TOPIC 5 EXAM QUESTIONS

Question 1

In photosynthesis, which chemicals are needed for the light-dependent
reaction?

Answer 1

NADP, ADP, Pi and water.

Question 2

Describe what happens during photoionisation in the light-dependent
reaction.

Answer 2

1. Chlorophyll absorbs light
   OR
   Light excites/moves electrons in chlorophyll;
   Ignore photosystems.
2. Electron/s are lost
   OR
   (Chlorophyll) becomes positively charged;
   Ignore site/molecule from where electrons are lost.
   Accept electrons go to electron transport/carrier chain for
   ‘electrons lost’.

Question 3

Describe the method the student used to separate the pigments after the
solution of pigments had been applied to the origin.

Answer 3

1. Level of solvent below origin/line;
   Reject water or any named aqueous solution.
   Accept named organic solvent.
2. Remove/stop before (solvent) reaches top/end;

Question 4

The pigments in leaves are different colours. Suggest and explain the
advantage of having different coloured pigments in leaves.
_________________________________________________

Answer 4

(Absorb) different/more wavelengths (of light) for photosynthesis;
Accept wider/larger range of wavelengths.
Accept frequency for wavelength.
Accept light-dependent reaction /photophosphorylation
/photoionisation for photosynthesis.

Question 5

Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction.

Answer 5

1. (Less/no) ATP;
2. (Less/no) reduced NADP;
   Accept NADPH, NADPH + H, NADPH2 NADPH +
   H+
   Reject reduced NAD, NADH etc,

Question 6

A decrease in the activity of the enzyme rubisco would limit the rate of
photosynthesis.
Explain why.

Answer 6

1. (Less/no) carbon dioxide (reacts) with RuBP;
2. (Less/no) GP;

Question 7

Where precisely is rubisco found in a cell?

Answer 7

Stroma (of/in chloroplast);

Question 8

In natural ecosystems, most of the light falling on producers is not used in
photosynthesis.
Suggest two reasons why

Answer 8

1. (Light is) reflected;
   Light is not absorbed on its own is not enough.
2. (Light is) wrong wavelength;

Question 9

The light absorbed by chlorophyll is used in the light-dependent reaction.
Name the two products of the light-dependent reaction that are required for
the light-independent reaction.

Answer 9

1. ATP;
2. Reduced NADP;

Question 10

) 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 in weeds.

Answer 10

1. Reduced transfer of protons across thylakoid membrane
   OR
   Reduced chemiosomotic gradient / proton gradient across thylakoid
   membrane;
2. (So) less ATP produced;
3. (So) less reduced NADP produced;
   Accept NADPH / NADPH2 / NADPH+
   Reject reduced NAD
4. (So) light-independent reaction slows / stops;
   OR
   Less reduction of GP to triose phosphate.

Question 11

Describe the process of glycolysis.

Answer 11

1. Phosphorylation of glucose using ATP;
2. Oxidation of triose phosphate to pyruvate;

Accept removal of hydrogen from triose phosphate
for oxidation.
3. Net gain of ATP;

Accept any description that indicates a net gain
e.g., 4 produced, 2 used.
4. NAD reduced;

Accept NADH/NADH2/NADH + H+ produced.
Accept all mark points in diagrams.

Question 12

Malonate inhibits a reaction in the Krebs cycle.
Explain why malonate would decrease the uptake of oxygen in a respiring
cell.

Answer 12

1. Less/no reduced NAD/coenzymes
   OR
   Fewer/no hydrogens/electrons removed (and passed to
   electron transfer chain);
   Accept less/no FAD reduced.
2. Oxygen is the final/terminal (electron) acceptor;

Question 13

In muscles, pyruvate is converted to lactate during prolonged exercise.
Explain why converting pyruvate to lactate allows the continued production
of ATP by anaerobic respiration.

Answer 13

1. Regenerates/produces NAD
   OR
   oxidises reduced NAD;
   Reject NADP and any reference to FAD.
   Accept descriptions of oxidation e.g. loss of hydrogen.
2. (So) glycolysis continues;
   Accept description of glycolysis e.g. glucose to pyruvate.
   Accept ‘for oxidising/converting triose phosphate to
   pyruvate’

Question 14

Describe the advantage of the Bohr effect during intense exercise.

Answer 14

1. Increases dissociation of oxygen;
   Accept unloading/ release/reduced affinity for
   dissociation
2. For aerobic respiration at the tissues/muscles/cells

OR

Anaerobic respiration delayed at the tissues/muscles/cells
OR
Less lactate at the tissues/muscles/cells;

Question 15

A heart attack is caused by a lack of glucose and oxygen being delivered to
cardiac muscle via the coronary arteries. The overuse of EPO can increase
the risk of a heart attack.

Answer 15

1. (EPO) causes blood to thicken;
   Accept descriptions of thickening, eg more viscous
2. (The thickened blood) could block the coronary arteries
   OR
   (The thickened blood) slows blood flow

Question 16

The normal haematocrit for human males is 47(±5)%. For professional
male cyclists, the maximum haematocrit allowed is 50%.
A student suggested that professional male cyclists should be allowed to
use EPO until their haematocrit is 50%.
Give two reasons why this suggestion is not valid.

Answer 16

1. Some cyclists will gain a bigger advantage/increase
   OR
   Cyclists with a haematocrit of 50% would not be able to gain an
   advantage;
   Accept use of the data, or suitable calculations, eg
   some may have an 8% increase, others 0%
   Some cyclists might naturally have a haematocrit
   over 50% (and so not be allowed to compete)
2. There are health risks (associated with) taking EPO;
   Accept dangerous side-effects of taking EPO, or
   examples of health risks

Question 17

Freshwater marshes have one of the highest rates of gross primary production
(GPP) and net primary production (NPP) of all ecosystems.
Carbon use efficiency (CUE) is the ratio of NPP:GPP. Freshwater marshes have
a high CUE.
(a) Use your knowledge of NPP to explain why freshwater marshes have a
high CUE and the advantage of this.

Answer 17

1. Low respiration;
   Accept less energy lost in respiration
2. More growth/biomass/colonisation;
   Allow examples of more carbon-containing
   molecules eg glucose

Question 18

Suggest one way in which an increase in the uptake of phosphate could
increase plant growth.

Answer 18

Used to produce named phosphate compound in cells;
e.g. ATP / ADP / phospholipids / DNA / RNA / RuBP / TP /GP etc

Question 19

Explain why an increase in shoot biomass can be taken as a measurement
of net primary productivity.

Answer 19

1. Represents dry mass / mass of carbon;
2. Represents gross production minus respiratory losses;

Question 20

Describe the light-independent reaction of photosynthesis.

Answer 20

1. Carbon dioxide
   combines/reacts with ribulose
   bisphosphate/RuBP;
2. Produces two glycerate (3-
   )phosphate/GP using
   (enzyme) Rubisco;
3. GP reduced to triose
   phosphate;
4. Using reduced NADP;
5. Using energy from ATP;
6. Triose phosphate converted to
   glucose/hexose/RuBP/ribulose
   bisphosphate/named organic
   substance

Question 21

Water is important in photosynthesis because……

Answer 21

It is needed for photolysis.
Light energy is used to split water into protons, electrons and oxygen. The protons are used to make ATP in photophosphorylation by chemiosmosis where they diffuse through ATPsynthase to phosphorylate ADP using Pi. The electrons are used to replace those lost by chlorophyll during photoionisation. Because of water, the electrons are used to produce NADPH. The oxygen from photolysis is used for aerobic respiration.

Question 22

Energy transfers are important in photosynthesis because……

Answer 22

The light dependent reactions use light energy to produce ATP and NADPH.
Light energy is used in photoionisation. Chlorophyll absorbs the light energy and it excites electrons. The energy in the electrons is used to actively transport H+ to produce a chemical gradient for chemiosmosis to occur. The energy used as H+ diffuses through ATPsynthase is used to phosphorylate ADP to produce ATP.
Light energy is also used for photolysis, to split water and replace the electrons lost by chlorophyll.

Question 23

Gradients are important in photosynthesis because……

Answer 23

They are needed for photophosphorylation.
When chlorophyl absorbs light energy, this releases electrons that are passed down the ETC. The energy released is used to actively transport H+ into the thylakoid spaces to produce a H+ gradient. Because of the gradient, the H+ will diffuse through ATPsynthase which is the chemiosmotic theory. As they diffuse down the gradient, ADP is phosphorylated to produce ATP.

Question 24

Membranes are important in photosynthesis because……

Answer 24

The thylakoid membrane is where the light dependent reactions occur.
This membrane contains chlorophyll which is where photoionisation occurs to release electrons and pass them down the electron transport chain. This ETC is a series of electron carriers and proton pumps that is also found on the thylakoid membrane. As the electrons are passed down the ETC, the pumps actively transport H+ across the membrane to produce a H+ gradient. The final use of the thylakoid membrane is to contain ATPase. The H+ diffuse through ATPsynthase to produce ATP.