5.3.3 - Energy transfers in ecosystems

Question 1

Define biomass and give units

Answer 1

he total mass of living material in a specific area (g m-2)

Question 2

How is biomass measured

Answer 2

• dry mass
• mass of sample weighed regularly to
• when mass is constant all water has been removed
• sample scaled up

Question 3

What is the purpose of calorimetry (and units of energy)

Answer 3

bomb calorimeter estimates how much energy is in dry mass which can be transferred between other organisms (KJ Kg-1)

Question 4

3 limitations of calorimetry

Answer 4

1. Measuring the energy within a sample - sample may not be representative of the entire population and repeats must be taken
2. To obtain dry mass the organisms must be killed - ethical issues
3. Some energy may escape the calorimeter rather than heat the water - not 100% accurate and only an estimate

Question 5

How is energy lost (from plants)?

Answer 5

1. Reflected light - to all wavelengths (green) are absorbed
2. Transmitted- light may not fall on a chlorophyll molecule and pass through the leaf
3. Light energy reflected back by the atmosphere and not reach the plant
4. Energy lost as heat as a waste product of respiration
5. A limiting factor might reduce the rate of photosynthesis (temperature, [CO2])

Question 6

How is energy lost in food chains?

Answer 6

• not all parts of the organism are consumes (e.g. bones)
• energy is lost in excretion (faeces and urine)
• some parts cannot be digested or absorbed (e.g. cellulose)
• energy is lost as heat (waste from respiration) - this is higher in mammals and birds as they are endotherms (warm blooded)

Question 7

Define primary productivity

Answer 7

PLANT production of biomass

Question 8

Define gross primary productivity (GPP)

Answer 8

the rate at which light energy is converted into chemical energy by photosynthesis (total amount of energy stored in plant biomass)

Question 9

Define net primary productivity (NPP) and equation

Answer 9

biomass of the plant that is available to consumers as potential food
(NPP = GPP - respiration)

Question 10

NPP and GPP units

Answer 10

KJ m-2 yr-1

Question 11

Define net production

Answer 11

energy left in an organism after respiration

Question 12

Define secondary productivity

Answer 12

consumer production of biomass

Question 13

Net production calculation

Answer 13

N = I - (F + R)
N - net production 
I - ingested chemical energy store 
F - loss through faeces and urine 
R - loss through respiration

Question 14

Biomass transfer efficiency equation

Answer 14

% efficiency = (energy available after the transfer / energy available before the transfer) x 100

Question 15

How does temperature affect respiration and energy loss?

Answer 15

In colder temperatures:
(E lost by respiration in form of heat energy)
- increased heat loss 
- increased respiration 
- to maintain body temperature