NCERT Solutions for Class 7 Science Chapter 2 - Nutrition In Animals

Answer:

Iodine is used to test the presence of starch in a sample. The appearance of blue-black colour on the addition of iodine in a sample indicates the presence of starch in it. Among the given food items, potato and bread contain starch. So, boiled and mashed potato and a slice of bread will give a blue-black colour when tested with iodine.
Hence, the correct answer is option (b).

Answer:

Incisors are sharp, chisel-shaped front teeth used for cutting and biting. Canines are sharp, pointed teeth on either side of our incisors are used to tearing and piercing the food. Premolars are bigger teeth with a flat surface with ridges for chewing and grinding food into smaller pieces. Molars are bigger than premolars and have more ridges for chewing and grinding the food. So, premolars and molars have similar functions though they differ in their structure.
Hence, the correct answer is option (b).   

Answer:

Oesophagus pushes the swallowed food from the mouth towards the stomach. The large intestine absorbs water and some salts from the undigested food. Rectum temporarily stores the semi-solid faeces till egestion. So, no digestion occurs in oesophagus, large intestine and rectum.
Hence, the correct answer is option (a).

Answer:

The food pipe or oesophagus is a hollow, muscular tube that carries food from the mouth to the stomach. When the food is swallowed from mouth into the oesophagus, the coordinated contractions of muscles present in the wall of the food pipe in a wave-like manner propel the food downwards.
Hence, the correct answer is option (d). 

Answer:

The harmful germs may enter our body along with the food. The acid produced by the stomach kills the harmful bacteria and other germs that enter along with food to protect our body.
Hence, the correct answer is option (a).

Answer:

The inner wall of the small intestine has many finger-like outgrowths called villi. These villi have a network of blood capillaries close to their surface. The digested food is absorbed from the surface of the villi and transported via the blood vessels to different organs of the body. Hence, the correct answer is option (c).

Answer:

Villi are the finger-like projections present in the inner walls of the small intestine. They have thin walls and a network of thin and small blood vessels called capillaries close to their surface. They absorb the digested food from their surface into the blood flowing in the capillaries for transport to different parts of the body. Hence, the correct statements are (i), (ii) and (iv) and the correct answer is option (a).

Answer:

Amoeba is a microscopic animal that constantly changes its shapes. It puts out finger-like projections called pseudopodia or false feet that help the Amoeba in movement and capturing of food.
Hence, the correct answer is option (c).

Answer:

Salivary glands present in our mouth secrete watery fluid called saliva. The saliva contains an enzyme called salivary amylase. This enzyme breaks down the starch present in our food into simple sugars.
Hence, the correct answer is option (b).

Answer:

Grass-eating animals like cows and buffaloes quickly swallow the grass and store it in a part of the stomach called the rumen. In the rumen, the food gets partially digested and is called cud.
Hence, the correct answer is option (b).

Answer:

Ruminants like cows and buffaloes quickly swallow their food and store it in their rumen. In the rumen, this food is partially digested and is called cud. Later, this cud returns to mouth in small amounts for chewing. This chewing of the cud is called rumination. After the cud is chewed completely, it is swallowed for complete digestion.
Hence, the correct order of steps of process of nutrition in ruminants is $Swallowing\to Partial digestion\to Chewing of cud\to Complete digestion$ and this is represent in option (a).

Answer:

Cellulose is a type of carbohydrate but it is not digested by humans due to the absence of cellulose-digesting enzymes. So, cellulose acts as roughage or dietary fibre and adds bulk to the food and helps move stools more easily through our digestive tract for their removal.
Hence, the correct answer is option (a).

Answer:

The parts of the alimentary canal where
(i) water gets absorbed from undigested food - Large intestine
(ii) digested food gets absorbed - Small intestine
(iii) taste of the food is perceived - Tongue (mouth)
(iv) bile juice is produced - Liver

Answer:

(a) Tongue is attached to the roof of the mouth cavity at the back. - False
Correct statement - Tongue is attached to the floor of the mouth at the back.
(b) The large intestine is longer and wider than the small intestine of the human alimentary canal. - False
Correct statement - The large intestine is shorter and wider than the small intestine of the human alimentary canal.
(c) Mucus protects the stomach lining from damage. - True
(d) All heterotrophs have a similar basic process of nutrition. - True
 

Answer:

The odd one out in each group is:
(i) liver, salivary gland, starch, gall bladder - Starch
Reason: Liver, salivary gland and gallbladder are the glands associated with the digestive system whereas starch is a nutrient. So, starch is an odd one.
(ii) stomach, liver, pancreas, salivary gland - Stomach
Reason: Liver, pancreas and salivary glands are the digestive glands that release their secretion in the digestive tract and no digestion of the food occurs in these organs. The liver releases bile, the pancreas secretes pancreatic juice and the salivary gland secretes saliva. The stomach is the part of the alimentary canal where digestion of the food occurs. So, the stomach is an odd one.
(iii) tongue, absorption, taste, swallow - Absorption
Reason: The tongue is a muscular organ present at the floor of the mouth. It helps in mixing the food with saliva and swallowing of food. It has different taste buds that help us detect different tastes of the food. The tongue does not have any role in the absorption of food. So, absorption is an odd one.
(iv) oesophagus, small intestine, large intestine, rectum - Small intestine
Reason: Small intestine is the part of the digestive tract where the digestion of food occurs. Oesophagus carries food from the buccal cavity to the stomach, large intestine absorbs water and some salts from the undigested food and rectum stores faeces temporarily before its egestion. So, the small intestine is an odd one.

Answer:

Our eyes help us see things whereas our tongue helps us taste the food. The tongue has taste buds that help us detect different tastes such as sweet, sour, salty, bitter, etc. So, even if we are blindfolded, we can identify the tastes of food items when asked to do so.

Answer:

(a) The alimentary canal stretches from mouth to anus.
(b) Teeth are rooted in separate sockets in between the gums.
(c) Digestion of food starts in buccal cavity and gets completed in small intestine.
(d) Liver is the largest gland in the human body.

Answer:

The terms describing the given processes are as follows:
(a) Transportation of absorbed food to different parts of body and their utilisation.- Assimilation
(b) Breaking of complex food substances into simpler and soluble substances. - Digestion
(c) Removal of undigested and unabsorbed solid residues of food from the body. - Egestion
(d) Taking food into the body. - Ingestion
(e) Transport of digested and soluble food from the intestine to blood vessels. - Absorption

Answer:

Answer:

Rice is rich in starch which can be tested by the change in colour to blue-black on the addition of iodine colour on it. When Boojho added 1–2 drops of iodine solution in the test tube 'A' with boiled rice, he observed the change in colour to blue-black. But when Paheli added 1–2 drops of iodine in the test tube 'B' with boiled and chewed rice, she did not observe any change in colour. This is because when boiled rice was chewed, salivary amylase present in the saliva broke down starch present in the boiled rice into sugars.

Answer:

The gallbladder stores the bile secreted by the liver and releases it in the small intestine. The bile helps in the digestion of fats. Since the gallbladder of 'A' removed, she is facing a problem in the digestion of food items rich in fats. 

Answer:

Answer:

Ruminants are grass-eating animals e.g. cattle, sheep, goats, etc. During grazing, they quickly swallow of grass without much chewing and store it in the rumen, the first chamber of the stomach. In the rumen, food is partially digested and is called cud. This partially-digested food is then sent back to the mouth in small amounts to be chewed again. After completely chewed, the food is sent back to the stomach and ultimately to the intestine for complete digestion and absorption of food. This is the reason why ruminants sit restfully and chew their food.

Answer:

When food is swallowed, it passes from the buccal cavity to a funnel-shaped pharynx. The pharynx is the common passage for food and air. During swallowing, a flap-like structure called the epiglottis covers the opening of the windpipe to prevent the entry of food in it. After swallowing, epiglottis returns to its original position. When one eats the food while talking or hurriedly, epiglottis did not get time to close the opening of the windpipe as a result, food enters the airways and the person coughs to clear it. Thus, Boojho started coughing violently on eating food hurriedly. 

Answer:

(a) The digestion of all food components is completed by the intestinal juice.
(b) Large intestine absorbs water and some salts from the undigested food.
(c) Tongue is attached at the back to the floor of the mouth cavity and is free at the front.
(d) Amoeba pushes out pseudopodia around the food and traps it in a food vacuole.

Answer:

(i) The cutting and biting teeth ‘A’ - Incisors
(ii) The piercing and tearing teeth ‘B’ - Canine
(iii) The grinding and chewing teeth ‘C’ - Premolars
(iv) The grinding teeth present only in adult ‘D’ - Molars
















 

Answer:

(a) Liver secretes the bile juice.
(b) Fat is insoluble in water and present as large globules. These large fat globules are difficult to break down. Thus, the digestion of fats is difficult as compared to that of other nutrients.
(c) Bile juice breaks down the big droplets of fats into smaller droplets for their easy digestion by the enzymes secreted by pancreas.
(d) The digestion of fat is completed in the small intestine,
(e) No, bile juice does not digest fat completely.

Answer:

The names of the given parts are:
(a) The largest gland in our body - Liver
(b) The organ where protein digestion starts - Stomach
(c) The organ that releases digestive juice into the small intestine - Pancreas
(d) The organ where bile juice gets stored - Gallbladder

The parts labelled in Figure 2.2 are:

Answer:

The observations on comparing the different types of teeth in my mouth with the Figure 2.3 are tabulated as below.

Answer: