Energy Transfer

Question 1

Define Biomass

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

Answer 2

Regularly weigh and Heat (less than 100 °C)
Until mass is constant

Question 3

The percer ntage of the light energy trapped by the producers is very low. Give two reasons why.

Answer 3

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

Question 4

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

Answer 4

(Light is) reflected;
Light absorbed on its own is not enough
2. (Light is) wrong wavelength;
Accept frequency for wavelength.
Accept reference to absorbing specified wavelengths/frequencies.
(Light) misses chlorophyll/ chloroplasts/photosynthetic tissue;
CO2 concentration or temperature is a limiting factor.

Question 5

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

Answer 5

Loss of energy/heat / use of energy / less energy to be passed on;
In respiration;
In excreta / excretion / urine / carbon dioxide:
Inedible parts / indigestible parts / egesta/ egestion / to decomposers;

Question 6

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

Answer 6

Some light energy fails to strike/is reflected/not of appropriate wavelength;
Efficiency of photosynthesis in plants is low
Respiratory loss / excretion / faeces / not eaten;
Loss as heat;

Efficiency of transfer to consumers greater than transfer to producers/
Efficiency lower in older animals/herbivores/ primary consumers/warm blooded animals;
Carnivores use more of their food than herbivores;

Question 7

Explain how the intensive rearing of domestic livestock increases net productivity

Answer 7

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

Question 8

Describe the need for plants to both photosynthesise AND respire

Answer 8

In the dark no ATP production in photosynthesis;
Some tissues unable to photosynthesise/produce ATP;
ATP cannot be moved from cell to cell/stored;
Plant uses more ATP than produced in photosynthesis;
ATP for active transport;
ATP for synthesis (of named substance);

Question 9

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.

Answer 9

High concentration of carbon dioxide linked with night/darkness;
No photosynthesis in dark/night / light required for photosynthesis/light-dependent reaction;
(In dark) plants (and other organisms) respire;
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;
Decrease in carbon dioxide concentration with height;
At ground level fewer leaves/less photosynthesising tissue/more animals/less light;

Question 10

Give the units for NPP/GPP

Answer 10

• kJ ha–1 year–1 OR kJ km–2 year–1 OR kJ km–3 year–1