Syllabus concepts to know

• 2.2.1 Ecosystems are sustained by supplies of energy and matter.
• 2.2.2 The first law of thermodynamics states that as energy flows through ecosystems, it can be transformed from one form to another but cannot be created or destroyed.
• 2.2.3 Photosynthesis and cellular respiration transform energy and matter in ecosystems.
• 2.2.4 Photosynthesis is the conversion of light energy to chemical energy in the form of glucose, some of which can be stored as biomass by autotrophs.
• 2.2.5 Producers form the first trophic level in a food chain.
• 2.2.6 Cellular respiration releases energy from glucose by converting it into a chemical form that can easily be used in carrying out active processes within living cells.
• 2.2.7 Some of the chemical energy released during cellular respiration is transformed into heat.
• 2.2.8 The second law of thermodynamics states that energy transformations in ecosystems are inefficient.
• 2.2.9 Consumers gain chemical energy from carbon (organic) compounds obtained from other organisms.
• 2.2.10 Because producers in ecosystems make their own carbon compounds by photosynthesis, they are at the start of food chains.
• 2.2.11 Carbon compounds and the energy they contain are passed from one organism to the next in a food chain.
• 2.2.12 There are losses of energy and organic matter as food is transferred along a food chain.
• 2.2.13 Gross productivity (GP) is the total gain in biomass by an organism.
• 2.2.14 The number of trophic levels in ecosystems is limited due to energy losses.
• 2.2.15 Food webs show the complexity of trophic relationships in communities.
• 2.2.16 Biomass of a trophic level can be measured by collecting and drying samples.
• 2.2.17 Ecological pyramids are used to represent relative numbers, biomass or energy of trophic levels in an ecosystem.
• 2.2.18 Pollutants that are non-biodegradable, such as polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (DDT) and mercury, cause changes to ecosystems through the processes of bioaccumulation and biomagnification.
• 2.2.19 Non-biodegradable pollutants are absorbed within microplastics, which increases their transmission in the food chain.
• 2.2.20 Human activities, such as burning fossil fuels, deforestation, urbanization and agriculture, have impacts on flows of energy and transfers of matter in ecosystems.
• 2.2.21 Autotrophs synthesize carbon compounds from inorganic sources of carbon and other elements.
• 2.2.22 Photoautotrophs use light as an external energy source in photosynthesis.
• 2.2.23 Primary productivity is the rate of production of biomass using an external energy source and inorganic sources of carbon and other elements.
• 2.2.24 Secondary productivity is the gain in biomass by consumers using carbon compounds absorbed and assimilated from ingested food.
• 2.2.25 Net primary productivity is the basis for food chains because it is the quantity of carbon compounds sustainably available to primary consumers.
• 2.2.26 Maximum sustainable yields (MSYs) are the net primary or net secondary productivity of a system.
• 2.2.27 Sustainable yields are higher for lower trophic levels.
• 2.2.28 Ecological efficiency is the percentage of energy received by one trophic level that is passed on to the next level.
• 2.2.29 The second law of thermodynamics shows how the entropy of a system increases as biomass passes through ecosystems.