Biology exam paper questions - new/ complete solutions

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Biology exam paper questions - new Use the data about the length of leaves in the two sites to explain why standard deviation is more useful than range as a measure of variation within a population.... ANS: Definition of range + SD / effect of outliers on range + SD; Ranges are similar in both areas; Suggests that variation within populations is similar; SD smaller in area of high light intensity; Shows that area of high light intensity is a more uniform population; describe the role of ribosomes in the production of a polypeptide. Do not include transcription in your answer ( 3 marks) ANS: mRNa binds to ribosome binding sites on the tRNa and the mRNA allows the anticodon to attach to the codon the ribosome catalyses the formation of peptide bonds between amino acids, so that the amino acids held by the tRNA molecule In humans after the gametes join at fertilisation, every cell of the developing embryo undergoes mitotic division before the embryo attaches to the uterus lining > the first division takes > the subsequent division each take 8 hours after 3 days, the embryo has a total volime of 4.2 x 10⁻³ mm What is the mean volume of each cell after 3 days? Express your answer in standard form. ( 2 marks ) ANS: How many divisions in total in 3 days = 7 - each division produces two daughter cells so 2 to the power of 7 = 128 cells produced in 3 days 128 cells have a volume of 4.2 x 10⁻³ mm to find out the volume of one cell we divide the 4.2 x 10⁻³ mm by 128 which equal to 3.28 x 10 ( to the minus 5 ) Some proteases are secreted as extracellular enzymes by bacteria ( saprobionts ) Suggest one advantage to a bacterium of secreting an extracellular protease in its natural environment ( 2 marks ) ANS: To digest protein; 2. (So) they can absorb amino acids for growth/reproduction/protein synthesis/synthesis of named cell component; OR (So) they can destroy a toxic substance/protein; '' the antibiotics were given to the mice at a dose of 25mgkg per day calculate how much antibiotic would be given to a 30 g mouse each day ANS: 25 mg per kg the mouse is 30 mg = 0.03 kg 25 mg x 0.03 kg = 0.75 mg The cell surface memebrane can be see with a TEM but not with an optical microscope Explain why ANS: higher resolution and maginification than an optical microscope Cell was stained before examination. suggest an explanation why the cell surface membrane appeared as two dark lines ANS: stain binds to the phosphate or glycerol heads of the phospholipid bilayer on the outside and inside of the membrane Describe how substances move across cell surface membranes by diffisusion ( 3 marks ) ANS: substance attaches to carrier or channel protein by complementary binding changes its shape causing it to open on the inside of the cell so that the substance can move DOWN its concentration gradient into the cell when is meiosis ANS: when 2 x n ( diploid cells ) - with 46 chromosomes and 46 chromatids divides into n ( haploid cells ) - with 23 chromosomes and 23 chromatids importance of condensed chromosomes ANS: when cellls divide and move dna over, it is easy as it makes it portable and organised Suggest and explain advantages of sexual and a sexual reproduction of sporangia ANS: Asexual - produces clones which maintains specific pheno and genotypes - can colonise new environments Sexual - increses genetic diversity so a greater chance of survival Effect of competitive inhibitor in rate of enzyme reaction ANS: If the substrate concentration is increased, the effect of the inhibitor is reduced > likehood of enzyme substrate complexes forming is increased as there is more active sites available all the substrates will eventually occupy the active site but the greater the concentration of the substrate, the longer this will take Non competitive inhibitor effect on rate of enzyme reaction ANS: as the substrate and the inhibitor are not competing for an active site, an increase in the substrate concentration does not decrease the effect of the inhibitor non competitors unable enzyme substrate complexes forming as they change their shape in their high concentration, the rate of reaction reduces and then eventually stops as all enzymes shapes are changed effect of subtrate concentration on rate of reaction ANS: low > too few substrates to occupy active site so rate of reaction is half the maximum for the number of enzymes available intermediate > all active sites are occupied at one time so the rate of reaction doubles to its maximum for the number of enzymes available high > no effect as all active sites are already occupied so no increase in rate of reaction ( graph may level off as enzyme concentration is now the limiting factor ( not enough enzymes so reaction stops or stays constant ) ) Give two reasons why the grassy stripes ( contain variety of plant species) increase the biodiversity of animals ANS: plant species provide more food sources for animals increase in variety of animals leads to increase in predator species increase in niche / habitat scientist investigated effect of grassy stripes ( variety of plant species ) on biodiversity of soil animals grew wheat plots between grassy stripes collected samples from soil of wheat and grassy stripes sorted each sample out by hand for 40 minutes to collect the soil animals within the sample ____________________________________________________________________________________ suggest how the scientist decided that 40 minutes was an approoiate time to sort sample ANS: the scientist repeated soil sorting for different times and recorded the number of species collected 40 minutes was an appropriate time because it allowed him to find the optimum time beyond which futher sorting does not lead to an increase in animal species found The number of copies of the AMY gene ( produces mouth amylase) is unlikely to affect peoples ability to digest starch ANS: little starch digestion in the mouth by salivary amylase - amylase secreted by the pancreas salivary amylase is denatured by hydrochloric acid in the stomach - and amylase is also secreted by the pancreas Starch futher digested by membrane bound dissacharidases ( amylases and maltase ) in the small intestine amy gene only affects salivary amylase and not pancreatic amylase in the stomach Explain how the organis bases help to stabilise the structure of DNA ANS: hydrogen bonds between the base base pairs hold the two strands together which collectively add strength Suggest an advantage of showing the genetic code as base sequences on mRNA rather than triplets on DNA ANS: because ribosomes assemble polypeptides using mRNA code - and not dna triplets DNA has two strands each with a different base sequence MRNA directly codes for a protein Suggest the role of stop codons ( 2 marks) ANS: they stop translation and result in the detachment of polypeptide chains from the ribosome EXplain the meaning of quanternary structure ANS: multiple polypeptide chains held together why is the genetic code described as degenerate ANS: because some amino acids have more than one codon/ mRNA code Give the formula for calculating the percentage saturation of haemoglobin with oxygen ANS: oxygenated haemoglobin / maximum saturation x 100 oxygen and association to the haemoglobin ANS: difficult to bind at first because polypeptide units are closely united - therefore at low partial pressure, little oxygen binds to haemoglobin - gradient of curve is shallow initially binding of first molecule changes haemoglobin quanternary structure and induces other subunits to bind to an oxygen molecule - gradient steepens due to positive cooperativity gradient of the cuve reduces and the graph flattens off as it is hard for a fourth molecule to find an empty site to bind to with the majority of the sites occupied positive coorperativity ANS: takes little increase in partial pressure of oxygen to bind the second molecule than it did the first one suggest advantage of change in affinity of oxygen at lungs ANS: ensures rapid and more intake of oxygen at lungs to release in the tissues give reasons why scientist used 100 degrees to dry plants in an oven ( experiment to detect radioactivity in powedered sample ) ( 2 marks ) ANS: It evaporates all water while it does not burn any oraganic compounds Suggest how scientists could adapt their method to determine which tissue carried the radioactively labelled sucrose ANS: Take thin horizontal sections of plant tissue / stem place against photographic film in dark for several hours carry out autoradiography Contrast the structure of bacterial cell and the structure of human cell ANS: Bacterial cell much smaller bacterial has cell wall bacterial cell lacks nucleus bacterial cell lacks membrane nound organelles bacterial ribosome smaller bacterial dna circular while dna is linear bacterial dna is naked whereas human dna is bound to histones Explain the presence of glycogen granules in skeletal muscle ANS: act as a store of glucose to be hydrolysed to glucose for respiration to provide energy for muscle contraction During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction suggest how 3 marks ANS: Low pH changes the shape of calcium ion receptors fewer calcium ions bind to tropomyosin fewer tropomyosins move away fewer binding sites on actin revealed fewer cross bridges can form fewer myosin heads can bind Why may a nerve pathway be regarded as a simple reflex arc ANS: only little amount of neurones/ nerve cells involved - short neurone pathway they bypass the brain hence why they are involuntary with no descision making means action is rapid suggest advantages of simple reflex arcs ANS: they are rapid protect against damage to body tissues do not have to be learnt - involuntary response as they bypass the brain help escape from predators enable homeostatic control i.e. to maintain optimum internal environment explain how synapses ensure that nerve impulses only travel towards the muscle fibre ANS: neurotransmitters are only made and stored in the pre synaptic neurone and the neurotransmitter receptors are only found on the post synaptic membrane what may cause impulses to travel faster ANS: myelinated axons to ensure saltatory conduction axons with large diameter so there is less resistance to the flow of ions Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain explain how this reduces the rate of photosynthesis ANS: reduced chemiosmotic gradient / proton gradient across thylakoid membrane less ATP produced less reduced NADP light independent reaction slows or stops as there is less reduction of GP to triosephosphate More than 99& of biological molecules are reabsorbed from the filtrate in the proximal convoluted tubule despite this, the concentration of fluid in this tubule remains constant explain why ANS: water is also reabsorbed along with the molecules Describe what is meant by epigenetics ANS: heritable changes in gene function without changes to the base sequence ..... ANS: oestrogen binds with proteins methyl groups bind with DNA acetyl groups bind with histones Explain how increased methylation could lead to cancer ANS: methyl groups could be added to both copies of a tumour surpressor gene this block the site and the transcription of tumour surpressor genes is inhibited leading to uncontrolled cell division - oncogenes? Give features of a climax community ANS: same species present and a stable community over a long time abiotic factors are more or less constant over time stable populations that are not fluctuating around the carrying capacity carrying capacity ANS: the size of population an ecosystem can support Explain why only reverse transcriptase and the gene machine would produce dna that bacteria could use to make a specific gene instead of using restriction enzymes ANS: reverse transcriptase and the gene machine produce DNA without introns bacteria cannot splice pre - mRNA to remove introns in protein synthesis Suggest the advantage of using gene machine over reverse transcriptase ANS: faster than all enzyme catalysed reactions Describe how the scientist attempts to insert copies of a gene into a plasmid ( 3 marks ) ANS: use the same endonucleases to cut open the plasmid as used to extract the gene from its human genome so that both have sticky ends using DNA ligase enzyme place the gene into the plasmids which will join the sticky ends by joining the phosphate backbones together Suggest advantage of using fluorescent protein to identify bacteria that have taken up the plasmid ANS: Can quickly identify transformed bacteria using UV light When is kinesis shown ANS: when movement is random and non directional or the insect is not moving towards a partcular stimulis explain how reduced movement in drier areas are adaptations to reduce water loss in insects ANS: less respiration so less gas exchange and oxygen used so spiracles spiracles open less ( for gas exchange) to reduce water loss when is taxis shown ANS: organisms stays in favourable areas and turns little directional response to stimuli tries to get out of the non favourable area to get to the favourable one Suggest reasons why the observed ratios are often not the same as the expected ratios ANS: fertilisation is random / fusion of gametes there is a small sample or population - not large enough there is selective advantage and disadvantage maybe due to lethal alleles what test used to compare observed and expected ANS: chi squared what is a codominant allele ANS: both alleles expressed in the phenotype if both are present Suggest and explain why a poor supply of phosphate ions results in poor groth of plants ANS: required to make ATP / glucose phosphate, so there is less respiration and energy for growth required to make nucleotides - less DNA mRNA / tRNA for cell division or protein production for growth required to make RUBP/NADP in photosynthesis , so less carbon dioxide fixed / reduced into a sugar required to make phospholipids for membranes Suggest how defensive enzymes produced by plants destroy bacteria ANS: by hydrolising the murein / glycoprotein in their cell wall The signal proteins secreted into the air by plants being attached by a pathogen act as stimuli leading to the expression of genes for defensive enzymes in other planst suggest how ANS: bind to receptors on target plant leads to prodcution of acts as transcription factor which binds to promoter or stimulates the transcription of genes that produce mRNA for the defensive enzymes Suggest and explain the advantage to tomato olants of transmitting signal proteins throygh mycoorizal networks rather than relesing them into air ANS: Direct plant to plant transmission so localised response faster reponse no dilution of signal protein Explain why the muscles that cause movement of body parts tend to operate as anatagonistic pairs ANS: as muscle contracts and shortens, the other relaxes and lengthens - body parts move when a muscle contracts across a joint Describe the relationship between muscles and joints ANS [Show More]

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