AQA A-LEVEL BIOLOGY PAPER 2 EXAM QUESTIONS
WITH SOLVED ANSWERS.
1) Describe and explain the steps in the light dependent reaction of photosynthesis --
t t t t t t t t t t t t t
Answer ✔✔ 1. Photoionisation: light reaches chlorophyll in PSII, which is absorbed by
t t t t t t t t t t t t t
an electron, which becomes excited and moves to a higher energy level.
t t t t t t t t t t t
2. The electron passes to a carrier protein in the thylakoid membrane, and is passed
t t t t t t t t t t t t t t
down a series of carrier molecules called an electron transfer chain.
t t t t t t t t t t t
3. As the electron moves down, energy is lost from the electron and is released as
t t t t t t t t t t t t t t t t
ATP.
4. The loss of electron from PSII is 'refilled' by an electron produced by photolysis,
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which also produces hydrogen and oxygen.
t t t t t
5. The lost electron reaches PSI, which absorbs light energy and boosts another
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electron to a higher energy level (excitation). t t t t t t
6. This electron also goes down an electron transport chain.
t t t t t t t t t
7. This reaches the final electron acceptor which is a proton. They combine to form
t t t t t t t t t t t t t t t
H and reduce NADP to NADPH.
t t t t t
2) Describe and explain the steps in the light independent reaction pf photosynthesis. --
t t t t t t t t t t t t t
Answer ✔✔ 1. CO2 diffuses into stroma and combines with ribulose bisphosphate
t t t t t t t t t t t t
(rubp) using the enzyme rubisco.
t t t t
2. This forms an unstable 6 carbon molecule, which splits into 2 3 carbon molecules,
t t t t t t t t t t t t t t
tglyercate-3-phosphate (G3P) . t t
3. G3P is reduced by NADPH to triose-phosphate (TP), which is aided by ATP for
t t t t t t t t t t t t t t t
energy. t
4. TP can be converted into useful organic substances.
t t t t t t t t
5. TP can also be reformed into rubp using ATP.
t t t t t t t t t
3) Describe glycolysis in respiration. Give net formation. -- Answer ✔✔ 1. Glucose is
t t t t t t t t t t t t t
converted into phosphorylated glucose by 2ATP. This makes it very reactive, so it
t t t t t t t t t t t t t
splits into 2 triose phosphate (TP).
t t t t t t
2. 2TP is then oxidised by 2NAD and 4 ATP is formed to form pyruvate.
t t t t t t t t t t t t t t
, 3. NET: 2ATP, 2Pyruvate, 2NADH, 2H+
t t t t t
4) Describe links reaction in respiration. Give net formation. -- Answer ✔✔ 1. Pyruvate
t t t t t t t t t t t t t
diffuses into the matrix of mitochondria.
t t t t t t
2. Pyruvate is oxidised by NAD. CO2 is lost. This forms acetate.
t t t t t t t t t t t t
3. Acetate and co-enzyme A combine to form acetyl co-enzyme A.
t t t t t t t t t t
4. NET: CO2, reduced NAD, acetyl co-enzyme A
t t t t t t t
5) Describe Krebs cycle in respiration. Give net formation. -- Answer ✔✔ 1. Acetyl co-
t t t t t t t t t t t t t
enzyme A combines with 4 carbon molecule (oxaloacetate) to form 6 carbon citric
t t t t t t t t t t t t t
acid.
2. CO2 is lost (decarboxylation), molecule is oxidised by NAD and ATP is produce.
t t t t t t t t t t t t t t
This forms 5 carbon compound.
t t t t
3. It is oxidised by 2NADH and FAD, and is decarboxylated.
t t t t t t t t t t
4. This forms 4 carbon molecule again.
t t t t t t
6) Describe oxidative phosphorylation in respiration. -- Answer ✔✔ 1. Reduced
t t t t t t t t t t
coenzyme passes its H to a carrier protein in the ETC. This splits into a proton and
t t t t t t t t t t t t t t t t t
electron.
2. The protons pass through the space between inner and outer mitochondrial
t t t t t t t t t t t t
membrane.
3. Electrons pass through proteins on ETC.
t t t t t t
4. Protons return back via ATP synthase in the membrane, producing ATP.
t t t t t t t t t t t
5. The protons and electrons recombine to form H, which combines with O to
t t t t t t t t t t t t t t
form water. t
6. Oxygen is the last electron acceptor in the ETC.
t t t t t t t t t
7) Define biomass -- Answer ✔✔ the total mass of organisms in a given area
t t t t t t t t t t t t t
8) What is the 'gross primary production' -- Answer ✔✔ the chemical energy stored in a
t t t t t t t t t t t t t t
plants biomass
t t
9) What is the 'net primary production' -- Answer ✔✔ the chemical energy stores in a
t t t t t t t t t t t t t t t
plants biomass after respiratory losses have been considered. This energy is available
t t t t t t t t t t t t
to consumers.
t
, 10) How can you calculate the net primary production? -- Answer ✔✔ NPP = GPP - R
t t t t t t t t t t t t t t t
11) Why is converting sunlight energy into biomass in producers inefficient? -- Answer
t t t t t t t t t t t t
✔✔ some light isn't the correct wavelength to be absorbed
t t t t t t t t t
Some light doesn’t hit chloroplast
t t t t
Some light is converted into heat energy
t t t t t t
Some light energy is reflected
t t t t
12) Describe the nitrogen cycle. -- Answer ✔✔ fixation:
t t t t t t t
Atmospheric nitrogen can be fixed by rhizobium bacteria. t t t t t t t
If struck by lightning, it becomes reactive and combines with oxygen to form NO.
t t t t t t t t t t t t t
Ammonification:
Saprobionts feed on organic matter and release ammonia, which then forms t t t t t t t t t t t
ammonium ions in the soil. t t t t t
Nitrification: t
Nitrifying bacteria convert ammonium ions into nitrite ions and then to nitrate ions.
t t t t t t t t t t t t
t
Denitrification:
Anaerobic denitrifying bacteria convert soil nitrates into gaseous nitrogen.
t t t t t t t t
13) Homeostasis -- Answer ✔✔ the maintenance of an internal environment within
t t t t t t t t t t t
restricted limits in organisms. All cells are in an environment that meets their
t t t t t t t t t t t t t
requirements and allows them to function normally despite external changes. t t t t t t t t t
14) Why is homeostasis important? -- Answer ✔✔ 1. The enzymes that control
t t t t t t t t t t t t
biochemical reactions in cells are sensitive to change e.g. In ph or temperature, which
t t t t t t t t t t t t t t
can cause them to denature. Homeostasis allows enzyme controlled reactions to take
t t t t t t t t t t t
tplace at a suitable rate.
t t t t
2. Homeostasis allows a constant blood glucose concentration to ensure a constant
t t t t t t t t t t t
water potential, so cells don't shrink or burst.
t t t t t t t t
3. Homeostasis allows organisms to be more independent of external changes.
t t t t t t t t t t
WITH SOLVED ANSWERS.
1) Describe and explain the steps in the light dependent reaction of photosynthesis --
t t t t t t t t t t t t t
Answer ✔✔ 1. Photoionisation: light reaches chlorophyll in PSII, which is absorbed by
t t t t t t t t t t t t t
an electron, which becomes excited and moves to a higher energy level.
t t t t t t t t t t t
2. The electron passes to a carrier protein in the thylakoid membrane, and is passed
t t t t t t t t t t t t t t
down a series of carrier molecules called an electron transfer chain.
t t t t t t t t t t t
3. As the electron moves down, energy is lost from the electron and is released as
t t t t t t t t t t t t t t t t
ATP.
4. The loss of electron from PSII is 'refilled' by an electron produced by photolysis,
t t t t t t t t t t t t t t t
which also produces hydrogen and oxygen.
t t t t t
5. The lost electron reaches PSI, which absorbs light energy and boosts another
t t t t t t t t t t t t t
electron to a higher energy level (excitation). t t t t t t
6. This electron also goes down an electron transport chain.
t t t t t t t t t
7. This reaches the final electron acceptor which is a proton. They combine to form
t t t t t t t t t t t t t t t
H and reduce NADP to NADPH.
t t t t t
2) Describe and explain the steps in the light independent reaction pf photosynthesis. --
t t t t t t t t t t t t t
Answer ✔✔ 1. CO2 diffuses into stroma and combines with ribulose bisphosphate
t t t t t t t t t t t t
(rubp) using the enzyme rubisco.
t t t t
2. This forms an unstable 6 carbon molecule, which splits into 2 3 carbon molecules,
t t t t t t t t t t t t t t
tglyercate-3-phosphate (G3P) . t t
3. G3P is reduced by NADPH to triose-phosphate (TP), which is aided by ATP for
t t t t t t t t t t t t t t t
energy. t
4. TP can be converted into useful organic substances.
t t t t t t t t
5. TP can also be reformed into rubp using ATP.
t t t t t t t t t
3) Describe glycolysis in respiration. Give net formation. -- Answer ✔✔ 1. Glucose is
t t t t t t t t t t t t t
converted into phosphorylated glucose by 2ATP. This makes it very reactive, so it
t t t t t t t t t t t t t
splits into 2 triose phosphate (TP).
t t t t t t
2. 2TP is then oxidised by 2NAD and 4 ATP is formed to form pyruvate.
t t t t t t t t t t t t t t
, 3. NET: 2ATP, 2Pyruvate, 2NADH, 2H+
t t t t t
4) Describe links reaction in respiration. Give net formation. -- Answer ✔✔ 1. Pyruvate
t t t t t t t t t t t t t
diffuses into the matrix of mitochondria.
t t t t t t
2. Pyruvate is oxidised by NAD. CO2 is lost. This forms acetate.
t t t t t t t t t t t t
3. Acetate and co-enzyme A combine to form acetyl co-enzyme A.
t t t t t t t t t t
4. NET: CO2, reduced NAD, acetyl co-enzyme A
t t t t t t t
5) Describe Krebs cycle in respiration. Give net formation. -- Answer ✔✔ 1. Acetyl co-
t t t t t t t t t t t t t
enzyme A combines with 4 carbon molecule (oxaloacetate) to form 6 carbon citric
t t t t t t t t t t t t t
acid.
2. CO2 is lost (decarboxylation), molecule is oxidised by NAD and ATP is produce.
t t t t t t t t t t t t t t
This forms 5 carbon compound.
t t t t
3. It is oxidised by 2NADH and FAD, and is decarboxylated.
t t t t t t t t t t
4. This forms 4 carbon molecule again.
t t t t t t
6) Describe oxidative phosphorylation in respiration. -- Answer ✔✔ 1. Reduced
t t t t t t t t t t
coenzyme passes its H to a carrier protein in the ETC. This splits into a proton and
t t t t t t t t t t t t t t t t t
electron.
2. The protons pass through the space between inner and outer mitochondrial
t t t t t t t t t t t t
membrane.
3. Electrons pass through proteins on ETC.
t t t t t t
4. Protons return back via ATP synthase in the membrane, producing ATP.
t t t t t t t t t t t
5. The protons and electrons recombine to form H, which combines with O to
t t t t t t t t t t t t t t
form water. t
6. Oxygen is the last electron acceptor in the ETC.
t t t t t t t t t
7) Define biomass -- Answer ✔✔ the total mass of organisms in a given area
t t t t t t t t t t t t t
8) What is the 'gross primary production' -- Answer ✔✔ the chemical energy stored in a
t t t t t t t t t t t t t t
plants biomass
t t
9) What is the 'net primary production' -- Answer ✔✔ the chemical energy stores in a
t t t t t t t t t t t t t t t
plants biomass after respiratory losses have been considered. This energy is available
t t t t t t t t t t t t
to consumers.
t
, 10) How can you calculate the net primary production? -- Answer ✔✔ NPP = GPP - R
t t t t t t t t t t t t t t t
11) Why is converting sunlight energy into biomass in producers inefficient? -- Answer
t t t t t t t t t t t t
✔✔ some light isn't the correct wavelength to be absorbed
t t t t t t t t t
Some light doesn’t hit chloroplast
t t t t
Some light is converted into heat energy
t t t t t t
Some light energy is reflected
t t t t
12) Describe the nitrogen cycle. -- Answer ✔✔ fixation:
t t t t t t t
Atmospheric nitrogen can be fixed by rhizobium bacteria. t t t t t t t
If struck by lightning, it becomes reactive and combines with oxygen to form NO.
t t t t t t t t t t t t t
Ammonification:
Saprobionts feed on organic matter and release ammonia, which then forms t t t t t t t t t t t
ammonium ions in the soil. t t t t t
Nitrification: t
Nitrifying bacteria convert ammonium ions into nitrite ions and then to nitrate ions.
t t t t t t t t t t t t
t
Denitrification:
Anaerobic denitrifying bacteria convert soil nitrates into gaseous nitrogen.
t t t t t t t t
13) Homeostasis -- Answer ✔✔ the maintenance of an internal environment within
t t t t t t t t t t t
restricted limits in organisms. All cells are in an environment that meets their
t t t t t t t t t t t t t
requirements and allows them to function normally despite external changes. t t t t t t t t t
14) Why is homeostasis important? -- Answer ✔✔ 1. The enzymes that control
t t t t t t t t t t t t
biochemical reactions in cells are sensitive to change e.g. In ph or temperature, which
t t t t t t t t t t t t t t
can cause them to denature. Homeostasis allows enzyme controlled reactions to take
t t t t t t t t t t t
tplace at a suitable rate.
t t t t
2. Homeostasis allows a constant blood glucose concentration to ensure a constant
t t t t t t t t t t t
water potential, so cells don't shrink or burst.
t t t t t t t t
3. Homeostasis allows organisms to be more independent of external changes.
t t t t t t t t t t
