Quick Revision Notes: Class 7 Science

Chapter 2: Nutrition in Animals

### 1. Introduction & Basic Terms

• Nutrition (पोषण): The process of taking in food and its utilization by the body for growth, energy, and repair.
• Ingestion (अंतर्ग्रहण): The process of taking food into the body.
• Digestion (पाचन): The breakdown of complex food components into simpler, soluble substances.
• Absorption (अवशोषण): The process by which digested food passes through the blood vessels in the intestinal wall.
• Assimilation (स्वांगीकरण): The process of utilizing absorbed food for energy, growth, and repair.
• Egestion (मलत्याग): The removal of undigested faecal matter from the body through the anus.

### 2. Digestion in Humans

The human digestive system consists of the alimentary canal (आहार नाल) and associated glands.

A. The Alimentary Canal (6 Main Parts):

1. Buccal Cavity (মুখ गुहा / Mouth): Contains teeth, tongue, and salivary glands.
   • Saliva (लार): Secreted by salivary glands. It contains an enzyme that breaks down starch into sugars.
   • Teeth Types: Incisors (cutting), Canines (piercing/tearing), Premolars & Molars (chewing/grinding).
2. Food Pipe / Oesophagus (ग्रसिका): Pushes the food down by wave-like movements called peristalsis (क्रमाकुंचन).
3. Stomach (आमाशय): A thick-walled bag. Its inner lining secretes:
   • Mucus: Protects the stomach lining.
   • Hydrochloric Acid (HCl): Kills bacteria and makes the medium acidic.
   • Digestive Juices: Break down proteins into simpler substances.
4. Small Intestine (छوٹی आंत):
   • Highly coiled, about 7.5 meters long.
   • The site of complete digestion of all food components (carbohydrates, fats, proteins).
   • Receives secretions from the Liver (bile juice for fats) and Pancreas (pancreatic juice for carbs and proteins).
   • Villi (रसांकुर): Finger-like projections on the inner walls that increase the surface area for absorption.
5. Large Intestine (बड़ी आंत):
   • Wider and shorter (about 1.5 meters).
   • Absorbs water and some salts from the undigested food material.
6. Anus (गुदा): Passes out the remaining waste as semi-solid faeces.

B. Digestive Glands (पाचन ग्रन्थियाँ):

• Salivary Glands: Produce saliva.
• Liver (यकृत): Largest gland in the body; secretes bile juice stored in the gall bladder. Helps in fat digestion.
• C. Pancreas (अग्न्याशय): Cream-colored gland just below the stomach; secretes pancreatic juice.

### 3. Digestion in Grass-Eating Animals (Ruminants)

• Ruminants (रोमंथ करने वाले पशु): Herbivores like cows, buffaloes, and deer that quickly swallow grass and store it in a rumen.
• Rumen: Part of the stomach where food gets partially digested and is called cud (जुगाली).
• Rumination: The cud returns to the mouth in small lumps, and the animal chews it slowly.
• Cellulose Digestion: Grass is rich in cellulose (a type of carbohydrate). Ruminants have a sac-like structure called rumen between the oesophagus and the small intestine where cellulose-digesting bacteria are present.

### 4. Feeding and Digestion in Amoeba

• Amoeba: A microscopic, single-celled organism found in pond water.
• Structure: Has a cell membrane, cytoplasm, and a nucleus. Constantly changes its shape.
• Pseudopodia (पादप / False feet): Finger-like projections pushed out for movement and capturing food.
• Food Vacuole: Food is trapped here and digested by digestive juices.

### Key Quick Facts for Exam

• Milk teeth: The first set of teeth that grow during infancy and fall off at the age of 6–8 years (20 in number).
• Permanent teeth: Replaces milk teeth (total 32 in adults).
• Tooth decay: Caused by the presence of bacteria that break down sugar and release acids which damage teeth.
• Bile juice plays an important role in the digestion of fats.