Paper 2 Exam Questions Flashcards
Describe what happens during photoionisation in the light dependent reaction (2 marks)
- light excites electrons in chlorophyll
- chlorophyll becomes positively charged
why is the origin in chromatography marked in pencil instead of ink?
Ink and leaf pigments would mix
suggest and explain the advantage of having different coloured pigments and leaves. ( 1 mark)
absorb different wavelengths of light for photosynthesis
Where is RuBisCO found?
stroma of chloroplast
Heat stress decreases the light dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light independent reaction
(2 marks)
- less ATP produced
- less reduced NADP
A decrease in the activity of the enzyme RuBisCO would limit the rate of photosynthesis. Explain why (2marks)
less CO2 reacts with RuBP
less GP
DCPIP is _____ when oxidised
blue
DCPIP is ____ when reduced
colourless
why is a control tube set up in the DCPIP practical?
2 marks
- to show light doesn’t affect DCPIP
- to show chloroplasts are required
name the the two products of the light dependent reaction that required for the light independent reaction
reduced NADP
ATP
What does cyclic phosphorylation produce?
ATP
describe how acteylcoenzyme A is formed in the link reaction
2 marks
1.hydrogen removed from pyruvate
2. and CO2 released
explain why converting pyruvate to lactate allows the continued production is ATP during anaerobic respiration
2 marks
- it regenerates ATP
- which is used in glycolysis
in muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. suggest one advantage of this
1 mark
lactic acid causes muscle fatigue
why is glucose not used as a respiratory substrate
2 marks
1.glucose is used during glycolysis
2. cannot cross mitochondrial membrane
describe the part played by the inner membrane of a mitochondrion in producing ATP
4 marks
- electrons transferred down ETC
- provide energy to take protons
- protons pass back through membrane
- energy used to combine ADP and phosphate
Describe the process of glycolysis
4 marks
- Phosphorylation of glucose using ATP
- oxidation of triose phosphate
- net gain of ATP
- NAD is reduced
Malonate inhibits a reaction in the Krebs Cycle. Explain why malonate would decrease the uptake of oxygen in a respiring cell
2 marks
- less reduced NAD
- oxygen is the final electron acceptor
Explain how resting potential is maintained across the axon membrane in a neurone.
3 marks
- Higher conc of NA+ outside and higher K+ inside.
- Membrane is more permeable to K+ leaving
- Na+ ions actively transported out
Explain why the speed of transmission of impulses is faster along a myelinated axon than a non-myelinated axon
3 marks
- myelination provides electrical insulation
- in myelinated saltatory conduction
- in non-myelinated depolarisation occurs along whole axon
Describe and explain how the PCR is used to amplify a DNA fragment
4 marks
- Requires DNA fragment, DNA polymerase, nucleotides and primers
- Heat to 95 to break H bonds
- Reduce temperature so primers can bind to DNA
- Increase temperature so DNA polymerase can join strands, REPEAT
Explain how succession results in a wide variety of fish living on coral reefs
2 marks
- increase in diversity
- provides different habitats
Describe a method that could be used to determine the mean percentage cover of algae on a coral reef
3 marks
- Use random no. generator to decide where to place quadrats
- Use a large sample of quadrats
- Divide total % by no. of quadrats
Loss of nutrients into a lake has caused a decrease in some fish populations. Explain why
4 marks
- Algae grows and blocks light
- Reduces photosynthesis so plants die
- Saprobiotic organisms respire aerobically
- Less oxygen for fish to respire
How does speciation occur to produce 2 different species of lemur from one original species?
5 marks
- geographical isolation
- reproductive isolation
- different selection pressures
- mutations
- different alleles will be selected
- no longer can interbreed to produce fertile offspring
Describe the light-dependent reaction of photosynthesis.
6 marks
- CO2 combines with RuBP
- producing 2 GP using rubisco
- GP reduced to triose phosphate
- using reduced NADP
- using energy from ATP
- TP converted to glucose
Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 ATP for each molecule of nitrogen that is reduced. When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit. Explain how
2 marks
- less ATP is being used up for the nitrogen fixation as it is occuring less
- therefore the bacteria will have more energy for growth and respiration
Scientists concluded that the obsereved frequencies of 4 phenotypes differed significantly from the expected. Use your knowledge of the Hardy-Weinberg principle to suggest 2 reasons why
2 marks
two from
1. selection
2. mutation
3. migration
give two reasons why transmission across a cholinergic synapse is unidirectional
2 marks
- only receptors on the post synaptic neurone can recieve messages
- only the presynaptic nerone has neurotransmitter
explain temporal summation
1 mark
there are several repeated impulses in a short time which provide enough neurotransmitter to reach threshold
explain the role of reverse transcriptase in RT-PCR
1 mark
makes cDNA from mRNA
explain the role of DNA polymerase in RT-PCR
1 mark
joins nucleotides to produce complementary strands of DNA
Any DNA in a sample taken for PCR is hydrolysed by enzymes before the sample is added to the reaction mixtre. Explain why
2 marks
- to remove any DNA present
- because this DNA would be amplified
suggest a reason why DNA replication stops in the polymerase chain reaction
1 mark
all of the free nucleotides have been used
Scientists use the RT-PCR method to detect the presence of different RNA virsuses in patients suffering from respiratory diseases.
The scientists produced a variety of primers for this procedure. Explain why
2 marks
- base sequences of the viruses differ
- different primers will be complementary to each virus so will bind to that one
Describe how you could estimate the size of a population of sundews in a small marsh
5 marks
- use a grid
- use a random no. generator to choose large no. of quadrats to sample
- count the no. of plant in each quadrat
- record a large sample and calculate mean
- multiply mean x no. of quadrats to stimate population
suggest and explain how digesting insects helps a plant grow in soil with very low concentrations of some nutrients
2 marks
- digestion of proteins
- providing amino acids
Succession occurs in a natural ecosystem. Describe and explain how succession occurs
4 marks
- colonisation by pioneer species
- pioneers change the conditions
- becomes less hostile for other species
- increase in biodiversity
- to climax community
Explain how a single base subsitution causes a change in the structure of the polypeptide
3 marks
- change in amino acid sequence
- changes in H bonds
- alters tertiary structure
What part of the plant produces IAA?
1 mark
the tip
Explain how a decrease in the concentration of calcium ions within muscle cells could cause a decreased in the force of muscle contraction
3 marks
- less tropomyosin moved from the binding site
- fewer actinmyosin bridges formed
- myosin head does not move
Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force muscle contraction
3 marks
- less tropomyosin moved from the binding site
- fewer actinmyosin bridges formed
- mysoin head does not move
Describe the role of glucagon in gluconeogenesis
2 marks
- activates enzymes
- glycerol into glucose
Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration
2 marks
- more insulin binds to receptors
- stimulates uptake of glucose
Explain how inhibiting adenylate cylase may help to lower the blood glucose concentration
3 marks
- less ATP converted to cAMP
- less kinase activated
- less glycogen converted to glucose
Describe what happens during photoionisation in the light dependent reaction
2 marks
- chlorophyll absorbs light
- chlorophyll becomes positively charged
What is a DNA probe?
2 marks
- (Short) single strand of DNA
- Bases complementary (with DNA/allele/gene)
Describe how the DNA is broken into smaller fragments
2 marks
- cut by restriction endonucleases
- cuts at specific base sequences
