5 Energy transfers in and between organisms

Question 1

In photosynthesis, what chemicals are needed for the light-dependent reaction? (1)

Answer 1

NADP, ADP, Pi and water.

Question 2

Describe what happens during photo ionisation in the light-dependent reaction. (2)

Answer 2

Chlorophyll absorbs light, and electrons are lost.

Question 3

Heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis.

Heat stress decreases the light-dependent reaction of photosynthesis.

Explain why this leads to a decrease in the light-independent reaction. (2)

Answer 3

Less ATP produced, so less reduced NADP is also produced.

Question 4

A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis. Explain why. (2)

Answer 4

Less carbon dioxide will react with RuBP, so less GP is produced.

Question 5

Where precisely is rubisco found in a cell? (1)

Answer 5

In the stroma of a chloroplast.

Question 6

In natural ecosystems, most of the light falling on producers is not used in photosynthesis. Suggest two reasons why. (2)

Answer 6

(Any 2 of these)
The light is reflected.

or

The light is the wrong wavelength.

or

Light misses the photosynthetic pigments.

Question 7

Name the two products of the light-dependent reaction that are required for the light-independent reaction. (2)

Answer 7

ATP

Reduced NADP

Question 8

Describe the process of glycolysis. (4)

Answer 8

Phosphorylation of glucose using ATP. This leads to the oxidation of triose phosphate to pyruvate which then results in a net gain of ATP. NAD is reduced.

Question 9

Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration. (2)

Answer 9

Converting the pyruvate to lactate regenerates NAD, which allows glycolysis to continue.

Question 10

Describe the advantage of the Bohr effect during intense exercise. (2)

Answer 10

The Bohr effect increases the dissociation of oxygen for aerobic respiration at the tissues.

Question 11

Describe the role of saprobionts in the nitrogen cycle. (2)

Answer 11

Saprobionts use enzymes to decompose proteins, which releases ammonium compounds.

Question 12

Artificial fertiliser is used to replace mineral ions removed from the land when crops are harvested. One of the mineral ions is nitrate.

Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested. (2)

Answer 12

(Any 2 of these)

Amino acids

Nucleic acids

DNA

RNA

ATP

NAD