Class 7 Science
Plants make their food by the process of photosynthesis, but animals cannot make their food themselves. Animals get their food from plants. Some animals eat plants directly while some animals eat plant eating animals. Thus, animals get their food from plants either directly or indirectly.
All organisms require food for energy and growth. Requirement of nutrients, mode of intake of food and its utilization in body are collectively known as nutrition.
Nutrition in complex animals involves following steps:
Ingestion: The intake of food is called ingestion. Method of ingestion, i.e. taking of food, varies from one animal to another. Crocodiles swallow large chunks of food, because crocodiles cannot chew food. Similarly, birds swallow their food in big chunks because they cannot chew. Humans, on the other hand, chew the food to break it into smaller pieces before swallowing it. Lizards use their sticky tongue to catch prey.
Digestion: The process of breaking down of complex component of food into simpler substances is called digestion. The process of digestion is different in human, grass eating animals, amoeba, etc. Various enzymes help in converting complex food into simple substances.
Absorption: The process of passing of digested food into blood vessels in the intestine is called the absorption. It is only after absorption that the food goes to different parts of the body for suitable utilisation.
Assimilation: The conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation. In other words, assimilation is the conversion of absorbed food (nutrients) into useful substances for living tissues. Some of these substances are utilised for growth and repair. Carbohydrate is utilised for producing energy.
Egestion: Removal of waste materials from the body is called egestion. The faecal matter is removed through the anus from time-to-time. Since the waste of food left after digestion is also called faeces, hence the process of egestion is also known as defecation. If we do not clear garbage from our home then it will result in filth all around and will eventually cause diseases. Similarly, if faecal material is not removed from the body, it will make us sick.
Different organism takes food in different ways.
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