IGCSE Organisms and their environment

What is the principal source of energy input to biological systems?

the sun

What does a food chain show?

the transfer of energy from one organism to the next, beginning with a producer

How is energy transferred between organisms in a food chain?

ingestion

What is a trophic level?

the position of an organism in a food chain, food web, pyramid of numbers or pyramid of biomass

What is a food web?

a network of interconnected food chains

What is a producer?

an organism that makes its own organic nutrients, usually using energy form sunlight, through photosynthesis

What is a consumer?

an organism that gets its energy from feeding on other organisms

What are the three classes of consumer?

primary, secondary, tertiary

What is a herbivore?

an animal that gets its energy from eating plants

What is a carnivore?

an animal that gets its energy from eating other animals

What is a detritovor/ decomposer?

an organism that feeds on dead or decaying organic matter

Why is the transfer of energy from one trophic level to the next inefficient?

energy is used for movement, growth and respiration

Why do food chains usually have less than 5 trophic levels?

Loss of energy limits the length

Why is there a greater efficiency in supplying plants as animal food, and there is a relative inefficiency in feeding crop plants to livestock who will be used as food?

Short food chains are much more efficient than long ones in providing energy to the top consumer

What does a pyramid of number represent?

the number of organisms at each trophic level

What does a pyramid of biomass represent?

the dry mass of living material in an ecosystem

Are pyramids of number always pyramid shaped?

no

What are the advantages of using a pyramid of biomass rather than a pyramid of numbers?

they provide a much better idea of the quantity of material at each trophic level

What is a decomposer?

an organism that gets its energy from dead or decaying organic matter

What are the six steps of the carbon cycle?

photosynthesis, respiration, feeding, decomposition, fossilisation and combustion

What are two factors that can increase carbon dioxide concentration in the atmosphere?

combustion of fossil fuels, deforestation

What are the four steps of the water cycle?

evaporation, transpiration, condensation and precipitation

What are the eight steps of the nitrogen cycle?

decomposition of plant and animal protein to ammonium ions, nitrification, nitrogen fixation, absorption of nitrate ions by plants, production of amino acids, feeding of proteins, deamination, denitrification

What is the role of bacteria in nitrogen fixing in the nitrogen cycle?

live in soil or root nodules and convert nitrogen in air into nitrates

what are NO₃?

nitrates

What is the role of bacteria in decomposition in the nitrogen cycle?

live in soil and convert proteins from dead organisms and urea into ammonium ions

what is the role of bacteria in nitrifying in the nitrogen cycle?

convert ammonia into nitrites then nitrates

What is the role of denitrifying bacteria in the nitrogen cycle?

change nitrates back into nitrogen gas