4.0 exam q's

Give the function of glycoproteins.

(surface / extrinsic protein) for cell recognition / binding to hormones / identification

Describe how phospholipid molecules are arranged in a plasma membrane.

The Bilayer is 2 molecules thick. The hydrophilic Head points outwards and the hydrophobic tail points inwards.

Describe two ways in which the appearance of a plant cell wall would differ from a cell membrane when viewed with an electron microscope.

Thicker; Single layer/presence of fibrils in cell wall; plasmodesmata;

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

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

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

(Simple / facilitated) diffusion from high to low concentration / down concentration gradient; Q Do not allow across / along / with concentration gradient 2. Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer; Reject: named molecule passing through membrane by an incorrect route Accept: diagrams if annotated OR 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; Only penalise once if active transport is not named e.g. 'movement against the concentration gradient involves proteins and requires ATP' = 2 marks 5. Active transport / facilitated diffusion involves proteins / carriers; Accept: facilitated diffusion involves channels Reject: active transport involves channels 6. Active transport requires energy / ATP; 7. Ref. to Na+ / glucose co-transport;

Describe how proteins are arranged in a plasma membrane and the part they play in transporting substances into and out of cells.

1 Some proteins pass right through membrane; 2 Some proteins associated with one layer; 3 Involved in facilitated diffusion; 4 Involved in active transport; 5 Proteins act as carriers; 6 Carrier changes shape / position; 7 Proteins form channels / pores; 8 Protein allows passage of water soluble molecules /charged particles /

The bacteria in the intestine are prokaryotic cells. The epithelial cells which line the small intestine are eukaryotic cells. Describe the ways in which prokaryotic cells and eukaryotic cells differ.

1.Prokaryotic cells do not have a nucleus but eukaryotes do. 2 DNA in loop for prokaryotes 3 Prokaryotes DNA is not associated with proteins and do not have chromosomes and do not divide by mitosis; 4 Smaller ribosomes; 5 No membrane-bound organelles such as mitochondria / lysosomes / endoplasmic reticulum /Golgi / chloroplasts; 7 Prokaryotic cells may have mesosomes; 8 Prokaryotic cells smaller; 9 May be enclosed by capsule

Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells.

A cell membrane would have a phospholipid bilayer, allowing only lipids solible substances and small molecules e.g. water to move through. Ions/water soluble substances move through channels in proteins; Some proteins are gated; Reference to diffusion; Protein carriers are associated with facilitated diffusion and active transport. Different cells have different proteins; Correct reference to cytosis;

Describe how the distribution of cell membranes in a prokaryotic cell such as a bacterium differs from that in a cell from a plant leaf

A plant cell has an absence of nuclear envelope/membrane; The plant membrane is bounded organelles; Such as mitchondria , chloroplast cacuole etc. Mesosomes in prokaryotes;

Galactose and glucose are absorbed by epithelial cells lining the small intestine but some other monosaccharides are not. Use your knowledge of active transport to explain this difference

Active transport. involves the use of carrier proteins; Molecules will have a different shape and only the ones that will fit will be absorbed.

Amino acids are absorbed from the lumen of the ileum. Describe how epithelial cells are able to absorb amino acids continuously.

Amino acids are removed from the cell into the blood stream by active transport using energy released from ATP. This maintains a low concentration in the cell which maintains a concentration gradient between the ileum and the cell. Then amino acids can enter by facilitated diffusion.

Describe how phospholipids are arranged in a plasma membrane.

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

The molecular formula of galactose is C6H12O6. What is the molecular formula of lactose?

C12 H22 O11

Suggest why glucagon is able to bind to liver cells but not to cells in other parts of the body.

Cells in other parts of the body do not have these receptors but Liver cells have these receptors;

Describe a chemical test you could carry out to show that a piece of coconut contains lipids.

Crush coconut in ethanol / alcohol; Add (to) water (Order of adding is critical for this point); Emulsion / white colour;

An optical microscope cannot be used to see a plasma membrane. Explain why.

Does not have the resolution / cannot distinguish between points this close together; As light has longer wavelength;

Explain how a lysosome is involved in the release of cholesterol from the vesicle.

Enzymes digest the molecules

Describe the function of the hydrophobic fatty acid tails within the phospholipid bilayer.

Form(water) impermeable barrier to water-soluble substances / selectively permeable / allows non-polar molecules to pass through; allows cell to maintain different concentrations either side; makes membranes self-sealing / able to fuse with other membranes / able to form vesicles / gives flexibility / fluidity;

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

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

Young carrots store sugars in their tissues but, in older carrots, some of this is converted to starch. How would using cylinders of tissue from older carrots affect the results obtained for a sucrose solution of 0.6 mol dm-3? Give a reason for your answer.

Greater decrease / length smaller; More water removed; Greater difference in water potential / cell with higher / less negative water potential; Starch is insoluble / has no effect on osmosis

Explain how amino acid molecules may be linked to form a polypeptide chain which is folded into a specific tertiary shape

In a condensation reaction, there is the removal of water molecule from amino and carboxyl groups and a peptide bonds is formed. Nonds form between R-groups e.g. sulphur-containing amino acids / ionic bonds / hydrogen bonds form which fold the protein into a specific tertiary structure.

Describe what causes ion movement in the ileum and what poison does to it.

Ion movement is by active transport; 3 ATP / energy needed for active transport; 4 respiration provides ATP / energy; 5 poison inhibits / stops respiration / ATP production;

When a suspension of mitochondria is prepared from liver, the tissue is ground in a buffer solution, then centrifuged. Explain why a buffer solution is used.

Keeps pH constant so proteins and enzymes in mitochondria are not denatured

Diarrhoea involves the production of large amounts of watery faeces. Explain the link between the presence of lactose in the intestine and diarrhoea.

Lactose produces a more negative water potential; So water moves into the intestine by osmosis down the water potential gradient.

Explain how you would use a graph to predict the concentration of sucrose that would result in no change in length of the carrot cylinders

Line / curve of best fit; Extrapolate (and read off) / find where it crosses x-axis

Explain how active transport of sodium ions out of the cell helps to ensure a rapid rate of diffusion of sodium ions into the cell.

Maintains diffusion gradient

Adaptations of the alveoli and ileum?

Many alveoli / alveoli walls folded provide a large surface area; Neutral: alveoli provide a large surface area 2. Many capillaries provide a large surface area; 3. (So) fast diffusion; Neutral: greater / better diffusion Neutral: fast gas exchange Allow 'fast diffusion' only once 4. Alveoli or capillary walls / epithelium / lining are thin / short distance between alveoli and blood; Reject: thin membranes / cell walls Accept: one cell thick for 'thin' 5. Flattened / squamous epithelium; Accept: endothelial 6. (So) short diffusion distance / pathway; 7. (So) fast diffusion; 8. Ventilation / circulation; Accept: descriptions for ventilation / circulation 9. Maintains a diffusion / concentration gradient; 10. (So) fast diffusion;

A plant cell was observed with an optical microscope. Describe how the length of the cell could be estimated.

Measure diameter of field with ruler; And proportion taken up by the cell; or Measure length with (eyepiece) graticule / eyepiece scale; Calibrated against stage micrometer / something of known length;

The water potential of a plant cell is -400 kPa. The cell is put in a solution with a water potential of -650 kPa. Describe and explain what will happen to the cell.

Membrane / cytoplasm shrinks / pulls away from cell wall / cell plasmolysed / goes flaccid; Water moves down water potential gradient / to lower / more negative water potential; By osmosis;

Sodium ions diffuse into the cell from the lumen of the intestine. They move out of the cell into the blood by active transport. There is a rapid rate of diffusion of sodium ions into the cell. (i) Explain how one structural feature shown on the diagram helps to ensure a rapid rate of diffusion.

Microvilli give a large SA for absorption

Explain the link between active transport and the presence of large numbers of the organelles labelled A in this cell.

Mitochondria are the site of respiration and they release energy through breaking down ATP and it is necessary for active transport to move substances against concentration gradient;

Suggest one advantage of milk-producing cells containing large numbers of mitochondria.

Mitochondria supply energy in the form of ATP for active transport , absorption against concentration gradient , synthesis , anabolism , exocytosis pinocytosis;

Cholesterol is a substance needed in human cells. It is carried in the blood in a particle called a low-density lipoprotein (LDL). Suggest why an LDL will only attach to certain areas on the plasma membrane of a cell.

Only parts of membrane with receptors will the LDL attach to.

Glucose moves into the cell by facilitated diffusion. Osmosis also takes place across the plasma membrane. Give two differences between facilitated diffusion and osmosis.

Osmosis only involves movement of water; Facilitated diffusion involves proteins / carriers;

Describe the property of the cell surface membrane which allows osmosis to take place.

Partially permeable and only allows water molecules through .

Osmosis has been described as a special case of diffusion. Describe two ways in which you would expect the movement of water into a cell by osmosis to be similar to the diffusion of oxygen into a cell.

Passive forms of transport and so does not require ATP; energy not required There is movement down gradient;

Some substances pass through the plasma membrane of a milk-producing cell by diffusion. Describe the structure of a plasma membrane and explain how different substances are able to pass through the membrane by diffusion.

Phospholipids form a bilayer with the hydrophilic heads pointing outside and the hydrophobic tails point inside. There are intrinsic and extrinsic proteins spanning the surface. Cholesterol and glycoproteins are on the surface. Substances move down concentration gradient Reject references to across or along a gradient Water/ions through channel proteins/pores; 7 Small/lipid soluble molecules/examples pass between phospholipids/through phospholipid layer; 8 Carrier proteins involved with facilitated diffusion;

Explain two ways, shown in the diagram, in which the structure and activities of this cell ensure efficient absorption of glucose from the inside of the kidney tubule.

Presence of microvilli formed from a folded membrane increases surface area; Removal of glucose out of cell increases / maintains concentration gradient;

Describe the role of proteins in the transport of molecules and ions across cell surface membranes.

Proteins allow the passage of charged particles, ions and water soluble molecules across the cell surface membrane. Channel proteins are specific o allow certain things or certain charged ion to pass through. Specificity lined to shape of receptor sites; functions by changing shape / conformation; facilitated diffusion with concentration gradient; active transport against concentration gradient; active transport requiring energy / ATP;

Describe and explain the effect of an increase in temperature on the rate of diffusion.

Rate of diffusion increases as temperature rises; (Molecules) have more (kinetic) energy; Molecules move faster;

A group of students investigated the effect of sucrose concentration on the change in length of cylinders of tissue cut from a young carrot. They measured the initial lengths of the carrot cylinders, then placed one in each of a number of sucrose solutions. After 18 hours, they removed the carrot cylinders and measured their final lengths. The carrot cylinders were left for 18 hours in the sucrose solutions. Explain why they were left for a long time.

Reaches equilibrium / no further / maximum change in length;

Amylase is an enzyme, found in saliva, which breaks down starch. It works best at a pH of 8. Explain why amylase does not function in the stomach where the pH is approximately 3.

The charges on the Hydrogen bonds are altered. So the tertiary structure changes and the enzyme is denatured which will affect active site Starch cannot bind to form enzyme-substrate complex so no starch is broken down.

Describe the structure of a cell membrane.

The membrane is made of a double layer of phospholipid molecules, with intrinsic protein molecules passing right through. There are some selective channels/pores to allow the exchange of molecules between inside and outside the cell. Extrinsic proteins lie on the surface; The membrane has cholesterol, giving it stability. Carbohydrates are attached to proteins.

Describe and explain how you would expect the height to breadth ratio of an epithelial cell from a lung alveolus to differ from the height to breadth ratio of a milk-producing cell.

The ratio would be smaller; Cell is thin, has large surface area and is adapted for diffusion;

The hormone glucagon is a protein. It targets liver cells but does not affect other cells in the body. Explain why.

The receptor molecules have a specific shape of the receptor site which is only complementary to the glucagon molecule shape so nothing else can fit into it.

The receptor molecules to which hormones bind are proteins. Glucagon is a hormone. (i) Explain why glucagon will only bind to one particular type of receptor molecule.

The receptor will have a particular tertiary structure. So glucagon will bind because only it has the complementary shape.

Some people who have a deficiency of galactokinase suffer from cataracts. These cataracts result from an increase in the amount of water in the lens of the eye. In the absence of galactokinase, galactose is converted to galacticol. Galacticol is a soluble substance whose molecules are too large to pass through cell membranes. Explain why galacticol causes an increase in the amount of water in the lens of the eye

The water potential of cells becomes more negative which allows water to enter by osmosis.

Explain why the water potential of the distilled water is higher than the water potential of the cytoplasm of the cell;

There are more "free" water molecules outside in distilled water; Water molecules inside cell "bound" to solute molecules; The more water molecules, the greater pressure they exert and the higher the water potential; water potential of distilled water =0; So the presence of solute reduces water potential

Explain how the amino acids from which proteins are built differ in structure from each other.

They have different R groups.

The lactose-containing vesicles increase in diameter as they move towards the plasma membrane of the milk-producing cell. Use your knowledge of water potential to explain why.

Water potential inside vesicle more negative/lower; Water moves into vesicle by osmosis/diffusion;

An artificial membrane was made. It consisted only of a bilayer of phospholipid molecules. In an investigation, the permeability of this artificial membrane was compared with the permeability of a plasma membrane from a cell. Explain why: (i) both membranes allowed lipid soluble molecules to pass through ii) only the plasma membrane allowed glucose to pass through.

i) Both membranes contain phospholipid / lipid (bilayer) ii) Glucose was unable to pass through artificial membrane as it is not lipid soluble; Glucose transported by proteins which are found in plasma membrane but not found in artificial membrane;

Explain why the structure of a membrane is described as fluid-mosaic.

idea of molecules / named molecules moving = Fluid; idea of both proteins and phospholipids = Mosaic;

Tradescantia is a house plant. There are small hairs on its flowers. These hairs are made of cells. What does Figure 2 suggest about the permeability of the plasma membranes surrounding these cells?

partially / selectively permeable accept semi-permeable allows water to pass through but not potassium nitrate / solute;

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

phospholipid bilayer (as a barrier); 2 forms a barrier to water soluble / charged substances / allows non-polar substances to pass OR 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;

What is present in the space labelled F? Explain your answer.

potassium nitrate (solution); cell wall permeable;

When pieces of carrot are placed in water, chloride ions are released from the cell vacuoles. Identical pieces of carrot were placed in water at different temperatures. The concentration of chloride ions in the water was measured after a set period of time. The graph shows the results. Describe and explain the shape of the curve.

slow rise, sharp rise, levelling off (reject 'becomes constant'); diffusion rate increases / description of diffusion rate, e.g. increase in kinetic energy increases loss of ions; sharp rise / above 50oC proteins are denatured; levelling off due to concentration of chloride ions in water becoming equal / maximum loss of Cl- ions;

Explain ow the evidence from the graph that this substance is entering the cell by facilitated diffusion and not by simple diffusion.

the curve levels off above a certain external concentration of substance; as channel proteins are saturated with molecules (and no more can be carried);

How would the water potential of the sap in the vacuole of cell E differ from the water potential of the sap in the vacuole of cell D? Explain your answer.

water potential more negative / lower in cell E; water removed; greater solute / sap concentration (in cell);