Chapter 2: Nutrition in Animals

 Chapter 2: Nutrition in Animals

1. Nutrition in Animals

Animals obtain food from plants directly or indirectly. Animal nutrition involves:

1. Nutrient requirement

2. Mode of intake of food

3. Utilisation of food in the body

The main steps of nutrition are:

Ingestion → Digestion → Absorption → Assimilation → Egestion.

2. Modes of Taking Food

Different animals take food in different ways:

- Humming-bird/bee: sucking nectar

- Python: swallowing prey

- Butterfly: siphoning

- Housefly: sponging

- Lice: sucking

- Some animals capture and swallow their food.

3. Human Digestive System

The alimentary canal consists of:

Buccal cavity → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus.

Important digestive glands:

- Salivary glands

- Liver

- Pancreas

4. Digestion in the Mouth

- Food enters the body through the mouth. This is called ingestion.

- Teeth cut, tear and grind food.

- The tongue mixes food with saliva and helps in swallowing.

- Saliva breaks down starch into sugars.

5. Types of Teeth

- Incisors: cutting and biting

- Canines: piercing and tearing

- Premolars and molars: chewing and grinding

Humans have two sets of teeth:

- Milk teeth

- Permanent teeth

6. Oesophagus:- The oesophagus or food pipe carries food from the mouth to the stomach.

Food is pushed down by rhythmic movements of the walls of the alimentary canal.

7. Stomach:- The stomach is a thick-walled, J-shaped organ.

It secretes:

- Mucus – protects the stomach lining

- Hydrochloric acid – makes the medium acidic and kills many bacteria

- Digestive juices – help digest proteins.

8. Small Intestine:- The small intestine is highly coiled and about 7.5 m long.

Here:

- Carbohydrates → simple sugars such as glucose

- Fats → fatty acids and glycerol

- Proteins → amino acids

The villi are finger-like projections in the small intestine. They increase the surface area for absorption of digested food.

9. Role of Liver and Pancreas

- Liver: produces bile; bile helps in digestion of fats.

- Pancreas: produces pancreatic juice which acts on carbohydrates, fats and proteins.

10. Absorption and Assimilation

Absorption: Digested food passes into the blood through the walls of the small intestine.

Assimilation: Absorbed nutrients are transported to body cells and used for growth, repair and energy.

11. Large Intestine:- The large intestine absorbs water and some salts from undigested food.

The remaining waste forms faeces and is stored in the rectum.

12. Egestion:- Removal of undigested food from the body through the anus is called egestion.

13. Digestion in Grass-Eating Animals:- Cows, buffaloes and deer are ruminants.

They:

1. Quickly swallow grass.

2. Store it in the rumen.

3. Partly digest it.

4. Bring it back to the mouth as cud.

5. Chew it again.

This process is called rumination.:- Ruminants can digest cellulose because bacteria in their rumen help digest it.

14. Feeding and Digestion in Amoeba:- Amoeba is a single-celled organism.

- It uses pseudopodia (false feet) to capture food.

- Food is enclosed in a food vacuole.

- Digestive juices break food into simpler substances.

- Digested food is absorbed.

- Undigested food is expelled outside.

15. Flowchart of Human Digestion

Food → Mouth (ingestion and chewing) → Oesophagus (movement by peristalsis) → Stomach (acid and protein digestion) → Small intestine (complete digestion and absorption by villi) → Large intestine (water absorption) → Rectum (storage of faeces) → Anus (egestion)

16. Comparison of Nutrition in Humans, Ruminants and Amoeba

Feature| Humans| Ruminants| Amoeba

Type of organism| Multicellular| Multicellular mammals| Single-celled

Mode of taking food| Through the mouth| Through the mouth; grass is swallowed quickly| Pseudopodia surround and engulf food

Main food| Mixed diet| Grass and other plant material| Small organisms and food particles

Site of digestion| Alimentary canal| Specialised stomach compartments and intestine| Food vacuole

Special adaptation| Teeth, digestive glands and villi| Rumen microbes digest cellulose; cud is chewed| Pseudopodia and food vacuole

Absorption| Mainly through villi in the small intestine| Mainly through the intestine| Directly from the food vacuole into the cell

Removal of waste| Through the anus| Through the anus| Undigested matter is expelled from the cell

NCERT Exercise – Questions with Answers

1. Fill in the blanks

(a) The main steps of nutrition in humans are ingestion, digestion, absorption, assimilation and egestion.

(b) The largest gland in the human body is liver.

(c) The stomach releases hydrochloric acid and digestive juices which act on food.

(d) The inner wall of the small intestine has many finger-like outgrowths called villi.

(e) Amoeba digests its food in the food vacuole.

2. Write True or False

(a) Digestion of starch starts in the stomach. — False

(b) The tongue helps in mixing food with saliva. — True

(c) The gall bladder temporarily stores bile. — True

(d) Ruminants bring back swallowed grass into their mouth and chew it for some time. — True

3. Choose the correct answer

(a) Fat is completely digested in the:

Answer: (iii) Small intestine

(b) Water from undigested food is absorbed mainly in the:

Answer: (iv) Large intestine

4. Match the following

Food Component| Product of Digestion

Carbohydrates| Sugar

Proteins| Amino acids

Fats| Fatty acids and glycerol

5. What are villi? What is their location and function?

Answer: Villi are tiny finger-like projections present on the inner wall of the small intestine. They increase the surface area for absorption of digested food. Their thin walls contain a network of blood vessels through which digested nutrients are absorbed into the blood.

6. Where is bile produced? Which component of food does it help to digest?

Answer: Bile is produced by the liver and stored in the gall bladder. It helps in the digestion of fats.

7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason.

Answer: The carbohydrate is cellulose.

Ruminants can digest cellulose because bacteria present in their rumen help digest it. Humans do not have these bacteria and therefore cannot digest cellulose.

8. Why do we get instant energy from glucose?

Answer: Glucose is a simple form of carbohydrate. It can be directly used by body cells for releasing energy, so it provides energy quickly.

9. Which part of the digestive canal is involved in:

(i) Absorption of food: Small intestine

(ii) Chewing of food: Buccal cavity

(iii) Killing of bacteria: Stomach

(iv) Complete digestion of food: Small intestine

(v) Formation of faeces: Large intestine

10. Write one similarity and one difference between nutrition in Amoeba and human beings.

Similarity: Both Amoeba and humans take in food, digest it, absorb useful substances and remove undigested waste.

Difference: Humans have a well-developed digestive system, whereas Amoeba digests food inside a food vacuole.

11. Match the following

Column I| Answer

(a) Salivary gland| (iii) Saliva secretion

(b) Stomach| (iv) Acid release

(c) Liver| (i) Bile juice secretion

(d) Rectum| (ii) Storage of undigested food

(e) Small intestine| (v) Digestion is completed

(f) Large intestine| (vi) Absorption of water

Note: The exercise also lists (vii) Release of faeces, which is associated with the anus, not the rectum.

12. Label the digestive system

The main parts to label are:

1. Buccal cavity

2. Oesophagus

3. Stomach

4. Liver

5. Gall bladder

6. Pancreas

7. Small intestine

8. Large intestine

9. Rectum

10. Anus

13. Can we survive only on raw, leafy vegetables/grass? Discuss.

Answer: No, humans cannot survive only on raw leafy vegetables or grass. Grass and many leafy materials contain a large amount of cellulose, which humans cannot digest. A balanced diet containing different nutrients is necessary for proper growth, repair and functioning of the body.