19. Organisms and their environment
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19.1 Energy flow
19.1.1Sun is the principal source of energy
• State that the Sun is the principal source of energy input to biological systems
19.1.2Flow of energy through living
• Describe the flow of energy through living organisms, including light energy from the Sun and chemical energy in organisms, and its eventual transfer to the environment
19.2 Food chains and food webs
19.2.1Food chain as showing the transfer
• Describe a food chain as showing the transfer of energy from one organism to the next, beginning with a producer
19.2.2Construct and interpret simple food
• Construct and interpret simple food chains
19.2.3Food web as a network
• Describe a food web as a network of interconnected food chains and interpret food webs
19.2.4Producer as an organism that makes its
• Describe a producer as an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis
19.2.5Consumer as an organism that gets its
• Describe a consumer as an organism that gets its energy by feeding on other organisms
19.2.6Consumers may be classed as primary
• State that consumers may be classed as primary, secondary, tertiary and quaternary according to their position in a food chain
19.2.7Herbivore as an animal that gets its
• Describe a herbivore as an animal that gets its energy by eating plants
19.2.8Carnivore as an animal that gets its
• Describe a carnivore as an animal that gets its energy by eating other animals
19.2.9Decomposer as an organism that gets
• Describe a decomposer as an organism that gets its energy from dead or waste organic material
19.2.10Food chains and food webs to describe
• Use food chains and food webs to describe the impact humans have through overharvesting of food species and through introducing foreign species to a habitat
19.2.11Pyramids of numbers and pyramids
• Draw, describe and interpret pyramids of numbers and pyramids of biomass
19.2.12Pyramids of biomass
• Discuss the advantages of using a pyramid of biomass rather than a pyramid of numbers to represent a food chain
19.2.13Trophic level as the position
• Describe a trophic level as the position of an organism in a food chain, food web or ecological pyramid
19.2.14Following as the trophic levels
• Identify the following as the trophic levels in food webs, food chains and ecological pyramids: producers, primary consumers, secondary consumers, tertiary consumers and quaternary consumers
19.2.15Pyramids of energy
• Draw, describe and interpret pyramids of energy
19.2.16Pyramids of energy
• Discuss the advantages of using a pyramid of energy rather than pyramids of numbers or biomass to represent a food chain
19.2.17Transfer of energy from one trophic
• Explain why the transfer of energy from one trophic level to another is often not efficient
19.2.18Explain, in terms of energy loss, why
• Explain, in terms of energy loss, why food chains usually have fewer than five trophic levels
19.2.19It is more energy efficient for humans
• Explain why it is more energy efficient for humans to eat crop plants than to eat livestock that have been fed on crop plants
19.3 Nutrient cycles
19.3.1Carbon cycle
• Describe the carbon cycle, limited to: photosynthesis, respiration, feeding, decomposition, formation of fossil fuels and combustion
19.3.2Nitrogen cycle with reference to: •
• Describe the nitrogen cycle with reference to: • decomposition of plant and animal protein to ammonium ions • nitrification • nitrogen fixation by lightning and bacteria • absorption of nitrate ions by plants • production of amino acids and proteins • feeding and digestion of proteins • deamination • denitrification
19.3.3Roles of microorganisms
• State the roles of microorganisms in the nitrogen cycle, limited to: decomposition, nitrification, nitrogen fixation and denitrification (generic names of individual bacteria, e.g. Rhizobium, are not required)
19.4 Populations
19.4.1Population as a group of organisms
• Describe a population as a group of organisms of one species, living in the same area, at the same time
19.4.2Community as all of the populations
• Describe a community as all of the populations of different species in an ecosystem
19.4.3Ecosystem as a unit containing
• Describe an ecosystem as a unit containing the community of organisms and their environment, interacting together
19.4.4Factors affecting the rate
• Identify and state the factors affecting the rate of population growth for a population of an organism, limited to food supply, competition, predation and disease
19.4.5Lag, exponential (log), stationary
• Identify the lag, exponential (log), stationary and death phases in the sigmoid curve of population growth for a population growing in an environment with limited resources
19.4.6Interpret graphs and diagrams
• Interpret graphs and diagrams of population growth
19.4.7Factors that lead to each phase
• Explain the factors that lead to each phase in the sigmoid curve of population growth, making reference, where appropriate, to the role of limiting factors