Nutrition is the essential organic nutrients that living organisms require for growth, maintenance, reproduction and repair. It is a process essential for the survival of the organism. Living organisms need energy to survive; this energy comes from nutrients or food. Ingestion, digestion, absorption and excretion are the stages of food processing. Heterotrophs are organisms that cannot synthesize their own food and therefore are completely dependent on organic substances for nourishment. Animals are heterotrophs and are divided into three categories: herbivores, carnivores and omnivores depending on how they obtain their food. Herbivores: Eat mainly plant material, seeds or fruits. (Gordon McL Dryden, 2008). Omnivores: Eat both plant and animal matter. Carnivores: eat meat (they can also eat insects and fish). Plants are autotrophic, they synthesize organic substances from inorganic molecules using solar energy. All animals, fungi, most protists and prokaryotes are heterotrophs (Raven et al. 2009), animals that cannot live on inorganic nutrients alone. They obtain the organic nutrients they need from the products of photosynthesis produced by autotrophs. An animal's ability to feed itself is closely linked to its reproductive success. According to (http://en.wikipedia.org/wiki/Nutrition (3/3/11, 12:44)), there are six main classes of nutrients needed by animals. These nutrients are either macronutrients (large amounts required) or micronutrients (small amounts required). Macronutrients include carbohydrates, fats, proteins and water. Micronutrients are mainly minerals and vitamins. Many nutrients and vitamins that animals need to survive cannot be synthesized and must be provided in the diet, these nuts...... middle of paper ......organic sources; Broomrapes are parasitic plants, they are not photosynthetic and obtain water and all necessary nutrients from the roots of their host plants. In conclusion, living organisms need many nutrients. These nutrients are necessary to ensure that energy is available for growth, maintenance, reproduction and repair. Some nutrients are needed in large amounts while others only in small amounts. All living organisms require different nutrients to survive, but if heterotrophs or autotrophs lack essential nutrients and cannot obtain them in their diet, they will show signs of deficiency and eventually die. Works Cited Animal Nutrition Science (Gordon McL Dryden, 2008) Biology (Raven et al. 2009)http://en.wikipedia.org/wiki/Nutrition (3/3/11, 12:44)New Higher Biology ( J Torrance, C Stevenson, J Fullarton, C Marsh, J Simms 2nd revised edition,2000)