3.5.3 Energy and ecosystems

Question 1

Suggest appropriate units for gross productivity.

Answer 1

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

Question 2

Explain the decrease in gross productivity as the woodland matures.

Answer 2

Less light / more shading / more competition for light;

Reduced photosynthesis.

Question 3

Use your knowledge of succession to explain the increase in biomass during the first 20 years.

Answer 3

Pioneer species;
Change in abiotic conditions / less hostile / more habitats / niches;
Increase in number / amount / diversity of species / plants / animals.

Question 4

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

Answer 4

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

Question 5

Suggest one reason for conserving woodlands.

Answer 5

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.

Question 6

Explain why the scientists measured the rate of production of oxygen in this investigation.

Answer 6

Oxygen produced in light-dependent reaction;
The faster (oxygen) is produced, the faster the light-dependent reaction.

Question 7

Suggest what the scientists should have done during the drying process to be sure that all of the water had been removed from the plant samples.

Answer 7

Weigh samples at intervals during drying;

To see if weighings became constant (by 3 days).

Question 8

Upwelling often results in high primary productivity in coastal waters.
Explain why some of the most productive fishing areas are found in coastal waters

Answer 8

Growth of algae / surface plants / algal bloom blocks light;
Reduced / no photosynthesis so (submerged) plants die;
Saprobiotic (microorganisms / bacteria);
Aerobically respire / use oxygen in respiration;
Less oxygen for fish to respire / aerobic organisms die;