OCR A Level 6.3.1 Ecosystems and Biomass

What explains why food chains rarely have more than five trophic levels?

• Parts of the food organism are not eaten by organisms higher in the food chain.

• Plants absorb only a small proportion of the Sun’s energy.

• There is a limit to the size to which a predator can grow.

• Transfer of biomass between trophic levels is inefficient.

The rate at which plants produce biomass is known as productivity.

What is a suitable unit with which to measure productivity at different depths in the ocean?

• kg day^–1 m^–2

• kg day^–1 m^–3

• kg year^–1 m²

• m kg^–1 year^–1

Biomass is transferred through ecosystems.

What process makes biomass available for transfer to the next trophic level in the food chain?

• Growth

• Excretion

• Removal of undigested food

• Respiration

In one year, 8.94 × 10⁹ kJ m^–2 of PAR fell on an area of heather moorland.

The heather plants then converted 9.08 × 10⁷ kJ m^–2 of this energy into biomass.

Calculate the energy in the PAR that the heather did not convert into biomass.

Mathematical Equivalence

OFF

Ash trees are common throughout the UK. They often grow in dense woodland.

Which of the following, A to D, is an abiotic factor that is likely to affect the growth of young ash trees?

• the availability of light underneath larger trees in the wood

• the availability of oxygen in the air

• the presence of a pathogen that causes ash dieback disease

• the species of bacteria present in the soil

A teacher wrote:

"A garden pond is a dynamic environment that is home to a variety of organisms. The temperature of the pond varies depending on the weather and the time of year, and this affects the populations of the species that live there."

Which of the following terms applies to the teacher’s description of the garden pond?

• a community

• an ecosystem

• a habitat

• a niche

Which of the following statements about ecosystems is not true?

A. An ecosystem is affected by biotic and abiotic factors.

B. An ecosystem is all of the organisms and habitats in a large area.

C. An ecosystem is dynamic.

D. There is a flow of biomass between trophic levels in an ecosystem.

Suggest one biotic factor that might affect the distribution of the buttercups.

Deep sea vents on the ocean floor are surrounded by unusual organisms such as chemosynthetic bacteria and eyeless shrimp.

Which of the following statement(s) about these ecosystems is / are true?

Statement 1:The temperature of the vents influences the organisms that live there.

Statement 2:A predatory octopus would affect the balance of these organisms.

Statement 3:The number of eyeless shrimp found at each vent is constant.

• 1. 1, 2 and 3

• 1. Only 1 and 2

• 1. Only 2 and 3

• 1. Only 1

Please refer to the diagram.

• Row A

• Row B

• Row C

• Row D