Chapter 2:
Nutrition in Animals

Class 7 Science | CBSE Curriculum

This chapter explains how animals obtain and utilise food, focusing on the human digestive system, digestion in ruminants and amoeba, and key processes like ingestion, absorption, and egestion.

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Quick Revision: Nutrition in Animals

  • Nutrition: The process of taking food and utilising it for growth, repair, and functioning of the body.
  • Digestion: The breakdown of complex components of food into simpler substances.
  • Modes of Feeding: Different organisms have different ways of taking food e.g., scraping (snail), sucking (hummingbird), swallowing (python), filtering (aquatic animals).
  • Human Digestive System: Consists of the alimentary canal (buccal cavity, oesophagus, stomach, small intestine, large intestine, rectum, anus) and associated glands (salivary glands, liver, pancreas).
  • Teeth: Incisors (cutting/biting), Canines (piercing/tearing), Premolars and Molars (chewing/grinding). First set: milk teeth; second set: permanent teeth.
  • Role of Saliva: Secreted by salivary glands; breaks down starch into sugars.
  • Tongue: Helps in talking, mixing food with saliva, swallowing, and tasting food via taste buds.
  • Tooth Decay: Caused by bacteria breaking down sugars into acids that damage teeth. Prevent by cleaning teeth twice daily and rinsing after meals.
  • Peristalsis: The rhythmic movement of the wall of the alimentary canal that pushes food downwards.
  • Stomach: A thick-walled J-shaped bag. Its inner lining secretes mucous (protects lining), hydrochloric acid (kills bacteria, makes medium acidic), and digestive juices (break down proteins).
  • Small Intestine: Long, coiled tube (~7.5 m). Receives bile from liver (digests fats), pancreatic juice (digests carbs, fats, proteins), and intestinal juice (completes digestion).
  • Absorption: Digested food passes into blood vessels. Inner walls have finger-like outgrowths called villi that increase surface area for absorption.
  • Assimilation: Absorbed nutrients are transported to body cells and used to build complex substances or release energy.
  • Large Intestine: Absorbs water and salts from undigested food; remaining waste (faeces) is removed through the anus (egestion).
  • Ruminants: Grass-eating animals like cows. They quickly swallow grass, store it in the rumen (part of stomach), and later bring it back as cud to chew peacefully (rumination). Bacteria in rumen digest cellulose.
  • Amoeba: A single-celled organism that ingests food using pseudopodia (false feet). Food is digested in food vacuoles.
  • Diarrhoea: Frequent watery stool due to infection or indigestion. Causes loss of water and salts; treated with Oral Rehydration Solution (ORS).

Chapter Summary: Nutrition in Animals

Animals, unlike plants, cannot synthesise their own food and depend on plants or other animals for nutrition. The chapter explores how different animals ingest food, with a detailed focus on the human digestive system. The process of nutrition involves five main steps: ingestion, digestion, absorption, assimilation, and egestion. The human alimentary canal is a long, continuous tube starting from the mouth and ending at the anus, with various parts specialized for different functions. Digestion begins in the mouth where teeth chew food and saliva breaks down starch. The food then travels via the oesophagus to the stomach, where proteins are partially digested. The small intestine is the primary site for complete digestion (with help from the liver and pancreas) and absorption through villi. The large intestine absorbs water, and undigested waste is egested.

The chapter also covers unique adaptations in other animals. Ruminants like cows have a complex stomach with a rumen where bacteria help digest cellulose through a process called rumination. Even single-celled organisms like Amoeba have a method to ingest and digest food using pseudopodia and food vacuoles. The chapter concludes with important health aspects, such as the causes and prevention of tooth decay and the management of diarrhoea using ORS. Understanding these processes highlights the diversity and complexity of how animals obtain and utilise nutrients from their food.