4.1 / 4.2 - Ecosystems
Assessment statements
| DCS Topic Code | Statement | Guidance |
| 4.1.U1 | Species are groups of organisms that can potentially interbreed to produce fertile offspring. | |
| 4.1.U2 | Members of a species may be reproductively isolated in separate populations. | |
| 4.1.U3 | Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods). | |
| 4.1.U4 | Consumers are heterotrophs that feed on living organisms by ingestion. | |
| 4.1.U5 | Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion. | |
| 4.1.U6 | Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion. | |
| 4.1.U7 | A community is formed by populations of different species living together and interacting with each other. | |
| 4.1.U8 | A community forms an ecosystem by its interactions with the abiotic environment. | |
| 4.1.U9 | Autotrophs obtain inorganic nutrients from the abiotic environment. | |
| 4.1.U10 | The supply of inorganic nutrients is maintained by nutrient cycling. | |
| 4.1.U11 | Ecosystems have the potential to be sustainable over long periods of time. | |
| 4.1.S1 | Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition. | |
| 4.1.S2 | Setting up sealed mesocosms to try to establish sustainability. (Practical 5) | Mesocosms can be set up in open tanks, but sealed glass vessels are preferable because entry and exit of matter can be prevented but light can enter and heat can leave. Aquatic systems are likely to be more successful than terrestrial ones. |
| 4.1.S3 | Testing for association between two species using the chi-squared test with data obtained by quadrat sampling. | To obtain data for the chi-squared test, an ecosystem should be chosen in which one or more factors affecting the distribution of the chosen species varies. Sampling should be based on random numbers. In each quadrat the presence or absence of the chosen species should be recorded. |
| 4.1.S4 | Recognizing and interpreting statistical significance. |
| DCS Topic Code | Statement | Guidance |
| 4.2.U1 | Most ecosystems rely on a supply of energy from sunlight. | |
| 4.2.U2 | Light energy is converted to chemical energy in carbon compounds by photosynthesis. | |
| 4.2.U3 | Chemical energy in carbon compounds flows through food chains by means of feeding. | Pyramids of number and biomass are not required. Students should be clear that biomass in terrestrial ecosystems diminishes with energy along food chains due to loss of carbon dioxide, water and other waste products, such as urea. |
| 4.2.U4 | Energy released from carbon compounds by respiration is used in living organisms and converted to heat. | |
| 4.2.U5 | Living organisms cannot convert heat to other forms of energy. | |
| 4.2.U6 | Heat is lost from ecosystems. | |
| 4.2.U7 | Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels. | The distinction between energy flow in ecosystems and cycling of inorganic nutrients should be stressed. Students should understand that there is a continuous but variable supply of energy in the form of sunlight but that the supply of nutrients in an ecosystem is finite and limited. |
| 4.2.S1 | Quantitative representations of energy flow using pyramids of energy. | Pyramids of energy should be drawn to scale and should be stepped, not triangular. The terms producer, first consumer and second consumer and so on should be used, rather than first trophic level, second trophic level and so on. |
Notes
| 4.1_4.2_-_notes.pdf |
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Review PowerPoint
| 4.1_4.2_ecology.ppt |
