BIOLOGY EDEXCEL IAL UNIT 1 - PAST PAPER QUESTIONS, Exams of Biology

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BIOLOGY: EDEXCEL IAL UNIT 1 - PAST PAPER

QUESTIONS

Bonding in unsaturated lipids - Answers- have double bonds between C atoms and between C and O atoms. method of amniocentesis and how its used to detect CF. - Answers- 1) amniotic fluid removed (from amniotic sac of the mother) / eq.

2. {fetal/embryonic} cells present in amniotic fluid /{fetal / embryonic} cells needed.
3. DNA can be analysed/ eq.
4. to detect {defective/eq} gene(s) (in sample)/ eq. method of chorionic villus sampling and how its used to detect CF. - Answers- 1) placental tissue removed (from the womb of the mother) / eq.
5. fetal cells present in {placenta/placental tissue / chorionic tissue} / fetal cells are needed.
6. DNA can be analysed / eq.
7. to detect {defective / eq} gene(s) (in sample) / eq. benefits, to a pregnant woman, of prenatal testing. - Answers- 1) it gives information about abnormalities in the fetus/eq.
8. {opportunity for choice/eq} OR {consider termination/eq} OR time for {preparation/treatment/eq}. risks, to a pregnant woman, of prenatal testing. - Answers- 1) possibility of miscarriage due to procedure/eq.
9. potentially a healthy baby would be lost/eq} / {risk to mother / eq}. OR
10. idea of a false positive/negative result.
11. a wrong decision made. OR
12. damage/harm to the fetus.
13. subsequent health issues/miscarriages/eq. Define causation - Answers- when a change in one variable is responsible for a change in another variable. define correlation - Answers- relationship between 2 variables such that a change in one of the variables is reflected by a change in the other variable / eq. define gene - Answers- a section of DNA/ sequence of bases that codes for a polypeptide / eq. and occupies a particular locus on a chromosome. define allele - Answers- different/variant form of a gene.

define recessive allele - Answers- allele that is only expressed in the phenotype of an organism if the dominant allele is not present / eq. define homozygous - Answers- alleles of a particular gene are the same / eq. amylose is an example of a: - Answers- polysaccharide The three dimensional structure of a protein is held together by: - Answers-. disulphide bridges.

. hydrogen bonds. . ionic bonds. What blood vessel carries deoxygenated blood to the lungs? - Answers- pulmonary artery. Define activation energy - Answers- 1) energy needed for a reaction to occur.

2. by causing bonds to break/weaken/form.
3. by increasing the number of collisions / eq. Explain why it is necessary to measure the initial rate of reaction when investigating the effect of enzyme concentration on the rate of reaction. - Answers- 1) there should be enough substrate molecules to saturate the enzyme.
4. to endure that the substrate is not a limiting factor / eq. Factors that increase the risk of CVDs - Answers- 1) genetics.
5. diet.
6. increasing age.
7. male.
8. high BP.
9. smoking.
10. inactivity/lack of exercise. advantages of the human circulatory system - Answers- 1) blood flows {faster/at higher pressure/eq} (to the body).
11. blood flows {slower/at lower pressure/eq} to the lung.
12. idea that this reduces risk of damage to lungs.
13. correct ref. to more efficient {exchange/ transport} of gases / eq. Describe the structure of an enzyme. - Answers- 1) ref to an enzyme as a protein.
14. ref. to {3D/tertiary/globular} structure.
15. ref. to named bonds (holding structure in place).
16. between the R groups.
17. ref. to active site.
18. idea of specificity of active site.

Describe the blood clotting process. - Answers- 1) idea that there is a cascade of events (leading to blood clotting).

2. ref. to thromboplastin (starting the cascade).
3. ref. to conversion of prothrombin into thrombin.
4. idea that {thromboplastin/thrombin} is {an enzyme / a catalyst} ;
5. ref. to conversion of fibrinogen into fibrin.
6. ref. to formation of mesh of {fibres/fibrin}.
7. ref. to requirement of {calcium ions/ Ca2+ / vitamin K} ;
8. ref. to {platelets/blood cells} getting trapped (in the mesh) ; Ethical and social issues relating to the use of prenatal testing. - Answers- 1) idea that fetus is living
9. abortion is wrong/murder/eq.
10. who has the right to decide id tests should be performed/eq.
11. implications of medical costs/disagreements over the next step.
12. who has the right to make the decision for the fetus/ fetus has rights.
13. the fetus is being denied the opportunity to live/ fetus has a right to live. Describe the roles of the atrioventricular valves during the cardiac cycle. - Answers- 1) valves separate atria from ventricles.
14. opens during atrial systole/contraction / eq.
15. so that blood can pass through to the ventricles / eq.
16. closed during ventricular systole/contraction / eq.
17. to prevent back flow into atria + to maintain pressure in ventricles.
18. open during diastole.
19. so that ventricles can start to fill up as atria are filling. Suggest reasons for the difference in the maximum pressures of the left and right ventricles. - Answers- 1) pressure in left is higher than right.
20. left ventricles pumps blood all around body / eq.
21. right ventricles pumps blood to lungs / eq.
22. if blood from right ventricle at high pressure there would be damage to lungs/capillaries / eq.
23. lots of muscle/thick wall of left ventricle. Suggest why cells from mouth swabs or blood samples are used rather than gametes - Answers- 1) idea that these cells are {easy/painless } to collect.
24. idea that a relatively {large amount of DNA / large number of cells} can be collected.
25. they {contain diploid cells/have (23) pairs of chromosomes}.
26. cells {are genetically identical/have same DNA / have same alleles}.
27. any {recessive allele/mutated (CF) gene} will be present in them / eq.
28. idea that if the gametes were tested they may not contain the {recessive allele/mutated (CF) gene} (as they are haploid).

Explain why it is necessary to test for several different recessive alleles in the screening for CF. - Answers- 1) cystic fibrosis results from one of a number of possible mutations (of this gene) /eq.

2. idea that testing for only one will miss other recessive alleles. Explain why the probability of having a child with CF is low and not zero when both parents aren't carriers. - Answers- 1) ref. to false negatives/eq.
3. idea that the screening programme does not test for all the possible mutations that can cause cystic fibrosis.
4. idea that a mutation may occur in the formation of the gametes.
5. idea of mutation in both gametes.
6. idea that a mutation may occur after fertilisation. Explain why family members of CF carriers are offered genetic screening. - Answers- 1) idea that any other family member could be a carrier.
7. idea that informed choices can be made about having children (if they know that they are carriers). Function of semi-lunar valves - Answers- 1) prevents back flow of blood into heart ventricles.
8. during diastole/atrial systole. Explain why a mammalian heart is divided into a right side and a left side - Answers- 1) idea that it keeps oxygenated and deoxygenated blood separate.
9. idea that this results in as much oxygen as possible being carried to the tissues/cells.
10. reference to need for different pressures in each side. Risk of using antihypertensives - Answers- blood pressure falls too low / coughs / swelling of ankles / impotence / tiredness / constipation / headache / confusion / depression / excessively low heart rate / allergy / stroke / provoked type II diabetes / frequent urination / fainting / dizziness / vomiting / dry mouth / breathing difficulties / irregular heart rate / chest pain / hives / rash / dehydration / reduced circulation effects / low potassium / blurred vision / eq. Explain the meaning of the term primary structure. - Answers- 1) sequence of amino acids
11. joined by peptide bonds. Explain the importance of the primary structure of an enzyme to its function. - Answers-
12. idea that primary structure determines (three-dimensional) folding/ eq.
13. reference to types of amino acids determine types of bonds formed.
14. reference to position of amino acids determines position of {bonds / correctly named bond}.

4. idea that {shape/position/eq} of active site is determined by position of amino acids.
5. reference to shape of active site being correct to bind to substrate.
6. reference to {amino acids/R groups} involved in {chemical reaction/ eq}.
7. reference to {globular/soluble/enzyme} molecules being {relatively short/small/made up of relatively few amino acids}.
8. reference to {globular/soluble proteins/enzyme} having relatively high number of {polar/ small {amino acids/R groups}.
9. reference to {polar R groups/eq} facing outwards. Roles of mRNA in protein synthesis. - Answers- 1) reference to mRNA as a copy of the {genetic code/DNA}.
10. holds the information of the protein (being synthesised)/eq.
11. moves out of the nucleus/to ribosomes/ eq.
12. idea that it acts as a template/has the instructions for translation. Roles of tRNA in protein synthesis. - Answers- 1) correct reference to translation.
13. binds to an amino acid/takes the amino acid to the ribosome/mRNA.
14. reference to tRNA being specific to amino acid.
15. holds the amino acid in place/eq. Describe the process of protein synthesis that occurs in the cytoplasm. - Answers- 1) reference to ribosome (attaches to mRNA).
16. idea that tRNA carries an amino acid.
17. idea of{ anti codon codon interaction/complementary base pairing } between tRNA and mRNA.
18. formation of hydrogen bonds (between the tRNA and mRNA).
19. reference to peptide bond (between amino acids).

6. (peptide bond) formed by a condensation reaction.

7. idea that tRNA released from {mRNA / ribosome).
8. idea that ribosome {attaches to/detaches from/ eq} {sequence / eq} on mRNA. Explain the effect of ethanol on the permeability of beetroot cell membranes. - Answers- 1) idea that ethanol causes the membrane to be{disrupted/ eq}.

2. idea that this is due (phospho)lipids dissolve in ethanol.
3. idea that (membrane) proteins denatured by ethanol.
4. comment on the disruption of the vacuole membrane/eq.
5. idea that {betalain/pigment}can escape from the {cell/ vacuole /eq } when the membrane is disrupted. Explain why water is an effective molecule for transporting other molecules around living molecules. - Answers- 1) Idea that water is a solvent.
6. idea that water is {slightly charged/dipole/polar/ eq}.
7. idea that polar molecules/ions/eq. can dissolve in water.
8. idea that water is viscous/fluid/ eq.
9. idea of water as a liquid assists mass flow.
10. correct reference to cohesion/adhesion. Suggest why a faulty atrioventricular valve could lead to symptoms of breathlessness and lack of energy. - Answers- 1) valve does not shut properly/eq.
11. some backflow of blood (from ventricle to atrium) / eq.
12. during ventricular systole/ when ventricles contract / eq.
13. idea of lower blood pressure.
14. idea of less efficient supply of oxygen.
15. idea that blood pressure in lungs increases. Explain how the circulatory system in mammals enables efficient gas exchange. - Answers- 1) idea that mass flow generated by heart.
16. idea that moving blood helps to maintain a concentration gradient.
17. idea that a steep/eq. concentration gradient gives a fast/eq. rate of diffusion.
18. idea of network/lots/e. of capillaries.
19. large surface area of capillaries/eq.
20. idea that large surface area increases the rate of diffusion.
21. idea that capillaries have very thin walls.
22. idea that diffusion is fastest over small distances.
23. idea that no organs/cells/tissues are far away from blood/capillaries cover alveoli/eq.
24. idea that efficiency is related to double circulation. Explain why the combination of a high-fat diet and low activity levels may lead to CVD. - Answers- 1) idea of energy imbalance.
25. idea of individual becoming overweight / obese / eq.
26. idea of increased blood pressure.
27. idea of obesity leads to diabetes a CVD risk factor.
28. idea of increased (blood) cholesterol / LDL

levels / LDL to HDL ratio.

6. idea of damage to endothelium / overloading of receptors.
7. formation of atheroma / plaque /atherosclerosis } / eq.
8. idea of loss of elasticity of artery / narrowing of lumen / eq. State what is meant by the term template for the synthesis of mRNA. - Answers- 1) idea that the RNA nucleotides attach to this strand.
9. idea of nucleotide / base sequence that directs the synthesis of complementary sequence / mRNA / eq. Differences between the processes of replication and transcription of DNA. - Answers- Replication:
10. uses DNA nucleotides.
11. uses DNA polymerase.
12. ref. to semi conservative.
13. copies both DNA strands.
14. makes DNA double helix. Transcription:
15. uses RNA nucleotides.
16. uses RNA polymerase.
17. not semi conservative.
18. cops only 1 DNA strand.
19. makes single RNA strand. Explain the meaning of the term recessive allele. - Answers- 1) idea that both of these alleles need to be present in order for the recessive phenotype to be expressed.
20. different form of a gene / eq.
21. same locus /position / eq.
22. different base sequence / eq. How is temperature controlled in an investigation? - Answers- heat shield. Explain why people with CF can have breathing difficulties. - Answers- 1) produces {thicker / stickier / more viscous / eq} mucus.
23. blocking { trachea / bronchi / bronchioles / airway / eq} / eq.
24. cilia are unable to move mucus out of lungs / eq.
25. idea of reduced flow of {air / oxygen } to alveoli.
26. idea of reduced concentration gradient for {oxygen / carbon dioxide} (in alveoli).
27. idea of loss of surface area / elasticity / eq.
28. idea of reduced gaseous exchange.
29. trapped bacteria may result in more respiratory infections / eq.

Explain the effect of the conc. of an enzyme on the initial rate of reaction of enzyme substrate complexes. - Answers- 1) idea that enzyme lowers activation energy / provides alternative reaction pathway.

2. idea that the higher concentration of enzyme means that more active sites are available.
3. more chance of a collision between {enzyme / active site } and substrate.
4. reference to enzyme - substrate complex / specific interaction between enzyme active site and substrate.
5. idea that substrate is in excess / enzyme concentration is limiting factor.
6. as the enzyme conc. increases the ROR increases. Explain how the information in a pedigree diagram suggests a disorder/disease is due to a ... allele. - Answers- Talk about:
7. how many people it has affected.
8. specific people and what their genotypes might be.
9. expand on point using pedigree.
10. the number of offspring with disorder/disease.
11. couples and their genotypes and what phenotypes they bring about in their children. Explain the ways in which the structures of amylose and glycogen make them suitable for energy storage. - Answers- 1) contain glucose / eq.
12. idea that they are compact so large {numbers of glucose / amylose / glycogen } molecules can fit into a small volume (large amounts of energy in small volume).
13. insoluble therefore does not affect osmosis / eq.
14. large molecules therefore remains in cells / too big to diffuse out or into cells / eq. Explain how rapid gas exchange takes place in a mammal. - Answers- 1) idea that large surface area provided by alveoli.
15. idea that large surface area provided by capillary network.
16. idea that concentration gradient maintained by ventilation of / air flow in / eq. the lungs.
17. idea that concentration gradient maintained by circulation / mass flow / eq. of blood.
18. idea that diffusion pathway is small because alveoli have a thin wall.
19. idea that diffusion pathway is small because capillaries have a thin wall / are in contact with alveoli / are only one cell thick / eq.
20. idea that air is warmed because lungs are in core of body.
21. warmer air enables faster movement / diffusion / eq. of gases / eq.
22. reference to respiratory pigment / haemoglobin / red blood cells / eq. to carry oxygen. Explain how the structure of an artery is related to its function. - Answers- 1) smooth endothelium lining to reduce friction (between wall and blood) / eq.
23. thick elastic wall to allow stretch and recoil /eq.
24. collagen layer to provide strength / withstand high blood pressure / eq.
25. smooth muscle in wall to enable artery to change diameter / eq.

Explain why mammals need a blood circulation system. - Answers- 1) mammals have a large volume to surface area ratio.

2. mammals have high nutrient / oxygen requirement.
3. heart and circulation provides a bulk / mass transport system.
4. that overcomes the limitations of diffusion. Suggest why BMI is used. - Answers- 1) idea that height has an impact on body mass.
5. BMI is related to both mass and height. Suggest why CVD is expressed as incidence per 1000. - Answers- to allow comparison between groups of different sizes / eq. Explain what is meant by the term fluid mosaic. - Answers- 1) randomly arranged / scattered / eq. proteins in the bilayer.
6. phospholipids forming the bilayer are free to move. Explain why a triplet code is required for the synthesis of protein. - Answers- 1) only four bases.
7. need to code for 20 / more than 16 amino acids.
8. three bases is the minimum number that provides sufficient combinations to code for each amino acid. Explain how Meselson and Stahl confirmed the semiconservative mechanism of DNA replication. - Answers- 1) Meselson and Stahl's experiment was designed to distinguish between different types of replication.
9. at the start of the experiment cells were grown in a medium with heavy nitrogen / 15N.
10. only a heavy DNA band was observed.
11. the cells were then transferred to a medium with light nitrogen / 14N.
12. after one round of replication an intermediate DNA band was observed.
13. after two rounds of replication intermediate and light bands were observed.
14. showing that replication was semiconservative / one strand of original DNA and one strand of newly synthesised DNA. Explain the meaning of the term semi-conservative replication. - Answers- 1) idea that new DNA is synthesised.
15. idea of a new DNA contains original strand and new strand. Compare and contrast exocytosis and endocytosis. - Answers- SIMILARITIES: º both used to transport large particles / large

quantities of material (1) º both involve (phospholipid) membrane vesicles (1) DIFFERENCE: º exocytosis is export and endocytosis is import of material (1) Compare and contrast the structures of glycogen and starch. - Answers- SIMILARITIES: º both polysaccharides / formed from many (alpha) glucose monomers (1) º joined by glycosidic bonds (1) DIFFERENCES: º starch is composed of two polysaccharides, glycogen only one (1) º amylose is a {straight / helical} chain, amylopectin and glycogen are both branched molecules (1) State what is meant by the term gene. - Answers- sequence of BASES of DNA that code for a polypeptide Explain why each codon for the DNA genetic code must contain at least three bases. - Answers- º enough codons needed for 20 different amino acids (1) º four bases are used in the genetic code (1) º triplet code provides enough / 43 / 64 possible codons (1) The CFTR protein coded for by this mutation has one missing amino acid compared to the functioning protein. Explain how this mutation results in a non-functioning CFTR protein. - Answers- º there will be a different sequence of R groups (1) º therefore the CFTR protein has a different tertiary structure (1) º because of different {types of / position of} bonds between the R groups (1) º therefore the movement of chloride ions through the cell membrane is affected (1) Explain why people with cystic fibrosis may develop lung infections. - Answers- º produces very thick, sticky mucus (1) º because of reduced water transport from cells (1) º cilia lining airways are unable to move mucus (1) º therefore microorganisms get trapped in the mucus (1) º mucus provides suitable growth conditions for growth of microorganisms (1)

Describe the roles of RNA in the synthesis of collagen. Collagen is an insoluble, fibrous protein. - Answers- º an mRNA molecule codes for each of the polypeptide chains in collagen (1). º mRNA carries a copy of the genetic code for collagen out of the nucleus to ribosome (1). º each tRNA carries its own specific amino acid to the ribosome. º anticodon on tRNA binds to codons on the mRNA (1). º tRNA holds the amino acid in place while peptide bonds form (1). º reference to start and stop codons on mRNA (1). Explain how the primary structure of collagen determines its properties. - Answers- º insoluble because there are hundreds of amino acids (1). º insoluble because there are many hydrophobic R groups (1). º strong because of the triple helix (1). º therefore there are many repeating amino acid sequences (1). º many small R groups so that the triple helix can form (1) Roles of mRNA. - Answers- º copy of the genetic code. º copy of the protein being synthesised. º moves to ribosome. º template for translation. Assess 2 graphs... - Answers- 1) general correlation.

2. the individual pieces of data.
3. pieces of data in each graph that stands out.
4. application of your own knowledge to explain data. describe the location of the elastic fibres and explain its function. - Answers- 1) middle layer of wall of vessel/eq/tunica media / in the muscle layer.
5. ref. to allows stretching/recoil/ description.
6. to prevent damage of the aorta/eq. /to maintain the pressure of the blood / eq.

Give one reason why many mammals have a circulatory system. - Answers- idea that it overcomes limitations of diffusion / it is involved in transport / heat transfer. Explain why glucose and galactose are classed as monosaccharides. - Answers- 1) reference to consisting of C, H and O / eq.

2. no glycosidic bonds / one sugar unit.
3. idea of ratio of C:H:O is 1:2:1. describe the structure of a fibrous protein. - Answers- 1) fibrous proteins are long / contain many amino acids.
4. amino acid sequence is repetitive / eq.
5. idea of limited folding.
6. polypeptides lie parallel to each other.
7. idea of bonds linking chains together. Suggest why enzymes can break down substrates quickly. - Answers- 1) enzymes are catalyst.
8. reference to lowering / eq. activation energy.
9. without being used up in the reaction / eq.
10. idea that once reaction is complete, the enzyme detaches from products.
11. and can then bind to another substrate. Explain how water is involved in the transport of molecules in living organisms. - Answers- 1) Dipole nature of water.
12. Hydrogen bonding.
13. Transport of polar molecules. Suggest how triglycerides are transported in the blood. - Answers- 1) triglycerides are insoluble (in water) / eq.
14. as lipoproteins / as LDL / as HDL.
15. formed into vesicles / micelles. blood clots form only when requires because the clotting factors used are... - Answers- present in an inactive form in the blood. Explain why statins reduce the risk of CVD. - Answers- 1) statins inhibit the synthesis / production of cholesterol in the liver.
16. reducing (total) blood cholesterol levels.
17. raises HDL levels / increases HDL : LDL ratio / lowers LDL. Suggest how cholesterol affects membrane fluidity. - Answers- 1) combines with fatty acid tails.
18. holds / pulls the fatty acid chains together.
19. reducing movement of the phospholipid / fatty acid tails. Explain the meaning of the term gene mutation. - Answers- 1) alteration in DNA.

2. change in base sequence. / eq. What is meant by the term relative risk? - Answers- 1) the chance / probability of an event.

2. in one {group / person} compared to another ; Suggest the health advice that could be given to someone with an obese BMI. - Answers- 1) individuals should take regular / more exercise.

2. reduce energy intake.
3. reduce BMI to less than 25. Explain one way in which the structure of a capillary is related to its function. - Answers-
4. thin walls / walls consist of single layer of flattened cells / eq.
5. idea of allowing rapid diffusion. OR
6. gaps between cells in the wall.
7. to allow exchange (of materials) / increase permeability. Describe the relationship between mass and surface are of alveoli. - Answers- 1) as mass increases demand for oxygen increases / eq.
8. surface area of alveoli increases to allow for increased gas exchange / eq. Explain why a pH buffer should be used in the investigation to measure the initial rate of reaction of an enzyme. - Answers- 1) controlling pH.
9. otherwise pH would change as the fatty acid was used up.
10. (changes in pH) affect the shape of the active site.
11. (changes in pH) change ionic bonds within the enzyme.
12. (changes in pH) change the rate of reaction. Describe the structure of the cell membrane. - Answers- 1) reference to phospholipid bilayer.
13. correct orientation and structure of the phospholipids in the bilayer.
14. phospholipids have polar / hydrophilic heads and non- polar / hydrophobic tails / eq.
15. proteins in the membrane.
16. idea of at least two different locations of proteins e.g. extrinsic, intrinsic, transmembrane.
17. reference to glycoproteins / glycolipids / lipoproteins ;
18. reference to cholesterol within the membrane. Explain the term genotype. - Answers- genotype is the combination of / pair of / two / all alleles present (in an organism). Explain the term phenotype - Answers- phenotype is the observable feature.

Describe how the primary structure of a protein results in a protein with a 3D structure. - Answers- 1) primary structure is the sequence of amino acids.

2. idea that amino acids each have different R groups.
3. idea that bonds form between R groups.
4. bonding determines the folding of the polypeptide. Explain how a genetic pedigree diagram could show how a recessive gene is inherited.

• Answers- 1) parents and offspring for each generation identified.

2. phenotype(s) identified.
3. for /recessive condition two normal/unaffected parents may have {one or more / some / eq. offspring that are affected. The sequence of events in the cardiac cycle is.. - Answers- atrial systole --> ventricular systole --> atrial diastole --> ventricular diastole. Explain why long term exercise reduced the risk of developing coronary heart disease. - Answers- 1) low blood pressure.
4. low heart rate.
5. heart/cardiac muscle is stronger.
6. not overweight.
7. changes LDL/HDL ratio/lowers cholesterol. Describe how sucrose is formed from monosaccharides. - Answers- 1) glucose and fructose.
8. joined by condensation reaction / water produced.
9. forming a glycosidic bond/link. describe the structure of starch - Answers- 1) (many) glucose molecules joined by glycosidic bonds /links.
10. amylose and amylopectin.
11. amylose is linear / is unbranched / is helical / has 1,4 bonds.
12. amylopectin is branched / has 1,4 and 1,6 bonds. Describe how a blood clot forms in large veins. - Answers- 1) Idea of slow blood flow in (large) veins.
13. initiates clotting cascade.
14. prothrombin converted to thrombin.
15. leading to conversion of fibrinogen to fibrin.
16. fibrin is insoluble.
17. trapping red blood cells / platelets to form a clot. Explain how the properties of phospholipids contribute to the fluid mosaic model of cell membranes. - Answers- 1) (phospholipids) form a bilayer as they have a polar head and non-polar tails.
18. proteins are located between the phospholipids.
19. because of interactions between R groups of proteins and phospholipids.

4. phospholipids are free to move which makes the membrane fluid. Explain how enzymes catalyse the break down of substrates. - Answers- 1) active site that fits /eq. the substrate.
5. lowers the activation energy (for the reaction).
6. detail of how the activation energy is lowered (bonds are weakened) Explain why smokers with a high LDL:HDL ratio have a greater risk of death from CVD than non-smokers. - Answers- 1) idea that smoking causes platelet damage.
7. increases the risk of formation of blood clots.
8. increases the risk of plaque formation/atheroma/ atherosclerosis.
9. increases blood pressure. Describe the roles of prothrombin in the formation of blood clots. - Answers- 1) idea that prothrombin is the inactive enzyme.
10. prothrombin is converted to thrombin /an active enzyme.
11. by thromboplastin.
12. thrombin converts fibrinogen to fibrin.
13. fibrin traps platelets/red blood cells to form clot. Suggest 2 differences between fibrinogen and fibrin. - Answers- 1) idea that fibrinogen is globular and fibrin is fibrous.
14. fibrinogen is soluble and fibrin in insoluble.
15. idea that they are different sizes. Explain the nature of the genetic code. - Answers- 1) triplet code/3 bases to each code/eq.
16. ref. to A,T,G,C.
17. idea that each triplet of bases codes for one amino acid.
18. idea that the code is not overlapping.
19. idea that the code is universal.
20. idea that the code is degenerate. fluid mosaic model of cell membrane - Answers- Describe the correct location for the CFTR protein. - Answers- 1) in the cell surface membrane.
21. of mucus producing cells. Explain why a faulty opening of the CFTR protein would affect the functioning of this protein. - Answers- 1) CFTR is a channel protein/eq.
22. idea that fewer/no chloride ions will be able to enter/bind to/pass through/eq. the CFTR protein.
23. idea that fewer chloride ions will leave the cell.

Explain 2 way in which the structures of amylose and glycogen make the suitable for energy storage. - Answers- 1) contain glucose / eq.

2. idea that they are compact so large numbers of glucose / amylose / glycogen molecules can fit into a small volume.
3. insoluble therefore does not affect osmosis / eq.
4. large molecules therefore remains in cells / too big to diffuse / eq. Using Fick's law of diffusion, explain how rapid gaseous exchange takes place in a mammal. - Answers- 1) idea that large surface area provided by alveoli.
5. idea that large surface area provided by capillary network.
6. idea that concentration gradient maintained by ventilation of / air flow in / eq. the lungs.
7. idea that concentration gradient maintained by circulation / mass flow / eq. of blood.
8. idea that diffusion pathway is small because alveoli have a thin wall.
9. idea that diffusion pathway is small because capillaries have a thin wall / are in contact with alveoli / are only one cell thick / eq.
10. idea that air is warmed because lungs are in core of body.
11. warmer air enables faster movement / diffusion / eq. of gases / eq.
12. ref. to respiratory pigment / haemoglobin / red blood cells / eq. to carry oxygen. Describe how a triglyceride is synthesised. - Answers- 1) one glycerol molecule and three fatty acid molecules (1)
13. which react via a condensation reaction (1)
14. and are joined by ester bonds (1) Describe how the two strands of DNA forming the double helix in a gene are held together. - Answers- 1) complementary bases / named pair of complementary bases (1)
15. it enables the formation of two hydrogen bonds between adenine and thymine / three hydrogen bonds between cytosine and guanine (1) Explain why the AV valves need to close. - Answers- 1) ventricle needs to contract and force blood into the aorta/pulmonary artery.
16. to prevent back flow from the ventricle into the atrium. Explain why smaller mammals require more oxygen than larger mammals. - Answers-
17. bigger mammals have a smaller surface area to volume ratio.

2. less heat is lost through the surface so less respiration is needed to replace lost heat. Compare and contrast the procedures used in amniocentesis and chorionic villus sampling to obtain fatal cells in prenatal tests. - Answers- DIFFERENCES:
3. fetal cells obtained from amniotic fluid in amniocentesis, fetal cells obtained from placental cells in CVS.
4. amniocentesis via abdomen and cvs either via abdomen or vagina. SIMILARITES:
5. use of needle in both amniocentesis and CVS. Advantages of CVS and amniocentesis. - Answers- CVS:
6. cvs can be performed earlier in pregnancy. (10 and 13 weeks) 2)cvs allows earlier decision to abort / termination less physically traumatic.
7. cvs results available sooner. AMNIO-:
8. amniocentesis there is a lower risk / 1% risk of miscarriage.
9. can detect gene problems on X chromosomes. Disadvantages of CVS and amniocentesis. - Answers- CVS:
10. cvs there is greater risk / risk is between 1-2% of miscarriage.
11. cvs cannot detect gene problems on X chromosomes (because they are inactivated in fetal placental cells). AMNIO-:
12. amniocentesis performed late in pregnancy. (14 and 20 weeks).
13. amniocentesis later decision to abort / termination more physically traumatic.
14. amniocentesis results not available until 2-3 weeks after test. LDL cholesterol found in the plasma bin to the receptor proteins and is taken into cells by endocytosis. The dominant allele (F) makes LDL receptor proteins that don't function. Explain why people who inherit the dominant allele have an increased risk of dying early. - Answers- 1) more LDL cholesterol found in the blood/ LDL cholesterol cannot enter the cell.
15. the allele makes the wrong protein/different protein due to different primary structure folding.
16. LDL cholesterol doesn't bind to receptor proteins.
17. cholesterol deposits in damaged tissue in arteries forming plaques leading to atherosclerosis - arteries narrow.

5. oxygen flow to heart cells is reduced - cells die.
6. increasing the risk of CVD's. Explain one treatment used to reduce the symptoms of cystic fibrosis. - Answers- 1)antibiotic to kill bacteria.
7. because more prone to bacterial infection. OR
8. physiotherapy dislodges mucus.
9. therefore more efficient gas exchange. Explain why a couple may choose not to carry out CVS test. - Answers- 1) test result may be inaccurate.
10. increased risk of miscarriage due to the procedure.
11. false positive may lead to termination of a healthy fetus.
12. prenatal testing/abortion against values or beliefs of the parents. Compare and contrast the structures of globular and fibrous proteins. - Answers- 1) both are chains of amino acids joined by peptide bonds.
13. both contain named bonds (holding molecule in its three dimensional shape).
14. globular proteins have hydrophilic groups on the outside whereas fibrous proteins have hydrophobic groups on the outside.
15. globular have tertiary or quaternary structures whereas fibrous have little or no tertiary structure.
16. globular are folded into compact shapes whereas fibrous have long chains. Describe the roles of transcription and translation in the synthesis of a globular protein by a muscle cell. - Answers- 1) the gene / sequence of DNA for the (globular) protein is transcribed.
17. complementary base pairing between RNA nucleotides and DNA (to produce mRNA).
18. mRNA leaves the nucleus and attaches to a ribosome.
19. pairing between codons on mRNA and anticodons on tRNA.
20. tRNA provides specific amino acids.
21. the sequence of bases / codons determines the sequence of amino acids / primary structure of the protein. Triglycerides can combine with protein to form a lipoprotein.

Explain the effect that having large quantities of this lipoprotein would have on blood cholesterol levels. - Answers- 1) increased (blood) cholesterol.

2. (because) the triglyceride is saturated.
3. The lipoprotein is an LDL.
4. lipoproteins / LDLs transport cholesterol.
5. LDL binds to receptors (on cell surface membranes) / LDL accumulates in blood if receptors overloaded. Explain why deletion and substitution have different effects on protein structure. - Answers- 1) deletion could affect every codon (on the mRNA) / substitution will only affect one codon.
6. deletion more likely to affect the position of stop codon/start codon.
7. deletion results in a different sequence of amino acids/substitution may not affect the sequence of amino acids.
8. substitution may code for the same amino acid.
9. (same amino acid) due to the degenerate nature of the genetic code. Describe how the structure of glycogen is related to its function as a storage molecule. - Answers- 1) branched molecule for more rapid hydrolysis.
10. compact so more can be stored. Explain how an experiment can be improved. - Answers- 1) improvement e.g repeats at each temp.
11. justification of improvement e.g to calculate mean/cancel out anomalies.