NIOS Class 12 Biology Nutrition And Digestion Terminal Solutions

NIOS Class 12 Biology Chapter 13 Nutrition and Digestion explains how living organisms obtain and process nutrients. The chapter covers types of nutrition, the human digestive system, enzymes, and the absorption of food.

With solved terminal exercises, learners get clear and structured answers for revision. This chapter is vital for understanding how energy is derived from food and supports exam preparation for NIOS Class 12 Biology, helping students strengthen their knowledge effectively.

NIOS Biology Chapter 13 Nutrition And Digestion

1. Explain the term “autotrophs”. How are animals different from plants in their mode of nutrition?

Autotrophs are green plants and certain bacteria manufacture their own food (organic substances) from inorganic substances (CO₂ and H₂O) using energy from sunlight. Animals have a holozoic mode of nutrition where they engulf food into their body and digest it to absorb the soluble nutrients. 

2. Enlist at least ten organs of the alimentary canal of man.

Mouth, oesophagus, stomach, pancreas, liver, gall bladder, small intestine, large intestine, rectum, anus. 

3. Define the term “digestion”. List the digestive processes occurring in the small intestine.

Digestion is the breaking down of complex constituents of food by enzymes into simpler soluble forms that can be absorbed and utilised by the cells of the body.

• Chymotrypsin – acts on milk protein casein to produce paracasein (curd), and also converts other proteins into peptides.
• Lipase – also called steapsin- acts on emulsified fats to produce fatty acids and glycerol.
• Carboxypeptidases – act on peptides to produce small peptides and amino acids.

4. How does the digestion of carbohydrates and proteins take place in humans?

Amylase enzyme in the saliva acts on carbohydrates to convert them into partially hydrolysed starch. Further digestion of carbohydrates happens in the small intestine, where pancreatic amylase completes the conversion of starch into maltose. 

• Digestion of proteins in humans starts in the stomach, where the enzyme pepsin in the gastric juice acts on proteins to break them into peptides and peptones.
• Later, in the small intestine, trypsinogen, chymotrypsin, and carboxypeptidases act on them to convert the partially digested proteoses and peptones into small peptides.
• In addition, peptidases in the intestinal juice break these peptides and dipeptides into smaller peptides and amino acids.

5. Explain the role of the following in the digestive process in humans:

(a) Gastrin (b) Hydrochloric acid (c) Secretin

• Gastrin: Stimulates the secretion of gastric juice. The mechanical stimulation of the stomach wall produces this gastrin hormone.
• Hydrochloric acid: HCl in the gastric juice turns the inactive pepsinogen into active pepsin to digest proteins. It also kills microbes in the food, loosens the fibrous food material, maintains an acidic medium for pepsin, and curdles milk to be acted upon later.
• Secretin: Secretin stimulates the flow of pancreatic juice, which is rich in bicarbonates (to neutralize acid).

6. Write short notes on

(a) absorption of the digested food

(b) assimilation

(c) defaecation

(d) role of liver in metabolism.

1. Absorption of the digested food

• Minute quantities of water, water-soluble vitamins, and simple sugars like glucose
• (as in honey) are absorbed in the mouth.
• Water, glucose, ethanol (alcohol), certain minerals, vitamins, and certain drugs may be absorbed into the cells lining the stomach through osmosis, diffusion, and active transport.
• Most absorption of digested food occurs in the small intestine.
• Products absorbed into the blood capillaries of the villi are amino acids and monosaccharides (glucose, fructose, galactose).
• Products absorbed into the lacteals (lymph vessels) of the villi are fatty acids and glycerol.
• Nutrients absorbed into the blood are carried by veins into the liver, and the nutrients absorbed by the lacteals (small lymph vessels) enter the lymphatic system.

2. Assimilation

The final conversion of the absorbed nutrients into the living substance, i.e., their utilization by the cells, is called assimilation.

After absorption from the food canal, the digested food is assimilated by the body in the following ways.

• (i) Fatty acids and glycerol are again converted into fats, which may be used or stored in adipose tissue.
• (ii) Simple sugars (monosaccharides), which are in excess, are converted into complex polysaccharides like glycogen in the liver.
• (iii) Amino acids are utilized in the synthesis of proteins for building up the body tissues and enzymes.
• (iv) Excess amino acids are deaminated (removal of nitrogenous part) to produce a simple sugar. (Amino acids cannot be stored.)

3. Defaecation

The undigested part (plant fibers) and the unabsorbed digested substances pass into the rectum. Such food remnants are temporarily stored in the rectum. More water is absorbed, and the remnants become semisolid to form faeces.

A special reflex called defaecation reflex causes emptying of the rectum, and the faeces are passed out via the anus by the relaxation of the sphincter muscle (A ring-shaped muscle that contracts and relaxes to close and open the anus or anal opening.

4. Role of the liver in metabolism

• (i) Regulation of blood sugar level by retaining excess glucose received as a product of carbohydrate digestion from the intestines, and storing it as insoluble glycogen to release it again as soluble glucose when the blood sugar level falls.
• (ii) Breakdown of excess amino acids. Amino acids are the end products of protein digestion. The liver breaks down excess amino acids into urea and sugar. Urea is excreted in urine, and sugar is stored for use.
• (iii) Synthesizes fatty acids from carbohydrates, which can be used or stored as fat.

7. Name the enzymes concerned with the digestion of various carbohydrates, the region of the gut where they act, and their products in the table given below:

Carbohydrate Enzyme Region of gut Product

1. Starch …………. …………. ………….

2. Dextrin …………. …………. ………….

3. Maltose …………. …………. ………….

4. Sucrose …………. …………. ………….

5. Lactose …………. …………. ………….

Carbohydrate	Enzyme	Region of Gut	Product
Starch	Amylase	Mouth	Maltose or dextrins
Dextrin	Pancreatic amylase	Small intestine	Glucose
Maltose	Maltase	Small Intestine	Glucose and glucose
Sucrose	Sucrase	Small Intestine	Glucose and fructose
Lactose	Lactase	Small Intestine	Glucose and galactose

8. Bile has no digestive enzymes, yet it plays a key role in digestion. What is its role?

Bile contains water, sodium carbonate, and bile salts. 

Sodium carbonate neutralizes the acid of the chyme or semi-digested food received from the stomach. It makes the food alkaline.

Bile salts are composed of sodium glycocholate and sodium taurocholate, which help emulsify fats. Emulsification is the breaking up of large lipid (fat) droplets into small droplets, which provides greater surface for enzyme action.

9. Draw a well-labelled diagram of the alimentary canal in humans.

10. List common digestive disorders. Add a note on ORS.

• Vomiting
• Diarrhoea
• Constipation
• Indigestion
• Jaundice

ORS- Oral Rehydration Solution is a special solution given to a person who is vomiting excessively. The ORS special powder contains sugar and salt in a specific amount. The powder is mixed with water as per instructions.

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