Energy and ecosystems

Question 1

Q1.The graph shows how gross productivity and biomass in an area changed with time in the
succession from bare soil to mature woodland.
(a) (i) Suggest appropriate units for gross productivity (1)

Answer 1

Unit of energy / mass, per area, per year.

Question 2

Q1-

ii) Explain the decrease in gross productivity as the woodland matures. (2

Answer 2

1. Less light / more shading / more competition for light;
   Neutral: references to animals
2. Reduced photosynthesis.
   Accept: no photosynthesis

Question 3

Q1-(b) Use your knowledge of succession to explain the increase in biomass during the
first 20 years. (3)

Answer 3

1. Pioneer species;
2. Change in abiotic conditions / less hostile / more habitats / niches;
   Accept: named abiotic change or example of change e.g.
   formation of soil / humus / organic matter / increase in
   nutrients
   Neutral: reference to change in environment unqualified
   Neutral: more hospitable / habitable / homes / shelters
3. Increase in number / amount / diversity of species / plants / animals.
   Accept: other / new species (colonise)

Question 4

Q1-(c) Use the information in the graph and your knowledge of net productivity to explain
why biomass shows little increase after 100 years.

Answer 4

1. Net productivity = gross productivity minus respiratory loss;
2. Decrease in gross productivity / photosynthesis / increase in respiration.

Question 5

(d) Suggest one reason for conserving woodlands.

1

Answer 5

1. Conserving / protecting habitats / niches;
2. Conserving / protecting (endangered) species / maintains / increases
   (bio) diversity;
3. Reduces global warming / greenhouse effect / climate change / remove /
   take up carbon dioxide;
4. Source of medicines / chemicals / wood;
5. Reduces erosion / eutrophication.
   Accept: tourism / aesthetics / named recreational activity

Question 6

Q2.Chloroplasts contain chlorophyll a and chlorophyll b. Scientists found tobacco plants with a
mutation that caused them to make more chlorophyll b than normal tobacco plants. They
investigated the effect of this mutation on the rate of photosynthesis.
The scientists carried out the following investigation.
• They grew normal and mutant tobacco plants. They grew some of each in low light
intensity and grew others in high light intensity.
• They isolated samples of chloroplasts from mature plants of both types.
• Finally, they measured oxygen production by the chloroplasts they had isolated from

(a) Explain why the scientists measured the rate of production of oxygen in this
investigation. (2)

Answer 6

1. Oxygen produced in light-dependent reaction;

2. The faster (oxygen) is produced, the faster the light-dependent reaction

Question 7

In each trial, the scientists collected oxygen for 15 minutes.
(b) Calculate the difference in the oxygen produced by the chloroplasts from mutant
plants grown in low and high light intensities at a light intensity of 500 μmol photons
m–2 s–1
.
Show your working.

Answer 7

35–36 μmol Oxygen per mg chlorophyll.
Correct difference at 500 μmol photons m–2 s–1 or incorrect
difference but division by 4 shown = 1 mark.

Question 8

(c) The scientists suggested that mutant plants producing more chlorophyll b would
grow faster than normal plants in all light intensities.
Explain how these data support this suggestion. (4)

Answer 8

At all light intensities, chloroplasts from mutant plants:
1. Have faster production of ATP and reduced NADP;
2. (So) have faster / more light-independent reaction;
3. (So) produce more sugars that can be used in respiration;
4. (So) have more energy for growth;
5. Have faster / more synthesis of new organic materials.
Accept converse points if clear answer relates to non-mutant
plants