5.3 Energy and Ecosystems

What is the ultimate source of energy for organisms found in an ecosystem?

• Sunlight

• This is converted to chemical energy by photosynthesising organisms and passes as food between other organisms

What do the arrows represent in a food chain?

The direction of energy transfer

Define Biomass

Total mass of living material in a specific area at a given time

What are the units of Biomass

• Grassland or seashore - gm^-2

• Pond or ocean - gm^-3

Explain why the dried mass of organisms are used

The presence of varying amounts of water in fresh mass makes it unreliable

Describe how dry mass of tissue can be measured

1. Sample dried in an oven eg. at 100°C (avoid combustion)

2. Sample weighed and reheated at regular intervals until mass remains constant (all water evapourated)

Explain why the biomass data collected from an ecosystem could be unreliable

Involves killing the organisms so only a small sample is taken which isn’t representative of a whole population in an ecosystem

Describe how the chemical energy stored in dry biomass can be estimated

Using Calorimetry:

• Known mass of dry biomass is fully combusted

• Heat energy released heat at a known volume of water

• Increase in temperature of water is used to calculate chemical energy of biomass

Explain how features of a calorimeter enable valid measurement of heat energy released

• Stirrer evenly distributes heat energy in the water

• Air/ insulation reduces heat loss and gain to surroundings

• Water has a high specific heat capacity

What is gross primary production (GPP)?

• Chemical energy store in plant biomass, in a given area or volume, in a given time

• Total energy transferred into chemical energy from light energy during photosynthesis

What is net primary production (NPP)?

Chemical energy store in plant biomass after respiratory losses to environment taken into account

State the formula for NPP

NPP = GPP - R

Explain the importance of NPP in ecosystems

• NPP is available for plant growth and reproduction

• NPP is als available to other trophic levels in the ecosystem, such as herbivores and decomposers

What is primary or secondary productivity and what are the units?

• The rate of primary or secondary production, respectively.

• kJ ha^-1 year^-1 (unit for energy, per unit area, per year)

Explain why these units for primary or secondary productivity are used

• Per unit area takes into account that different environments vary in size. Standardising…