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
... [Show More] 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 Less]