BIOLOGY

Control of the heartbeat in terms of myogenic muscle contraction, the role of the pacemaker, nerves, the medulla of the brain and epinephrine (adrenaline).

- Contraction of the heart tissue is myogenic - SA node (pacemaker) stimulates atria to contract hence initiating each heartbeat - it is located in the right atrium and under control of medulla oblongata in brain - autonomic nerves (and hormones!) carry impulses from the brain to speed up/slow down the heart: ..Secretion of epinephrine/adrenaline/noradrenaline increases the pace ..Secretion of acetylcholine reduces the pace - Adrenal glands release epinephrine/adrenaline, carried by blood to heart to increase pace

Limiting factors that contribute to K (carrying capacity).

- Food and water availability - Space for territories and nesting - Availability of mates - Disease - Predation - Environmental change

Importance of SA:vol ratio

- The rate of metabolism of a cell is a function of its mass / volume - The rate of material exchange in and out of a cell is a function of its surface area - As the cell grows, volume increases faster than surface area (leading to a decreased SA:Vol ratio) - If the metabolic rate is greater than the rate of exchange of vital materials and wastes, the cell will eventually die - Hence the cell must consequently divide in order to restore a viable SA:Vol ratio and survive - Cells and tissues specialised for gas or material exchange (e.g. alveoli) will increase their surface area to optimise the transfer of materials

Explain the consequence of a base substitution mutation in relation to the process of transcription and translation using the example of sickle cell anaemia.

- caused by a gene mutation - single base substitution of the haemoglobin gene - changes the code on the DNA, which leads to a change in the mRNA (transcription) and polypeptide chain (translation) as tRNA adds the wrong amino acid to the polypeptide chain - DNA copy: GAG to GTG / CTC to CAC / T to A - mRNA copy: GUG to GAG - polypeptide: valine instead of glutamic acid In homozygotes: abnormal hemoglobin is produced, causing abnormal red blood cells (which have a sickle-shape) - this lowers their ability to carry oxygen and they do not survive long (burst) - sickle-cell allele is codominant - symptoms include: physical weakness, pain, blood vessels/capillaries/circulatory problems, organ failure, heart/kidney damage. Blood vessels become blocked, capillaries may cause pain or organ failure - In heterozygotes: both the normal allele and sickle cell allele are codominant - resulting in malaria resistance

Explain the action of the heart in terms of collection of blood, pumping blood and opening and closing of valves.

1. Blood returning from all parts of the body (except lungs) enter the right atrium via the vena cava - this blood is relatively deoxygenated 2. Walls of the atria contract, pushing blood from the atria into the ventricles through the atrioventricular valves (which are open). Semilunar valves are closed, so the ventricles fill with blood. 3. Walls of the ventricles contract forcefully, causing blood pressure to rapidly rise inside them. This rise in pressure causes: a. Closing of atrioventricular valves, preventing back-flow (into atria) b. Opening of semilunar valves, allowing blood to be pumped out into arteries. c. Forcing of blood into the aorta and pulmonary artery. At the same time, the atria starts to refill as they collect blood from the veins. 4. The ventricles stop contracting, and as pressure falls inside them, the semilunar valves close, preventing back-flow of blood from arteries to ventricles. When the ventricular pressure drops below the atrial pressure, the atrioventricular valves open. Blood entering the atrium from veins then flows on to begin filling the ventricles. 5. The next heartbeat begins when walls of the atria contract again.

Role of hormones in menstrual cycle

1. Increase in FSH levels stimulates follicle development in ovary, and causes estrogen secretion by follicle cells - enhancing follicle's response to FSH. This positive feedback increases estrogen levels and stimulates repair of uterus lining 2. Estrogen levels rise to a peak, stimulating LH secretion - causing ovulation (release of egg from follicle) 3. LH levels rise to a peak, causing follicle cells to secrete less estrogen (negative feedback) and more progesterone. After ovulation, LH stimulates follicle to develop into corpus luteum 4. Corpus luteum secrets large amounts of progesterone, causing uterus lining to prepare for an embryo 5. High progesterone and estrogen levels inhibit FSH and LH secretion - negative feedback because FSH and LH stimulated estrogen and progesterone secretion 6. No formation of embryo/fertilisation of egg a. LH levels fall, corpus luteum degenerates b. Progesterone and estrogen levels fall c. Fall in progesterone stimulates breakdown of uterus lining 7. FSH no longer inhibited, so a new follicle is stimulated and cycle begins again. If fertilisation of egg occurs, the zygote releases a hormone (HCG) which maintains the corpus luteum

Explain the principles of synaptic transmission.

1. Nerve impulse reaches end of pre-synaptic neuron 2. Calcium ions diffuse in to axon terminal through calcium channels 3. Vesicles of neurotransmitter move towards pre-synaptic membrane, fuse with it and release their contents into synaptic cleft 4. Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the post-synaptic membrane 5. Sodium ions enter post-synaptic neuron, causing depolarisation. An action potential is hence initiated. 6. Calcium is pumped out (with help of ATP). Neurotransmitter broke down in the clef and reabsorbed into vesicles

Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass.

1. Release of O2 (by-product) • Aquatic plants release bubbles of oxygen when they carry out photosynthesis. • Measure of volume through a gas syringe (drawing gas bubble into a capillary tube and measuring length), counting rising oxygen bubbles or using an oxygen probe (to find concentration of O2) 2. Uptake of CO2 (raw material) • Leaves take CO2 from the air/water around them, but this cannot be measured directly. It can be measured using an aquatic plant. • Measured by change in pH (increase in pH shows increase in CO2 fixation) • As CO2 is absorbed from the water, the pH of the water rises. This can be monitored with pH indicators/meters by measuring colour change of pH indicator. The change in pH thus measures CO2 uptake by a plant (increased CO2 uptake = more alkaline pH) 3. Increase in biomass (products are used to produce cell walls and new tissue). • Glucose production can also be indirectly measured by a change in a plant's biomass (weight). • If batches of plants are harvested at a series of times, and the biomass of the batches is determined, the rate of increase in biomass gives an indirect measure of rate of photosynthesis • Can also test change in starch levels in a plant via iodine staining (resulting solution turns purple) and quantified using a colorimeter

Outline the evidence for evolution provided by the fossil record.

A fossil is the preserved remains or traces of any organism from the remote past Fossil evidence may be either: - Direct (body fossils): Bones, teeth, shells, leaves, etc. - Indirect (trace fossils): Footprints, tooth marks, tracks, burrows, etc. Types of Fossils The totality of fossils (both discovered and undiscovered) is known as the fossil record The fossil record reveals that, over time, changes have occurred in features of organisms living on the planet (evolution) Moreover, different kinds of organisms do not occur randomly but are found in rocks of particular ages in a consistent order (law of fossil succession) This suggests that changes to an ancestral species was likely responsible for the appearance of subsequent species (speciation via evolution) Furthermore, the occurrence of transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken within a single genus. While fossils may provide clues regarding evolutionary processes and ancestral relationships, it is important to realise that the fossil record is incomplete Fossilization requires a unusual combination of specific circumstances to occur, meaning there are many gaps in the fossil record Only the hard parts of an organism are preserved and often only fragments of fossilized remains are discovered

Deduce the genotype and phenotype of individuals in pedigree charts.

AUTOSOMAL DOMINANCE • The trait will be shown in all generations • All affected individuals must have at least one affected parent • If two parents are unaffected, all offspring must be unaffected • If two parents are affected, they may have offspring who are unaffected (if parents are heterozygous) AUTOSOMAL RECESSIVE • If two parents show a trait, all children must also show the trait (homozygous recessive) • Two unaffected parent may have a children that show the trait • An affected individual may have two normal parents (if parents are both heterozygous carriers) X-LINKED RECESSIVE • If a female shows the trait, so will all sons as well as her father • The disorder is more common in males

Calculating actual size of molecules

Actual size = Size of image (with ruler) ÷ Magnification Magnification = Size of image (with ruler) ÷ Actual size of object (according to scale bar)

Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.

Antibiotic resistance can be inherited; the alleles for resistance can be passed from one cell to another by exchange of plasmids •some varieties are more resistant than others •bacteria reproduce very rapidly and have high mutation rates - causing evolution to also occur rapidly •some bacteria will have this gene (and become resistant), while others will lack the gene and die if exposed to the antibiotic; this results in a change in the genetic makeup of a population •increased exposure to antibiotics is the environmental change that selects for resistant varities •eg in hospitals, misuse of antibiotics, inappropriate prescriptions or not fnishing them, animal feed

Explain why antibiotics are effective against bacteria but not against viruses.

Antibiotics are substances that kill / inhibit growth of bacteria by targeting the metabolic pathways of prokaryotes • they can target specific prokaryotic features (eg key enzymes, 70S ribosomes and the bacterial cell wall) • eukaryotic cells lack these features; antibiotics can kill bacterial cells without harming humans (or viruses) • Viruses do not carry out metabolic reactions themselves (so antibiotics are ineffective towards them) but instead infect host cells and take over their cellular machinery • Viruses need to be treated with specific antiviral agents that target features specific to viruses (e.g. reverse transcriptase in retroviruses)

Distinguish between antigens and antibodies.

Antigens: foreign substances that stimulate the production of antibodies. Antibodies: globular proteins produced by certain white blood cells (B lymphocytes, plasma cells) that recognize and bind to specific antigens.

Discuss the ethical issues of therapeutic cloning in humans.

Arguments for Therapeutic Cloning May be used to cure serious diseases or disabilities with cell therapy (replacing bad cells with good ones) Stem cell research may pave the way for future discoveries and beneficial technologies that would not have occurred if their use had been banned Stem cells can be taken from embryos that have stopped developing and would have died anyway (e.g. abortions) Cells are taken at a stage when the embryo has no nervous system and can arguably feel no pain Arguments Against Therapeutic Cloning Involves the creation and destruction of human embryos (at what point do we afford the right to life?) Embryonic stem cells are capable of continued division and may develop into cancerous cells and cause tumors More embryos are generally produced than are needed, so excess embryos are killed With additional cost and effort, alternative technologies may fulfil similar roles (e.g. nuclear reprogramming of differentiated cell lines)

Explain the relationship between the structure and function of arteries, capillaries and veins (all three are blood vessels)

Arteries - Arteries carry blood at high pressure (80 - 120 mm Hg) - They have a narrower lumen (to maintain high pressure) surround by a thick wall made of two layers - The middle layer (tunica media) contains muscle and elastin to help maintain pulse flow (it can contract and stretch) - The outer layer contains collagen which prevents the artery rupturing due to the high pressure blood flow Veins - Veins carry blood under low pressure (<10 mm Hg) - Very wide lumen (keeps pressure low and allows greater flow of blood) - Tissue walls surrounding the vein are thin (blood is not travelling in rhythmic pulses) - Have valves to prevent blood pooling at extremities (arteries do not have valves) Capillaries - Involved with material and gas exchange with the surrounding body tissue - Blood pressure in the capillaries is relatively low (~15 mm Hg) and they have a very small diameter (~5 micrometers wide) - Their wall is made up a a single layer of cells to allow for ease of diffusion - Capillaries may contain pores to aid the transport of material

Distinguish between autotroph, heterotroph and sapotrophs.

Autotrophs: synthesise their own food from inorganic molecules; use a non-organic energy source (light) - some autotrophs use light (photosynthesis), whilst others use inorganic chemical reactions (chemosynthesis) Heterotrophs: derive energy from organic molecules/other organisms - ingest/consume food Saprotrophs: obtain energy from non-living matter/dead organisms - digest organic matter extracellularly

Outline one therapeutic use of stem cells.

Blood cells - placenta and umbilical cord of a baby 1. At the end of childbirth, the umbilical cord is taken and blood is collected from the cord (containing many hematopoietic stem cells that divide / differentiate into any type of blood cell) 2. Red blood cells are removed from the blood and remaining fluid is checked for disease-causing organisms and stored in liquid nitrogen 3. Cord blood can be used to treat patients, especially children, who have developed certain forms of leukaemia (a cancer in which the cells in bone marrow divide uncontrollably, producing far too many white blood cells). Hence the patient's tissue type is matched with cord blood in the band. If suitable cord blood is available; the patient is given chemotherapy drugs to kill bone marrow cells. 4. The cord blood is then introduced into the patient's blood system. The hematopoietic stem cells establish in the bone marrow, where they divide repeatedly to build up a population of bone marrow cells to replace those killed by chemotherapy drugs.

Describe the inheritance of colour blindness and haemophilia as examples of sex linkage.

COLOUR BLINDNESS • The gene for normal vision occurs on the sex chromosome. • Many men are affected compared to the number of affected women. This is because women with normal colour vision may be homozygous for normal vision or heterozygous for normal colour vision. • For a female to have colour blindness, she must be homozygous recessive for this allele, which is extremely rare. However, male with a single recessive allele for colour blindness will be affected. • XA = unaffected ; Xa = affected HAEMOPHILIA • The genes controlling the production of blood proteins are located on the X chromosome. • It is caused by a recessive allele. • In a male, a single X chromosome carrying a defective allele will result in the disease. For a female, she must be homozygous recessive. • XH = unaffected ; Xh = affected

Discuss the cause, transmission and social implications of AIDS.

Cause Acquired Immunodeficieny Syndrome (AIDS) is a collection of symptoms and infections caused by the destruction of the immune system by HIV While HIV infection results in a lowering in immunity over a number of years, AIDS describes the final stages when observable symptoms develop Transmission HIV is transmitted through the exchange of bodily fluids (including unprotected sex, blood transfusions, breast feeding, child birth, etc.) The risk of exposure to HIV through sexual contact can be reduced by using latex protection (condoms) A minority of people are immune to HIV infection (they do not have the CD4+ T cell receptor that HIV needs to infect the cell) Social Implications People with HIV may be stigmatised and discriminated against, potentially leading to unemployment and poverty Majority of people who die from AIDS are at a productive age, which may cripple a country's workforce and economic growth It can result in an increased number of orphans, taxing a country's welfare resources Poverty may increase transmission of AIDS (due to poor education and high cost of treatments), creating a moral obligation for assistance from wealthier countries

Define cell respiration.

Cell respiration: the controlled release of energy in the form of ATP (adenosine triphosphate) from organic compounds in a cell. A cell's energy sources from sugars and other substances which can be broken down to release the energy that holds their molecules together.

Consequences of a global temperature rise on arctic ecosystems

Changes in climate of earth, salinity of oceans, ocean currents Rising sea levels, flooding, glaciers melting Expansion of temperate species increasing competition with native species (e.g. red fox vs arctic fox) Decomposition of detritus / release of organic matter previously trapped in ice will significantly increase CO2 greenhouse gas levels (potentially worsening temperature changes) Increased spread of pest species / pathogens (threatening local wildlife) Behavioural changes in native species (e.g. hibernation patterns of polar bears, migration of birds and fish, seasonal blooms of oceanic algae) Loss of habitat (e.g. early spring rains may wash away seal dens) Extinction and resultant loss of biodiversity as food chains are disrupted

Outline the differences in absorption of red, blue and green light by chlorophyll.

Chlorophyll is the main pigment used to absorb light in photosynthesis. Its structure allows it to absorb some colours or wavelengths of light better than others in the light dependent stage of photosynthesis. Chlorophyll absorbs red and blue light more readily, but it cannot absorb green light and instead reflects it. • This explains why leaves of plants are green - except when the presence of other pigmented substances (e.g. anthocyanins) produces a different colour. • Deciduous trees stop producing high amounts of chlorophyll in the winter (due to insufficient sunlight), allowing other photosynthetic pigments (e.g. xanthophylls, carotenoids) to come to the fore, which changes the colour of the leaf

Define clone.

Clone: group of genetically identical organisms / group of genetically identical cells derived from a single parent cell.

Describe ABO blood groups as an example of codominance and multiple alleles.

Codominant alleles: pairs of alleles that both affect the phenotype when present together in a heterozygote. When assigning alleles for codominance, the convention is to use a common letter to represent dominant / recessive and use superscripts to represent the different codominant alleles • I stands for immunoglobulin (antigenic protein on blood cells) • A and B stand for the codominant variants The ABO gene has three alleles: IA, IB and i • IA (blood group A) and IB (blood group B) are codominant, whereas i (blood group O) is recessive (no antigenic protein is produced) Codominance means that both IA and IB alleles will be expressed within a given phenotype

Outline the evidence for evolution provided by homologous structures.

Comparative anatomy of groups of animals or plants shows certain structural features are basically similar, implying a common ancestry Homologous structures are those that are similar in shape in different types of organisms despite being used in different ways An example is the pentadactyl limb structure in vertebrates, whereby many animals show a common bone composition, despite the limb being used for different forms of locomotion (e.g. whale fin for swimming, bat wing for flying, human hand for manipulating tools, horse hoof for galloping, etc.) This illustrates adaptive radiation (divergent evolution) as a similar basic plan has been adapted to suit various environmental niches The more similar the homologous structures between two species are, the more closely related they are likely to be

Distinguish between consumers, detritivores and saprotrophs.

Consumers: ingest organic matter which is living / has been recently killed; derive energy by eating each other / the producers • Primary (herbivores) • Secondary (carnivores & omnivores) Decomposers: derive energy from non-living / dead organic matter • Detritivores (earthworms, woodlice): ingests non-living / dead organic matter • Saprotrophs (bacteria, fungi): lives in or on non-living / dead organic matter, secreting digestive enzymes into it & absorbing digestive products

Outline the digestion, absorption and assimilation of proteins, carbohydrates and lipids in humans.

DIGESTION - large molecules must be digested into small molecules - pepsin (ONLY from stomach, aciditiy ~1.5pH) digests proteins into polypeptides - polypeptides are further digested by trypsin (from small intestine, aciditiy ~8pH) into amino acids ABSORPTION The movement of a fluid or dissolved substances across a membrane. It occurs in the microvilli of the small intestine. -Amino acids and glucose are absorbed via diffusion/active transport into the capillaries, and are then carried away by the bloodstream throughout body. Amino acids and glucose then diffuse into cells and are absorbed via active transport. -Fatty acids and glycerol are taken into the lacteal, and travel into the lymphatic system ASSIMILATION Assimilation: conversion of nutrients into fluid/solid parts of an organisation; ie when amino acids become part of a cell. - Amino acids form part of the reserve for building new proteins. They are synthesised by ribosomes. - Glucose is transported to the liver, which maintains a constant level of blood sugar - Fatty acids and glycerol enter bloodstream from lymph vessels near the heart for energy and to build larger molecules.

Explain the significance of complementary base pairing in the conservation of the base sequence of DNA.

DNA Replication • New DNA strands are perfect copies of the original one. • Complete genome of the organism is successfully copied. All the genes remain intact and are passed on to the next generation. • Opposite pairs are attracted to each other, and their structure means that the DNA polymerase can "back check" for mistakes in replication. Transcription • Produces mRNA sequence complementary to DNA sequence • Triplets of nucleotides on mRNA are codons Translation • Converts mRNA sequence into a chain of amino acids (polypeptide) • Carries specific triplet of 3 bases (anticodon) complementary to mRNA • mRNA sequence translates into specific amino acid sequence • Enables conservation of information from DNA to RNA to polypeptide

Explain how mitosis produces two genetically identical nuclei.

Daughter cells produced by mitosis have a set of chromosomes identical to each other and to the parent from which they were formed. This is because: • An exact copy of each chromosome is made by replication during Interphase • Chromatids remain attached by their centromere during metaphase and becomes attached to spindle fibre • Centromere divide during anaphase and chromatids are pulled apart to opposite poles, one copy of each chromosome moves to each pole • The chromosomes form the two nuclei • Two cells formed have an exact copy original nucleus

Define denaturation.

Denaturation: structural change in proteins that alters its three-dimensional shape so that it can no longer carry out its function. Denaturation is usually permanent. Heat and pH are two agents which may cause denaturation of an enzyme.

Define dominant, recessive and codominant alleles.

Dominant allele: an allele that affects the phenotype of an organism, whether it is present in the heterozygous or homozygous condition Recessive allele: an allele that affects the phenotype of an organism only when it is present in the homozygous condition (when the dominant allele is absent) Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygote

Define species, habitat, population, community, ecosystem and ecology.

Ecology: the study of relationships between living organisms and between organisms and their environment Population: a group of organisms of the same species living in the same area at the same time Ecosystem: a community and its abiotic environment Community: a group of populations living / interacting with each other in an area Species: a group of organisms that can interbreed to produce fertile offspring Habitat: the environment in which a species normally lives (location of a living organism)

Process of Endocytosis

Endocytosis: uptake of external substances by an inward pouching of the plasma membrane, forming a vesicle. Eg white blood cells taking up bacteria. - Two types of Endocytosis - Pinocytosis (when substance is fluid) and Phagocytosis (when substance is solid). - Fluidity of membrane permits movement of membrane - Membrane sinks inwardly/invaginates to enclose particle - Membrane seals back on itself - One membrane layer/two phospholipid layers enclose particle making vesicle - Inner phospholipid layer of initial membrane becomes outer phospholipid layer of vesicle membrane - Outer phospholipid layer of initial membrane becomes inner phospholipid layer of vesicle membrane - Vesicle breaks away from membrane + moves into cytoplasm - Changes in membrane require energy (ATP)

Functions of Lipids

Energy storage: triglycerides can be used as a long-term energy storage source (fat in humans and oil in plants) Structure: Phospholipids are a main component of cell membranes Hormonal signalling: Steroids are involved in hormonal signalling (e.g. estrogen, progesterone, testosterone) Heat insulation: a layer of fat under the skin reduces heat loss Buoyancy: lipids are less dense than water so help animals to float Protection: Triglycerides may form a tissue layer around many key internal organs and provide protection against physical injury

Define enzyme and active site.

Enzymes: A globular protein that increases the rate of a biochemical reaction by lowering the activation energy threshold (i.e. a biological catalyst) Active site: Region on the surface of an enzyme to which substrates bind and which catalyses a chemical reaction involving the substrates.

Define evolution.

Evolution: process of cumulative changes in the heritable characteristics of a population

Discuss the potential benefits and potential harmful effects of one example of genetic modification.

Example: Maize introduced with a bacterial gene encoding a toxin to the European Corn Borer (i.e. Bt Corn) Potential Benefits Allows for the introduction of a characteristic that wasn't present within the gene pool (selective breeding could not have produced desired phenotype) Results in increased productivity of food production (requires less land for comparable yield) Less use of chemical pesticides, reducing the economic cost of farming Can now grow in regions that, previously, may not have been viable (reduces need for deforestation) Potential Harmful Effects Could have currently unknown harmful effects (e.g. toxin may cause allergic reactions in a percentage of the population) Accidental release of transgenic organism into the environment may result in competition with native plant species Possibility of cross pollination (if gene crosses the species barrier and is introduced to weeds, may have a hard time controlling weed growth) Reduces genetic variation / biodiversity (corn borer may play a crucial role in local ecosystem)

Process of Exocytosis

Exocytosis: release of substances from a cell when a vesicle joins with the cell membrane 1. Proteins synthesised by ribosomes enter the rER where they are modified 2. Vesicle forms from the end of rER and carry the proteins to the Golgi apparatus 3. Vesicle fuses with Golgi membranes and proteins are secreted into lumens of Golgi apparatus 4. Golgi apparatus further modifies vesicle by adding lipids / polysaccharides to the protein 5. New vesicle formed from Golgi membrane breaks away and carries the modified proteins to the plasma membrane 6. Vesicle fuses with plasma membrane and its contents is secreted out of the cell

Define gene mutation.

Gene mutation: a change in the nucleotide sequence of a section of DNA coding for a particular feature • Cumulative effects of millions of mutations and natural selection that have allowed all organisms to evolve from simpler ancestors. Even though DNA replication is protected by base pairing, mistakes can still occur. • This is more likely after exposure to mutagens such as radiation and some chemicals. The mutation may cause a gene to be wrongly expressed - a genetic disease

Outline a basic technique used for gene transfer involving plasmids, a host cell (bacterium, yeast or other cell), restriction enzymes (endonucleases) and DNA ligase.

Gene transfer takes a gene from an organism and inserts it into another 1. Reverse transcriptase used to obtain gene from mRNA 2. Restriction enzymes (endonuclease) used to extract plasmid from a bacterium 3. Same restriction enzymes used to excise the desired gene from the donor (sticky ends link gene to plasmid) 4. DNA ligase mix the desired gene and plasmid together by sealing gaps in DNA through making sugar-phosphate bonds - this creates a recombinant plasmid 5. The recombinant plasmid is transferred to a bacterium Example: human insulin from bacterium

Define gene, allele and genome.

Gene: a heritable factor that controls a specific characteristic, consisting of a length of DNA occupying a particular position on a chromosome (locus) Allele: One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same locus as other alleles of the gene. The difference between alleles of a gene is their BASE SEQUENCE. Genome: The whole of the genetic information of an organism

Discuss the relationship between one gene and one polypeptide.

Gene: a sequence of DNA which encodes a polypeptide sequence. A gene codes for a specific sequences of polypeptides via the processes of transcription (mRNA synthesis) and translation (polypeptide synthesis). Translation uses tRNA molecules and ribosomes to join amino acids into a polypeptide chain, according to the mRNA sequence (as read in codons). • The universality of the genetic code means all organisms show the same relationship between genes and polypeptides (indicating a common ancestry / allowing for transgenic techniques to be employed) • Some proteins may consist of a number of polypeptide chains and thus need multiple genes (e.g. haemoglobin consists of 4 polypeptide subunits encoded by 2 different genes) • The sequence of amino acids determines tertiary structure of a protein and the shape of active site on an enzyme • When a gene is mutated it may lead to the synthesis of a defective polypeptide, hence affecting protein function Eexceptions: 1. Genes encoding for tRNA and mRNA do not code for polypeptide sequences (only mRNA sequences code for polypeptides) 2. A single gene may code for multiple polypeptides if alternative splicing occurs (the removal of exons as well as introns)

Define genotype and phenotype.

Genotype: the combination of alleles of a gene carried by an organism Phenotype: expression of alleles of a gene carried by an organism (determined by a combination of genotype + environmental factors)

Examples of Food Chains

Hazel tree --> wood mouse --> tawny owl Phytoplankton --> zoo plankton --> herring --> harbour seal Bacteria --> copepods --> shrimp -> zoarcid fish

Explain the control of blood glucose concentration, including the roles of insulin, glucagon and α and β cells.

High levels of Glucose (requires insulin) • Stimulates β cells of islets of Langerhan in pancreas to secrete insulin into capillary network • Insulin stimulates uptake of glucose into cells throughout body (esp. in liver/muscles) • Insulin also triggers conversion of glucose into glycogen (stored in liver) • As blood glucose reverts to normal, this is detected by the islets of Langerhan and insulin secretion is stopped Low levels of Glucose (requires glucagon) • Stimulates α cells of islets of Langerhan in pancreas to secrete glucagon • Glucagon activates the enzyme that covert glycogen back into glycoogen • Glucagon also reduces rate of respiration • As blood glucose level reverts back to normal, glucagon production ceases and the hormone is removed from the blood in the kidney tubule

Define homologous chromosomes.

Homologous chromosomes are chromosomes that share: • The same structural features (e.g. same size, same banding pattern, same centromere position) • The same genes at the same loci positions (while genes are the same, alleles may be different)

Define homozygous, heterozygous and carrier.

Homozygous: having two identical alleles of a gene Heterozygous: having two different alleles of a gene Carrier: an individual with a recessive allele of a gene that does not affect their phenotype

DNA profiling using gel electrophoresis

Humans and other organisms have short sequences of bases that are repeated many times called satellite DNA. This satellite DNA varies greatly between different individuals in the number of repeats. If it is copied using PCR and then cut up into short fragments using restriction enzymes, the lengths of the fragments vary greatly between individuals. Gel electrophoresis can be used to separate fragmented pieces of DNA according to their charge / size. The pattern of bands on the gel is very unlikely to be the same for any two individuals. Hence, this technique called DNA profiling / fingerprinting has many applications, including forensic investigations + investigating paternity. 1. A DNA sample is collected (blood, saliva, semen, etc.) and amplified using PCR 2. DNA is cut into fragments using specialised restriction enzymes to generate fragments. For every person, the sizes of the cut fragments are unique - except for identical twins 3. The fragments are separated with gel electrophoresis using an electrical field (smaller fragments move quicker through the gel and vice versa) The presence of particular bands correlates with the probability of a certain allele / phenotype • Paternity testing: DNA of offspring will be compared against potential fathers. Children inherit half of their alleles from each parent; thus should possess a combination of their parents' alleles • Forensic investigations: suspects / victims are identified based on crime-scene DNA. Suspect DNA should be a complete match with the sample taken from a crime scene if a conviction is to occur

Explain how sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans.

Humans have 23 pairs of chromosomes for a total of 46 (excluding instances of aneuploidy) The first 22 pairs are autosomes: each chromosome pair possesses the same genes + structural features The 23rd pair of chromosomes are heterosomes (sex chromosomes) and determine gender • Females are XX - they possess two X chromosomes • Males are XY - they possess one X chromosome and a much shorter Y chromosome • The Y chromosome contains the genes for developing male sex characteristic; the father is always responsible for determining gender o If the male sperm contains the X chromosome the growing embryo will develop into a girl o If the male sperm contains a Y chromosome the growing embryo will develop into a boy • In all cases the female egg will contain an X chromosome (as the mother is XX) Because the X and Y chromosomes are of a different size, they cannot undergo crossing over / recombination during meiosis. This ensures that the gene responsible for gender always remains on the Y chromosome, meaning that there is always ~ 50% chance of a boy or girl

Explain how sexual reproduction promotes variation in a species.

Independent Assortment - metaphase I - paired chromosomes randomly arrange themselves in one of two orientations - during anaphase I the final gametes differ depending on whether they got the maternal or paternal chromosome - creates 2n different gamete combinations (n = haploid number of chromosomes) Crossing Over - prophase I - homologous chromosomes pair up as bivalents, forming chiasma - exchange of alleles between non-sister chromatids - the further apart two genes are on a chromosome, the more likely they are to recombine - creates recombinants; greatly increases number of potential gamete variations by creating new genetic combinations Random Fertilisation - results from fusion of male/female gametes - results in offspring with a combination of both paternal/maternal traits - fertilisation is random; offspring receive different combinations of traits every time - near infinite genetic variability

Explain reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases

Initially, population growth may be slow, as there is a shortage of reproducing individuals which may be widely dispersed As numbers increase and reproduction gets underway, three stages of population growth are seen: Exponential Growth Phase There is a rapid increase in population size and growth as the natality rate exceeds the mortality rate This is because there is abundant resources (e.g. food, shelter and water) and limited environmental resistance (disease and predation uncommon) Transitional Phase As the population continues to grow, eventually competition increases as availability of resources are reduced Natality starts to fall and mortality starts to rise, leading to a slower rate of population increase Plateau Phase Eventually the increasing mortality rate equals the natality rate and population size becomes constant The population has reached the carrying capacity (K) of the environment Limited resources, predation and disease all contribute to keeping the population size balanced While the population size at this point may not be static, it will oscillate around the carrying capacity to remain relatively even (no net growth)

Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles

Inspiration Diaphragm muscles contract and flatten downwards External intercostal muscles contract, pulling ribs upwards and outwards This increases the volume of the thoracic cavity (and therefore lung volume) The pressure of air in the lungs is decreased below atmospheric pressure Air flows into the lungs to equalise the pressure Expiration Diaphragm muscles relax and diphragm curves upwards Abdominal muscles contract, pushing diaphragm upwards External intercostal muscles relax, allowing the ribs to fall Internal intercostal muscles contract, pulling ribs downwards This decreases the volume of the thoracic cavity (and therefore lung volume) The pressure of air in the lungs is increased above atmospheric pressure Air flows out of the lungs to equalise the pressure

Outline the positions and functions of proteins in membranes.

Integral proteins are embedded in the phospholipid bilayer (membrane), whilst peripheral proteins are found on surface of membrane. Some integral proteins are transmembrane proteins that extend from one side of the membrane to the other. These proteins have the following functions: • Hormone binding sites eg insulin • Enzymes eg sucrase • Cell adhesion • Cell-to-cell communication recognition/glycoproteins • Channels or pores for passive transport and facilitated diffusion • Pumps/carriers for active transport • Receptors for neurotransmitters eg acetylcholine • Electron carriers eg ETC of cell respiration • Pigments

Interphase (cell division)

Interphase is an active period in the life of a cell - many events need to occur before a cell can successfully undergo division: G1: period of growth, DNA transcription and protein synthesis (to enable it to grow, copy contents and divide), increase in number of organelles (to ensure both daughter cells have necessary number of organelles to survive) S: synthesises and replicates DNA G2: chromosomes begin condensing and preparing for cell division G1, S and G2 make up internphase - also need enough ATP to successfully divide During mitosis, nuclear division occurs (all 4 stages listed) During cytokinesis the cytoplas/cell divides to form daughter cells

Karyotyping

Karyotyping is the number and type of chromosomes in a cell. 1. Fetal cells are obtained from the fetus via amniocentesis or chorionic villus sampling 2. Fetal cells are incubated with chemicals that stimulate them to divide by mitosis 3. Mitosis is stoppedp during METAPHASE (when chromosomes are most easily visible) 4. A fluid is used to burst the cells and spread out the chromosomes 5. A microscope is used to examine the burst cells, and a photograph of the chromosomes from one cell are taken, cut out and arranged into (homologous) pairs according to their size and structural features Two common purposes of karyotyping are: • Determine gender of an unborn child (via identification of sex chromosomes - females XX while males XY) • Test for chromosomal abnormalities in an unborn child resulting from non-disjunction •Pre-natal diagnosis of chromosome abnormalities, may lead to a decision to abort the fetus or prepare for consequences of abnormality in offspring

Explain the use of lactase in the production of lactose-free milk.

Lactose is a disaccharide sugar found naturally found in milk. Lactase is an enzyme produced naturally by yeast, that can digest lactose into galactose and glucose Biotechnology companies isolate lactase for use in food processing by: - adding lactase to milk to reduce level of lactose (final product contains the enyme) - immobilised on a surface or in beads of a porous material; avoids contamination of the product with lactase Reasons for using lactase in food processing: • Some people are lactose intolerant/cannot digest milk • Glucose and galactose are sweeter than lactose, so less sugar is needed in food production from milk • glucose and galactose are more soluble; can improve texture of ice-cream • bacteria ferment glucose and galactose more quickly than lactose, so production of cheese and yoghurt if faster.

Define gene locus.

Locus: the position along a chromosome where genes occur

Outline three outcomes of the sequencing of the complete human genome

Mapping: We now know the number, location and basic sequence of human genes Screening: This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic disease conditions Medicine: With the discovery of new proteins and their functions, we can develop improved treatments (pharmacogenetics and rational drug design) Ancestry: It will give us improved insight into the origins, evolution and historical migratory patterns of humans

Meiosis

Meiosis: a reduction division of a diploid nucleus to form haploid nuclei. • Most sexually reproducing animals are diploid; they have 2 copies of every chromosome (one of maternal/paternal origin). • To reproduce, these organisms need to make gametes that are haploid (have only one copy of each chromosome). • Fertilisation of 2 haploid gametes (egg + sperm) forms a diploid zygote that will grow into a new organism Meiosis consists of two cell divisions: • First division: reduction division of the diploid nucleus to form haploid nuclei • Second division: separation of sister chromatids (this division is necessary because meiosis is preceded by interphase, wherein DNA is replicated)

Describe the induced-fit model.

Metabolic pathways consist of chains and cycles of reactions, with each step controlled by a separate specific enzyme. This allows for a far greater level of control / regulation of metabolic pathways (eg photosynthesis and cell respiration). Very few chemical changes in a cell results from a single reaction. Detailed study on the structure of the active sites and substrates show that though they are complementary to each other, they do not exactly fit - binding happens. The induced-fit model explains how this occurs - when substrate binds, they cause the structure and shape of the active site to change so that it fits the substrate. Both substrate and active site undergo changes during binding and these changes help to weaken / break bonds in the substrate, lowering the activation energy and catalysing the reaction.

Explain how the structure of the villus is related to its role in absorption and transport of products of digestion.

Microvilli: Increases SA for higher rate of absorption Single layer of epithelial cells: One thin layer of cells - small area for food to pass through for absorption. Also ensures minimal diffusion distance between intestinal lumen and capillary network (more efficient) Rich capillary networks: large SA for uptake of amino acids, monosaccharides, fatty acids and glycerol into blood circulation. Also helps maintain a concentration gradient for absorption by rapidly transporting absorbed products away Lacteals (branch of lymphatic system): close to surface; allows lipids to be easily absorbed from intestine into lymphatic system (which are later reabsorbed back into normal circulation) Intestinal crypts: Located between villi, releases juices that act as a carrier fluid for nutrients Mitochondria in epithelium: provide ATP needed for active transport into cells (contents then passively diffuse into bloodstream) Protein channels and pumps: Located in microvilli membranes; aAllow rapid absorption of foods by facilitated diffusion (protein channels) or active transport (pumps)

Explain the need for a ventilation system.

Most cellular respiration is aerobic - requires oxygen + produces carbon dioxide Ventilation system exchanges gases between inhaled air and lungs/blood stream Ventilation system maintains high concentration gradient of gases in alveoli (in lungs)

Outline how population size is affected by natality, immigration, mortality and emigration.

Natality: increases population size as offspring are added to the population. Immigration: increases population size as individuals have moved into the area from somewhere else Mortality: decreases population size as some individuals are eaten, have died of old age or gotten sick Emigration: decreases population size as individuals have moved out of the area to live somewhere else

State two examples of current uses of genetically modified crops or animals.

PLANT EXAMPLES • Golden Rice: enriched with beta-carotene, which is converted to vitamin A in the body. Can prevent malnutrition-related blindness in developing countries • Insect-resistant corn: produces proteins which pests do not like, therefore toxic • Salt-resistant tomatoes: can be grown in saline soils ANIMAL EXAMPLES • Factor IX-producing sheep: produce human clotting factors in their milk, for use in the treatment of haemophilia • Glowing pigs: cells from these specimens are used to study transplants and grafts and the final destinations of transplanted cells in the host body

Outline two roles of extracellular components.

Plants - cell wall in plants is made from cellulose (polysaccharide) secreted from the cell, which: • Provides support and mechanical strength for the cell (maintains cell shape) • Prevents excessive water uptake by maintaining a stable, turgid state • Serves as a barrier against infection by pathogens Animals - extracellular matrix (ECM) made from glycoproteins secreted from the cell, which: • Provides support and anchorage for cells • Segregates tissues from one another • Regulates intercellular communication by sequestering growth factors

Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA

Polymerase Chain Reaction Used to amplify small samples of DNA in order to use them for DNA profiling, recombination, species identification or other research. Eg crime scene samples of blood / semen / tissue / hair etc. The process needs a thermal cycler, primers, free DNA nucleotides and DNA polymerase. 1. Denaturation - DNA sample is heated in a thermal recycler, denaturing the hydrogen bonds, separating it into two strands (thus exposing the bases) 2. Annealing - After the mixture is cooled, DNA primers attach to the start of target genes (only one small section of DNA) 3. Elongation - A heat-tolerant DNA polymerase (Taq) copies the strands / replicates the DNA by complementary base pairing 4. Amplification - Cycle is repeated many times until there are thousands of copies - enough to amplify even tiny samples found at a crime scene.

Precautionary Principle

Precautionary Principle: when an activity raises threats of harm, measures should be taken, even if a cause-and-effect relationship has not yet been established scientifically. People planning to do something must prove that it will not do harm before actually doing it. It is their responsibility to provide the evidence that it is safe. This principle should be followed when the possible consequences / risks of human actions are very large / catastrophic. The burden of proof lies on those whose actions may possibly do harm. Action depends on: • Most likely consequences that may result from failure to slow down rising level of atmospheric CO2 and then reduce it to earlier values • Actions needed to deliver measures that enable us to achieve this

Explain the four levels of protein structure, indicating the significance of each level.

Primary Structure • Primary structure - chain of amino acids attached by peptide bonds • Determined by the base sequences of the gene (ie DNA of chromosomes in nucleus) that codes for the polypeptide • Determines next three levels of protein organisation • Changing one amino acid in the sequence of a protein may alter its structure / function (eg sickle cell disease) Secondary Structure • Secondary structure - develops when parts of the polypeptide chain take up a particular shape. • Most common shapes are formed by coiling to produce alpha-helix or folding into beta-sheets (both have regular repeating patterns) • These shapes are permanent, held in place by hydrogen bonds (between CO and NH groups) • They are the structure of fibrous proteins; provide stability of structure. Does not involve side chains, R groups Tertiary Structure • Tertiary structure - three-dimensional conformation of a polypeptide • Is the precise, compact structure which arises when the molecule is further folded and held in a particular complex shape. • Shape is made permanent by four different types of bonding - hydrogen (between polar side chains), van der Waals' (among hydrophobic side chains of amino acids), ionic (between positively and negatively charged side chains), covalent (between sulphur atoms to create disulphide bonds) • Particularly important in determining the specificity of enzymes Quaternary Structure • Quaternary structure - linking of two or more polypeptides to form a single protein. • Eg haemoglobin consisting of four polypeptide chains held around a non-protein haem group. • In some cases proteins also contain a non-polypeptide structure (prosthetic group), known as conjugated proteins • Bonding is same as tertiary structure

Explain the energy flow in a food chain.

Producers receive their energy from light energy (the sun) through photosynthesis. This energy is transferred into sugar, lipids, amino acids, and used in the growth / development of the plant. Energy is stored in the organic molecules of new cells / tissues of the plant body. The energy in organic matter flows / transfers every time the tissues of a green plant are consumed by herbivores, and then passed on to the carnivores as they are eaten and so on. However, between these trophic levels, energy is lost through muscular movements (hunting/feeding) when some of the food eaten remains undigested or passes through the faeces, or lost as cell respiration / metabolism / heat energy. On the death of a consumer, the remaining energy passes to detritivores / saprotrophs where dead matter is broken down and decayed. They also lose energy as heat through cell respiration.

Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).

Prophase • Chromosomes become visible as long, thin threads • Chromatin shorten / thicken through supercoiling (DNA is combined with histone and non-histone proteins to form the readily stainable chromatin). Supercoiling makes structure so dense it can be seen with a light microscope during mitosis • The two chromatids are held together at the centromere • During this time, the nucleolus disappears and the nuclear membrane breaks down. Metaphase • Centrioles move to opposite ends of the cell. • Microtubules in the cytoplasm start to form a spindle, radiating out from the centrioles. These attach to the centromeres and are arranged at the equator of the spindle. Anaphase • Centromeres divide, spindle fibres shorten, and chromatids are pulled by their centromere to opposite poles. • Once separated, they are referred to as chromatids. Telophase • Nuclear membrane reforms around both groups of chromosomes at opposite ends of the cell. • They begin to decondense and become chromatin again. • Nucleolus reforms. Interphase then follows the division of the cytoplasm.

Define resting potential and action potential (depolarisation and repolarisation).

Resting Potential: electrical potential across plasma membrane of a cell that is not conducting an impulse. Action Potential: the reversal and restoration of the electrical potential across the plasma membrane of a cell as an electrical impulse passes along it (depolarisation and repolarisation) - Depolarisation: change from a negative resting potential to a positive action potential (caused by opening of SODIUM channels) - Repolarisation: change from a positive action potential back to a negative resting potential (caused by opening of POTASSIUM channels)

Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites and mRNA binding sites.

Ribosomes are the site of protein synthesis. Free ribosomes occur in the cytoplasm and synthesise proteins for use within the cell. Bound ribosomes can be attached to membranes of the endoplasm reticulum, and synthesise proteins for secretion from the cell or for lysosomes. Ribosomes have a complex structure with the following features: • Two subunits, one large and one small, both built of protein and ribosomal RNA (rRNA) • Three tRNA binding sites on the surface of the ribosome (site 1, site 2 and exit site) and one mRNA binding site • Two charged tRNA molecules can bind to a ribosome at one time • Polypeptide chains are built up in the groove between the two subunits.

Outline the evidence for evolution provided by selective breeding.

Selective breeding of domesticated animals is an example of artificial selection, which occurs when man directly intervenes in the breeding of animals to produce desired traits in offspring As a result of many generations of selective breeding, domesticated breeds can show significant variation compared to the wild counterparts, demonstrating evolutionary changes in a much shorter time frame than might have occurred naturally Examples of selective breeding include: Breeding horses for speed (race horses) versus strength and endurance (draft horses) Breeding dogs for herding (sheepdogs), hunting (beagles) or racing (greyhounds) Breeding cattle for increased meat production or milk Breeding zebras in an attempt to retrieve the colouration gene from the extinct Quagga

Explain the need for enzymes in digestion.

Several different enzymes are secreted on to the food as it passes through the body. To complete digestion, enzymes secreted onto food work together with those held in plasma membrane cells. • Enzymes are biological catalysts which speed up the rate of a chemical reaction (e.g. digestion) by lowering the activation energy • Enzymes allow digestive processes to occur at body temperature and at sufficient speed to meet the organism's survival requirements • Enzymes are specific for a given substrate and so can allow digestion of certain molecules to occur independently of others

Define sex linkage.

Sex linkage: when a gene controlling a characteristic is found on a sex chromosome (and so we associate the trait with a predominant gender). The gene is usually located on the X-chromosome, as very few genes exist on the shorter Y chromosome.

Outline the role of skin and mucous membranes in defence against pathogens.

Skin • Protects external structures (outer body areas) • Tough outer layer of skin covered by keratinised cells • Contains an enzyme lysozyme in sweat and saliva - breaks down pathogens and keep the bacterial growth in check • Releases acidic secretions to lower pH and prevent bacteria from growing (acts as a chemical barrier) • Low pH of skin is unfavourable to many pathogens and acts as chemical barrier Mucous Membrane • Protects internal structures (externally accessible cavities / tubes eg trachea, vagina and urethra) • A thin region containing living surface cells that release fluids to wash away pathogens (eg mucus, tears, saliva) • Contains biochemical defence agents (secretions contain lysozyme, which can destroy cell walls + cause cell lysis) • Mucous membranes may be ciliated to aid in the removal of pathogens (along with physical actions such as coughing or sneezing)

Draw and label a diagram showing the structure of water molecules to show their polarity and hydrogen bond formation.

Structure of a Water Molecule: • Water (H2O) is made up of two hydrogen atoms covalently bound to an oxygen atom • While this bonding involves the sharing of electrons, they are not shared equally • The oxygen atom, having more protons (+ve), attract the electrons (-ve) more strongly (i.e. the oxygen has a higher electronegativity) • Thus the oxygen atom becomes slightly negative and the hydrogen atoms become slightly positive Hydrogen Bonding between Water Molecules • Covalently bonded molecules that have a slight potential charge are said to be polar • The slightly charged regions of the water molecule can attract other polar or charged compounds • Water molecules can associate via weak hydrogen bonds (F/O/N bonding with H)

Define test cross.

Test cross: testing a suspected heterozygote by crossing it with a known homozygous recessive

Distinguish between the sense strand and antisense

The antisense strand is complementary to the sense strand. It is also known as the template strand, as this is the strand which is used for transcription (making mRNA). The sense strand is the coding strand of DNA (the genes). The sense strand has the same base sequence as the mRNA with uracil instead of thymine. It carries the promoter sequence of bases to which RNA polymerase binds and begins transcription. The antisense strand is the template strand that is transcribed.

Explain how natural selection leads to evolution

The theory of natural selection was postulated by Charles Darwin (and also independently by Alfred Wallace) who described it as 'survival of the fittest' - There is genetic variation within a population (which can be inherited) - There is competition for survival (populations tend to produce more offspring than the environment can support) - Environmental selective pressures lead to differential reproduction - Organisms with beneficial adaptations will be more suited to their environment and more likely to survive to reproduce and pass on their genes - Over generations there will be a change in allele frequency within a population (evolution)

State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.

The three types of neurons and their functions are: • Sensory neurons - carry nerve impulses from receptors (sensory cells) to the CNS. • Motor neurons - carry impulses from the CNS to the effectors (muscle and gland cells). • Relay neurons - carry impulses within the CNS, from one neuron to another.

Explain that each tRNA molecule is recognized by a tRNA-activating enzyme that binds to a specific amino acid to the tRNA, using ATP for energy.

There are many different types of tRNA in a cell, which have an important role in translation. All tRNA molecules have the following features which allow them to bind to three sites on the ribosome: • Sections that become double stranded by base pairing, creating loops • A triplet of bases called the anticodon, in a loop of 7 bases • Two other loops • The base sequence CCA at the 3' terminal, which forms a site for attaching an amino acid The base sequence of tRNA molecules varies and this causes some variable features in its structure: • An extra small loop is sometimes present • The base paired sections are sometimes helical The variable features give each type of tRNA a distinctive 3D shape and chemical properties. This allows the correct amino acid to be attached to the 3' terminal by a tRNA activating enzyme using ATP for energy. A high energy bond is created between the amino acid and the tRNA, which is later used to link the amino acid from the growing polypeptide chain during translation.

Describe the features of alveoli that adapt them to gas exchange

Thin wall: Made of a single layer of flattened cells --> small diffusion distance Rich capillary network: covered by a dense network of capillaries that help to maintain a concentration gradient Increased SA:Vol ratio: High numbers of spherically-shaped alveoli optimise surface area for gas exchange Moist layer covering inner surface of alveoli: Some cells in the lining secrete fluid to allow gases to dissolve and to prevent alveoli from collapsing (through cohesion)

Explain the process of transcription in prokaryotes, including the role of the promoter region, RNA polymerase, nucleoside triphosphates and the terminator.

Transcription of a gene results in an mRNA molecule which can be posted out of the nucleus. RNA polymerase moves along the antisense strand of DNA, using free nucleoside triphosphates to make a strand of mRNA. mRNA is an intermediate molecule between the information in the gene and the formation of the protein it codes for, out in the cytoplasm. mRNA is formed during transcription. 1. RNA polymerase binds to a promoter on the DNA and unwinds the DNA strands 2. Free nucleoside triphosphates (found in nucleus) are used by RNA polymerase to elongate the growing mRNA molecule - by attaching to the antisense strand of DNA. Two phosphates are removed as they are linked on, converting them into RNA nucleotides. The 5' end of the nucleotide is added to the 3' end of the growing chain (transcription moves in a 5' 3' direction) 3. mRNA is elongated until the RNA polymerase reaches the terminator region. 4. RNA polymerase detaches and releases the terminator region. DNA rewinds *Introns have to be removed in eukaryotes to form mature mRNA.

Process of Translation

Translation: process that decodes the information of mRNA into the sequence of amino acids that eventually form a protein. It consists of four stages: 1. Initiation: begins at a start codon (AUG) near the 5' end of the mRNA strand • Small ribosomal subunit binds to 5' end of mRNA and moves along until it reaches the start codon (AUG) • tRNA activating enzymes link amino acids to a specific tRNA • Anticodon of an activated tRNA carrying 'Met' also binds to the start codon at P-site via complementary base pairing and formation of hydrogen bonds. • Large ribosomal subunit aligns itself to tRNA molecule and forms a complex with the small ribosomal subunit 2. Elongation: formation of peptides • A second activated tRNA with the anticodon corresponding to the next codon enters A-site and binds to the next codon via CBP (second amino acid is added) • The ribosome catalyses the formation of a peptide bond between the two adjacent amino acids • Met becomes detached from its tRNA. Ribosome moves along the mRNA and the first tRNA is released to connect another Methionine molecule. 3. Translocation: movement of the ribosome along the mRNA strand one codon at a time • As the ribosome moves along, the unattached tRNA moves into the E-site and is released into the cytoplasm where it will pick up another amino acid • Another tRNA attaches to the next codon in the newly emptied site 1 and the process is repeated • The ribosome moves in a 5' to 3' direction along the mRNA 4. Termination: final stage of translation • Translocation and elongation are repeated until one of the three stop codons (UAA, UAG, UGA) is reached • Ribosome releases the polypeptide chain and mRNA, and separates into two subunits • Translation occurs at many places along an mRNA molecule at the same time. A polysome is a group of ribosomes translating a single mRNA strand simultaneously.

Define trophic level.

Trophic level: any class of organisms that occupy the same position in a food chain

Outline the process of in vitro fertilisation (IVF).

Used when women have blocked fallopian tubes, are infertile, cannot sustain a pregnancy, or when male has low sperm count 1. Female is given drugs to down-regulate/stop menstrual cycle: FSH to stimulate development of many follicles, whilst HCG to cause maturing of follicles 2. Eggs harvested/extracted from the follicles (in ovaries) 3. Sample of semen produced/collected and then processed to concentrate it (healthy sperm selected) 4. Eggs cells mixed with the sperm in a dish (outside the body) and are cultivated to allow fertilisation 6. Embryos/blastocyst placed in uterus/oviduct 7. Up to four embryos can be implanted 8. Pregnancy test to see if procedure has been successful; genetic screening to assess health of fetus

Distinguish between ventilation, gas exchange and cell respiration.

• Cellular respiration: controlled release of energy in the form of ATP from organic compounds in cells. It occurs in cytoplasm and mitochondria + a continuous process in all cells. • Gaseous exchange: exchange of gases between an organism and its surroundings, including uptake of oxygen and release of CO2 in animals and plants. It occurs in alveoli of human lungs. • Ventilation: movement of air into and out of the lungs in two stages - inspiration and expiration.

Outline the effects of HIV on the immune system.

• Human immunodeficiency virus (HIV) - cause of a disease of the human immune system known as acquired immune deficiency syndrome (AIDS) • Reduces the number of active lymphocytes; hence reducing effectiveness of immune system • Infects T-helper cells/lymphocytes; causes a loss of ability to produce antibodies

Explain the significance of polar and non-polar amino acids.

• Non-polar amino acids cause channel proteins to embed in a membrane • Polar amino acids at either end cause channel proteins to be transmembrane/retain protein position in membrane • Polar amino acids lining pore allow polar particles to pass through - they form hydrophilic channels through membranes • Polar amino acids on surface enzyme allow it to dissolve in water • Polar and non-polar amino acids contribute to the specificity of an enzyme • Non-polar amino acids of surface of enzyme allow it to embed in a membrane • Polar amino acids at active site of enzyme attract polar substrates • Positively charged amino acids attract negatively charged substrate/vice versa • Non-polar amino acids at active site attract non-polar substrate

Role of testosterone in males.

• Promotes male secondary sex characteristics • Growth and activity of male reproductive organs • Important in spermatogenesis • Enhanced sexual desire (libido) • Enhances immune function • Protects against osteoporosis (medical condition in which bones become brittle/fragile from loss of tissue - due to hormonal changes)

State one role for each of the elements needed by living organisms

• Sulphur: needed to make some of the amino acids that proteins contain • Calcium: found in bones and teeth, also a neurotransmitter release in synapses • Phosphorous: part of phosphate groups in ATP and DNA molecule • Iron: found in haemoglobin, allowing for oxygen transport • Sodium: pumped into cytoplasm to raise solute concentration and cause water to enter by osmosis • Nitrogen: structure of organic molecules / proteins / nucleotides

Outline a technique for cloning using differentiated animal cells.

• Udder cells are taken from a donor sheep. The cells were cultured in a low nutrient medium to make them switch off their genes and become inactive. • Unfertilized egg cells are taken from another sheep. The nucleus is removed from the egg cell. • The egg cells without nuclei are fused with the donor cells. • These fused cells develop like zygotes and become embryos. • The embryos are implanted into another sheep who becomes the surrogate mother. • A lamb is born which is genetically identical to the sheep whose udder cells were used.