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Bio All AO1 q's
Bio recall questions for autumn exam (261)
| Question | Answer |
|---|---|
| 1) Describe the difference between the structure of a triglyceride molecule and the structure of a phospholipid molecule. | In phospholipid, one fatty acid replaced by a phosphate; |
| 2) Describe how you would test for the presence of a lipid in a sample of food. | Add ethanol, then add water; White (emulsion shows lipid); |
| 3) Describe how a saturated fatty acid is different from an unsaturated fatty acid. | Saturated single/no double bonds (between carbons) OR Unsaturated has (at least one) double bond (between carbons); |
| 4) Name the monosaccharides of which the following disaccharides are composed. (i) Sucrose monosaccharides...........................and............................... (ii) Lactose monosaccharides........................and ……………….. | (i) Glucose and fructose; (ii) Glucose and galactose; |
| 5) Statement Starch Cellulose Glycogen Found in plant cells Contains glycosidic bonds Contains β-glucose | Starch = Found in plants and contains glycosidic bonds Cellulose = Found in plants, contains glycosidic bonds and contains B-glucose Glycogen = Contains glycosidic bonds |
| 6) Name the type of reaction that would break down carbohydrates into their monomers. | Hydrolysis |
| 7) Give one feature of starch and explain how this feature enables it to act as a storage substance. | 1. Coiled 2. So compact can fit lots into a small space 3. Insoluble 4. So does not affect water potential 5. Large molecule / long chain 6. So contains large number of glucose units 7. Branched chains 8. So easy to remove glucose |
| 8) An arteriole is described as an organ. Explain why. | Made of more than one tissue; |
| 9) An arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries | (Muscle) contracts; 2. (Arteriole) narrows / constricts / reduces size of lumen / vessel / vasoconstriction; |
| 10 A capillary has a thin wall. This leads to rapid exchange of substances between the blood and tissue fluid. Explain why. Short diffusion distance | Short diffusion distance |
| 11) Blood flow in capillaries is slow. Give the advantage of this. | (More) time for exchange / diffusion (of substances); |
| 12) Explain why a lack of protein in the blood causes a build up of tissue fluid. | 1. Water potential (in capillary) is higher / less negative 2. Less / no water removed (into capillary); 3. By osmosis |
| 13) An enzyme catalyses only one reaction. Explain why. | (Enzyme has) active site; (Reject active site is same shape as substrate) 2. Only substrate fits (the active site); |
| 14) The genetic code is described as being degenerate. What does this mean? | An amino acid (can be) coded for by more than one triplet; |
| 15) What is a codon? | Triplet / three bases on mRNA; 2. That code for an amino acid; |
| 16) What is the role of RNA polymerase during transcription? | To join nucleotides together to form mRNA / premRNA / RNA; |
| 17) mRNA can be converted to cDNA. Name the enzyme used in this process. | Reverse transcriptase; |
| 18) Explain how downward movement of the diaphragm leads to air entering the lungs | Increases volume (in lungs / thorax); 2. Lowers pressure (in lungs / thorax); 3. Air (pushed) in by higher outside pressure / down pressure gradient; |
| 19) Explain the decrease in gross productivity as a woodland matures. | Less light / more shading / more competition for light; 2. Reduced photosynthesis. |
| 20) Use your knowledge of succession to explain the increase in biomass during the first 20 years. | 1. Pioneer species; 2. Change in abiotic conditions / more habitats / niches; 3. Increase in number / amount / diversity of species / plants / animals. |
| 21) Use your knowledge of net productivity to explain why biomass shows little increase after 100 years. | 1. Net productivity = gross productivity minus respiratory loss; 2. Decrease in gross productivity / photosynthesis / increase in respiration. |
| 22) Suggest one reason for conserving woodlands. | 1. Conserving /protecting habitats / niches 2. Conserving endangered species / increases biodiversity 3. Reduces global warming greenhouse effect take up carbon dioxide 4. Source of medicines, wood 5. Reduces eutrophication |
| 23) A myelinated axon conducts impulses faster than a non-myelinated axon. Explain this difference. | 1. (In myelinated) action potential / depolarisation only at node(s); 2. (In myelinated, nerve impulse) jumps from node to node / saltatory; 3. (In myelinated) action potential / impulse does not travel along whole length; |
| 24) Describe the role of the centromere in mitosis. | 1. Holds chromatids together; 2. Attaches (chromatids) to spindle; 3. (Allows) chromatids to be separated / move to (opposite) poles / (centromere) divides / splits at metaphase / anaphase; |
| 25) Homologous chromosomes carry the same genes but they are not genetically identical. Explain why. | (Homologous chromosomes) carry different alleles; |
| 26) Other than independent segregation, give one way in which meiosis allows the production of genetically different cells. | Crossing over / alleles exchanged between chromosomes or chromatids / chiasmata formation / genetic recombination; |
| 27) Explain what is meant by the term phenotype. | 1. characteristic due to genetic constitution / genotype / allele(s); 2. (characteristic) due to environment; |
| 28) What is meant by a hierarchy? | 1. Groups within groups; 2. No overlap (between groups); |
| 29) Explain the role of independent segregation in meiosis. | 1. (To provide) genetic variation; 2. (Allows) different combinations of maternal and paternal chromosomes / alleles; |
| 30) What is a transcription factor? | 1. (Protein / molecule) that moves from cytoplasm to DNA; 2. (TF) binds to specific gene 3. blocks (pre)mRNA production / allows RNA polymerase to work; |
| 31) Both slow and fast muscle fibres contain ATPase. Explain why. | 1. hydrolysis of ATP; 2. (Muscle) contraction requires ATP; 3. Use of ATP by myosin. |
| 32) Describe how bacteria are destroyed by phagocytes. | 1. (Phagocyte engulfs) to form vesicle / phagosome; 2. Lysosome empties contents into vesicle / phagosome; 3. (Releasing) enzymes that hydrolyse bacteria; |
| 33) Give two structures a bacterial cell may have that a white blood cell does not have. | 1. Cell wall; 2. Capsule / slime layer; 3. Circular DNA; Reject “circular chromosome” 4. Naked DNA / DNA without histones; 5. Flagellum; 6. Plasmid; 7. Pilus; 8. 70s / smaller ribosomes; 9. Mesosome; |
| 34) Why is the genetic code described as being universal? | (In all organisms) the same triplet codes for the same amino acid |
| 35) Name the process that removes base sequences from pre-mRNA to form mRNA. | Splicing; |
| 36) Describe how phospholipids are arranged in a plasma membrane. | 1. Bilayer; 2. Hydrophobic tails to inside; 3. Polar / hydrophilic head to outside; |
| 37) Describe how the RER is involved in the production of enzymes. | 1. (Rough endoplasmic reticulum has) ribosomes; 2. To make protein (which an enzyme is); |
| 38) Describe how the Golgi apparatus is involved in the secretion of enzymes. | (Golgi apparatus) modifies (protein) then packages / put into (Golgi) vesicles then transport to cell surface; |
| 39) A mutation of a tumour suppressor gene can result in the formation of a tumour. Explain how. | 1. (Tumour suppressor) gene inactivated and not able to control / slow down cell division; 2. Rate of cell division too fast / out of control. |
| 40) Not all mutations result in a change to the amino acid sequence of the encoded polypeptide. Explain why. | 1. (Genetic) code degenerate; 2. Mutation in intron. |
| 41) Describe how acetylcoenzyme A is formed in the link reaction. | 1. Oxidation of / hydrogen removed from pyruvate and carbon dioxide released; 2. Addition of coenzyme A. |
| 42) Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration. | 1. Regenerates / produces NAD / oxidises reduced NAD; 2. (NAD used) in glycolysis. |
| 43) In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this. | (Pyruvate used) in aerobic respiration / (lactate / lactic acid) is toxic / harmful / causes cramp / (muscle) fatigue. |
| 44) What is the function of the coronary arteries? | 1. (Carry) oxygen / glucose; 2. (To) heart muscle / tissue / cells / myocytes. |
| 45) The rise and fall in blood pressure in the aorta is greater than in the small arteries. Suggest why. | (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. |
| 46) Give two ways in which the structure of starch is similar to cellulose. | (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). |
| 47) Give two ways in which the structure of starch is different from cellulose. | Starch 1. Contains alpha glucose; 2. compact /coiled/ 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 |
| 48) Suggest and explain one way in which sieve cells are adapted for mass transport. | 1. No / few organelles / very little cytoplasm / cytoplasm at edge / more room / hollow / large vacuole / large space / thick walls; 2. (So) easier / more flow / (thick / strong walls) resist pressure. |
| 49) Suggest and explain one way in which companion cells are adapted for the transport of sugars between cells. | 1. Mitochondria release energy / ATP 2. For active transport / uptake against concentration gradient. 3. Ribosomes / rough endoplasmic reticulum produce(s) proteins; 4. (Proteins) linked to transport e.g. carrier proteins / enzymes. |
| 50) The volume of blood leaving the capillary network into the veins is less than the volume of blood entering from the arteries. Explain why. | (Fluid) in tissue fluid / (fluid) in lymph. |
| 51) Explain what is meant by codominant alleles. | Both alleles are expressed / shown (in the phenotype). |
| 52) Give two ways in which pathogens can cause disease. | 1. (Releases) toxins; 2. Kills cells / tissues. |
| 53) Describe the role of DNA polymerase in DNA replication. | Joins nucleotides (to form new strand). |
| 54) Other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA. | (Prokaryotic DNA) 1. Circular / non-linear (DNA); 2. Not (associated) with histones; 3. No introns |
| 55) Give two assumptions made when using the mark-release-recapture method. | 1. No emigration / immigration; 2. No losses to predation; 3. Marking does not affect survival; 4. Birth rate and death rate equal |
| 56) Describe how ATP is resynthesised in cells. | 1. From ADP and phosphate; 2. By ATP synthase; 3. During respiration/photosynthesis; |
| 57) Give two ways in which the hydrolysis of ATP is used in cells. | 1. To provide energy for other reactions/named process; 2. To add phosphate to other substances and make them more reactive |
| 58) Explain the difference in the structure of the starch molecule and the cellulose molecule | 1. Starch formed from α-glucose but cellulose formed from β-glucose; 2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted. |
| 59) Explain one way in which starch molecules are adapted for their function in plant cells. | 1. Insoluble; 2. so Don’t affect water potential 3. Helical; 4. so Compact 5. Large molecule; 6. so Cannot leave cell. |
| 60) Explain how cellulose molecules are adapted for their function in plant cells. | 1. Long and straight chains; 2. Become linked together by many hydrogen bonds to form fibrils; 3. Provide strength (to cell wall). |
| 61) Name two ways in which meiosis produces genetic variation. | 1. Independent segregation (of homologous chromosomes); 2. Crossing over / formation of chiasmata. |
| 62) The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why. | Loss of water / loss of fluid |
| 63) High blood pressure leads to an accumulation of tissue fluid. Explain how. | 1. High blood pressure = high hydrostatic pressure; 2. Increases outward pressure from (arterial) end of capillary 3. (So) more tissue fluid formed / less tissue fluid is reabsorbed. |
| 64) 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. | 1. Water has left the capillary; 2. Proteins (in blood) too large to leave capillary; 3. Increasing / giving higher concentration of blood proteins |
| 65) Name the products of the hydrolysis of sucrose. | 1. Glucose; 2. Fructose; |
| 66) 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. | Dipeptidase |
| 67) Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own. | 1. Endopeptidases hydrolyse internal (peptide bonds) OR Exopeptidases remove amino acids/hydrolyse (bonds) at end(s); 2. More ends or increase in surface area (for exopeptidases); |
| 68) Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue. | 1. How to break open cells and remove debris; 2. Solution is cold / isotonic / buffered; 3. Second pellet is chloroplast. |
| 69) Name two structures in a eukaryotic cell that cannot be identified using an optical microscope. | Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane. |
| 70) explain how two features of the body of the tubifex worm allow efficient gas exchange. | 1. Thin/small so short diffusion pathway; 2. Flat/long/small/thin so large surface area to volume ratio/surface area : volume; |
| 71) A glucose biosensor detects only glucose. Use your knowledge of the way in which enzymes work to explain why. | Enzyme / active site has a (specific) tertiary structure; Only glucose is complementary / will bind / fit to active site; (Forming) enzyme-substrate complex; |
| 72) Give two ways in which pathogens can cause disease when they enter the body of their host.Damage / destruction of cells / tissues; | Damage / destruction of cells / tissues; Production of toxins; |
| 73) What is a vaccine? | Contains antigen / proteins / dead / weakened microorganism / pathogen / virus / bacteria; Stimulates production of antibodies / plasma cells / memory cells; |
| 74) Describe how you could test a solution for the presence of protein | Add Biuret reagent. Protein will give purple / lilac / mauve; |
| 75) Suggest how the student could use a microscope to find the number of stomata per cm2 on a leaf | Method of determining area of field of view / area seen using microscope; Count number of stomata in field of view; Repeats and calculation of mean; |
| 76) The stomata on the leaves of pine trees are found in pits below the leaf surface. Explain how this helps to reduce water loss. | Water vapour accumulates Water potential reduced; |
| 77) An increase in respiration in the tissues of a mammal affects the oxygen dissociation curve of haemoglobin. Describe and explain how. | Increase in carbon dioxide; Curve moves to the right |
| 78) Explain how a change in a sequence of DNA bases could result in a non-functional enzyme. | Change in (sequence of) amino acids / primary structure; Change in hydrogen / ionic / disulfide bonds leads to change in tertiary structure / active site (of enzyme); Substrate cannot bind / no enzyme-substrate complexes form; |
| 79) Describe the path by which oxygen goes from an alveolus to the blood. | Through alveolar epithelium; Through capillary epithelium / endothelium; |
| 80) The structure of cellulose is related to its role in plant cell walls. Explain how. | Long / straight / unbranched chains (of glucose joined by) hydrogen bonds; Form (micro)fibrils / (macro)fibrils; Provide rigidity / strength / support; |
| 81) Oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells. Explain how an activated oestrogen receptor affects the target cell. | (Receptor / transcription factor) binds to promoter which stimulates RNA polymerase / enzyme X; Transcribes gene / increase transcription; Other cells do not have the oestrogen receptors; |
| 82) Suggest one advantage of using cytochrome c to determine relationships between species. | Is present in all eukaryotes |
| 83) Comparing the base sequence of a gene provides more information than comparing the amino acid sequence for which the gene codes. Explain why | Reference to more bases than amino acids / longer base sequence than amino acid sequence; Introns / non-coding DNA; DNA code is degenerate; |
| 84) Explain what is meant by a quaternary structure. | More than one polypeptide chain; |
| 85) What name is used for the non-coding sections of a gene? | Introns; |
| 86) During which part of the cell cycle are gene mutations most likely to occur? | (i) Interphase / S / synthesis (phase); (ii) DNA replication occurs |
| 87) Hydrogen bonds are important in cellulose molecules. Explain why. | Holds chains / cellulose molecules together / forms cross links between chains / Hydrogen bonds strong in large numbers |
| 88) A starch molecule has a spiral shape. Explain why this shape is important to its function in cells. | Compact / occupies small space / tightly packed; |
| 89) Name the type of bond that joins amino acids together in a polypeptide. | Peptide; |
| 90)Scientists homogenised tissue before cell fractionation to isolate mitochondria. Explain why (i) homogenised the tissue (ii) filtered the resulting suspension (iii) kept the suspension ice cold (iv) used isotonic solution | (i) Breaks open cells / disrupts cell membrane / releases cell contents / releases organelles / break up cells; (ii) Removes cell debris (iii) reduced enzyme activity; (iv) Prevents osmosis so organelle / named organelle is not damaged |
| 91) What is an antigen? | Protein Causes an immune response |
| 92) A vaccine can be used to produce immunity. Describe how memory cells are important in this process. | Memory cells produced / remain (from previous infection); Rapid / secondary / greater response / many more antibodies produced; Destroys virus / antigen before it can cause harm / symptoms |
| 93) Explain the importance of elastic fibres in the wall of the aorta. | Stretches under high pressure when ventricle contracts and recoils under low pressure when ventricle relaxes Smooths blood flow / maintains blood pressure / reduces pressure surges; |
| 94) Explain the importance of muscle fibres in the wall of an arteriole. | (Muscle) contracts; (Arteriole) constricts / narrows / alters size of lumen / regulates blood flow (to capillaries); |
| 95) Efficient exchange of substances in the capillaries is linked to the rate of blood flow. Explain how. | (More) time for exchange of substances; |
| 96) The haemoglobin in one organism may have a different chemical structure from the haemoglobin in another organism. Describe how. | Different primary structure / amino acids / different number of polypeptide chains; |
| 97) Give one advantage of using a TEM rather than a SEM. | Higher resolution / higher (maximum) magnification / higher detail (of image); Allows internal details / structures within (cells) to be seen / cross section to be taken; |
| 98) Give one advantage of using a SEM rather than a TEM | Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images; |
| 99) Synapses are unidirectional. Explain how acetylcholine contributes to a synapse being unidirectional. | 1. (Acetylcholine) released from presynaptic side; 2. Receptors in postsynaptic (side) / binds on postsynaptic (side); |
| 100) Name the process by which oxygen reaches the cells inside the body of a flatworm. | Diffusion; |
| 101) A leaf is an organ. What is an organ? | A group of tissues; |
| 102) Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf. | 102 Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf. (Carbon dioxide enters) via stomata; 2. Stomata opened by guard cells; 3. Diffuses through air spaces 4. Down diffusion gradient |
| 103) What is an unsaturated fatty acid? | Double bond(s); (Bonds) between carbon; |
| 104) Name the monomers that form a cellulose molecule. | β / Beta glucose; |
| 105) Name two ways in which the structure of cellulose is different from the structure of starch. | Starch = 1. branching 2. All glucose monomers same way up 3. coiled / compact 4. Alpha glucose 5. No fibres Cellulose unbranched / straight; 2. monomers upside down; 3. Straight; 4. Beta glucose; 5. Micro / macro fibrils / fibres; |
| 106) Describe what happens in metaphase | Spindle formed / chromosome / centromere / chromatids attaches to spindle; Chromosomes / chromatids line up / move to middle / equator of cell |
| 107) Describe what happens in anaphase. | Chromosome / centromere splits / chromatids / ‘chromosomes’ separate / pulled apart; To (opposite) sides / poles / centrioles (of cell); |
| 108) Explain, in terms of pressure, why the semilunar valves open. | Pressure is greater below valve / in ventricle than (artery); |
| 109) 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. | Allow atria to empty / contract / ventricles to fill; Before ventricles contract; OR Delays contraction of ventricles; Until after atria have contracted / ventricles have filled; |
| 110) Give two ways in which the properties of ATP make it a suitable source of energy in biological processes. | 1. Energy released in small / suitable amounts; 2. Soluble; 3. Involves a single / simple reaction; |
| 111) 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. | 1. ATP cannot be stored / is an immediate source of energy; 2. ATP only releases a small amount of energy at a time; |
| 112) Explain what is meant by genetic diversity. | Difference in DNA / base sequence / difference in alleles / genes / gene pool |
| 113) Give one way in which the structure of an mRNA molecule is different from the structure of a tRNA molecule. | Does not contain hydrogen bonds / base pairs / contains codons / does not contain anticodon / straight / not folded / no amino acid binding site / longer; |
| 114) Explain the difference between pre-mRNA and mRNA. | (pre-mRNA) contains introns / mRNA contains only exons; |
| 115) Explain what is meant by a dominant allele. | Is always expressed (in the phenotype); |
| 116) Describe how you would use a biochemical test to show that a reducing sugar is present. | Add Benedict’s (reagent) and heat; Red / orange / yellow / green (colour); |
| 117) Describe the function of a chloroplast. | 1. Absorbs / traps / uses light; 2. For photosynthesis; 3. Produces carbohydrates / sugars / lipids / protein; |
| 118) Describe how you could use the emulsion test to show that a seed contains lipids. | 1. Crush / grind; 2. With ethanol 3. Then add water 4. Forms emulsion / goes white / cloudy; |
| 119) The structure of a phospholipid molecule is different from that of a triglyceride. Describe how a phospholipid is different. | 1. Phosphate / PO4; 2. Instead of one of the fatty acids / and two fatty acids; |
| 120) Explain how the gills of a fish are adapted for efficient gas exchange. | Large surface area provided by lamellae increase diffusion Thin epithelium Water and blood flow opposite directions countercurrent maintains concentration gradient along gill Circulation replaces blood saturated with oxygen Ventilation replaces water |
| 121) A plasmid may be used as a vector. Explain what is meant by a vector in this context | A plasmid may be used as a vector. Explain what is meant by a vector in this context |
| 122) Explain how oxygen in a red blood cell is made available for respiration in active tissues. | Low pH / (more)H+ ; due to (increased) CO2 (increased) dissociation of haemoglobin; Oxygen diffuses from r.b.c. to tissues; |
| 123) Explain how the release of acetylcholine at an excitatory synapse reduces the membrane potential of the postsynaptic membrane. | Binds to receptor / proteins; and opens Na+ channels; Na+ enter and make membrane potential less negative / depolarised |
| 124) Explain what causes transmission at a synapse to occur in only one direction. | (Vesicles containing) neurotransmitter only in presynaptic membrane; receptor / proteins only in postsynaptic membrane; |
| 125) What is the biological importance of reducing the chromosome number when the cell divides by meiosis? | Later fertilisation / cell fusion; Restoring diploid / original number / not doubling chromosome number; |
| 126) In anaerobic respiration, what is the net yield of ATP molecules per molecule of glucose? | 2 (molecules) |
| 127) Give two advantages of ATP as an energy-storage molecule within a cell | Cannot pass out of cell; Quickly / easily broken down (hydrolysed) / broken down in a one-step reaction / immediate source of energy; Stores / releases small amounts of energy; |
| 128) Describe how NAD is regenerated in anaerobic respiration in yeast cells. | Formed when reduced NAD used to reduce / donate H ions to pyruvate / convert pyruvate to ethanol; |
| 129) Molecular biologists often use plasmids which contain antibiotic resistance genes. Explain the reason for this. | Act as marker gene; Allows detection of cells containing plasmid / DNA; |
| 130) Describe the part played by the diaphragm in causing air to enter the lungs during breathing. | Diaphragm (muscle) contracts; Flattens / Increases volume of chest; Reduced pressure allows air to enter; |
| 131) Explain how the shape of a red blood cell allows it to take up a large amount of oxygen in a short time. | Large surface area to volume ratio; For diffusion; OR Flat / thin; So oxygen can reach all haemoglobin / centre rapidly / short pathway; |
| 132) Describe the features of a succession that would bring about an increase in the index of diversity. | Initial environment hostile / few organisms adapted; These organisms change the environment / suitable example; More niches / more habitats; Allowing other organisms to become established; |
| 133) Describe how bacteria can be genetically modified to produce human insulin. | 1. Cut out insulin gene / cut open plasmid with restriction enzyme; 2. Use same restriction enzyme on second DNA; 3. Reference to (complementary) sticky ends; 4. Use ligase to join 2 DNA molecules; 5. Modified plasmid taken up by bacteria; |
| 134) 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; |
| 135) Describe what is meant by negative feedback. | where a change triggers a response which reduces the effect of a change; |
| 136) Explain how ADH increases the movement of water from the lumen of the collecting duct into the blood | 1. ADH causes vesicles containing aquaporins to be inserted into membrane / collecting duct wall; 2. water enters cell through aquaporins; 3. by osmosis down a water potential gradient; 4. (from cell) to capillary; |
| 137) Deforestation reduces the diversity index of an area. Explain why | deforestation removes many habitats / niches fewer species / fewer types of organisms; |
| 138) Describe how the resting potential is established in an axon by the movement of ions across the membrane. | active transport / pump of Na+ out of axon; diffusion of K+ out of axon / little diffusion of Na+ into the axon; |
| 139) Sodium and potassium ions can only cross the axon membrane through proteins. Explain why. | Cannot pass through phospholipid bilayer; because water soluble / not lipid soluble / charged / hydrophilic; |
| 140) Describe how crossing over occurs during meiosis I. | chromosomes in each (homologous) pair twist around each other; chromatids break and rejoin to chromatid on sister chromosome; |
| 141) The intercostal muscles are between the ribs. In normal breathing, describe the part played by the intercostal muscles (i) during inspiration; (ii) during expiration. | (i) contract; ribs move upwards / out; increasing volume / decreasing pressure in chest / thorax / lungs; (ii) intercostal muscles relax; |
| 142) A particular gene is 562 base-pairs long. However, the resulting mRNA is only 441 nucleotides long. Explain this difference. | idea that DNA contains introns / mRNA is only exons / mRNA is “edited’; |
| 143) Explain how electrophoresis separates the fragments of DNA | Move towards anode / move because charged; Different rates of movement related to charge / size; |
| 144) What is a DNA probe? | Piece of single stranded DNA; Complementary to / binds to known base sequence / gene; |
| 145) Explain why radioactive DNA probes are used to locate specific DNA fragments. | DNA invisible on gel / membrane; Allows detection; |
| 146) Describe the role of the spindle during mitosis. | Attachment of centromeres / chromosomes / chromatids; Separation of centromeres / chromatids / chromosomes; |
| 147) Meiosis also occurs during the life cycle of organisms. What is the importance of meiosis? | Halves chromosome number / haploid; Diploid / full number restored at fertilisation; |
| 148) Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion | ATP formed as electrons pass along transport chain; oxygen is electron acceptor / accepts electrons from electron transport chain chain if no O2 to accept them; forms H2O / accepts H+ from reduced NAD / FAD / oxidises reduced NAD / FAD; |
| 149) Describe the part played by arterioles in redistributing blood to different organs. | The muscle in the wall / sphincter contracts; Reducing blood flow / narrowing / closing arteriole; |
| 150) Cut plasmids and lengths of foreign DNA can join. What features of their ends allows them to join? | unpaired bases sticky ends; complementary / explained; |
| 151) Describe how B-lymphocytes respond when they are stimulated by antigens. | divide by mitosis / form clones; produce plasma cells; (plasma cells) make antibodies; (plasma cells) produce memory cells; |
| 152) What is meant by a gene? | a length of DNA; that codes for a single protein; |
| 153) Explain how the strands of DNA are separated during the PCR. | by heating; to break the H-bonds (between complementary bases); |
| 154) In a particular PCR, two different primers are added to the DNA. (i) Why are primers required? (ii) Suggest why two different primers are required. | (i) to allow the DNA polymerase to attach / mark start and end of sequence to be copied / prevents strands re-joining; (ii) because the sequences at the ends of the target sequence are different / one is at the beginning and one at the end; |
| 155) Phagocytes and lysosomes are involved in destroying microorganisms. Describe how. | Phagocytes engulf pathogens / microorganisms; Enclosed in a vacuole / vesicle / phagosome; Lysosomes have enzymes; That digest / hydrolyse molecules in the microorganism; |
| 156) Explain how fluid leaves the capillary at the arterial end. | hydrostatic pressure; greater than osmotic effect which forces molecules / fluid out; |
| 157) Describe how urea is removed from the blood. | Hydrostatic pressure Causes ultrafiltration at Bowman’s capsule / glomeruli / renal capsule; Through basement membrane; Enabled by small size urea molecule; |
| 158) Explain how urea is concentrated in the filtrate. | Reabsorption of water / by osmosis; At the PCT / descending LoH; At the DCT / CD; Active transport of ions / glucose creates gradient (in context); |
| 159) Suggest two other sources of evidence which scientists may have used to classify cheetahs and leopards in different genera | fossil record; evolutionary history / phylogeny; biochemical differences e.g. DNA / proteins / cytochromes; homologous features / named feature; karyotype / number and form of chromosomes; |
| 160) Apart from water and glucose, name two substances which will be present in the glomerular filtrate | urea / amino acids / fatty acids / glycerol / ion / small protein; |
| 161) Selective reabsorption from the glomerular filtrate occurs in the proximal convoluted tubule. Explain two ways in which the cells of the proximal convoluted tubule are adapted for reabsorption. | microvilli provide large surface area; carrier proteins (in membrane) for active transport; channel proteins for facilitated diffusion; specific carriers for specific molecules / sodium pumps; (many) mitochondria for active transport; |
| 162) Explain how three features of a plasma membrane adapt it for its functions | forms a barrier allow non-polar substances to pass bilayer is fluid channel protein let water soluble through facilitated diffusion carrier proteins allow active transport glycoproteins / glycolipids act as receptors cholesterol increase stability |
| 163) Explain how the structure of the gill makes oxygen uptake efficient. | (many) filaments / lamellae / secondary lamellae; so large surface area; large number of capillaries; (NOT “good blood supply”) maintains a diffusion gradient / removes oxygen; thin epithelium / lamellae wall; short diffusion pathway; |
| 164) Name the type of reaction that converts cellulose to its monomers. | hydrolysis; |
| 165) Palisade cells are the main site of photosynthesis. Explain one way in which a palisade cell is adapted for photosynthesis. | idea of many chloroplasts / lots of chlorophyll; to trap or absorb light (energy); range of pigments; can absorb a range of wavelengths / for max light absorption; large S.A. or cell wall feature e.g. thin / permeable; for (rapid) CO2 absorption; |
| 166) Explain how a large increase in a person’s body temperature can cause harm. | enzymes denatured / secondary structure altered / altered active sites / prevents named chemical reactions / metabolic pathways; |
| 167) Give two factors, other than cost, that should be considered when selecting an antibiotic to treat a bacterial disease. | side effects / allergic reactions / low toxicity to cells; interaction with other drugs / effective in conditions of use / reasonably stable; should only act on the problem bacteria / narrow spectrum; how much resistance the bacteria have built up; |
| 168) Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane. | action potential arrives / depolarisation occurs; calcium ions enter synaptic knob; vesicles fuse with membrane; acetylcholine diffuses (across synaptic cleft); binds to receptors; |
| 169) Name two substances formed from pyruvate. | CO2, water, ATP, reduced NAD / FAD; |
| 170) Explain the role of calcium ions and ATP in bringing about contraction of a muscle fibre. | Calcium ions: Bind to troponin; Remove blocking action of tropomyosin / expose myosin binding sites; ATP: Allows myosin to detach from actin / to break cross bridge; Releases energy to activate myosin head / drive power stroke; |
| 171) Explain how the structure of capillaries is related to their function. | walls / endothelium one cell thick / made of flattened cells; short diffusion pathway OR narrow lumen; reduces rate of flow / more time for diffusion; OR gaps / pores between cells; increased rate of diffusion / fluid movement out of vessel; |
| 172) Explain how the cuticle of a leaf reduces water loss. | (waxy so) impermeable to water / waterproof / stops water passing through; |
| 173) Describe the role of restriction endonucleases in the formation of plasmids that contain donor DNA. | cut open plasmid; cut donor DNA, to remove gene / length of DNA; cut donor DNA and plasmid with the same enzyme that cuts at the same base sequence; sticky ends with bases exposed; association / attachment / pairing of complementary strand; |
| 174) Describe the role of DNA ligase in the production of plasmids containing donor DNA. | annealing / splicing / backbones joined / phosphodiester bonds; |
| 175) Apart from increasing genetic variation, explain why meiosis is important in organisms which reproduce sexually. | haploid cells produced / halves chromosome number; fertilisation / fusion of gametes, diploid number restored; chromosome number constant at each generation; |
| 176) What is the role of RNA polymerase in transcription? | join / attach nucleotides, to form a strand / along backbone / phosphodiester bonds; |
| 177) Explain why the replication of DNA is described as semi-conservative. | each strand copied / acts as a template; (daughter) DNA one new strand and one original / parent strand; |
| 178) Give one similarity in the way in which active transport and facilitated diffusion transport substances across the membrane. | involves carrier / transmembrane / transport proteins; (reject channel proteins) |
| 179) Give one way in which active transport differs from facilitated diffusion. | requires energy / requires use of ATP / moves substances / ions / molecules against a concentration gradient; |
| 180) Explain one way in which the behaviour of chromosomes during meiosis produces genetic variation in gametes. | Different combinations of alleles / linkage groups changed / broken; OR Independent assortment / alignment of (homologous) chromosomes; Different combinations of (maternal and paternal) chromosomes / alleles; |
| 181) Explain how the structure of protein molecules allows them to form channels through which only water molecules can pass. | (Each) protein has a tertiary structure; Gives specific / correct shape / size to (inside of) channel / pore; |
| 182) Explain how the cells of the collecting duct are able to absorb water from the filtrate through the protein channels in their plasma membranes. | More negative / lower WP (inside tubule cells); Water enters / moves by diffusion / osmosis; |
| 183) What is homeostasis? | Maintaining a constant internal environment; |
| 184) Describe the role of the hormone glucagon in the control of blood sugar concentration. | Binds to (specific) receptor; On muscle / liver cell; Activation of enzymes (in liver); Hydrolysis of glycogen; (Facilitated) diffusion of glucose out of (liver cells) cells; Increases blood glucose levels; |
| 185) Where does ultrafiltration occur? | Renal capsule / Bowman’s capsule / glomerulus / basement membrane; |
| 186) Give one component of the blood which is not normally present in the filtrate. | blood cells / platelets / proteins / named plasma protein |
| 187) What is meant by a recessive allele? | Only expressed in the homozygote |
| 188) The hydrostatic pressure of the blood at the arteriole end of the capillary helps to form tissue fluid. Explain how. | Hydrostatic pressure higher than osmotic “effect”; Forces / squeezes / pushes out / water / small molecules / ions / examples; |
| 189) What is meant by codominant? | both alleles will be expressed (in the phenotype); |
| 190) Describe how calcium ions cause the myofibril to start contracting. | Ca2+ binds to [part of] the actin / troponin; this causes tropomyosin to be displaced; uncovers [myosin] binding sites [on actin] / allows actin to bind; |
| 191) Describe the events that occur within a myofibril which enable it to contract. | myosin heads bind to actin / cross bridge formation / actomyosin formed; myosin heads / crossbridges swivel / ratchet mechanism; causing actin to slide relative to myosin; energy provided by hydrolysis of ATP; |
| 192) Describe what happens to pyruvate in anaerobic conditions and explain why anaerobic respiration is advantageous to human skeletal muscle. | Forms lactate; Use of reduced NAD / NADH; Regenerates NAD; NAD can be re-used to oxidise more respiratory substrate / correct e.g. / allows glycolysis to continue; Can still release energy / form ATP when oxygen in short supply / when no oxygen; |
| 193) The photolysis of water is an important part of the process of photosynthesis. Describe what happens in the photolysis of water. | (Water) forms H+ / hydrogen ions and electrons / e– ; O2 / oxygen formed; [NOT ‘O’, NOT ‘O–’] (Light) excites electrons / raises energy level of electrons / electrons to chlorophyll / to photosystem; |
| 194) ATP and reduced NADP are two products of the light-dependent reactions. Describe one function of each of these substances in the light-independent reactions. | (ATP) Provides energy for GP → TP / provides P for RuP / TP → RuBP; (Reduced NADP) Provides H / electrons for GP → TP / reduces GP to TP; |
| 195) Give one way in which a benign tumour differs from a malignant tumour. | benign does not cause cancer / does not invade other tissues causing damage / with benign cancer, pieces which break off do not start new tumours elsewhere in body / metastasis; |
| 196) Describe two ways in which both types of tumour may cause harm to the body. | may damage organ concerned; may cause blockages / obstructions; may damage / exert pressure on other organs; |
| 197) The elastin fibres in the wall of the artery help to smooth out the flow of blood. What happens to these fibres as the pressure of the blood in the artery changes? | Stretch as pressure increases; Recoil / spring back as pressure drops; |
| 198) Give one way in which the structure of the wall of an artery is similar to the structure of the wall of a capillary. | Both have an endothelium / epithelium / squamous cells; |
| 199) During meiosis, one chromosome from each homologous pair goes to each of the cells produced. Explain why this is important. | to get haploid / n / half number of chromosomes (in cells); so that each cell gets one copy of each chromosome/ so that fertilisation produces diploid; results in independent assortment; |
| 200) The total volume of fluid that passes from the capillaries to the surrounding tissue fluid is normally greater than the volume that is reabsorbed into them. Describe what happens to this extra fluid. | removed by lymphatic system / lymph; returned to blood; |
| 201) 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; |
| 202) Describe two events during interphase which prepare a cell for mitosis. | DNA replication; synthesis of proteins / increase in cytoplasm; replication of organelles / named example; |
| 203) Explain the reason for each of the following in the polymerase chain reaction (PCR). (i) DNA is heated to 95 °C. (ii) DNA polymerase used is heat-stable. (iii) The reaction mixture is cooled to 40 °C. | DNA replication; synthesis of proteins; replication of organelles / named example; (i) to separate polynucleotide strands / form single strands (ii) not denatured at 95°C (iii) for binding of primers / nucleotides to DNA strands |
| 204) Explain how the shape of an enzyme molecule is related to its function. | specific 3D tertiary structure / shape; substrate complementary shape; substrate (can bind) to active site / can fit into each active site; |
| 205) Give two processes, other than crossing over, which result in genetic variation. Explain how each process contributes to genetic variation. | mutation; different / new allele formed / genes deleted or duplicated / sequence of genes changed; random fusion of gametes / fertilisation; new combination of alleles; independent assortment of chromosomes new combination of alleles; |
| 206) Explain what causes the conduction of impulses along a non-myelinated axon to be slower than along a myelinated axon. | non-myelinated – next section of membrane depolarised / whole membrane; myelinated – depolarisation / ion movement only at nodes; impulse jumps from node to node / saltatory conduction; |
| 207) Give two factors which might increase the frequency at which a mutation in DNA occurs. | high energy radiation / X rays / ultraviolet light / gamma rays; high energy particles / alpha or beta particles named chemical mutagens e.g. benzene / caffeine / free radicals; length of time of exposure (to a mutagen); dosage (of mutagen); |
| 208) Give one advantage of DNA molecules having two strands. | stability / protects bases / replication; |
| 209) What is meant by gene therapy? | introduction of healthy gene / ‘replacement’ of defective gene; |
| 210) Give two advantages of using a virus in gene therapy | can enter cells / infect cells / inject DNA into cells; targets specific cells; replicates (in cells); |
| 211) Give two ways in which the polymerase chain reaction differs from the process of transcription. | (transcription uses) RNA polymerase; RNA nucleotides / uracil; one (template) strand / PCR both strands; start / stop codons; |
| 212) Give one reason why not all the light energy falling on the producers is used in photosynthesis. | reflected / misses chlorophyll / chloroplasts / wrong wavelength; |
| 213) Some species of seaweed are submerged in water for most of the time. Explain how being under water might affect the rate of photosynthesis. | effect on photosynthesis; some effects are less light / light absorbed by water different wavelength of light temperature availability of carbon dioxide availability of water |
| 214) What is meant by a community? | populations of different species; living in the same environment / habitat; |
| 215) Explain how sodium ions are transported through the membranes. | active transport; by specific carrier proteins / pumps; |
| 216) Explain the principles which biologists use to classify organisms into groups | large groups are divided into smaller groups; members of a group have features in common based on anatomy / fossils / embryology / DNA / specific aspect of cell biology/ homologous structures; reflects evolutionary history; |
| 217) Suggest how information on amino acid sequences is used to construct a phylogenetic tree. | those with similar sequences put in same groups / are more closely related; the greater difference in amino acid sequence the longer ago the groups diverged; |
| 218) Suggest one advantage and one disadvantage of using cytochrome c to construct a phylogenetic tree. | A - present in all (eukaryotic) species or organisms / quantifiable; D - extinct species not considered / no timing of events available / only limited number of amino acid sequences / can’t include prokaryotic species |
| 219) Explain two advantages for a farmer of removing hedgerows. | source of pests / animals, and effect on crop; source of weeds / no longer taking nutrients, hence competition / reduced yield; hedgerows have to be maintained, so removal saves time / money; |
| 220) Explain two advantages for a farmer of removing hedgerows. Apart from providing a habitat for predators of crop pests, give two biological benefits of replanting hedgerows. | increases biodiversity; source of food for animals; habitat / nest for animals; reduce need for insecticides / attracts insects away from crop; windbreaks / prevent erosion / run-off / leaching; migratory corridors; |
| 221) Explain what is meant by an allele. | different form of a gene; |
| 222) Explain how DNA replicates. | hydrogen bonds broken; semi-conservative replication / both strands used (as templates); nucleotides line up complementary / specific base pairing / A and T / C and G; DNA polymerase; |
| 223) Explain why a mutation involving the deletion of a base may have a greater effect than one involving substitution of one base for another. | deletion causes frame shift; changes many amino acids / sequence of amino acids (from this point); substitution alters one codon / triplet / one amino acid altered / code degenerate / same amino acid coded for; |
| 224) Explain the importance of reflex actions. | 1. automatic (adjustments to changes in environment) / involuntary; 2. reducing damage to tissues / prevents injury 3. role in homeostasis ; 4. posture / balance; 5. finding / obtaining food / mate / suitable conditions; 6. escape from predators; |
| 225) Describe the sequence of events which allows information to pass from one neurone to the next neurone across a cholinergic synapse. | impulse causes Ca2+ enter axon; vesicles fuse w. preS membrane; AC released; AC diffuses across synaptic cleft binds with receptors on POS membrane; Na+ enter POS neurone; depolarises membrane; 8. if above threshold action potential made |
| 226) Give two differences between a cholinergic synapse and a neuromuscular junction. | neurone to neurone & neurone to muscle; action potential in neurone and no action potential in muscle; no summation in muscle; muscle response always excitatory (never inhibitory); some neuromuscular junctions have different neurotransmitters; |
| 227) Explain how aerobic respiration in cells leads to a change in the pH of blood plasma | CO2 is produced (in respiration); forms carbonic acid / hydrogen ions released; |
| 228) What is the advantage to tissue cells of a reduction in the affinity of haemoglobin for oxygen when the plasma pH decreases? | low pH because high rate of respiration; cells need more O2; more O2 released / O2 released faster; |
| 229) Explain the advantage for mice living at high altitude in having a dissociation curve which is to the left of the curve for mice living at low altitude. | high altitudes have a low partial pressure of O2; high saturation / affinity of Hb with O2 (at low partial pressure O2); so sufficient / enough O2 supplied to cells / tissues; |
| 230) Which two substances are formed when two amino acid molecules join together? | (di)peptide and water; |
| 231) Name the type of bond formed between the joined pair of amino acid molecules. | peptide |
| 232) Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure. | sequence of amino acids changes; tertiary structure changes / folds in a different way; bonds form in different places; |
| 233) Describe how you would use quadrats to determine whether a particular plant species has a clustered or a random distribution. | use of random numbers to place quadrats; number of individuals counted in large number of quadrats; little variation random, large variation - clustered; |
| 234) Describe what causes the different bands seen in the muscle fibril. | A / dark band is mainly due to myosin filaments; H zone only myosin filaments; darker band has both types of filament; light band has only actin filaments; |
| 235) Describe how the banding pattern will be different when the muscle fibril is contracted. | H zone narrows; light band narrows; outer darker regions of A / dark band widen; |
| 236) Explain the importance of ATPase during muscle contraction. | breaks down ATP yielding energy; used to form / break actomyosin bridges; |
| 237) Describe the role of tRNA in the process of translation. | anticodon complementary to codon / reads message on mRNA; specific amino acid; carried / transferred (to ribosome); correct sequence of amino acids along polypeptide; |
| 238) Name two substances for which there would be net movement into the mitochondrion. | pyruvate; ADP; P / inorganic phosphate; reduced NAD; oxygen; |
| 239) The mitochondria in muscles contain many cristae. Explain the advantage of this | larger surface area for electron carrier system / oxidative phosphorylation; provide ATP / energy for contraction; |
| 240) Explain how a resting potential is maintained in a neurone. | membrane relatively impermeable / less permeable to sodium ions ; sodium ions pumped / actively transported out; by sodium ion carrier / intrinsic proteins; inside negative compared to outside / 3 sodium ions out for two potassium ions in; |
| 241) Describe how the release of acetylcholine into a neuromuscular junction causes the cell membrane of a muscle fibre to depolarise. | movement by diffusion; binding to receptors on (post-synaptic) membrane; causing sodium channels to open / sodium ions to move in to muscle (cell); |
| 242) Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP. | NAD / FAD reduced H+ ions / e- transferred from carrier to carrier series of redox reactions energy made available as e- passed on energy used synthesise ATP from ADP and Pi H+ passed into intermembrane space H+ flow back through stalked particle |
| 243) Explain what is meant when two species are described as being closely related. | more recent common ancestor / DNA in common; |
| 244) A difference in the molecular structure of cytochrome c may arise in a small population that becomes geographically isolated. Explain how the difference may arise and how it may spread in the population. | mutation causes variation; genes for protein with different structures; individuals with a modified cytochrome c have a selective advantage ,these individuals are more likely to survive have more offspring; allele frequency changes over time; |
| 245) Describe the part played by RNA in protein synthesis. | Carries coded information about the sequence of amino acids; Copied from DNA/gene; Code is in sequence of bases / triplet / three bases / a codon codes for one amino acid; Moves out of nucleus/goes into cytoplasm; To ribosomes; |
| 246) What is an attenuated microorganism? | Microorganism alive/active;But does not cause symptoms of disease/Avirulent; Accept does not make you ill/harm |
| 247) When glucose is respired what happens to the energy which is not incorporated into ATP? | released as heat; |
| 248) When one mole of glucose is respired anaerobically, only 2 moles of ATP are produced. Explain why less energy is released in anaerobic respiration | glucose only partly broken down / only broken down to lactate; |
| 249) At the end of a sprint race, a runner continues to breathe rapidly for some time. Explain the advantage of this. | lactate / lactic acid has built up / been produced; oxygen used to break down lactate / convert it back to pyruvate / glucose / glycogen; |
| 250) Starting with mRNA, describe how the process of translation leads to the production of a polypeptide. | mRNA attaches to ribosome; codon on mRNA; binds to an anti-codon on tRNA; each tRNA brings a specific amino acid; sequence of codons on mRNA determines order of amino acids; formation of peptide bonds / amino acids joined by condensation reactions; |
| 251) Describe and explain the relationship between humidity and transpiration rate. | increased humidity leads to decreased transpiration; high humidity means more water in the air / increased water potential; reduced diffusion gradient / water potential gradient; slower rate of water loss / less evaporation; |
| 252) Describe two features of the xerophytic leaf which reduce transpiration rate. Explain how each of these features contributes to a lower transpiration rate. | thick cuticle; impermeable to water / waterproof; sunken stomata; reduces water diffusion gradient; shape of leaf / rounded / small surface area; small surface area : volume ratio; (explanation must be linked to feature) |
| 253) Explain how crossing over can contribute to genetic variation. | sections of chromatids exchanged; sections have different alleles; new combinations of (linked) alleles; |
| 254) Describe how a gene can be isolated from human DNA. | use restriction enzyme / endonuclease / named, e.g. Bam / Eco; to cut DNA in specific place / base sequence; |
| 255) Describe how an isolated gene can be replicated by the polymerase chain reaction (PCR). | heat DNA to 90 – 95 °C; strands separate; add primers; and nucleotides; cool so that primers bind to DNA; (DNA) polymerase forms new strands / joins nucleotides; |
| 256) Explain why the enzyme is called reverse transcriptase. | makes DNA from RNA |
| 257) Explain why triglycerides are not considered to be polymers. | not made of monomers / many repeating units; |
| 258) Explain why an electron microscope shows more detail of cell structure than a light microscope. | electron microscope has a greater resolving power / objects closer together can be distinguished; electron (beams) have a shorter wavelength; |
| 259) What is meant by an abiotic factor? | the non-living / physical part (of an ecosystem / environment); |
| 260) Describe how you would collect the necessary data to estimate the size of a population by the mark-release-recapture technique. | capture, count and release; carefully mark to avoid detection; recapture, count marked and unmarked; |
| 261) Explain how succession resulted in the formation of the forest. | pioneers / suitable example colonise land; example of change in environment; enables change in species; conditions change further / example to favour trees; |
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ksatti12