5.3 - Energy and Ecosystems

Question 1

How do plants use the sugars from photosynthesis?

Answer 1

• Primarily as respiratory substrates
• To synthesise other biological molecules e.g. cellulose

Question 2

What is biomass?

Answer 2

Total dry mass of tissue or mass of carbon measured over a given time in a specific area.

Question 3

Suggest when the units for biomass.

Answer 3

• When an area is being sampled: gm^-2
• When a volume is being sampled: gm^-3

Question 4

How can the chemical energy store in dry biomass be estimated?

Answer 4

Using calorimetry.
Energy realsed = specific heat capacity of water x volume of water (cm3) x temp increase of water

Question 5

Why is bomb calorimetry preferable to simple calorimetry?

Answer 5

Reduces heat loss to surroundings.

Question 6

How could a student ensure that all water had been removed from a sample before weighing?

Answer 6

Heat the sample and reweigh it until the mass reading is constant.

Question 7

Define Gross Primary Production (GPP).

Answer 7

Total chemical energy in plant biomass within a given volume or area.

Question 9

Define Net Primary Productivity (NPP).

Answer 9

Total chemical energy available for plant growth, plant reproduction and energy transfer to other trophic levels after respiratory losses.

Question 10

What is the mathematical relationship between GPP and NPP

Answer 10

NPP = GPP - R
where R represents respiratory losses.