19. Organisms and their environment
19.1 Energy flow
Core
State that the Sun is the principal source of energy input to biological systems
Supplement
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
Energy transfer in ecosystems intro
Energy transfer in ecosystems - Supplement
19.2 Food chains and food webs
Core
Define a food chain as showing the transfer of energy from one organism to the next, beginning with a producer
State that energy is transferred between organisms in a food chain by ingestion
Construct simple food chains
Supplement
Describe how energy is transferred between trophic levels
Define trophic level as the position of an organism in a food chain, food web, pyramid of numbers or pyramid of biomass
Explain why the transfer of energy from one trophic level to another is inefficient
Explain why food chains usually have fewer than five trophic levels
Food chains
Trophic levels
Pyramids of Biomass
19.2 Food chains and food webs continued
Core
Define a food web as a network of interconnected food chains
Define producer as an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis
Define consumer as an organism that gets its energy by feeding on other organisms
State that consumers may be classed as primary, secondary and tertiary according to their position in a food chain
Define herbivore as an animal that gets its energy by eating plants
Define carnivore as an animal that gets its energy by eating other animals
Define decomposer as an organism that gets its energy from dead or waste organic material
Interpret food chains and food webs in terms of identifying producers and consumers
Use food chains and food webs to describe the impacts humans have through over-harvesting of food species and through introducing foreign species to a habitat
Draw, describe and interpret pyramids of numbers
Supplement
Explain why there is a greater efficiency in supplying plants as human food, and that there is a relative inefficiency in feeding crop plants to livestock that will be used as food
Identify producers, primary consumers, secondary consumers, tertiary consumers and quaternary consumers as the trophic levels in food webs, food chains, pyramids of numbers and pyramids of biomass
Draw, describe and interpret pyramids of biomass
Discuss the advantages of using a pyramid of biomass rather than a pyramid of numbers to represent a food chain
Food chains and food webs
Pyramids of number and biomass explained
Drawing pyramids of number and biomass
19.3 Nutrient cycles
Core
Describe the carbon cycle, limited to photosynthesis, respiration, feeding, decomposition, fossilisation and combustion
Discuss the effects of the combustion of fossil fuels and the cutting down of forests on the carbon dioxide concentrations in the atmosphere
Describe the water cycle, limited to evaporation, transpiration, condensation and precipitation
Supplement
Describe the nitrogen cycle in terms of:
– 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
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)
The Carbon and Water cycle
The Nitrogen cycle
Nutrient cycles overview
19.4 Population size
Core
Define population as a group of organisms of one species, living in the same area, at the same time
Identify and state the factors affecting the rate of population growth for a population of an organism, limited to food supply, predation and disease
Discuss the increase in human population size over the past 250 years and its social and environmental implications
Interpret graphs and diagrams of human population growth
Supplement
Define community as all of the populations of different species in an ecosystem
Define ecosystem as a unit containing the community of organisms and their environment, interacting together, e.g. a decomposing log, or a lake
Identify the lag, exponential (log), stationary and death phases in the sigmoid population growth curve for a population growing in an environment with limited resources
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
Key ecological definitions
Topic overview