NCERT Solutions for Class 7 Science Chapter 2 – Nutrition in Animals

Digestion in Humans (Nutrition in Animals)

Human beings consume their food with the help of the mouth. The food particles are then digested and utilized for various bodily functions. The ingested food that remains undigested gets defecated. What exactly happens after the food is chewed and swallowed? 

The food enters the stomach through a continuous canal that starts at the buccal cavity and ends at the anus. This canal is divided into several parts which include:

• The buccal cavity
• Food pipe or Esophagus
• Stomach
• Small intestine
• Large intestine ending in the rectum
• The anus

These parts together make the alimentary canal or the digestive tract. When the food travels through the different compartments of the canal, it gradually gets digested and reaches our system. The digestion process is done through the secretion of digestive juices from the inner walls of the stomach, small intestine and other glands that are associated with the digestion process including salivary glands, pancreas and the liver. The digestive juice makes the digestion process easier by breaking the food particles into simpler forms. Now, let’s find out what happens to the food in the various parts of the digestive tract.

NCERT Solutions for Class 7 Science Chapter 1 – Nutrition in Plants

The Mouth and Buccal Cavity

Whatever food we eat, is taken into the body through our mouth. This process of taking the food into the body is known to be ingestion. The teeth in our mouth help in chewing and further break down mechanically to form tiny particles. Each root of a tooth has a separate socket that goes right into the gums. Even teeth are categorized based on their functionalities and appearance. These functionalities are:

• Cutting and biting
• Piercing and tearing
• Chewing and grinding

Milk Teeth and Permanent Teeth

The first set of teeth that grow during infancy are known as milk teeth. They fall off between the ages of six to eight years. Each tooth comes off from the root randomly to replace it with a permanent tooth. These sets of teeth may last the entire life or fall off when an adult becomes old enough. Permanent teeth may also come off due to dental diseases.

Sweets and Tooth Decay (Nutrition in Animals)

Usually, bacteria can be found in our mouths, but they are not always harmful. However, if we do not take care of our teeth and gums, these bacteria can start creating ill effects. They tend to find a good place and grow between the gaps and crevices of your teeth.

Therefore, it is crucial to thoroughly clean and floss your mouth after every meal. The bacteria harm our teeth by releasing acids, which are used for breaking down sugar from the leftover food particles inside the mouth. This process is called tooth decay. If it’s overlooked, over time, tooth decay can cause severe toothache or loss of the tooth.

Chocolates, candies, soft drinks and other sugar products are the sources of causing tooth decay. Therefore, it is pivotal to clean your teeth with a brush and also use a tongue scraper to clean accumulated bacteria from the pores of the tongue. Using dental floss is also a good consideration for extracting trapped food particles between two teeth. Make sure not to put unwashed or dirty fingers inside your mouth.

The Food Pipe/Esophagus

After the food is swallowed, it passes through a food pipe or oesophagus. The food pipe starts from the neck to the ends of the chest. Basically, it connects our stomach with the neck. In the food pipe, through the movement in the wall, food is pushed down to the stomach. Actually, this movement is very common in the entire alimentary canal as the system continuously tends to push the food downwards. Sometimes, based on specific situations and types of food, our stomach does not accept the ingested food particles and this causes vomiting.

The Stomach

The stomach is known to be a large compartment in the alimentary canal. It is a thick-walled bag that looks like a flattened U. This part is the broadest in the entire canal. Our stomach receives food from one end (food pipe) and releases it to the other. The other opening leads the food particles to the small intestine. There is the inner lining of the wall inside the stomach secretes mucus, hydrochloric acid and digestive juices to extract the contents from the food, for example, protein, carbohydrates, minerals, water, and others. The internal lining of the stomach is protected by the mucus, and the acid released is responsible for killing different types of bacteria which enter along with the food. The digestive juice naturally digests the core contents of the food. It further helps to break proteins into simpler versions of substances.

Small Intestine

The small intestine is known to be a tube that is extremely coiled and measures around 7.5 meters long. The secretion from the liver and pancreas reaches into the small intestine. Also, the inner wall of the intestine secretes juice to digest the remaining part of the food. The liver secretes bile, which is stored in a large sac known as the gallbladder. Bile is an important part of digestion, especially when it comes to fats. The half-digested food then reaches to the lower part of the intestine to complete the last stage of digestion.

Absorption in the Small Intestine

All digested food passes through the wall of the intestine to enter our blood vessels. This is known as absorption. The inner wall of the intestine is filled with finger-like outgrowths called villi. They are responsible for increasing the surface area to absorb the digested food.

Large Intestine

The large instance is a bit wider and shorter when compared with the small intestine. It measures about 1.5 meters long. It is responsible for absorbing water and salts from the undigested food particles. The undigested food, in the form of waste, passes to the rectum. They are stored like semi-solid faeces. Fecal matter is then removed from the body through the anus. The procedure is called egestion.

Diarrhea

Sometimes when our digestive system fails, it leads to diarrhea. This may trigger an infection, indigestion or food poisoning. This is a very common case in children, and under severe conditions, it may turn out to be fatal. The excessive loss of salt and water from the body can be harmful to us.

Key Points at a Glance (Nutrition in Animals)

Let us look into some of the important takeaways of the chapter.

• Animal nutrition encompasses nutrient requirements, food consumption methods, and food usage in the body.
• The gastrointestinal tract and secretory glands make up the human digestive system.
• The salivary glands, the liver, and the pancreas are the parts of the glandular system that secrete digestive juices.
• Digestive enzymes are also produced by the stomach and intestinal tract walls.
• Carbohydrate digestion, such as starch digestion, begins in the buccal cavity.
• Protein digestion begins in the stomach.
• In the small intestine, bile, pancreatic juice and digestive juice accomplish the digestion of all ingested elements.
• The small intestine absorbs the digested food through the blood vessels.
• The large intestine absorbs water and salts from the undigested material.
• Through the anus, the unabsorbed leftovers are ejected from the body as faeces.
• Ruminants are grazing animals such as cows, buffaloes, and deer.
• They quickly ingest and retain their green diet in the rumen. The meal eventually returns to the animal’s mouth, where it is chewed.
• The meal is ingested by the amoeba using its false feet, or pseudopodia. The food vacuole is where the meal is processed.

Solutions for Class 7 Science Chapter 2 – Nutrition in Animals

1. Fill in the blanks: (Nutrition in Animals)

(a) The main steps of nutrition in humans are _________, __________, __________, _________ and __________.

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

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

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

(e) Amoeba digests its food in the ____________.

Solution:

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

(b) The largest gland in the human body is the 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. Mark ‘T’ if the statement is true and ‘F’ if it is false: (Nutrition in Animals)

(a) Digestion of starch starts in the stomach. (T/F)

(b) The tongue helps in mixing food with saliva. (T/F)

(c) The gall bladder temporarily stores bile. (T/F)

(d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (T/F)

Solution:

a) F

b) T

c) T

d) T

3. Tick (✓) mark the correct answer in each of the following: (Nutrition in Animals)

(a) Fat is completely digested in the

(i) stomach (ii) mouth (iii) small intestine (iv) large intestine

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

(i) stomach (ii) food pipe (iii) small intestine (iv) large intestine

Solution:

a) (iii) small intestine

b) (iv) large intestine

4. Match the items of Column I with those given in Column II: (Nutrition in Animals)

Solution:

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

Solution:

Villi are finger-like projections or outgrowth. They are present in the small intestine of our digestive system. The villi increase the surface area for absorption of the digested food.

UNDERSTANDING THE COMPLEX FACTORS BEHIND CLIMATE CHANGE

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

Solution:

Bile juice is produced in the liver, and it helps in the digestion of fats by breaking large fat globules into smaller ones.

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

Solution:

Cellulose is a carbohydrate that can be digested by ruminants but not by humans because humans lack the cellulase enzyme required to digest the cellulose.

8. Why do we get instant energy from glucose?

Solution:

Glucose is a simple sugar which is easily absorbed into the blood whereas other carbohydrates are first broken down into glucose and then absorbed; hence, glucose gives instant energy.

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

(i) absorption of food ________________.

(ii) chewing of food ________________.

(iii) killing of bacteria ________________.

(iv) complete digestion of food ________________.

(v) formation of faeces ________________.

Solution:

i) Small intestine

ii) Buccal cavity

iii)Stomach

iv) Small intestine

v) Large Intestine

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

Solution:

Similarity: Both amoeba and human beings follow the holozoic type of nutrition.

Difference:

Humans intake food through the buccal cavity. In amoeba, food is ingested through pseudopodia.

11. Match the items of Column I with suitable items in Column II

Solution:

12. Label Fig. 2.11 of the digestive system.

Solution:

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

Solution:

No, we cannot survive only on raw, leafy vegetables because they mainly consist of Cellulose which cannot be digested by us due to lack of cellulose-digesting enzyme in our body.