5B Ecosystems

What is meant by gross primary productivity?

• The amount of chemical energy that is available to heterotrophs in an ecosystem.

• The rate of chemical energy fixture during photosynthesis by all producers in an ecosystem.

• The position that an organism holds in a food chain or food web.

• The rate of transferring energy from one trophic level to another trophic level.

How is net primary productivity calculated?

Answer explanation

net primary production (NPP) = gross primary production (GPP) - respiratory losses (R)

What is a trophic level?

• The functional position and role of an organism within its environment.

• The activity patterns of the organism.

• The resources it obtains from the environment.

• The position that an organism holds in a food chain, food web, pyramid of numbers or pyramid of biomass.

What is biomass?

• The total weight of living matter in a certain area, transferred up trophic levels through consumption.

• A large body matter with no definite shape.

• A body's relative mass or the quantity of matter contained by it, giving rise to a downward force.

• Non-renewable material from animals and plants.

How can we measure biomass?

• Measured in terms of mass of carbon and oxygen.

• Measured in terms of mass of carbon, or dry mass of tissue.

• Measured in terms of total energy storage.

• Measured in terms of numbers of organisms.

State the formula for efficiency of biomass transfer.

Answer explanation

Efficiency = (biomass transferred / biomass intake) x 100

Why are biomass transfers not 100% efficient?

Answer explanation

Energy is lost through:

- Egestion (removal of faeces)

- Excretion (removal of waste products)

- Respiration (lost as heat)

- Not every part of the food organism is eaten / digestible

Define population.

• The region where an organism normally lives.

• All of the populations of different species living together in a habitat.

• All organisms of the same species living with one another in a habitat at the same time.

• The community of organisms (biotic) and non-living (abiotic) components of an area and their interactions.

Define ecosystem.

• The community of organisms and non-living components of an area and their interactions.

• All of the populations of different species living together in a habitat.

• The functional position and role of an organism within its environment.

• The interactions that occur with other species in the region.

Describe biotic factors, giving examples.

Answer explanation

Biotic factors are living factors that influence populations within their community.

Examples - predations, disease, competitions, mutualism, commensalism, parasitism.