Adaptations of Companion Cells for Sugar Transport, Exams of Medicine

Download Adaptations of Companion Cells for Sugar Transport and more Exams Medicine in PDF only on Docsity! Biology Unit 2 Resit Past Paper Questions June 2015 - What is the function of the coronary arteries? [2 marks] - - To carry oxygen/glucose/oxygenated blood; - To heart muscles/tissues/cells/myocytes; June 2015 - The rise and fall in blood pressure in the aorta is greater than in the small intestine. Suggest why? [3 marks] - - Aorta is close / directly linked to the heart/venrticle/pressure is higher/is very high; - Aorta has elastic tissue/elasticity OR small arteries has little/less elastic tissue/elasticity; - Aorta has stretch/recoil OR small arteries has little/less stretch/recoil; June 2015 - Ecologists measured the body lengths of male and female thorny lizards living in the same habitat. The ecologists measured the body lengths to the nearest 5mm. Figure 3 shows how they presented their results. Give two differences in the variation in body length of male and female thorny lizards. [2 marks] - - Females are (generally) longer/larger/bigger/up to 115mm/males are (generally) shorter/smaller/up to 100mm OR females have a larger/90 modal/peak/most common value and males have a smaller/80 modal/peak/most common value OR mean lengths of females greater/mean lengths of males shorter; - Females show a greater range/variation/males show a narrower range/variation OR the range of males is 50-100 and females is 50-115/the spread is 50 for males and 65 for females; June 2015 - The ecologists also determined the index diversity of lizards in an oil palm plantation, next to the woodland area. They found that fewer species of plant in the oil palm plantation. Lizards feed on plants and insects. Explain why fewer species of plants would lead to fewer species of lizard in the oil palm plantation. [3 marks] - - Fewer plant species and so therefore fewer habitats/niches; - So lower diversity of insects/fewer insect species/fewer insect types OR less variety of insects; - So fewer food sources/less variety of food for lizards; 1 | P a g e June 2015 - Give two ways in which the structure of starch is similar to cellulose. [2 marks] - - Both are polymers/polysaccharides/are made of monomers/monosaccharides; - Both contain glucose - carbon, hydrogen, oxygen; - Both contain glycosidic bonds; - Both have 1-4 links; - Both posses hydrogen bonding (within structures); June 2015 - Give two ways in which the structure of starch is different to cellulose [2 marks] - - Starch contains alpha glucose/glycosidic bonds. Whereas cellulose contains beta glucose/glycosidic bonds; - Starch is helical/coiled/compact/branched/not straight whereas cellulose is the opposite of this; - Starch has 1,6 bonds/1,6 branching, cellulose does not; - In starch the glucose/monomers are the same way up whereas in cellulose they are orientated 180 degrees from the last; June 2015 - Ways in which sieve cells are adapted for mass transport. [2 marks] - - No/few organelles/very little cytoplasm/cytoplasm at edge/more room/hallowed/large vacuole/large space/thick walls/strong walls; - So easier/more flow/thick/strong walls/resist pressure/low resistance to flow; June 2015 - Ways in which companion cells are adapted to the transport of sugars between cells. [2 marks] - - Mitochondria release energy/ATP/site of respiration/produces energy in the formation of ATP; - For active transport/uptake against concentration gradient ; OR - Ribosomes/rough endoplasmic reticulum produces proteins; - Proteins linked to transport e.g. carrier proteins/enzymes; June 2015 - Describe the role of DNA polymerase in DNA replication. [1 marks] - - Joins nucleotides (to form a new strand) OR joins sugar phosphate backbone; 2 | P a g e 1. Change/mutation in base/nucleotide sequence (of DNA/gene) OR changes triplets/codons; 2. Change in amino acid sequence/primary structure (of enzyme) OR different amino acid(s) coded for; 3. Change in hydrogen /ionic/disulphide bonds; 4. Change in the tertiary structure/shape; 5. Change in active site; 6. Substrate not complementary/cannot bind (to enzyme/active site) /no enzyme-substrate complexes form OR no E-S complexes form; June 2014 - what is meant by a heirarchy? [2 marks] - - Groups within groups OR larger groups at the top or smaller groups at the bottom; - No overlap between groups; June 2014 - Explain the role of independent segregation in meiosis. [2 marks] - - To provide genetic variation; - Allows different combinations of material and paternal chromosomes/alleles OR any allele of one gene can combine with any allele of another gene; - To produce haploid cells/half the chromosome number; - Allows homologous chromosomes/ homologous pairs to arrange randomly (at equator/middle of cell)/separate; June 2014 - A zeedonk is the offspring produced from breeding a mountain zebra with a donkey. The body cells of a mountain zebra contain 32 chromosomes. The body cells of a donkey contain 62 chromosomes. Use this information to suggest why zeedonks are usually infertile. [2 marks] - - (Zeedonk) has 47/odd/ uneven number of chromosomes OR diploid number would be odd; - Chromosomes cannot pair/are not homologous/ chromosome number cannot be halved/meiosis cannot occur/sex cells/haploid cells are not produced OR cannot have half a chromosome June 2014 - What is selective breeding? [1 mark] - (Humans breed) organisms with certain/chosen characteristics/alleles 5 | P a g e June 2014 - Explain one potential problem that can be caused by selective breeding. [2 marks] - - Inbreeding/breed closely related organisms; - (So higher probability of) mutations being passed on/recessive alleles being expressed/health problems /example given/increase in genetic disease; - Reduced genetic variation/diversity/smaller gene pool/less variety of alleles; - (So) can be killed by/ susceptible to the same/a disease/reduces ability to adapt/survive (future) environmental changes/ may not be benificial to future breeding programmes; June 2014 - The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. Explain the advantage of this shift. [3 marks] - - Lower affinity for oxygen/releases more oxygen/oxygen is relased quicker/oxygen dissociates/unloads more readily; - (To) muscles/tissues/cells; (For) high/rapid respiration OR (for) respiration to produce more energy in the form of ATP/release more energy; June 2014 - Explain how the body shape of a Weddell seal is an adaptation to living in a cold environment [2 marks] - - Small SA:Vol OR large Vol:SA; - (So) reduces heat loss/ (more) heat retained; June 2014 - Describe and explain the changes in the rate of blood flow to the different organs during a long dive. [3 marks] - - Brain is the same, others fall OR blood flow is reduced to all organs except for the brain; - Brain controls other organs/remains active/ needs constant supply of oxygen OR seal would die = brain remains active; - Lungs not used/are used less/seal is not breathing; - Heart rate decreases/ heart pumps less; - Blood diverted to muscles; - Oxygen (in blood) will last longer/less oxygen used/oxygen is conserved; June 2014 - Describe and explain how the countercurrent system leads to efficient gas exchange across the gills of a fish [3 marks] - - Water and blood flow in opposite directions; 6 | P a g e - Maintains concentration/ diffusion gradient/ equilibrium not reached/ water always next to blood with a lower concentration of oxygen OR constant concentration/diffusion gradient; - Along whole/length of gill/lamellae OR gill plate/gill filament; June 2014 - Amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some species of fish. The disease causes the lamellae to become thicker and to fuse together. AGD reduces the efficiency of gas exchange in fish. Give two reasons why [2 marks] - - (Thicker lamellae so) greater/longer diffusion distance/pathway; - (Lamellae fuse so) reduced surface area OR reduced SA:Vol; June 2014 - The volume of water passing over the gills increases if the temperature of the water increases. Suggest why [2 marks] - - Increases metabolism/respiration/enzyme activity OR enzymes work more efficiently; - Less oxygen (dissolved in water); June 2014 - The antibiotic tetracycline binds to ribosomes in bacterial cells. Explain how this causes the death of bacterial cells. [2 marks] - - Prevents protein synthesis OR ribosomes produce proteins/chains of amino acids/polypeptides and tetracycline prevents this; - (So) enzymes not produced/ any names process involving proteins/enzymes is inhibited OR no DNA replication OR cannot form a cell wall; June 2014 - Tetracycline can enter a bacterium through protein A. This protein is found in the plasma membrane. Suggest how a change in the amino acid sequence of this protein could make a bacterium resistant to tetracycline. [2 marks] - - Different tertiary structure/tertiary shape; - (So tetracycline) does not fit/bind/is not complementary/does not enter/pass through (protein/into cell) OR (so) more tetracycline pumped out of cell; June 2014 - Evolutionary relationships between different primates can be found by comparing their proteins and DNA. All primates produce a species-specific type of haemoglobin. An antibody against human haemoglobin could be used to compare the evolutionary relationships between different primates. Describe and explain how. [3 marks] - 7 | P a g e - (Scientists) can't show bias/influence/may have a vested interest/work for the company developing the vaccine OR reduces the 'Hawthorne effect'/demand characteristics; - Volunteers can't show psychological/mental effects/'placebo effect'/expectations; June 2014 - The scientists measured the concentration of nicotine in the blood of two volunteers who smoked the same number of cigarettes per day. Suggest two reasons why the concentration of nicotine in the blood of these smokers might be different. [2 marks] - Any two suitable suggestions e.g. - Amount of nicotine in cigarettes - Amount inhaled/absorbed/time since last cigarette OR absorption by mouth; - (Different) amounts excreted/metabolism/rate of binding (of nicotine) to protein OR broken down differently; - (Different) blood volumes; - Nicotine from passive smoking/other smokers/other sources; - Some volunteers recieved the vaccine/placebo OR some volunteers would have/would not have the antibodies; June 2014 - Suggest how this vaccine could help people to stop smoking. [3 marks] - - Antibodies to nicotine produced/antibodies bind to nicotine; - (So) nicotine does not bind to protein/does not reach the brain; - (So) cigarettes/smoking does not satisfy addiction/reward smokers/release (reward) chemicals; June 2014 - Some people have suggested that this vaccine should not be given free to smokers on the National Health Service (NHS). Evaluate this suggestion. [3 marks] - Agree - People choose to smoke and so should know the risks; - Should spend thi smoney on education/preventing people from starting to smoke/treating other health problems/vaccines are expensive; Disagree - Unethical not to treat; 10 | P a g e - Less money needed to treat the effects of smoking/cancer/smokers pay taxes so are entitled to treatment; June 2013 - Describe the role of the centromere in mitosis. [2 marks] - - Holds cromatids/chromosomes together; - Attaches (chromatids/chromosomes) to spindle; - (Allows) chromatids to be separated/move to (opposite) poles/(centromere) divides/splits at metaphase/anaphase; June 2013 - Homologous chromosomes carry the same genes but are not genetically identical. Explain why. [1 mark] - (Homologous chromosomes) carry different alleles/different forms of the same gene/different base sequences; June 2013 - Other than independent segregation, give one way in which meiosis allows the production of genetically different cells. [1 mark] - Crossing over (sections of chromatids break and rejoin)/alleles exchanged between chromosomes or chromatids/chiasmata formation/genetic recombination; June 2013 - What is a species? [2 marks] - - Group of similar organisms/organisms with similar features/organisms with same genes/chromosomes OR same number of chromosomes OR smallest taxonomic group; - Reproduce/produce offspring OR breed/mate; - That are fertile; June 2013 - The forest .............. was cleared to make more land available for agriculture. After the forest was cleared the species diversity of insects in the area decreases. Explain why. [3 marks] - - Decrease in variety of plants/fewer plant species OR land becomes monoculture; - Fewer habitats/niches - Decrease in variety of food/fewer food sources OR less variety of prey; - Aspect of clearing forest (killing insects) e.g. machiner, pesticides; 11 | P a g e June 2013 - Explain what is meant by a hierarchy. [2 marks] - - Groups within groups OR idea of larger groups at the top/smaller groups at the bottom; - No overlap (between groups); June 2013 - Explain what is meant by a phylogenetic group. [1 mark] - (Grouped according to) evolutionary links/history/relationships/common ancestry; June 2013 - Cytochrome c is more useful than haemoglobin for studying how closely related different organisms are. Suggest one reason why. [1 mark] - - All organisms/animals respire/have cytochrome c OR not all organisms/animals use haemoglobin (iron) to carry oxygen around the body e.g. horseshoe crabs use copper; - (Cytochrome c structure) is more conserved/less varied (between organisms/animals; June 2013 - DNA helicase is important in DNA replication. Explain why. [2 marks] - - Seperates/unwinds/unzips strands/helix/breaks hydrogen bonds/H-bonds OR unzips bases; - (So) nucleotides can attach/are attached/strands can act as templates; June 2013 - Cytarabine is a drug used to treat certain cancers. It prevents DNA replication. The diagram shows the structures of cytarabine and the DNA base cytosine. Use information in the diagram to suggest how cytarabine prevents DNA replication. [2 marks] - - Similar shape-structure (to cytosine)/added instead of cytosine/binds to guanine; - Prevents (complementary) base pairing/prevents hydrogen bonds/H-bonds forming/prevents formation of new strand/prevents strand elongation/inhibits/binds to (DNA) polymerase OR prevents cytosine binding; June 2013 - Cytarabine has a greater effect on cancer cells than on healthy cells. Explain why. [1 mark] - (Cancer cells/DNA) divide/replicate fast(er)/uncontrollably OR healthy cells replicate slower/controllable; June 2013 - Give one way in which antibiotics can prevent the growth of bacteria. [1 mark] - Prevents cell wall formation (OR weaken the cell wall)/causes (cell) lysis/inhibit ribosomes (OR bind to ribosomes)/ inhibit protein synthesis/prevent DNA replication/affect function of cell membrane; 12 | P a g e June 2013 - Explain how water enters xylem from the epidermis in the root and is then transported to the leaves. [6 marks] - (In the root) 1. Casparian strip blocks apoplast pathway/only allows symplast pathway; 2. Active transport by endodermis; 3. (Of) ions/salts into xylem; 4. Lower water potential in xylem/water enters xylem by osmosis/down a water potential gradient; (Xylem to leaf) 5. Evaporation/transpiration (from leaves); 6. (Creates) cohesion/tension/hydrogen bonding/H-bonding between water molecules/negative pressure; 7. Adhesion/water molecules bind to xylem; 8.(Creates continuous) water column; June 2013 - Large insects contract muscles associated with the abdomen to force air in and out of the spiracles. This is known as 'abdominal pumping'. The table shows the mean rate of abdominal pumping of an insect before and during flight. Abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of the insect. Explain why. [2 marks] - - More air/oxygen enters/air/oxygen enters quickly/quicker; - (So) maintains/greater diffusion or concentration gradient; June 2013 - Abdominal pumping is an adaptation not found in many small insects. These small insects obtain sufficient oxygen by diffusion. Explain how their small size enables gas exchange to be efficient without the need for abdominal pumping. [1 mark] - Large(r) SA:Vol/short(er) diffusion distance (to tissues); 15 | P a g e June 2013 - The insect opens its spiracles at a lower frequency in very dry conditions. Suggest one advantage of this. [1 mark] - Less/no water lost/(more) water retained OR dehydration/less evaporation; June 2013 - The ends of tracheoles connect directly with the insect's muscle tissue and are filled with water. When flying, water is absorbed into the muscle tissue. Removal of water from the tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle tissue. Suggest one reason why. [1 mark] - - Greater surface area exposed to air; - Gases move/diffuse faster in air than through water OR gases diffuse directly, rather than through water; - Increases volume/amount of air; June 2013 - Apart from the size of the female, suggest two factors that should have been kept constant in order to obtain reliable results. [2 marks] - - Volume/concentration of skin lipid; -Age/sexual maturity; - Species of snake; - Size of male; - Colour; - Temperature; - Light; - Time of day/year/breeding season; - Duration/length of time observing; - Diet; - Filter paper; - Size of cage; June 2013 - The male snakes used for each trial were selected at random. Explain why this was important. [1 mark] - To avoid bias 16 | P a g e June 2013 - The scientists used different male snakes in each trial. Suggest why. [1 mark] - - To avoid change in (courtship) behaviour (due to past experience); - To observe a typical/general/ representative (response); - Ethical arguements e.g. causing distress to snakes June 2013 - What should the scientists have placed in the cage as a control, to show that males were responding to lipids from females? [1 mark] - Filter paper without (skin) lipids/ untreated filter paper/ filter paper with water/ (female) snakes with lipids removed OR only filter paper; June 2013 - Suggest two advantages of male snakes courting with longer female snakes. [2 marks] - (Parent/offspring) - Produce more/larger offspring/eggs; - Better predators/fitter/more successful at gaining food/less likely to be eaten/more able to protect offspring eggs; - (More) sexually mature/fertile; - Have more food stores for offspring/eggs; June 2013 - The females of other species of snake secrete lipids on their skin. These lipids also contain unsaturated fatty acids. Male garter snakes do not show courtship behaviour towards thee females. Suggest why. [1 mark] - (Other females/species) produce different fatty acids OR lack of receptors; January 2013 Name the type of reaction that would break down these carbohydrates into their monomers. [1 mark] - Hydrolysis January 2013 - Give one feature of starch and explain how this feature enables it to act as a storage substance. [2 marks] - - Feature: Coiled/helical/spiral; - Explanation: (So) compact/tightly packed/can fit (lots) into a small space; 17 | P a g e - Age; - Sex/Gender; - Family/medical history; - No use of recreational drugs; - Ethnic origins; January 2013 - Give two precautions that students should have taken when setting up the photometer to obtain reliable measurements of water uptake by the plant shoot. [2 marks] - - Seal joints/ensure airtight/ensure watertight; - Cut shoot under water; - Cut shoot at a slant; - Dry off leaves; - Insert into apparatus under water; - Ensure no air bubbles are present; - Shut tap; - Note where bubble is at start/move bubble to the start position; January 2013 - - Water used for support/turgidity; - Water used in photosynthesis; - Water produced in respiration; - Apparatus not sealed/'leaked'; OR water used in the cells by hydrolysis and condensation reactions; January 2013 - Explain the relationship between the number of leaves removed form the plant shoot and the mean rate of water uptake. [3 marks] - As number of leaves are reduced, no mark - Less surface area; - Fewer stomata; - Less evaporation/transpiration; - Less cohesion/tension/pulling (force); 20 | P a g e January 2013 - Treatment with Isoniazid leads to the osmotic lysis of this bacterium. Use information in the diagram to suggest how. [2 marks] - - Cell wall not formed / production inhibited; - Lower water potential in bacterium; - Water enters and causes lysis/expansion/pressure; January 2013 - Human cells also produce fatty acids. Isoniazid does not affect the production of these fatty acids. Use the information in the diagram to suggest one reason why Isoniazid does not affect the production of fatty acids in human cells. - Human cells lack enzyme B/have a different enzyme/produce fatty acids/use different sunstrates; January 2013 - A mutation in the gene coding for enzyme B could lead to the production of a non- functional enzyme. Explain how. [3 marks] - - Change in the base sequence (of DNA/gene) - Change in amino acid sequence/primary structure (of enzyme) OR different amino acids coded for; - Change in hydrogen/ionic/disulphide bonds; - Change in the tertiary structure/active site (of enzyme); - Substrate not complementary/cannot bind (to enzyme/active site)/no enzyme-substrate complexes form; January 2013 - Using Isoniazid to treat diseased caused by other species of bacteria could increase the chance of the bacterium that causes tuberculosis becoming resistant to Isoniazid. Use your knowledge of gene transmission to explain how. [3 marks] - - Resistance gene/allele; - On plasmid; - (Spread by) horizontal transmission; - (Involves) conjugation/pilus; 21 | P a g e January 2013 - There are ethical and economic arguements for maintaining biodiversity. Suggest one ethical arguement and one economic arguement for maintaining biodiversity. [2 marks] - Ethical - Prevent extinction - Prevent loss of populations - Prevent reduction in populations - Prevent loss of habitat - Save organisms for future generations Economic - Medical/pharmaceutical uses - Commercial products - Tourism - Agriculture - Saving local forest communities; January 2013 - Explain the relationship between the percentage of original forest area remaining and the percentage of bird species that have become extinct. [2 marks] - - Fewer plant species/decrease in plant diversity; - Fewer habitats/nesting sites; - Fewer niches; - Fewer food sources/varieties; - Less protection from predators/hunters/environment; January 2013 - What two measurements would the ecologists have needed to obtain to calculate the index of diversity of birds on each island. [2 marks] - - Number of (individuals/birds of) each species; - Total number of individuals/birds of all species; January 2013 - The ecologists noted that the species of birds surviving on the coldest islands had a larger body size than those surviving on warmer islands. 22 | P a g e June 2012 - What chemical group is attached at the end. [1 mark] - OH/hydroxyl/HO June 2012 - Differences between the structure of starch and the structure of cellulose. [2 marks] - - Starch: (1,4 and) 1,6 bonds/contains 1,6 bonds/branching - Cellulose: 1,4 bonds/no 1,6 bonds/unbranched/straight; - Starch: All glucoses/monomers are the same way up; - Cellulose: Alternate glucoses/monomers upside down - Starch: Helix/coiled/compact - Cellulose: Straight - Starch: Alpha glucose - Cellulose: Beta glucose - Starch: no (micro/macro) fibriles/fibres; - Cellulose: Micro/Macro fibrils/fibres; June 2012 - Explain one way in which the structure of cellulose is linked to its function. [2 marks] - - H-bonds/micro/macro fibrils/fibres; - Strength/rigidity/inelasticity; June 2012 - Mitosis is important in the life of an organism. Give two reasons why. [2 marks] - - Growth/increase in cell number; - Replace cells/repair tissue/organs/body; - Genetically identical cells; - Asexual reproduction/cloning; June 2012 - Explain why the biologists chose a generic large sample size. [1 mark] - (Ensures) representative (sample); 25 | P a g e June 2012 - Explain how the standard deviation helps in the interpretation of these data. [2 marks] - - Shows the spread of the data/how data varies; - Overlap = no difference/due to chance/not significant OR No-Overlap = difference/not due to chance/are significant; - Low SD means results are more reliable/repeatbale; June 2012 - Explain the importance of ............ being chosen at random. [1 mark] - Removes bias June 2012 - Explain why the values for the pressure in the xylem are negative. [2 marks] - (Inside xylem) lower than atmospheric pressure / (water is under) tension; June 2012 - Explain the difference in thickness between the pulmonary artery and the pulmonary vein. [1 mark] - High pressure/smoothes out blood flow/artery wall contains more collagen/muscle/elastic (fibres)/connective tissue; June 2012 - The thickness of the aorta wall changes all the time during each cardiac cycle. Explain why. [3 marks] - - (Aorta wall) stretches; - Because vetricle/heart contracts/systole/pressure increases; - (Aorta wall) recoils; - Because ventricle relaxes/heart relaxes/diastole/pressure falls; - Maintain smooth flow/pessure; June 2012 - Describe how tissue fluid is formed and how it is returned to the circulatory system. [6 marks] - Formation 1. High blood/hydrostatic pressure/pressure filtration; 2. Forces water/fluid out; 3. Large proteins remain in capillary; 26 | P a g e Return 4. Low water potential in capillary/blood; 5. Due to (plasma) proteins; 6. Water enters capillary/blood; 7. (By) osmosis; 8. Correct reference to lymph; June 2012 - Staphylococcus aureus is a bacterium that causes disease in humans. Scientists carried out an investigation to find the most effective concentration of antibiotic to treat this disease. The scientists put equal volumes of a culture of S. aureus in five flasks. I They added nothing further to one flask. This was the control. l They added different concentrations of antibiotic to the other four flasks. The scientists incubated all the flasks at 35 degreesC for 3 hours. They then estimated the number of living bacteria in each flask. The flasks were incubated at 35 degreesC. Suggest why they were incubated at this temperature. [1 mark] The scientist put the same volume of bacterial culture into each flask. Explain why [1 mark] What was the purpose of the control flask? [1 mark] Give two ways in which a bacterium could become resistant to an antibiotic. [2 marks] The people chosen to be included in t - Fastest rate of growth/division/enzymes don't denature/optimum temperature for enzymes/at or close to body temperature Same amount/number of bacteria/only one variable in the investigation 27 | P a g e - Closer the (amino acid) sequence the closer the relationship; - (Protein structure) related to (DNA) base/triplet sequence; OR More closely related (species) have more similarities in amino acid sequence/primary structure OR Amino acid sequence is related to (DNA) base/triplet sequence January 2012 - Comparing the base sequence of genes provides more evolutionary infromation than comparing the stucture of proteins. Explain why. [2 marks] - - Reference to base triplets/triplet code/more bases than amino acids/longer base sequence than amino acid sequence; - Introns/non-coding DNA; - Degeneracy of code/more than one code for each amino acid OR more than one base sequence can code for a protein; OR Different (base) triplets code for same amino acids OR Degeneracy of triplet code January 2012 - A student investigated the diversity of plants at several sites on a golf course. At each site she took a large number of random sample. Explain the importance of taking a large number of samples at each site. [1 mark] Explain the importance of taking samples at random. [1 mark] - The larger the number of samples taken the more representative (of the whole population) the results are. Random samples reduces bias. 30 | P a g e January 2012 - The golf course was surrounded by undeveloped grassland from which it has been produced. The golf course had: some areas of very short grass which cut frequently; some areas of longer grass which was cut less frequently; some areas of ling grass and shrubs which were never cut. The index of diversity for the insects on the golf course was higher than that for the surrounding undeveloped grassland. Explain the effect of developing this golf course on the index diversity of insects. [3 marks] - - Increase in variety of grass/plants/shrubs; - More habits / niches; - Greater variety of food sources/more food sources; January 2012 - Root pressure moves through the xylem. Describe what causes root pressure. [3 marks] - - Active transport by endodermis; - Ions/salts into xylem; - Lowers water potential (in xylem); - (Water enters) by osmosis; January 2012 - Explain how oxygen is loaded, transported and unloaded in the blood. [6 marks] - 1. Haemoglobin carries oxygen/has a high affinity for oxygen/oxyhaemoglobin; 2. In red blood cells; 3. Loading/uptake/association in lungs; 4. at high partial pressure; 5. Unloads/dossociates/releases to respiring cells/tissues; 6. at low partial pressure; 7. Unloading linked to higher carbon dioxide (concentration); June 2011 - Explain what is meant by the term genetic diversity. [1 mark] - 31 | P a g e Difference in DNA/base sequence/difference in alleles/genes/gene pool June 2011 - Apart from genetic factors what other type of factor causes variation within a species? [1 mark] - Environment(al) June 2011 - The spotted owl is a bird. Numbers of spotted owls have decreased over the past 50 years. Explain how this decrease may affect genetic diversity. [2 marks] - - Reduced (genetic diversity); - As fewer different/varied alleles/genes/reduced gene pool; - (Genetic) bottleneck; June 2011 - The number of amino acids in X could be fewer than your answer. Give one reason why. [1 mark] - - Introns/non-coding DNA/junk DNA; - Start/stop code/triplet; June 2011 - Explain how a change in the DNA base sequence for a protein may result in a change in the structure of the protein. [3 marks] - - Change in amino acid(s)/primary structure; - Change in hydrogen.ionic/disulfide bonds; - Alters tertiary structure; June 2011 - Describe what happens in metaphase. [2 marks] - - Spindle formed/chromosome/centromere/chromatids attaches to spindle; - Chromosomes/chromatids line up/move to middle/equator (of cell); June 2011 - Describe what happens om anaphase. [2 marks] - - Chromosome/centromere splits/chromatids/'chromosomes' seperate/pulled apart; - To (opposite) sides/poles/centrioles (of cell); June 2011 - Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cells completing the cell cycle in a short time. [1 mark] - 32 | P a g e Frogs lay their eggs in pools of water. These eggs are small. Use this information to explain why frogs' eggs are very likely yo be affected by pesticides in the water. [2 marks] - - Large surface area to volume (ratio); - Correct reference to diffusion; - (Eggs) cannot move (out of water); - Permeable/thin (outer layer); June 2011 - An increase in temperature leads to evaporation of water. Suggest how evaporation may increase the effect of pesticides on frogs' eggs. [1 mark] - Concentration (of pesticide) is increased; June 2011 - Explain why they measured the dose per unit mass and per unit time. [2 marks] - - Allows comparison to be made; - Different masses/weights (of volunteers); - Different weeks/lengths of treatment; June 2011 - Clostridium difficile is a bacterium that is present in the git of up to 3% of healthy adults and 66% of healthy infants. C. difficile rarely causes problems, either in healthy adults or infants. This is because its numbers are kept low by competition with harmless bacteria that normally live in the intestine. Use this information to explain why some patients treated with antibiotics can be affected by C. difficile. [2 marks] - - Antibiotics kill other bacteria/Clostridium is resistant; - Less/no competition so (Clostridium) reproduces/replicates/multiplies/increases in number; June 2011 - Clostridium difficile is a bacterium that is present in the git of up to 3% of healthy adults and 66% of healthy infants. Suggest why older people are more likely to be affected by C. difficile. [1 mark] - Immune system less effective/more likely to have other infections/been in hospital; OR weaker/lower immune system 35 | P a g e June 2011 - The antibiotic methicillinn inhibits the enzyme transpeptodase. The enzyme is used by some bacteria to join monomers together during cell wall formation. Methicillin has a similar structure to these monomers. Use this information to explain how methicillin inhibits the enzyme transpeptidase. [2 marks] - - Attaches to active site (of enzyme); - (Methicillin) is a competive inhibitor/prevents monomers/substrate attaching (to enzyme); June 2011 - It may be difficult to identify MRSA as the actual cause of death. Explain why. [1 mark] - Have other illness/medical condition/'weak' immune system/disease/infection; June 2011 - Describe how gene transmission and selection have increased the difficulty of treating bacterial infections with antibiotics. [6 marks] - 1. (Antibiotic) resistant gene/allele; 2. Vertical (gene) transmisison; 3. Resistant bacteria (survive and) reproduce (binary fission)/population of resistant bacteria increases; 4. Increase in frequency of (resistant) allele/gene (in future generations); 5. Horizontal (gene) transmission/transfer; 6. Plasmid; 7. Conjugation/pilus (tube); 8. (Horizontal transmission/transfer conjugation) can occur between bacteria of different species; January 2011 - Hydrogen bonds are important in cellulose molecules. Explain why. [2 marks] - - Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils; - Providing strength/rigidity to (cellulose/cell wall); - Hydrogen bonds strong in large numbers; January 2011 - A starch molecule has a spiral shape. Explain why this shape is important to its function in cells. [1 mark] - Compact/occupies small space/tightly packed; 36 | P a g e January 2011 - What evidence if there for heamoglobin having a qauternary structure? [1 mark] - More than one polypeptide chain; January 2011 - A gene codes for a polypepride chain. There are 423 bases in this gene that code for amino acids. How many amino acids are there in the polypeptide chain. [1 mark] - 141 January 2011 - The total number of bases in the DNA of the polypeptide chain is more than 423. Give two reasons why there are more than 423 bases. [2 marks] - - Stop/start codons; - Non coding DNA (in the gene)/introns/multiple repeats/junk DNA; - Two chains/a non-coding strand/complementary base pairs; - Addition of base by mutation; January 2011- The haemoglobin in one organism may have a different chemical structure from the haemoglobin in another organism. Describe how. [1 mark] - Different primary structure/amino acids/different number of polypeptide chains; January 2011 - Explain why llamas are better adapted to live in high mountains than horses. [3 marks] - - Low partial pressure of oxygen; - In lungs; - (Llama) haemoglobin able to load more oxygen/(llama) haemoglobin saturated (at low/particular partial pressure of oxygen); - Higher affinity for oxygen; January 2011 - An order is a taxonomic group. Fruit flies and mosquitoes belong to the same order of insects. Name the other three taxonomic groups to which fruit flies and mosquitoes both belong. - - Kingdom; - Phylum; - Class; January 2011 - Explain what is meant by a phylogenetic relationship. [1 mark] - 37 | P a g e C - 2.3 During transpiration, water diffuses from cells to the air surrounding a leaf. Suggest an explanation for the difference in transpiration rate between conditions A and B. [2 marks] - - Removes water vapour/moisture/saturated air; - Increases water potential gradient/more diffusion/more evaporation; January 2011 - Students measured the rate of transpiration of a plant growing in a pot under different environmental conditions. Their results are shown in the table. Conditions A - Still Air 15degreesC B - Moving Air 15degreesC C - Still Air 25degreesC Transpiration Rate / gh-1 A - 1.2 B - 1.7 C - 2.3 During transpiration, water diffuses from cells to the air surrounding a leaf. Suggest an explanation for the difference in transpiration rate between conditions A and C. [2 marks] - - Increases kinetic energy; - Water molecules move faster; - Increases diffusion/evaporation; January 2011 - Describe the relationship between the rate of water movement through the xylem and the light intensity. [1 mark] - Positive correlation/as light intensity increases so does rate of water movement/follows same pattern/directly proportional; 40 | P a g e January 2011 - Explain why the rate of water movement through the xylem is high during the day. [2 marks] - - Stomata open; - Photosynthesis increases/transpiration increases; - More water pulled up; - Cohesion between water molecules/by cohesion tension; January 2011 - Explain why the diameter of a tree trunk is shorter in the day than at night. [2 marks] - During the day - Water pulled up trunk/moves up at a fast rate; - (Water column under) tension; - Sticking/adhesion (between water and) cells/walls/xylem; - Pulls xylem in; January 2011 - Arteries and arterioles take blood away from the heart. Explain how the structures of the walls of arteries and arterioles are related to their functions. [6 marks] - Elastic Tissue - Elastic tissue stretches under pressure/when heart beats; - Recoils/springs back; - Evens out pressure/flow; Muscle - Muscle contracts; - Reduces diameter of lumen/vasoconstriction/constricts vessel; - Changes flow/pressure; Epithelium - Epithelium smooth; - Reduces friction/blood clots/less resistance; 41 | P a g e June 2010 - Give one feature of starch and explain how this feature enables it to act as a storage substance. [2 marks] - Feature - Helical/spiral/coiled; Explanation - Compact/description e.g. 'tightly packed'; Feature - Insoluble; Explanation - Prevents osmosis/uptake of water/does not affect water potential/(starch) does not leave cell; Feature - Large molecule/long chain; Explanation - Does not leave cell; June 2010 - Name the monomer that makes up starch. [1 mark] - beta glucose June 2010 - Name the bond that joints these monomers together. [1 mark] - Glycosidic June 2010 - The structure of cellulose is related to its role in plant cell walls. Explain how. [3 marks] - - Long/straight/unbranched chains (of glucose); - (Joined by) hydrogen bonds; - Form (micro)fibrils/(macro)fibrils; - Provide rigidity/strength/support; June 2010 - The aorta has many elastic fibres in its walls. An arteriole has many muscle fibres in its wall. Explain the importance of elastic fibres in the wall of the aorta. [2 marks] - - Stretches/'expands' under high pressure/when ventricle contracts/systole; - Recoils/'springs back' under low pressure/when ventricle relaxes/diastole; - Smooths blood flow/maintains blood pressure/reduces pressure surges; June 2010 - The aorta has many elastic fibres in its walls. An arteriole has many muscle fibres in its wall. Explain the importance of muscle fibres in the wall of an arteriole. [2 mark] - 42 | P a g e June 2010 - Explain the appearence of a chromosome. [2 marks] - - Two/sister chromatids; - Due to DNA replication; - Joined by a centromere; June 2010 - Some gametes formed during meiosis have new combinations of alleles. Explain. [2 marks] - - Crossing over/chiasma/chiasmata; - Exchange (of alleles) between chromatids/chromosomes; June 2010 - Suggest why only a few gametes posses this. [1 mark] - Is infrequent/rare June 2010 - Suggest one advantage of using cytochrome c to determine relationships between species. [1 mark] - Is present in all eukaryotes; June 2010 - Comparing the base sequence of a gene provides more information than comparing the amino acid sequence for which the gene codes. Explain why. [2 marks] - - Reference to base/triplet code/more bases than amino acids/longer base sequence than amino acid sequence; - Introns/non-coding DNA; - Same amino acid may be coded for/DNA code is degenerate; June 2010 - Describe hoe haemoglobin loads and unloads oxygen in the body. [3 marks] - - Loading/uptake/association of oxygen at high p.O2; - In lungs (haemoglobin) is (almost) fully saturated/in lungs haemoglobin has a high affinity for oxygen OR in tissues haemoglobin has a low affinity for oxygen/releases most of its oxygen; - Unloads/releases/dissociated oxygen at low p.O2; - Unloading linked to higher carbon dioxide concentration; June 2010 - Describe the relationship between the size of mammals and the oxygen dissociation curves of their haemolgobins. [1 mark] - 45 | P a g e Larger the mammal the more to the left/steeper/'higher' is the curve/the higher the affinity for oxygen; June 2010 - Heat from respiration helps mammals to maintain a constant body temperature. Use this information to explain the relationship between the surface are to volume ration of mammals and the oxygen dissociation curves of their heamoglobins. [4 marks] - - Smaller mammal has greater surface area to volume ratio; - Smaller mammal/larger SA:Vol ratio more heat lose (per unit body mass); - Smaller mammal/larger SA:Vol ratio has greater rate of respiration/metabolism; - Oxygen required for respiration; - (Haemoglobin) releases more oxygen/oxygen released more readily/haemoglobin has lower affinity; June 2010 - The number of patients infected with the bacterium MRSA has increased in some hospitals. Scientists have suggested ways to reduce the transmission of MRSA in hospitals. Suggest two ways to reduce the transmission of MRSA in hospitals. [2 marks] - - Isolation/quarantine/'kept seperate'; - Screening/testing (of patients/doctors etc); - Sterilisation of wards/equipment/method to improve hygiene; June 2010 - The minimum inhibitory concentration (MIC) is the lowest concentration of a substance that prevents the growth of a microorganism. When antibiotics are prescribed for treating patients, higher doses than the MIC are recommended. Suggest two reasons why. [2 marks] - - May not all be absorbed; - May be broken down/metabolised/excreted quickly; - To kill the microorganisms/bacteria; - Reference to antibiotic resistance; June 2010 - Suggest two ways in which a double-blind trial improves reliability. [2 marks] - - Prevents bias; - Vested interest (of scientists); - Prevents 'placebo'/positive/negative/psychological effects/'demand characteristics' (in volunteers); 46 | P a g e June 2010 - Suggest two factors the scientists should have conmsidered when selecting adult volunteers for this trial. [2 marks] - - Age - Ethnicity - Lifestyle - Body Mass - Health - Sex/gender of person June 2010 - Give one difference in the response of adults and children to the treatmnet of tablets that contain extra iron to combat anaemia. [1 mark] - Faster/greater/more effective response in children; January 2010 - Name the process in which cells become adapted for different functions. [1 mark] - Cell Differentiation OR Cell Specialistion June 2010 - Haemolgobin has a qauternary structure. Explain what is meant by a qauternary structure. [1 mark] - More than one polypeptide chain. June 2010 - Pernuicious anaemia is another type of anaemia. One method of identifying pernicious anaemia is to measure the diameter of the red blood cells in a sample of blood that has been diluted with an isotonic salt solution. Explain why an isotonic salt solution is used to dilute the blood sample. [3 marks] - - HAs same water potential; - No (net) water movement/osmosis; - Cells will not swell/burst/change size; June 2010 - Describe two differences between the blood of a person with pernicious anaemia and with someone without pernicious anaemia. [2 marks] - - Pernicious anaemia (cells) greater range/spread/variation of diameter/widths; - Some pernicious anaemia (cells) wider than 9 (micrometer)/some less than 5.5 (micrometer)/without pernicious anaemia none more than 9 (micrometer)/none less than 5.5 (micrometer); 47 | P a g e January 2010 - An increase in respiration in the tissues of a mammal affects the oxygen dissociaiton curve of haemoglobin. Describe and explain how. [2 marks] - - Increase in/more carbon dioxide; - Curve moves to the right/depressed; January 2010 - There is less oxygen at high altitudes than at sea level. People living at high altitudes have more red blood cells than people living at sea level. Explain the advantage of this to people living at high altitude. [2 marks] - More red blood cells means more haemoglobin molecules which means that more oxygen can be loaded from the lungs. January 2010 - Explain the advantage to people living at high altitude of having the oxygen dissociation curve showing a shift to the right. [2 marks] - - (Haemoglobin) has lower affinity for oxygen/ more oxygen released; - Into the cells/tissues; January 2010 - A student found the number of stomata per cm2 on the lower surface of a daffodil leaf. He removed a small, thin piece of lower epidermis and mounted it on a microscope slide. He examined the slide using an optical microscope. Explain why it was important that the piece of the epidermis that the student removed was thin. [2 marks] - So that it is one cell thick. SO that the cells are not on top of each other and potential blocking features. To allows light to penetrate though/more/easier. January 2010 - A student found the number of stomata per cm2 on the lower surface of a daffodil leaf. He removed a small, thin piece of lower epidermis and mounted it on a microscope slide. He examined the slide using an optical microscope. Suggest how the student could have used his slide to find the number of stomata per cm2. [3 marks] - Measure the area of the slide. Then count how many stomata are present on the slide. Then divide 1cm2 by the area of the slide. Take this value and times it by how many stomata you counted. 50 | P a g e January 2010 - The stomata on the leaves of pine treed are found in pits below the surface. Explain how this helps to reduce water loss. [2 marks] - - Water vapour accumulates / increases humidity / reduced air movement (around stomata); - Water potential/diffusion gradient reduced; January 2010 - Give one way in which the blood plasma is different from the tissue fluid. [1 mark] - In the Blood Plasma: - More/larger proteins - Less urea - Less carbon dioxide - More glucose - More amino acids - More fatty acids - More oxygen - High (hydrostatic pressure January 2010 - The blood pressure is high at the start of the capillary. Explain how the left ventricle causes the blood to be at high pressure. [1 mark] - Contracts January 2010 - The blood pressure decreases along the length of the capillary. What causes this decrease in pressure? [1 mark] - - Loss of fluid/volume - Friction/resistance (of capillary wall) January 2010 - In children, some diets may result in a low concentration of protein in blood plasma. This can cause the accumuation of tissue fluid. Explain the link between a low concentration of protein in blood plasma and the accumulation of tissue fluid. [3 marks] - The decrease in concentration of protein in blood plasma increases the water potential of the blood plasma. This means more tissue fluid is formed at the arteriole end and less water is absorbed into the blood capillary by osmosis. January 2010 - Explain why it may be more useful to calculate the index of diversity than to record only the number of species present. [2 marks] - 51 | P a g e - Measures number of individuals (of each species) and number of species; - Some species only present in small numbers; January 2010 - The demand for increases food production has led to areas of heath being used to grow wheat. Explain the effect of this on: The species diversity of plants [2 marks] - - Reduced as one crop/species grown/other species removed; - Use of herbicides/weeding/ploughing; - Wheat (better) competitor for names factor e.g. light/nutrients; January 2010 - The demand for increases food production has led to areas of heath being used to grow wheat. Explain the effect of this on: The species diversity of animals [2 marks] - - Reduced as less variety of food sources; - Reduced as fewer habitats/niches; - Reduced by pesticides/chemicals; January 2010 - Gas exchnage in fish takes place in gills. Explain how two features of gills allow efficient gas exchange. [2 marks] - - Filaments/lamellae provide large surface area; - Thin/flattened epithelium/one/two cell layers so short diffusion pathway (between water and blood); - Countercurrent blood flow maintains concentration/diffusion gradient; January 2010 - The scale for plotting body mass is a logarithmic scale. Explain why a logarithmic scale was used to plot body mass. [1 mark] - Large/wide range of values (so can fit on graph) January 2010 - Describe the relationship between body mass and oxygen uptake. [1 mark] - As body mass/Kg increases the oxygen uptake per gram of body mass/cm3h-1 decreases / negative correlation. 52 | P a g e