NCERT 7th Class (CBSE) Science: Nutrition in Animals

Question: What is peristalsis? Explain with the help of diagram.

Answer: After the food is swallowed, it slides down the pharynx into the oesophagus (food pipe). The oesophagus leads from our mouth to the stomach. It is made up of muscles. These muscles gently push food down to our stomach in a wave like action called peristalsis. This movement takes place throughout the alimentary canal to push the food forward.

 

Question: Explain through diagrams ingestion of food in Amoeba and Hydra.

Answer: Amoeba: The unicellular Amoeba engulfs tiny particles of food by throwing its false feet, known as pseudopodia around it. The pseudopodia join together to form a small cavity known as a food vacuole. The food inside the vacuole is digested by digestive juices. It is absorbed and assimilated there to provide energy and perform other functions.

 

Hydra: Hydra is a simple, multicellular animal. It has a number of tentacles around its mouth, which are used for ingestion of food. The tentacles entangle small aquatic animals and kill them with their stinging cells. They then push them into the mouth. Inside the body cavity the digestive juices secreted by the surrounding cells help to digest the food. This is then absorbed through the cavity walls and assimilated in the cells.

 

Question: Write one similarity and one difference between the nutrition of amoeba and human beings.

Answer: One Similarity and difference between the nutrition of amoeba and human being is:

similarity: In both, the process of digestion involves ingestion, digestion, absorption, assimilation and egestion.

Difference: In Amoeba, the enzymes secreted by the cell cytoplasm digest the ingested food. In man, there are special organs for the digestion of food. The food passes through the alimentary canal. Here several digestive enzymes are secreted.These enzymes break the complex food materials into simpler ones.

Question: Can we survive only on raw, leafy vegetables? Discuss.

Answer: Animals, fungi, bacteria, noon – green plants human being do not have the ability to make there own food. They depend upon autotrophs for their food directly or indirectly. The green plant (leafy vegetable grass) trap solar energy and make their own food in the form of glucose. Therefore, we can say that leafy vegetables and grass can provide sufficient energy to survive us.

Question: What is the function of saliva, bile juice and pancreatic juice?

Answer: The functions are:

1. Saliva: The saliva in our mouth helps to break down starch of the food into sugars that are easier to digest. It also makes food easier to swallow by making it wet and slippery.
2. Bile Juice: The liver secretes bile juice which is stored in gall bladder. The bile juice breaks up fats into droplets that can be digested and absorbed more easily. They are broken down into fatty acids and glycerol.
3. Pancreatic Juice: The pancreas secretes the pancreatic juice that changes starch into simple sugars, and proteins into simpler compounds called amino acid.