Energy and Ecosystems

Question 1

In any ecosystem, plants synthesise ________________ compounds from atmospheric, or aquatic, carbon dioxide.

Answer 1

organic

Question 2

ost of the sugars synthesised by plants are used as respiratory substrates. The rest are used to make other groups of biological molecules. These biological molecules form the ______________ of the plants.

Answer 2

biomass

Question 3

Primary consumers obtain their energy by feeding on ___________.

Answer 3

producers

Question 4

____________________ are a group of microorganisms that break down the organic materials in dead organic matter and faeces into simple ones.

Answer 4

Saprobionts / decomposers

Question 5

n natural ecosystems, most of the light energy falling onto producers is NOT used in photosynthesis. Explain why (2 marks).

Answer 5

1. Light being reflected
2. Pigments may not absorb the wavelength of light received
3. Light may miss the chlorophyll
4. There is another limiting factor that means that the light cannot be used e.g. carbon dioxide concentration

Question 6

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

Answer 6

1. Energy lost during transfer between trophic levels;

(Humans eating cattled adds a trophic level)

2. Energy lost via respiration / heat loss / maintaining temperature / muscle contraction / movement

Also accept: excretion / faeces / parts of food not eaten e.g. roots/bones;

Question 7

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

Answer 7

1. Heat loss from respiration;
2. Food not digested / not all eaten OR faeces;
3. Excretion OR urine;

Question 8

Energy efficiency equation

Answer 8

(energy available after transfer / energy available before transfer) x 100

Question 9

Biomass definition

Answer 9

Total mass of carbon per given area per given time

Question 10

The chemical energy stored in dry biomass can be estimated using _____________.

Answer 10

calorimetry

Question 11

Suggest how you could determine the dry mass of a sample of plant material (2 marks).

Answer 11

1. Heat at 100°C to evaporate water;
2. Weigh and heat until no further change in mass

Question 12

What is the advantage of using dry mass and not fresh mass to compare the yield of plants (2 marks).

Answer 12

1. Water content present will vary in fresh mass;
2. This issue will not affect dry mass;

Question 13

Gross primary production (GPP) is the ____________ energy store in plant biomass, in a given area or volume.

Answer 13

chemical

Question 14

The higher GPP, the higher the rate of ______________

Answer 14

photosynthesis

Question 15

Net Primary Production (NPP) equation

Answer 15

NPP = GPP-R
Where:
GPP = Gross primary production
R = respiratory losses

Question 16

Net production of consumers (N) equation

Answer 16

N = I - (F+R)

Question 17

What does I represent?

N = I - (F+R)

Answer 17

I = Chemical energy/store of ingested/consumed food

Question 18

What does F represent?

N = I - (F+R)

Answer 18

energy loses due to

F = faeces AND urine

Question 19

What does R represent?

N = I - (F+R)

Answer 19

R = respiratory losses

Question 20

Units for the energy stored in biomass

Answer 20

KJ m^-2 year ^-1

Question 21

Describe how calorimetry can estimate the energy stored in biomass.

Answer 21

Sample of (dry) biomass is combusted;

This releases heat energy;

This warms the surrounding water;

The larger the temperature increases of water, the more energy stored in the biomass;

Water is used because it has a high specific heat capacity
(we know much energy is required to heat 1cm3 of water by 1oC).

Question 22

To increase the net productivity (N) of domestic livestock, farmers aim to decrease energy losses due to ________.

Answer 22

Respiration / heat loss / maintaining body temperature / movement;

Question 23

Explain why farmers try to reduce respiratory losses (e.g. by keeping animals indoors during the winter)

Answer 23

More energy is available for growth/biomass

Question 24

Explain why simplifying food webs reduces energy losses to non-human food chains (2 marks).

Answer 24

1. Insecticides/pesticides/fungicides are used to exclude competitors who may feed on crops;
2. This means a higher N (net production of consumers) / more energy available for growth/biomass of crops