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ENERGY AND ECOSYSTEMS A habitat is where an organism lives e.g. giant panda in mountain forests, Gobi bear in the Gobi Desert. A population is a group of the same species living in an area at the same time that can interbreed with each other e.g. all the people in Shenzhen, the barnacles on a rocky shore A community is made up of all of the different species living in a habitat e.g. all the organisms in a rock pool. An ecosystem is made up of all the living organisms together with all of the non living factors that are in an area and how they interact e.g. the mountain forest community with the rainfall, soil, temperature, light etc. or a mangrove ecosystem. A niche is an organism’s role in an ecosystem and the sum total of its use of the abiotic (non living) and biotic (living) resources e.g. a hibiscus tree is a producer, provider of food, habitat etc. No two organisms can occupy the same ecological niche for a long time as they compete for the same resources. A producer can make its own food e.g. lily. A consumer must eat ready made food. Herbivores eat plants e.g. cows eat grass, carnivores e.g. tigers eat meat and omnivores e.g. pigs eat both plant and animal food. Decomposers are bacteria and fungi that ?break down dead and decaying things also waste substances and help to release materials that can be used again. Detritivores tend to be the larger animals that do this e.g. earthworm. A trophic level is a feeding level, for example the trophic level of producers and primary consumers. From page 95 the oak and grass are producers. The rabbit and sparrowhawks are consumers. The fox is an omnivore. The sparrowhawk belongs to the tertiary consumer trophic level. A food chain can show what eats what in an area and the flow of energy through it. Grass cow man In nature a complicated food chain is a food web. Grass sheep Grass cow man man Energy is never recycled but enters the ecosystem as light energy from the sun. Plants convert this light energy into chemical energy. Not all of the light falling on the plant is used. Some is reflected, passes through the leaves etc and the plant uses some of this energy for its own activities e.g. active transport. Only one tenth of the energy in a producer passes to a primary consumer. Not all of the plant may be eaten, not all of the plant may be digestible. A lot of energy is lost as heat into the environment from respiration. Only one tenth of the energy will pass onto the secondary consumer and so on. Between levels energy can pass to the decomposers as dead leaves, urine, faeces etc. These energy loses limit the numbers of trophic levels and top carnivores in a food chain. The rate at which plants convert light energy into chemical potential energy is productivity or primary productivity. It is usually measured in kilojoules of energy transferred per square metre per year. The total energy transferred is the gross primary productivity and the net primary productivity is the gross primary productivity minus the loss from respiration. The efficiency of transfer between trophic levels is calculated by comparing the energy available to a trophic level with the energy available to the next trophic level, for example Energy available to tertiary consumers x Energy available to secondary consumers 100% Matter cycles round ecosystems but energy does not. Nitrogen is found in proteins, amino acids and nucleic acids. Although 78% of the air is nitrogen, most organisms cannot use it. It has to be converted into a more reactive form by nitrogen fixation. One type of nitrogen fixing bacteria is Rhizobium, which lives in the soil and in some plants including leguminous plants (have a pod). The bacteria and legume live together and both benefit from the relationship. This is called mutualism. The roots of a germinating legume seed make lectins which join to polysaccharides on the surface of the bacteria. The bacteria enter the roots and stimulate some cells to divide to form nodules. There are colonies of bacteria in the lumps. The bacteria make an enzyme nitrogenase that is a catalyst for the conversion of N gas to ammonium ions. Hydrogen, ATP and anaerobic conditions are needed for this nitrogen fixation. The fixed nitrogen is used to make amino acids. These are transported to other plant cells in the xylem, where they are used to make proteins Fixation can also be caused by lightning, where nitrogen oxides are formed when nitrogen and oxygen join. The oxides dissolve in rain and this falls to the ground. In the Haber process when fertilizers are made, nitrogen and hydrogen gas are reacted together to form ammonia. Other plants take up nitrates by active transport in their root hairs. In many plants the nitrate is changed to nitrite, then to ammonia and then to amino acids, which are transported in xylem. Cells convert most of these to proteins. Other plants transport nitrates in the xylem. Most N becomes part of proteins. Animals get their nitrogen from eating, mainly from proteins. Proteins are digested into amino acids before they enter the blood. They are used by cells to make proteins. Excess amino acids are deaminated by the liver and urea is made. Urea is excreted in urine. When plants and animals die decomposers – mainly bacteria and fungi - break down the proteins into amino acids. Those amino acids that are not used by the decomposers for growth are broken down into ammonia, which is also broken down from urea in urine. The process is ammonification. Ammonia is converted to nitrite ions during an oxidation process by bacteria e.g. Nitrosomonas and then by oxidation into nitrate ions by bacteria e.g. Nitrobacter. This process is nitrification and needs well aerated soils. Denitrifying bacteria gain energy by converting nitrates into nitrogen gas that goes into the air. This happens in places such as waterlogged soils where there is little or no oxygen.