3.5.3 - Energy and Ecosystems

Question 1

biomass

Answer 1

• mass of carbon or dry mass of tissue per given area
• chemical energy store in dry biomass can be estimated using calorimetry

Question 2

why is most light energy not converted to organic matter by photosynthesis?

Answer 2

• reflected back into space by clouds and dust or absorbed by the atmosphere
• not all wavelengths of light can be absorbed and used for photosynthesis
• light may not fall on a chlorophyll molecule
• a factor may limit the rate of photosynthesis (e.g. carbon dioxide)

Question 3

gross primary production (GPP)

Answer 3

the chemical energy store in plant biomass, in a given area or volume

Question 4

net primary production (NPP)

Answer 4

the chemical energy store in plant biomass, after respiratory losses to the environment have been taken into account

• NPP = GPP - R
• available for plant growth and reproduction, also available to other trophic levels in the ecosystem

Question 5

why is such a low % of energy transferred between trophic levels?

Answer 5

• some of the organism is not consumed
• some parts are consumed but cannot be digested and are therefore lost in faeces
• some of the energy is lost in excretory materials, e.g. urine
• some energy losses occur as heat from respiration and lost to the environment

Question 6

net production of consumers (N)

Answer 6

N = I – ( F + R)

I = chemical energy store in ingested food
F = chemical energy lost in faeces and urine
R = respiratory losses to the environment