Photosynthesis general questions

Question 1

Explain why, between 0 and 300 seconds, the concentration of radioactive GP remained constant

Answer 1

GP reduced to phosphate
GP formed at the same rate as it is used

Question 2

Explain why, between 300 seconds and 380 seconds, the concentration of radioactive RuBP increased

Answer 2

No CO2 to combine with/not enough CO2 to combine with RuBP
RuBP not changed into GP

Question 3

Some bacteria use hydrogen sulphide to produce organic compounds. The hydrogen sulphide has a similar role to that of water in photosynthesis.
hydrogen sulphide + carbon dioxide –> glucose + sulphur + water
Suggest what the hydrogen sulphide is used for in these bacteria

Answer 3

Provide protons and electrons
For reduction

Question 4

The investigation was carried out in bright light. Explain why reducing the light intensity would affect the amount of oxygen released by the seaweeds

Answer 4

Light intensity limiting factor
Fewer electrons (released) from chlorophyll
Less photolysis therefore (less) oxygen from water

Question 5

The scientists kept the temperature at 15. A student suggested that repeating the investigation at 20 would not affect the amount of O2 released by seaweed. Evaluate this conclusion

Answer 5

Photolysis / splitting of water does not use enzymes;
May increase respiration
Respiration uses oxygen

Question 6

Explain why it was important to grow the plants under the same conditions up to ten days before the experiment

Answer 6

So that any difference is due to iron

Question 7

The plants were left in the dark for 6 hours before the experiment. Explain why

Answer 7

So amount of triose phosphate will be similar

Question 8

Give one dependent variable you could measure in order to determine the rate of photosynthesis in an aquatic plant

Answer 8

Count number of bubbles

Question 9

A suspension of chloroplasts was isolated from an aquatic plant and a reagent was added. The reagent if blue when oxidised and is colourless when reduced.
The suspension of chloroplasts in blue reagent was exposed to sunlight. The blue colour disappeared. Use your knowledge of the LDR of photosynthesis to explain why

Answer 9

chlorophyll excited
electrons from chlorophyll changes the dye colour

Question 10

The cells were supplied with radioactively labelled 14CO2. Explain why the CO2 used was radioactively labelled

Answer 10

used in photosynthesis allows detection of products

Question 10

A suspension of chloroplasts was isolated from an aquatic plant and a reagent was added. The reagent if blue when oxidised and is colourless when reduced.
Another suspension of chloroplasts was set up as before. Small quantities of ADP and phosphate ions were added and then the tube was exposed to light. The blue colour disappeared more quickly. Explain why.

Answer 10

ADP and phosphate needed to produce ATP
ADP levels are a limiting factor;

Question 11

Explain what caused the amount of radioactively labelled glucose to decrease after the light was switched off

Answer 11

Used in respiration

Question 12

The temperature was kept constant during this investigation. Explain why

Answer 12

Temperature affects photosynthesis
So that any change in photosynthesis rate is result of carbon dioxide / light intensity

Question 13

In leaves at the top of the trees in a forest, CO2 is often the limiting factor for photosynthesis.
Use your knowledge of photosynthesis to suggest and explain one reason why.

Answer 13

Light not limiting / lots of light (as no shading)
Light-dependent reaction not limiting / fast