Trophic Levels and Food Chains

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Each stage of the food chain is also known as a trophic level. The trophic level describes a position in the food chain. There are usually four links in the chain. In order for the first link to develop, the non-living environment has to receive both energy from the sun and other factors (water, CO2, etc) needed for photosynthesis. Insolation comes in two forms – heat and light energy. The heat from the sun cannot be used directly by plants and animals, but it does warm their surroundings and speed up chemical reactions. The sun’s light energy is far more important. It is captured by the green pigment in plant leaves (chlorophyll) which converts carbon dioxide and water into their organic compounds. These so-called ‘building blocks’ of plants are tissue and food energy in the form of chemicals called carbohydrates. Carbohydrates contain amino acids, sugars, starches, proteins, fats and vitamins – all the organic materials needed by animals for growth, movement and reproduction. Plants therefore, form the basis of all nutrition and energy for the whole ecosystem. This is because they provide food for other organisms, which in turn feed others in what we call the food chain. The first trophic level is made up of producers (autotrophs), these are ‘self feeders’ and include green plants capable of producing their own food by photosynthesis. All other levels are made up of consumers (hetrotrophs) these are ‘other-feeders’ and include animals that their energy from either eating green plants directly or by eating animals that have previously eaten green plants. The second trophic level is where herbivores, the primary consumers, eat the producers. The third trophic level is where smaller carnivores act as secondary consumers feeding upon the herbivores. The fourth trophic level is occupied by the large carnivores, the tertiary consumers. Also known as omnivores (or

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