5- Energy & Ecosystems =)

Question 1

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

Answer 1

• pioneer species
• change abiotic conditions (↓ hostile)
• ↑ no. of plants

Question 2

Use your knowledge of net productivity to explain why biomass shows little increase after 100 years. (2)

Answer 2

• net prod = gross prod - respiratory loss
• gross prod./ photos ↓ // resp. ↑

Question 3

Suggest one reason for conserving woodlands. (1)

Answer 3

• protecting habitats
• conserving endangered species –> maintains biodiversity
• reduces global warming (photos)
• source of chemicals / medicines / wood
• ↓ erosion / eutrophication

Question 4

Explain why the net primary production of an area does not represent the total amount of plant biomass formed per year by photosynthesis. (2)

Answer 4

biomass lost as CO2 in resp.

Question 5

July has the highest temperature.
Explain why the gross productivity of the plants in the field was highest in July. (2)

Answer 5

• high temp- ↑ rate of enzyme action
• ↑ rate of photos

Question 6

A horse was kept in the field from March to October. During the summer months, the horse was able to eat more than it needed to meet its minimum daily requirements.
Suggest how the horse used the extra nutrients absorbed. (2)

Answer 6

1. stored as fat
2. used for growth

Question 7

Describe how you could measure the dry biomass of the parts of the herbaceous plants above ground in a sample area of 1 m2. (3)

Answer 7

1. collect + dry all above ground plant material;
   (reject collect one/ small sample/whole plants)
2. in an oven at or just below 100 oC;
3. weigh and repeat until constant mass;
   - other precaution, e.g. cooling in desiccator;

Question 8

Suggest two limitations involved in measuring the rate of increase in plant biomass in a large area of a forest which would affect the accuracy of the data. (2)

Answer 8

• drying destroys plants, so different samples needed;
• large area, so difficult to get representative samples;
• difficult to measure biomass of trees;
• variability in growing conditions;
• variability of abiotic conditions in different areas of forest;

Question 9

They dried the plant material in an oven at 90 °C for 3 days.
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. (2)

Answer 9

1. weigh sample at intervals during drying
2. to see if weighings became constant

Question 10

In an investigation of growth of shoots and roots, explain why determination of dry mass was an appropriate method to use in this investigation. (2)

Answer 10

1. dry mass measures ↑ in biological/ organic material
2. water content varies

Question 11

Explain why an increase in shoot biomass can be taken as a measurement of net primary productivity. (2)

Answer 11

• represents dry mass/ mass of carbon
• NPP = GPP - R
• gross prod; respiratory losses

Question 12

Give three reasons for the low efficiency of energy transfer from secondary consumers to tertiary consumers in an ecosystem. (3)

Answer 12

1. heat loss from resp
2. food x digested
3. excretion

Question 13

In pigs, the efficiency of conversion of food to biomass is lower at 0’C than it is at 20’C.
Suggest an explanation for the lower efficiency. (2)

Answer 13

• lose ↑ heat (∵energy used to maintain body temp)
• heat from resp
• ↑ food used in resp

Question 14

Farming cattle for humans to eat is less efficient than farming crops because of energy transfer.
Explain why. (2)

Answer 14

1. energy lost betw trophic levels
2. energy lost in resp/ excretion