[13.2] energy transfer and productivity

Question 1

what percentage of energy is lost between different stages of a food chain?

Answer 1

• 97% is lost when plant absorbs sun’s energy
• 90% is lost between producer and primary consmer
• ~80% of biomass is lost between consumers

Question 2

why is only 3% of sunlight converted in chemical energy? [6]

Answer 2

• light falls onto non-photosynthetic part of the plant
• light misses the plant and hits the ground
• green light is reflected by the leaves
• only some wavelengths absorbed
• some light passes through the leaf (transmission)
• inefficient conversion of light energy to organic molecules by chlorophyll

Question 3

why are there energy losses between producer and consumer? [4]

Answer 3

• not all parts of plant can be eaten
• not all parts can be digested, so lost as faeces
• some energy lost via excretory processes eg. urine
• heat energy losses during consumer’s digestive process

Question 4

what is gross primary production (GPP)?

Answer 4

• amount of light energy converted to chemical energy in the biomass in a given area
• unit = kJ m⁻²
• 50% of GPP is lost by plant as heat through respiration

Question 5

what is net primary production (NPP)?

Answer 5

• amount of chemical energy left after respiration
• unit = kJ m⁻²

Question 6

what is the equation for NPP?

Answer 6

NPP = GPP - R

Question 7

what is net production in consumers (N)?

sometimes called secondary production

Answer 7

energy left in animals after it ingests plants and loses energy to faeces / urine and heat through respiration

Question 8

what is the equation for net production in consumers (N)?

Answer 8

N = I - (F + R)

• I = ingested chemical energy
• F = chemical energy in faeces and urine
• R = energy lost through heat in respiration