Populations and communities practice questions.

In a food chain, organisms that convert light energy into chemical energy are called

• consumers
• producers
• decomposers
• detritivores

Answer: producers

Producers (autotrophs) synthesise organic molecules from inorganic sources, typically by photosynthesis.

Organisms that break down dead organic matter and release nutrients are called

• producers
• decomposers
• primary consumers
• apex predators

Answer: decomposers

Decomposers (e.g. bacteria and fungi) recycle nutrients back into the ecosystem.

A pyramid of energy shows

• the number of organisms at each level
• the energy at each trophic level
• the mass of producers only
• the age of an ecosystem

Answer: the energy at each trophic level

Pyramids of energy are always narrower towards the top because energy is lost between trophic levels.

Which is the ecological definition of a population?

• Same-species organisms in one area at one time
• All the organisms of different species in an ecosystem
• The living and non-living components of an area
• A group of organisms occupying the same trophic level

Answer: Same-species organisms in one area at one time

A population consists of individuals of a single species in the same area at the same time; a community is all populations together, and an ecosystem also includes abiotic factors.

A population of bacteria grows in unlimited nutrients with no predators. Determine which growth pattern best describes this phase.

• Exponential growth
• Logistic plateau at carrying capacity
• A gradual linear decline
• Constant size with no change

Answer: Exponential growth

With abundant resources and no limiting factors, the population grows exponentially; growth later slows and plateaus at the carrying capacity as resources become limiting.

Explain what is meant by the carrying capacity of an environment for a given species.

• The maximum population an environment can sustain
• The total number of species an ecosystem contains
• The rate at which a population grows exponentially
• The minimum population needed to avoid extinction

Answer: The maximum population an environment can sustain

Carrying capacity is the maximum number of individuals of a species an environment can support long-term, set by limiting factors such as food, space and disease.