones; Plasmid; Flagellum; Pilus; Small / less dense / 70s ribosomes;

Homologous chromosome carry the same genes but they are not genetically identical. Explain why. (1)

Carry different alleles.

Some scientists support the theory that mitochondria are organelles that evolved from prokaryotic cells. Give one piece of evidence that supports the theory that mitochondria evolved from prokaryotic cells. (1)

Circular DNA / smaller/70S ribosomes / no introns / no histones/proteins associated with DNA;

What term is used to describe populations of different species living in the same habitat? (1)

Community;

A starch molecule has a spiral shape. Explain why this shape is important to its function in cells. (1)

Compact / occupies small space / tightly packed;

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (6)

Comparisons 1. Nucleotide structure is identical; 2. Nucleotides joined by phosphodiester bond; OR 2. Deoxyribose joined to phosphate (in sugar,phosphate backbone); 3. DNA in mitochondria / chloroplasts same /similar (structure) to DNA in prokaryotes; Contrasts 4. Eukaryotic DNA is longer; 5. Eukaryotic DNA contain introns, prokaryotic DNA does not; 6. Eukaryotic DNA is linear, prokaryotic DNA is circular; 7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells. (5)

Comparisons 1. Nucleotide structure is identical; 2. Nucleotides joined by phosphodiester bond; OR 2. Deoxyribose joined to phosphate (in sugar, phosphate backbone); 3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes; Contrasts 4. Eukaryotic DNA is longer; 5. Eukaryotic DNA contain introns, prokaryotic DNA does not; 6. Eukaryotic DNA is linear, prokaryotic DNA is circular; 7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

Name the type of reaction that joins monosaccharides together (1)

Condensation (reaction)

Name the type of reaction that joins monosaccharides together. (1)

Condensation (reaction);

The blood pressure is high at the start of the capillary. Explain how the left ventricle causes the blood to be at high pressure. (1)

Contracts;

Name the blood vessels that carry blood to the heart muscle (1)

Coronary arteries;

Other than independent segregation, give one way in which meiosis allows the production of genetically different cells. (1)

Crossing over / alleles exchanged between chromosomes or chromatids / chiasmata formation / genetic recombination;

A particular gene is 562 base-pairs long. However, the resulting mRNA is only 441 nucleotides long. Explain this difference. (1)

DNA contains introns / mRNA is only exons / mRNA is "edited";

The genetic code is degenerate and non-overlapping explain the meaning of these terms. (2)

Degenerate : More than one (base) triplet for each amino acid. Non-overlapping : Each base is part of only one triplet.

What is meant by genetic diversity? (1)

Differences in DNA / differences in base sequence of DNA;

The haemoglobin in one organism may have a different chemical structure from the haemoglobin in another organism. Describe how. (1)

Different primary structure/amino acids/different number of polypeptide chains;

Name the process in which cells become adapted for different functions. (1)

Differentiation/specialisation

The student produced the sucrose solutions with different concentrations from a concentrated sucrose solution. Name the method she would have used to produce these sucrose solutions. (1)

Dilution series;

Endopeptidases and exopeptidases are involved in the hydrolysis of proteins. Name the other type of enzyme required for the complete hydrolysis of proteins to amino acids. (1)

Dipeptidase/s;

Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?

Double bond(s); (Bonds) between carbon

Explain how the structures of the walls of arteries and arterioles are related to their functions (4)

Elastic tissue 1. Elastic tissue stretches under pressure / when heart beats then recoils / springs back; 2. Evens out pressure / flow; Muscle 3. Muscle contracts to reduce diameter of lumen / vasoconstriction / constricts vessel; 4. Changes flow / pressure; Epithelium 5. Epithelium smooth; 6. Reduces friction / blood clots / less resistance;

Arteries and arterioles take blood away from the heart. Explain how the structures of the walls of arteries and arterioles are related to their functions. (6)

Elastic tissue 1. Elastic tissue stretches under pressure/when heart beats; 2. Recoils/springs back; 3. Evens out pressure/flow; Muscle 4. Muscle contracts; 5. Reduces diameter of lumen/vasoconstriction/constricts vessel; 6. Changes flow/pressure; Epithelium 7. Epithelium smooth; 8. Reduces friction/blood clots/less resistance;

Describe the part played by the inner membrane of a mitochondrion in producing ATP. (3)

Electrons transferred down electron transport chain; Provide energy to take protons / H+ into space between membranes; Protons / H+ pass back, through membrane / into matrix / through ATPase; Energy used to combine ADP and phosphate / to produce ATP;

Apart from genetic factors what other type of factor causes variation within a species? (1)

Environmental;

Name the type of bond between A and fatty acid X. (1)

Ester.

Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system. Suggest how a blockage in the lymphatic system could cause lymphoedema. (1)

Excess tissue fluid cannot be (re)absorbed / builds up;

Explain why the pH decreases when the lipase is added to the milk (1)

Fatty acids produced;

Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cells completing the cell cycle in a short time. (1)

Form/replace cells quickly/rapidly / divide/multiply/replicate rapidly;

Describe how tissue fluid is formed and how it is returned to the circulatory system (6)

Formation 1. High blood / hydrostatic pressure / pressure filtration; 2. Forces water / fluid out; 2 3. Large proteins remain in capillary; Return 4. Low water potential in capillary / blood; 5. Due to (plasma) proteins; 6. Water enters capillary / blood; 7. (By) osmosis; 8. Correct reference to lymph;

The part of the phospholipid labelled A is formed from a particular molecule. Name this molecule. (1)

Glycerol.

Describe how two amino acids differ from one another. (1)

Have different R group.

Explain the difference in thickness between the pulmonary artery and the pulmonary vein. (1)

High pressure / smoothes out blood flow / artery wall contains more collagen / muscle / elastic (fibres) / connective tissue;

Give one advantage of using a TEM rather than a SEM. (1)

Higher resolution / higher (maximum) magnification / higher detail (of image); OR Allows internal details / structures within (cells) to be seen / cross section to be taken;

In the cell wall, bonds hold the cellulose molecules together side by side. Tick () one box that describes the type of bond that holds the cellulose molecules together side by side. (1)

Hydrogen;

Name the type of chemical reaction which produces amino acids from proteins. (1)

Hydrolysis (reaction);

Phospholipids are one of the storage molecules found in cherry seeds. Name the type of reaction used to break down phospholipids to release phosphate. (1)

Hydrolysis (reaction);

Name the type of reaction that would break down these carbohydrates into their monomers (1)

Hydrolysis;

In 1990 the life expectancy was 70 years. Suggest one reason for the change in life expectancy since 1990. (1)

Improved medical care / improved nutrition / improved sanitation/water treatment / lower infection rates / less disease;

Give two factors which could lead to a decrease in the death rate in a human population. (1)

Improved medical care, improved nutrition, more food, improved sanitation, less disease, improved living conditions, improved economy, war ends;

Chlamydomonas lives in fresh water ponds. Use your knowledge of osmosis to suggest an advantage of using starch as a carbohydrate store. (2)

Insoluble; Reduces/'stops' water entry/osmosis / does not affect water potential / is osmotically inactive;

Gene mutations occur spontaneously. During which part of the cell cycle are gene mutations most likely to occur? Suggest an explanation for your answer. (2)

Interphase / S / synthesis (phase) DNA / gene replication / synthesis occurs / longest stage;

What name is used for the non-coding sections of a gene? (1)

Introns

Identify the test which would be used to show the presence of starch. (1)

Iodine/potassium iodide;

Give three properties of water that are important in biology (3)

Is a metabolite Is a solvent Has a (relatively) high heat capacity Has a (relatively) large latent heat of vaporisation / evaporation Has cohesion / hydrogen bonds between molecules

Describe the function of DNA polymerase (1)

Joins adjacent nucleotides forms sugar-phosphaye backbone.

Describe the role of DNA polymerase in DNA replication (1)

Joins nucleotides ( to form new strand)

An order is a taxonomic group. Fruit flies and mosquitoes belong to the same order of insects. Name the other three taxonomic groups to which fruit flies and mosquitoes both belong (2)

Kingdom, phylum and class;;

The rate of blood flow decreases from the aorta to the capillaries. Use information from the graph to explain why. (1)

Large/increase in (total) cross sectional area / friction / resistance;

Describe the relationship between the size of mammals and the oxygen dissociation curves of their haemoglobins. (1)

Larger the mammal the more to the left/steeper/'higher' is the curve / the higher the affinity for oxygen;

The human heart has four chambers. In which one of the four chambers of the human heart does pressure reach the highest value? (1)

Left ventricle;

What is the name of a position of a gene on a chromosome? (1)

Locus;

The blood pressure decreases along the length of the capillary. What causes this decrease in pressure? (1)

Loss of fluid/volume; Friction/resistance (of capillary wall);

The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why. (1)

Loss of water / loss of fluid / friction (against capillary lining).

An arteriole is described as an organ. Explain why (1)

Made of (different) tissues / more than one tissue;

This cell is adapted for the three functions listed below. Use the diagram to explain how this cell is adapted for each of these functions. Use a different feature in the diagram for each of your answers. - rapid diffusion of substances from the lumen of the gut into the cytoplasm (1)

Microvilli increase area / have large area;

Name two structures in a eukaryotic cell that cannot be identified using an optical microscope. (1)

Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane.

What is the evidence from the diagram that haemoglobin has a quaternary structure? (1)

More that one polypeptide/chain;

Give one way in which blood plasma is different from tissue fluid. (1)

More/larger proteins / less urea/carbon dioxide / more glucose/amino acids/fatty acids/oxygen/ high(hydrostatic) pressure;

High blood cholesterol concentration is a risk factor associated with coronary heart disease. Give two other risk factors associated with coronary heart disease (2)

Named dietary factor(s) / (cigarette) smoking / high blood pressure / gender / age / alcohol / genes / lack of exercise / obesity / stress

Name the chemical element found in all amino acids that is not found in triglycerides. (1)

Nitrogen;

Name two structures present in an epithelial cell from the small intestine that are not present in a cholera bacterium. (2)

Nucleus / nuclear envelope / nuclear membrane / nucleolus; Mitochondrion; (Smooth / rough) ER; Lysosome; Microvillus / brush border; Golgi; Linear / non-circular DNA / chromosome; 80S / denser / heavier / larger ribosomes;

what is meant by genetic diversity? (1)

Number of different alleles of each gene

What is meant by species diversity? (1)

Number of species in a community;

Give the two types of molecule from which a ribosome is made (1)

One of RNA / ribonucleic acid (s) / nucelotide(s) / nucleic acid(s) / rRNA / ribosomal RNA / ribosomal ribonucleic acid One of protein(s) / polypeptide(s) / amino acid (s) / peptide(s) / ribosomal protein.

The genetic code is described as being degenerate. What does this mean? (1)

One/an amino acid (can be) coded for by more than one triplet;

Explain what is meant by a recessive allele (1)

Only expressed/shown (in the phenotype) when homozygous / two (alleles) are present / when no dominant allele / is not expressed when heterozygous;

There are many different types of cell in a leaf, each with its own function. What term is used to describe a structure such as a leaf? (1)

Organ;

Some cells lining the bronchi of the lungs secrete large amounts of mucus. Mucus contains protein. Name one organelle that you would expect to find in large numbers in a mucus-secreting cell and describe its role in the production of mucus. (2)

Organelle named; Function in protein production/secretion; 1. Golgi (apparatus); 2. Package/process proteins; OR 3. Rough endoplasmic reticulum/ribosomes; 4. Make polypeptide/protein/forming peptide bonds; OR 5. Mitochondria; 6. Release of energy/make ATP; OR 7. Vesicles; 8. Secretion/transport of protein;

Explain what is meant by the term population. (1)

Organisms/individuals of one species in a habitat / same place;

Name the type of bond hydrolysed when the short chain of amino acids is removed. (1)

Peptide (bond);

Name the type of bond that joins amino acids together in a polypeptide. (1)

Peptide;

Name the two substances that make up part X. (1)

Phosphate and ribose;

Explain, in terms of pressure, why the semilunar valves open (1)

Pressure is greater below valve / in ventricle than (artery);

Describe the principles and limitations of using a transmission electron microscope to investigate cell structure (5)

Principles 1. Electrons pass through / enter (thin) specimen 2. Denser parts absorb more electrons 3. (So) denser parts appear darker 4. Electrons have short wavelength so give high resolution Limitations 5. Cannot look at living material / Must be in a vacuum 6. Specimen must be (very) thin 7. Artefacts present 8. Complex staining method / complex / long preparation time 9. Image not in 3D / only 2D images produced

What term is used to describe the structure of a protein made of two or more polypeptides? (1)

Quaternary (structure);

Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum. (1)

Red blood cells free in blood / not supported by other cells so cholesterol helps to maintain shape;

Explain why the scientists kept the suspension ice cold during the process (1) [fractionation]

Reduces / prevents enzyme activity;

Explain why the scientists filtered the resulting suspension (1) [fractionation]

Removes (cell) debris / complete cells / tissue;

DNA is a polymer. What is the evidence from the diagram that DNA is a polymer? (1)

Repeating units / nucleotides / monomer / molecules

Name an organelle found in both a chloroplast and a prokaryotic cell. (1)

Ribosome

Trypsin is a protease. It is produced in an inactive form inside some of the cells of the pancreas. Name the part of a pancreatic cell that produces the inactive form of trypsin (1)

Ribosome/rough endoplasmic reticulum;

Describe how a saturated fatty acid is different from an unsaturated fatty acid. (1)

Saturated single/no double bonds (between carbons) OR Unsaturated has (at least one) double bond (between carbons);

Identify one event that occurs during meiosis division 2 but not during division 1 (1)

Separation of (sister) chromatids / division of centromer

A bacterial infection that cannot be treated with one sort of penicillin can be treated with a different sort. Use your knowledge of enzyme action to explain why the different sort of penicillin is effective in treating the infection. (3)

Shape 1. Different penicillin has different shape/structure/ enzyme/active site has specific shape/structure; Binding 2. No longer fits/binds to active site/not complementary to active site/does not form E-S complex; Consequence 3. (Different) penicillin not broken down;

A capillary has a thin wall. This leads to rapid exchange of substances between the blood and tissue fluid. Explain why. (1)

Short diffusion distance/pathway;

Explain what is meant by a phylogenetic relationship. (1)

Shows evolutionary relationship;

Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose. Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose. (2)

Similarity 1. Both contain galactose / a glycosidic bond; Difference 2. Lactulose contains fructose, whereas lactose contains glucose;

Explain why the student pressed down firmly on the coverslip. (1)

Single / thin layer of cells / spread out cells so light passes through (making cells / nuclei visible)

Give one factor, other than asbestos, which increases the risk of developing lung cancer (1)

Smoking / air pollution / specified industrial source;

Scientists who investigate disease may look at risk factors. What is a risk factor? (1)

Something that increases chance / increases probability / makes it more likely;

Species richness and an index of diversity can be used to measure biodiversity within a community. What is the difference between these two measures of biodiversity? (1)

Species richness measures only number of (different) species / does not measure number of individuals;

Name the process that removes base sequences from pre-mRNA to form mRNA. (1)

Splicing;

Describe how the structures of starch and cellulose molecules are related to their functions. (5)

Starch 1. Helical/ spiral shape so compact; 2. Large (molecule)/insoluble so osmotically inactive; 3. Branched so glucose is (easily) released for respiration; 4. Large (molecule) so cannot leave cell/cross cell-surface membrane; Cellulose 5. Long, straight/unbranched chains of β glucose; 6. Joined by hydrogen bonding; 7. To form (micro/macro)fibrils; 8. Provides rigidity/strength;

Explain how the highest blood pressure is produced in the left ventricle (1)

Strongest/stronger contractions;

What is the genome of a cell? (1)

The genome is the complete set of genes in a cell.

Use your knowledge of semi-conservative replication to suggest the role of the single-stranded DNA fragments and the role of the DNA nucleotides. (3)

The role of the single-stranded DNA fragments 1. Template 2. Determines order of nucleotides / bases The role of the DNA nucleotides 3. Forms complementary pairs / A-T , C-G OR 3. Forms complementary (DNA) strand

Give the function of a mitochondrion (1)

The site of aerobic respiration (reactions) OR ATP is made / ADP is phosphorylated;

Explain how the structure of this chamber (left ventricle) causes this high pressure. (1)

Thick muscle/thick walls;

Give one advantage of using a SEM rather than a TEM (1)

Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;

What is the role of RNA polymerase during transcription? (1)

To join nucleotides together to form mRNA/premRNA/RNA;

Explain what is meant by the independent variable. (1)

Variable that is changed;

Other than bacteria, name one type of pathogen (1)

Virus / fungus / protozoan;

Name the two scientists who proposed models of the chemical structure of DNA and DNA replication (1)

Watson and Crick

What factor limits the minimum internal diameter of the lumen of a capillary? (1)

Width / size / diameter of blood cell

When one mole of glucose is respired anaerobically, only 2 moles of ATP are produced. Explain why less energy is released in anaerobic respiration. (1)

glucose only partly broken down / only broken down to lactate;

Explain the importance of the villi (1)

increase the surface area for absorption;

At the end of a sprint race, a runner continues to breathe rapidly for some time. Explain the advantage of this. (2)

lactate / lactic acid has built up / been produced; oxygen used to break down lactate / convert it back to pyruvate / glucose / glycogen;

Give two factors, other than smoking, which increase the risk of coronary heart disease. (2)

more stress / more saturated fats in diet / less time to exercise / reliance on cars;

When glucose is respired what happens to the energy which is not incorporated into ATP? (1)

released as heat;

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