The World of the Living (VI–VIII) • Topic 2 of 5

Animals: Nutrition & Body Systems

Animals cannot make their own food, so they are heterotrophs — they depend on plants or other animals. CTET tests two strands here: modes of nutrition and the human body systems from the Class VII NCERT. Nutrition involves five steps — ingestion (taking in food), digestion (breaking it down), absorption, assimilation and egestion (removing undigested waste). In the human digestive system, food travels through the alimentary canal: mouth (teeth and saliva; saliva's enzyme begins breaking down starch) -> food pipe/oesophagus -> stomach (churns food, gastric juice) -> small intestine (most digestion and absorption; bile from the liver and juices from the pancreas act here) -> large intestine (absorbs water) -> rectum/anus. The respiratory system brings in oxygen and removes carbon dioxide; in humans the lungs are the main organ, and breathing in is inhalation. The circulatory system — heart, blood and blood vessels — transports oxygen, food and wastes; the heart pumps blood, arteries carry blood away from the heart and veins carry it back. Know that fish breathe through gills, and that ruminants like cows have a special stomach and chew the cud. The classic misconception: children think the stomach is where 'all' digestion finishes — in fact most digestion and nearly all absorption happen in the small intestine. How it is tested: a labelled-diagram blank, a 'which organ does X' match, or the mode-of-nutrition term (autotroph vs heterotroph; parasite vs saprophyte).

✅ Solved examples

1. In the human digestive system, where does most of the digestion and absorption of food take place?
In the small intestine. Although the stomach churns food and begins protein digestion, the small intestine completes digestion (with bile and pancreatic juice) and absorbs the digested nutrients.
2. Animals that cannot make their own food and depend on plants or other animals are called:
Heterotrophs. (Plants, which make their own food, are autotrophs.) This is a high-frequency term match.
3. Through which organ do fish take in oxygen dissolved in water?
Through their gills. The gills extract dissolved oxygen from water, just as lungs extract oxygen from air in humans.
4. A teacher asks which blood vessels carry blood AWAY from the heart. What is the correct term?
Arteries carry blood away from the heart; veins carry blood back to the heart. (Memory hook: Arteries = Away.)

✏️ Practice — try these, take hints as needed

1. Name the process by which undigested food is removed from the body.
The last step of nutrition.
Not the same as digestion.
Egestion
2. Which digestive juice, produced by the liver, helps in the digestion of fats in the small intestine?
Greenish-yellow fluid.
Stored in the gall bladder.
Bile
3. Cows and buffaloes quickly swallow grass and later bring it back to chew. What are such animals called?
They chew the cud.
Special four-chambered stomach.
Ruminants
4. Which is the main organ of the human respiratory system where exchange of gases takes place?
A pair of spongy organs in the chest.
You inhale into them.
Lungs

📝 Topic test — 8 questions

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