Energy Transfers 5.3

Question 1

Define biomass (2)

Answer 1

• Mass of carbon (organic compounds);
• Dry mass of tissue per given area

Question 2

Suggest what you should do to ensure all water is removed from a tissue / sample (2)

Answer 2

• Regularly weigh and HEAT (less than 100 degrees)
• Until mass is constant

Question 3

What is Gross Primary Productivity? (1)

Answer 3

Chemical energy store in plant biomass, in a given area or volume.
(Rate of photosynthesis)

Question 4

What is Net Primary Production? (1)

Answer 4

• Chemical energy store in plant biomass after respiratory losses to the environment have been taken into account.
NET PP = GROSS PP - R
• NPP is available for new plant growth and reproduction
OR
available for other trophic levels in the ecosystem, such as herbivores and saprobionts.
• kJ ha-1 year’ OR kJ km-2 year OR kJ km-3 year

Question 5

The percentage of the light energy trapped by the producers is very low. Give two reasons why (2)

Answer 5

• Reflected / absorbed by water vapour;
• Reflected from producers / wrong wavelength;
• Transmitted / passes between chloroplasts/ between plants / too few chloroplasts;

Question 6

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

Answer 6

1. Light is reflected/not absorbed;
2. Light is wrong wavelength;
3. Light misses chlorophyll;
4. CO2 concentration or temperature is a limiting factor.

Question 7

The biomass of primary consumers is less than the biomass of producers. Explain why

Answer 7

• Loss of heat / less energy passed on
• In/for respiration
• In excretion / urine / CO2
• Inedible parts / indigestible / egestion / to decomposers.

Question 8

Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer

Answer 8

1. Some light energy fails to strike/is reflected/not of appropriate wavelength;
2. Efficiency of photosynthesis in plants is low/around 2% efficient;
3. Respiratory loss / excretion / faeces / not eaten;
4. Loss as heat;
5. Efficiency of transfer to consumers greater than transfer to producers/approximately 10%;
6. Efficiency lower in older animals/herbivores/primary consumers/warm blooded animals;
7. Carnivores use more of their food than herbivores;

Question 9

Explain how the intensive rearing of domestic livestock increased net productivity (4)

Answer 9

1. Slaughtered when still growing/before maturity so more energy transferred to biomass/tissue/production;
2. Fed on concentrate /controlled diet/conditions so higher proportion of (digested) food absorbed/lower proportion lost in faces;
3. Movement restricted so less respiratory loss / less energy used;
   Kept inside/heating/shelter / confined so less heat loss / no predators;
4. Genetically selected for high productivity;

Question 10

Describe the need for plants to both photosynthesis AND respire

Answer 10

1. Plants do not photosynthesise in the dark;
2. Requires energy for non-photosynthesising tissues/cells I.e root hair cells;
3. ATP cannot be stored/leave cells;
4. Plant uses more ATP than produced;
5. ATP for active transport / synthesis of (named substance)

Question 11

The concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours.
Use your knowledge of photosynthesis to describe these changes and explain why they occur (6)

Answer 11

1. High concentration of carbon dioxide linked with night/darkness;
2. No photosynthesis at night/in dark/light required for photosynthesis/light-dependent reaction;
3. (In dark) plants (and other organisms) respire;
4. In light net uptake of carbon dioxide by plants/plants use more carbon dioxide than they produce/ rate of photosynthesis greater than rate of respiration;
5. Decrease in carbon dioxide concentration with height;
6. At ground level fewer leaves/less photosynthesising tissue/more animals/less light.