3.5.3 Energy & Ecosystems

Question 1

(Energy & Ecosystems) How do plants use the sugars from photosynthesis?

Answer 1

• Primarily as respiratory substrates
• to synthesise other biological molecules, e.g. cellulose

Question 2

(Energy & Ecosystems) What is biomass?

Answer 2

Total dry mass of tissue or mass of carbon measured over a given time in a specific area.

Question 3

(Energy & Ecosystems) Suggest the units for biomass.

Answer 3

• When the area is being sampled: gm^-2
• When a volume (e.g. a pond) is being sampled: gm^-3

Question 4

(Energy & Ecosystems) How can the chemical energy stored in dry mass be estimated?

Answer 4

Using calorimetry.

Energy released = specific heat capacity of water x volume of water (cm^3) x temperature increase of water

Question 5

(Energy & Ecosystems) Why is bomb calorimetry preferable to simple calorimetry?

Answer 5

Reduces heat loss to surroundings.

Question 6

(Energy & Ecosystems) How could a student ensure that all water had been removed from a sample before weighing?

Answer 6

Heat the sample and reweigh it until the mass reading is constant.

Question 7

(Energy & Ecosystems) Define gross primary production (GPP).

Answer 7

Total chemical energy in plant biomass within a given volume or area.

Question 8

(Energy & Ecosystems) Define net primary productivity (NPP).

Answer 8

Total chemical energy available for plant growth, plant reproduction and energy transfer to other trophic levels after respiratory losses.

Question 9

(Energy & Ecosystems) Give the mathematical relationship between GPP and NPP.

Answer 9

NPP = GPP - R
where R represents respiratory losses

Question 10

(Energy & Ecosystems) Why is most of the Sun’s energy not converted to organic matter? (4)

Answer 10

• Most solar energy is absorbed by the atmosphere or reflected by clouds.
• Photosynthetic pigments cannot absorb some wavelengths of light.
• Not all light falls directly on a chlorophyll molecule.
• Energy lost as heat during respiration/photosynthesis.

Question 11

(Energy & Ecosystems) How can the net production of consumers be calculated?

Answer 11

N = I - (F + R)
I: chemical energy from ingested food
F: energy lost as faeces and urine
R: respiratory losses

Question 12

(Energy & Ecosystems) Why does biomass decrease along a food chain? (3)

Answer 12

• Energy lost in nitrogenous waste (urine) and faeces.
• Some of the organism is not consumed.
• Energy lost to surroundings as heat.

Question 13

(Energy & Ecosystems) Define primary and secondary productivity.

Answer 13

• Rate of primary or secondary production.
• Biomass in a specific area over a given time period e.g. kJ ha^-1 year^-1

Question 14

(Energy & Ecosystems) Outline some common farming practices used to increase the efficiency of energy transfer. (4)

Answer 14

• Exclusion of predators: no energy lost to other organisms in food web.
• Artificial heating: reduce energy lost to maintain constant body temperature.
• Resitricirton of movement.
• Feeding is controlled at the optimum.

Question 15

(Energy & Ecosystems) Give a general equation for % efficiency.

Answer 15

Energy converted to a useful form (J) x 100 / total energy supplied (J)

Question 16

(Energy & Ecosystems) Explain why the length of food chains is limited.

Answer 16

Energy is lost at each trophic level.
So there is insufficient energy to support a higher trophic level.

Question 17

(Energy & Ecosystems) What is a pyramid of biomass?

Answer 17

A diagram that shows the biomass at each trophic level.

Question 18

(Energy & Ecosystems) Why is the pyramid of biomass preferable to a pyramid of numbers?

Answer 18

The shape of a pyramid of numbers may be skewed since a small number of producers can support many consumers.