Relationships of organisms with one another and with the environment flashcards

Topic 19: Relationships of organisms with one another and with the environment

Energy flow through an ecosystem (O Level)

The Sun is the principal energy source. Photosynthesis brings light energy into food chains as chemical energy. Energy flows one way and is eventually transferred to the environment as heat; it is not recycled.

Producer, consumer and decomposer (O Level)

Producer: makes its own organic nutrients, usually by photosynthesis. Consumer: gets energy by feeding on other organisms. Decomposer: gets energy from dead or waste organic material.

Reasons energy is lost between trophic levels

Parts not eaten; parts eaten but not digested (faeces); energy released in respiration and lost as heat; energy used for movement; some lost in excretory products.

Wheat contains 1500 kJ and mice eating it 120 kJ. Efficiency of transfer?

120 ÷ 1500 × 100 = 8%.

Pyramids of numbers, biomass and energy: can they be inverted?

Numbers: yes (one tree, many insects). Biomass: rarely. Energy: never, because energy is lost at every transfer.

Carbon cycle processes that add carbon dioxide to the air

Respiration (by plants, animals and decomposers), decomposition and combustion of fossil fuels and wood. Photosynthesis removes it.

Nitrogen fixation, nitrification and denitrification

Fixation: nitrogen gas → compounds plants can use (lightning or nitrogen-fixing bacteria). Nitrification: ammonium ions → nitrate ions (nitrifying bacteria). Denitrification: nitrate ions → nitrogen gas (denitrifying bacteria).

Population, community, ecosystem and biodiversity

Population: one species, same area, same time. Community: all the populations of different species in an ecosystem. Ecosystem: the community and its environment interacting. Biodiversity: the number of different species in an area.

Non-native species

No natural predators or diseases; spreads fast; out-competes or eats native species.

Eutrophication chain (O Level)

More nitrate and other ions → more growth of producers → more decomposition when they die → more aerobic respiration by decomposers → less dissolved oxygen → organisms that need dissolved oxygen die.

Sustainable resource

One produced as rapidly as it is removed from the environment, so that it does not run out.

Fish stocks

Education, closed seasons, protected areas, controlled net types and mesh size, quotas, monitoring.