Energy Transfers

Question 1

Methods of measuring biomass

Answer 1

• Dry biomass / kg m^-2 (heat sample on scale until mass remains constant)
• Mass of carbon / kg m^-2 yr^-1 (carbon is usually about 50% of dry biomass)

Question 2

How can you calculate energy stored in biomass?

Answer 2

• Burn sample completely in a calorimeter
• Heat with a known volume of water
• Measure temperature change of water
• Calculate energy released / J

Question 3

What is gross primary production (GPP)?

Answer 3

Total amount of energy made by producers / J m^-2 yr^-1

Question 4

What is respiratory loss (R)?

Answer 4

The energy used by organisms for respiration / J m^-2 yr^-1
(active transport, muscle contraction, heat)

Question 5

What is net primary production (NPP)?

Answer 5

The amount of chemical energy a producer stores as biomass / J m^-2 yr^-1

Question 6

Primary productivity formula

Answer 6

NPP = GPP - R

Question 7

Secondary productivity formula

Answer 7

N = I - (R + F)

N = net production
I = chemical energy in ingested food
F = chemical energy in faeces + urine

Question 8

Efficiency of energy transfer formula

Answer 8

% efficiency = (net production of tropic level / net production of pervious tropic level) x100

Question 9

Energy transfer efficiency between tropic levels

Answer 9

Sun —> producer (2%)
Producer —> primary consumer (10%)
Primary consumer —> secondary consumer (15%)

Question 10

Why isn’t all energy transferred between tropic levels?

Answer 10

• Wrong wavelength
• Light reflected
• Lost as heat
• Respiratory loss
• Not all plant/animal eaten
• Not all food digested

Question 11

How can energy transfer efficiency be increased?

Answer 11

• Shorten food web (reduce competition so plant has more energy to create biomass)
• Fertilisers (prevent plant growth being limited by lack of nutrients)
• Reduce respiratory loss (restrict livestock movement + keep warm)
• Slaughter animal while still growing
• Keep predators away
• Artificially select organisms with high yield