Class 7 Science Chapter 2 Question Answers - Nutrition in Animals

Q1. Write about pseudopodia.
Ans: Pseudopodia are fascinating features found in certain single-celled organisms, such as Amoeba. The term 'pseudopodia' directly translates to 'false feet', and they certainly live up to their name. 

• These structures are not permanent, but rather, they are temporary projections that an amoeba can create for itself out of its own body whenever they are required. 
• The primary functions of these pseudopodia are to aid in the amoeba's movement and to assist in the capture and ingestion of its food. 
• These 'false feet' reach out and envelop the food particles, pulling them into the amoeba's body for digestion, which is an amazing adaptation for survival in its microscopic world.

Q2. Name some of the components of food.
Ans: Food, which is essential for our survival and well-being, is made up of various important components. 

• These include carbohydrates, which are the main source of energy for our bodies. Proteins are another vital component, which are essential for growth and repair of body tissues. 
• Minerals and vitamins are needed in smaller amounts but are crucial for various bodily functions. Fats, although often seen negatively, are also necessary as they provide energy and help absorb certain vitamins. 
• Water is another key component, making up about 60% of our body and playing a central role in many bodily functions. Lastly, roughage or dietary fibre is necessary for maintaining a healthy digestive system.

Q3. Write the names of various digestive organs of the body.
Ans:

• The process of digestion involves a number of organs, each playing a unique role in breaking down the food we eat into nutrients that our bodies can use. 
• The process begins in the buccal cavity or mouth, where the food is mechanically broken down by our teeth and chemically broken down by enzymes present in saliva. 
• The food then travels down the oesophagus, through the process of peristalsis, into the stomach where it is broken down further by stomach acid. 
• The partially digested food then enters the small intestine where final digestion and absorption of nutrients take place. 
• The indigestible remains then move into the large intestine, where water is absorbed, and the remaining waste forms faeces, which are stored in the rectum until they are expelled through the anus. 

Q4. Explain the mode of feeding of starfish.
Ans: The starfish, although a simple and slow-moving creature, has a rather unique and interesting method of feeding. 

• Typically, starfish prey upon animals that are protected by hard shells of calcium carbonate, such as clams or oysters. 
• The starfish uses its strong and flexible arms to pry open the shell of its prey. Once the shell is open, the starfish extends its stomach out of its body and into the shell of the prey. 
• It then envelops and digests the soft-bodied animal inside, after which the stomach retracts back into the starfish's body, leaving only the empty shell of its prey behind. 
• This mode of feeding is not only unique to starfish but also demonstrates the incredible adaptability of life in the sea.

Q5. Write the functions of different types of teeth in human beings.
Ans:

• Incisors: They help in cutting and biting food.
• Canines: They help in piercing and tearing food.
• Premolars: They help in chewing and grinding food.
• Molars: They also help in chewing and grinding food.

Q6. Explain rumination.
Ans: The grass-eating animals quickly swallow the grass while eating which gets stored in a separate part of their stomach called ‘rumen’. Here, the food gets digested partially and is called ‘cud’. Later, this cud again returns to the mouth in small lumps and the animal chews it properly. This process is called ‘rumination’.

Q7. Define tongue. What are its functions?
Ans: The fleshy muscular organ attached at back to the floor of the buccal cavity is called tongue. It is free at front and can move in all directions.
The functions of tongue are:

• It mixes saliva with food.
• It helps in swallowing the food.
• It helps in identifying the various tastes of different food materials, as it has various taste buds which help in detecting them.

Q8. Write about Amoeba.
Ans: Amoeba is a fascinating creature. It can be described as a small, microscopic, single-celled organism that is typically found in the water of ponds. 

• This intriguing organism is characterized by a cell membrane, a dense and round nucleus, and numerous small, bubble-like vacuoles which are located within its cytoplasm. 
• One of the most fascinating characteristics of an Amoeba is its ability to constantly change both its shape and position. This trait makes it an organism of great interest in the field of biology.

Q9. Explain digestion of food in mouth.
Ans: The digestion of food begins in the mouth, specifically in the buccal cavity. 

• The food enters this cavity through the mouth, where it is subsequently chewed by the teeth and mixed with saliva with the assistance of the tongue. 
• This saliva contains an enzyme known as ptyalin, which is also referred to as salivary amylase. This enzyme is responsible for converting complex carbohydrates such as starch into sugars. 
• The saliva also serves to moisten the food and shapes it into a round, swallowable mass known as a bolus.

Q10. Why the large intestine is shorter and wider than small intestine?
Ans: 

• The large intestine has a specific function in the digestive system. It is primarily responsible for the absorption of water from the undigested food. As a result of this function, it is designed to be shorter and wider. 
• On the other hand, the small intestine is where the majority of digestion takes place. For this reason, it requires a larger surface area for the absorption of nutrients. Thus, the small intestine is narrower and longer.

Q11. Define dental plaque. What harm can it cause? How can the formation of plaque be prevented?
Ans: If teeth are not cleaned regularly and properly they get covered with a sticky, yellowish layer of food particles and bacteria. This is called ‘dental plaque’.
Because plaque entirely covers the teeth by its layer, the alkaline saliva cannot reach their surface to neutralise the acid formed by bacteria. Hence, tooth decay is caused. Tooth decay can be prevented by brushing and cleaning the teeth as well as mouth properly and regularly.

Q12. Explain feeding and digestion in Amoeba with a labelled diagram.
Ans: Amoeba feeds on microscopic organisms. When it senses food, it pushes out pseudopodia around the food particle and engulfs it. The food becomes trapped in a food vacuole. Digestive juices are secreted into the food vacuole which act on the food and break down it into simpler substances. Digested food is absorbed into the cell and undigested food is expelled outside by the vacuole.

Q13. What is diarrhoea? How is it caused? How can it be prevented?
Ans: Diarrhoea is the frequent and watery bowel movement. It could be caused by infection or food poisoning or indigestion. It can be fatal under severe conditions. This disease causes excessive loss of water and salts from the body.
It can be prevented by taking plenty of boiled and cooled water, along with a pinch of salt and sugar dissolved in it. This is called Oral Rehydration Solution (ORS).

Q14. Explain the process of nutrition in human beings from ingestion to egestion.
Ans:
(i) Ingestion: It is the process of taking food into the mouth; i.e., starting point of the alimentary canal.

(ii) Digestion: Digestion is the process of breaking of ingested food into simpler substances. Digestion occurs through two processes, i.e., mechanical (chewing, grinding, mixing, churning) and chemical (enzymes, bile, acid). Mechanical processes helps in breaking the large food particles into smaller ones and mixing them well with the chemicals secreted by alimentary canal.
Digestion of starch starts at mouth with the action of salivary amylase. Digestion of protein starts in stomach with the help of enzyme pepsin and digestion of all the three components of food, viz., carbohydrate, protein and fat is completed in the small intestine.
(iii) Absorption: Digested food is absorbed into the blood through finger-like structures, called villi, present in the small intestine.
(iv) Assimilation: It is the process where absorbed substances are transported to different organs of the body via blood vessels to build complex substances like protein, enzyme, etc.
(v) Egestion: The process of elimination of undigested food through anus is called egestion.

Q15. Explain human digestive system with a labelled diagram.
Ans:
The digestive system in humans consists of an alimentary canal and digestive glands which help in digestion. Different parts of alimentary canal are:

• Mouth: Digestion begins in mouth. Teeth cuts the food into small bits. Saliva digest starch in food and softens the food to pulp. Tongue helps to mix the food with saliva and converting food into bolus.
• Oesophagus: Wall of oesophagus contracts and transports food from mouth to stomach.
• Stomach: It is a big muscular bag which secretes digestive juice. Hydrochloric acid in digestive juice kill germs and enzyme pepsin breaks protein to amino acids. In stomach food get converted into a semi-fluid, chyme.
• Small intestine: Secretions from liver and pancreas act on the food in small intestine. Bile helps in breaking large fat molecules into tiny droplets. Pancreatic juice helps in digestion of starch and protein. Intestinal juice acts on starch, protein and fat and completes the digestion. Villi in small intestine absorbs these digested nutrients into the blood vessels.
• Large intestine: Large intestine absorbs water and some useful nutrients from the undigested food. The undigested food is then eliminated as faeces from the anus.

Q16. Write a short note on nutrition in ruminants.
Ans: 

• Grass-eating animals swallow the food quickly and store it in the rumen. Rumen inhabits cellulose digesting bacteria.
• The partially digested food then goes to next chamber of the stomach the reticulum.
• Digestive juices of the reticulum turns food into cud.
• While resting, cow brings back the cud into mouth for regurgitation.
• Food is chewed completely and swallowed into omasum for further digestion.
• Then the food moves into abomasum for digestion brought about by digestive juices.
• A large sac-like structure called the caecum lies between the small and large intestines.
• The symbiotic bacteria present in the caecum help incomplete digestion of cellulose. Digestion of food is completed in the small intestine.
  

Q17. With the help of labelled diagram show the gradual decay of tooth.
Ans: Sweets and Tooth Decay The tooth is covered by white, hard outer covering of tooth called Enamel enamel below which dentine is present. It is similar to bone which Pulp cavity (with nerves and blood vessels) protects the pulp cavity having nerves and blood vessels. Bacteria are Gum present in our mouth but they are not harmful to us. However, if we do not clean our teeth and mouth after eating, many harmful bacteria also begin to live and grow in it. These bacteria breakdown the sugars present from the leftover food and release acids. The acids gradually damage the tooth. This is called tooth decay.
Therefore, tooth decay is defined as the process of rotting of tooth and formation of cavity or holes in it which leads to the toothache.
When the holes or cavity reaches to the pulp cavity, it causes pain. If these cavities are not treated on time it causes severe toothache and may result in tooth loss.

Tooth decay can be prevented by adapting following measures.
(i) One should rinse and clean its teeth thoroughly after every Pulp cavity meal.
(ii) We should clean our teeth with the help of datun or brush Gradual decaying of human tooth and toothpaste, twice a day.
(iii) We should use dental floss which is a special strong thread. It is moved between two teeth to take out trapped food particles.
(iv) Dirty fingers or unwashed objects must be avoided to put in the mouth.
(v) We should avoid the use of sweets, chocolates, toffees, ice-cream, etc. Much use of cold drink should also be avoided.”

Q18. Name the various components of food and their simpler forms.
Ans: The various components of food and their simpler forms are

Q19. Discuss the various associated glands of digestive system and their role in digestion.
Ans: The various associated glands of digestive system and their role in digestion are as follows

• Salivary gland digestion of starch in mouth.
• Liver secretes bile juices which help in the digestion of fats.
• Pancreas secretes pancreatic juices which act on carbohydrate, fats and proteins and change them into simpler compounds.

Q20. List the preventive measures that one should adopt for avoiding tooth decay.
Ans: Sweets and Tooth Decay The tooth is covered by white, hard outer covering of tooth called Enamel enamel below which dentine is present. It is similar to bone which Pulp cavity (with nerves and blood vessels) protects the pulp cavity having nerves and blood vessels. Bacteria are Gum present in our mouth but they are not harmful to us. However, if we do not clean our teeth and mouth after eating, many harmful bacteria also begin to live and grow in it. These bacteria breakdown the sugars present from the leftover food and release acids. The acids gradually damage the tooth. This is called tooth decay.
Therefore, tooth decay is defined as the process of rotting of tooth and formation of cavity or holes in it which leads to the toothache.
When the holes or cavity reaches to the pulp cavity, it causes pain. If these cavities are not treated on time it causes severe toothache and may result in tooth loss.


Tooth decay can be prevented by adapting following measures.
(i) One should rinse and clean its teeth thoroughly after every Pulp cavity meal.
(ii) We should clean our teeth with the help of datun or brush Gradual decaying of human tooth and toothpaste, twice a day.
(iii) We should use dental floss which is a special strong thread. It is moved between two teeth to take out trapped food particles.
(iv) Dirty fingers or unwashed objects must be avoided to put in the mouth.
(v) We should avoid the use of sweets, chocolates, toffees, ice-cream, etc. Much use of cold drink should also be avoided.”

Q21. Write the difference between milk teeth and permanent teeth.
Ans: The difference between milk teeth and permanent teeth are

Q22. Label the given figure as directed below in A to D and give the name of each type of teeth.
(a) The cutting and biting teeth as A
(b) The piercing and tearing teeth as B
(c) The grinding and chewing teeth as C
(d) The grinding teeth present only in adult as D

Ans: 

Q23. Define oral rehydration solution and when it is given to the patient? How can you prepare ORS at home?
Ans: Oral rehydration solution is the solution of sugar and salt in a particular ratio in the clean water.

•  When a person passes out watery stools frequently, the disease is called diarrhoea. In this condition there is a loss of water and salt from the body of a person.
• This is called dehydration which may be fatal if not cured at proper time. In order to prevent dehydration, the person or patient should be given ORS. ORS makes up the loss of water and salts in the body and sugar provides energy which helps in the recovery of disease. It should be given to a patient suffering from diarrhoea at a regular interval.
• At home the ORS can be prepared by dissolving a teaspoonful of sugar and pinch of salt in a glass of clean water. The water used for preparing ORS should be first boiled and then cooled so that all the microorganisms or harmful bacteria may be killed.

Q24. Explain how the digestion of cellulose occurs in grass eating animals.
Ans: Digestion in Grass-Eating Animals
The herbivorous animals such as cow, buffaloes, etc eat grass. These animals quickly swallow the grass and store it in a part of stomach called rumen. The food is not chewed completely. Rumen possess cellulose digesting bacteria which breakdown the food by fermentation. This partially digested food or grass present in the rumen of cow is called cud.
This cud is brought back into the mouth of the cow from the rumen into small lumps and animal chews it again. This process is called rumination and animals are called ruminants.
When this cud is thoroughly chewed in the mouth of the cow, it is swallowed again. This time the chewed cud does not go back to rumen but enter into the other compartments of cow’s stomach and then into the small intestine for complete digestion and absorption of food. The cellulose digesting bacteria are not present in the body of human being, therefore human beings and other carnivore cannot digest cellulose present in plant food items.