Paper 2 - Energy In Ecosystems

Question 1

Bomb Calorimetry

Answer 1

Biomass is the total mass of living material in a specific area at a given time.

• Measuring the mass of carbon or dry mass overcomes the problem of varying amounts of water
but, because the organisms must be killed, it is usually only made on a small sample, and this
sample may not be representative.

• Biomass is measured using dry mass per given area, in a given time e.g. grams per square metre (g
m-2) where an area is being sampled, for example, on grassland or a seashore.

• Where a volume is being sampled, for example, in a pond or an ocean, it is measured in grams per
cubic metre (g m-3).

• The chemical energy store in dry mass can be estimated using calorimetry. In bomb calorimetry, a sample of dry material is weighed and is then burnt in pure oxygen within a sealed chamber called a bomb. The bomb is surrounded by a water bath and the heat of combustion causes a small temperature rise in this water. As we know how much heat (energy) is required to raise the temperature of 1g of water by 1°C, if we know the volume of water and the temperature rise, we can calculate the energy released from the mass of burnt biomass in units such as kJ kg-1

Question 2

What is biomass ?

Answer 2

The total mass of living material in an organism at a given time.

Question 3

How is biomass measured ?

Answer 3

Dry mass = mass of an organism with the water removed - a sample of organism is dried in the oven

Sample is then weighed every day until it reaches a constant mass

Dry mass is used to measure biomass rather than wet mass

Question 4

What is GPP ?

Answer 4

The total amount of chemical energy converted from light energy by plants in a given area in a given time

Question 5

How to calculate net primary production (NPP)

Answer 5

NPP = GPP - R

Question 6

What is net primary production ?

Answer 6

The energy available to the plant for growth and reproduction from plant’s biomass

Question 7

How is energy lost ?

Answer 7

• Lost as heat in respiration
• Excretion of urine
• Indigestable so egested as faeces

Question 8

How to calculate efficiency

Answer 8

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

Question 9

What is productivity ?

Answer 9

The rate at which biomass is added.

Question 10

Intensive rearing of livestock

Answer 10

• Keeping the environment warm and indoors = less energy wasted by generating body heat
• Restricting movement to reduce rate of respiration and to reduce amount of energy used in muscle contraction