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Introduction |
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All organisms require energy in order to stay alive. Energy is utilised to do the various bodily functions such as breathing, ingesting and digesting food, excreting, reproducing, locomotion, etc. |
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Nutrients |
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Food contains various organic and inorganic substances. Those which are required by the organisms to carry out life functions are called nutrients. |
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Modes of Nutrition |
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The mechanism by which organisms obtain food are referred to as modes of nutrition. The organisms either synthesize their own food or obtain food prepared by other organisms in various ways. |
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Types of Heterotrophic Nutrition - Holozoic Nutrition |
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This type of nutrition involves the taking in of solid particles of food which have to be further broken down into simpler particles inside the organism. |
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Types of Heterotrophic Nutrition - Saprophytic |
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The food is digested outside the cells or even the body of the organism - extracellular digestion. The organism secretes digestive juices that contain enzymes directly on to the food. |
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Types of Heterotrophic Nutrition - Parasitic |
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The benefiting partner is called the parasite and the other partner is called the host. The parasite is dependent on the host for food or shelter or both. |
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Nutrition in Plants |
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The green plants, also called the producers, trap the solar energy and convert it into chemical energy of the food. |
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Photosynthesis |
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'Photo' refers to light and 'synthesis' means preparation. Thus, photosynthesis is the process by which the green plants use light energy of the sun to synthesize carbohydrates. |
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Photosynthesis - Reactants |
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During photosynthesis, carbon dioxide is converted into carbohydrates and this is called fixing of carbon dioxide. Many processes like respiration, combustion, volcanic activity, etc. release carbon dioxide into the atmosphere. |
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Photosynthetic Apparatus |
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The photosynthetic pigments chlorophylls are present in the leaves because of which the leaves are green in colour and are called the photosynthetic organs. |
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Factors Affecting Photosynthesis |
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Low light intensity lowers the rate of photosynthesis. As the intensity is increased the rate also increases. |
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Photosynthesis - Some Activities |
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The occurrence of starch in the leaves proves that photosynthesis has taken place. Starch can be tested with the help of iodine solution. |
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Nutrition in Animals |
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All animals are heterotrophic (there are exceptions like Euglena, which has chlorophyll). |
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Nutrition in Amoeba |
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Nutrition in amoeba is holozoic. Thus, solid food particles are ingested which are then acted upon by enzymes and digested. It is an omnivore, feeding on both plants and animals. |
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Nutrition in Paramoecium |
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Only micro food particles reach cytopharynx through cytostome with water current. When cytopharynx is full with food particles it forms a food vacuole which pinches off from cytopharynx and is ingested. |
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Human Digestive System - The Mouth Cavity |
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Man is omnivorous - feeding on different kinds of food. Thus, the structure of the digestive system should be adapted to this diet. |
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Human Digestive System - The Alimentary Canal |
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It has an inner circular and the outer longitudinal muscles. Both these layers facilitate the movement of food along the alimentary canal. |
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Gastric Glands and Their Secretions |
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Salivary glands are in the mouth and their secretion is called saliva. Saliva is a slightly alkaline secretion which is 99% water. |
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Other Digestive Juices |
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It is secreted by the secretory glands of the stomach wall. It is highly acidic as it contains hydrochloric acid (HCl). It also contains enzymes like pepsin and renin. Both act on proteins. |
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Mechanism of Digestion |
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Once the food is ingested into the mouth the action of the upper and the lower jaw crushes and grinds the food. |
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Summary |
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Organisms that synthesise, food with the help of the light energy of the sun, carbon dioxide and water by a process called photosynthesis are called photoautotrophic organisms. |
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Question and Answers |
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Multiple Choice Questions |
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