CBSE Class 7 Science Advanced Biology Nutrition in Plants and Animals Short Answer Questions Set 01

Short Answer Questions

Question 1. What is nutrition? Name different types of nutrition.
Answer:
Nutrition is the process by which an organism obtains the nutrients it needs for energy and survival. It includes intake of food, digestion, absorption, use of the food in body activities and removal of waste.
Types: autotrophic nutrition and heterotrophic nutrition. Heterotrophic nutrition is further divided into saprophytic, parasitic and holozoic nutrition.
In simple words: Nutrition is how a living thing gets and uses food; it is autotrophic or heterotrophic.

Teacher's Note:
1. Draw a small chart of the types.
2. Do not forget that heterotrophic has three sub-types.

Question 2. Write the difference between parasitic and saprophytic nutrition.
Answer:
Parasitic nutrition: the parasite takes food from a living organism, the host. The host gets no benefit and may be harmed. Example: head lice.
Saprophytic nutrition: the organism feeds on dead and decaying plants and animals. Such organisms are saprophytes. Example: fungus.
In simple words: Parasites live on living hosts; saprophytes live on dead matter.

Teacher's Note:
1. Key word for parasites: living host.
2. Key word for saprophytes: dead and decaying matter.

Question 3. What is peristalsis and why is it useful?
Answer:
The contracting and relaxing movement of the muscles of the oesophagus is called peristalsis. It is useful because it pushes the food down easily into the stomach.
In simple words: The oesophagus squeezes and relaxes in waves to move food downwards.

Teacher's Note:
1. Peristalsis happens in the whole food canal.
2. Only the oesophagus is asked here.

Question 4. What are intestinal villi? Write its significance.
Answer:
The small intestine is a long tube that has many finger-like projections called villi. Villi increase the surface of the intestine and help in absorbing the nutrients and energy into the blood after digestion.
In simple words: Villi are tiny fingers in the small intestine that absorb digested food.

Teacher's Note:
1. Mention both the shape and the function.
2. More surface means faster absorption.

Question 5. What is the difference between ingestion and egestion?
Answer:
Ingestion is the intake of food into the body through the mouth. It varies from one animal to another.
Egestion is the removal of undigested waste from the body. In humans it takes place through the anus.
In simple words: Ingestion takes food in, egestion sends waste out.

Teacher's Note:
1. They are the first and the last steps of nutrition.
2. Link ingestion with the mouth and egestion with the anus.

Question 6. Give the functions of the following: (a) Salivary glands (b) Stomach (c) Pancreas (d) Liver
Answer:
(a) Salivary glands: produce saliva, which turns the food into a soft paste and starts the digestion of carbohydrates.
(b) Stomach: produces gastric juice and hydrochloric acid, and helps in the digestion of proteins.
(c) Pancreas: produces pancreatic juice, which helps in digesting proteins, carbohydrates and fats.
(d) Liver: produces bile, which helps in fat digestion.
In simple words: Each organ makes a juice that digests a particular food.

Teacher's Note:
1. Match organ, juice and food type.
2. Bile is made in the liver and stored in the gall bladder.

Question 7. Explain predator–prey relationship taking suitable example.
Answer:
A predator is an animal that kills another animal for food, and the animal that is killed is the prey. For example, a tiger is a carnivore that kills a deer for food. The tiger is the predator and the deer is the prey.
In simple words: The hunter is the predator and the hunted animal is the prey.

Teacher's Note:
1. Always give an example with both names.
2. The predator is always a carnivore.

Question 8. Fungus is a saprophyte. Justify the statement.
Answer:
Fungus grows on dead and decaying organisms and takes its nourishment from them. Organisms that feed on dead and decaying matter are called saprophytes, so a fungus is a saprophyte. Example: bread mould on spoiled bread.
In simple words: A fungus lives on dead matter, so it is a saprophyte.

Teacher's Note:
1. Define a saprophyte first, then link it to fungus.
2. Bread mould is a good example.

Question 9. Human digestion is holozoic type. Justify the statement.
Answer:
Holozoic nutrition means intake of solid or liquid food, digestion, absorption, use of the energy and removal of waste. In humans, the digestive organs carry out all the five steps: ingestion, digestion, absorption, assimilation and egestion. So human digestion is holozoic.
In simple words: Humans take in ready-made food and go through all five steps.

Teacher's Note:
1. Name all five steps in the answer.
2. Mention that the food is taken in as solid or liquid.

Question 10. When we take a bite of bread, it does not taste sweet initially. But after sometimes, it starts to taste sweet. Why?
Answer:
Bread contains starch, which does not taste sweet. Saliva contains the enzyme amylase, which breaks down starch into smaller sugars like maltose and glucose. These taste sweet, so after chewing for some time, the bread tastes sweet.
In simple words: Saliva slowly changes the starch of bread into sugar.

Teacher's Note:
1. Name the enzyme amylase and the sugar maltose.
2. Chewing longer gives the enzyme more time to work.

Question 11. Aakriti made a mistake while writing down the steps of human digestion. Can you correct them?
Ingestion → Absorption → Assimilation → Digestion → Egestion
Answer:
The correct order is: Ingestion → Digestion → Absorption → Assimilation → Egestion.
In simple words: Food must be digested before it can be absorbed and used.

Teacher's Note:
1. Digestion comes second, after the intake of food.
2. Egestion is always the last step.

Question 12. Think of some meat-eating animals that you have seen in a zoo, like tiger, lion. Have you noticed that their canines are different from the canines of a cow? Think and answer why.
Answer:
Meat-eating animals like the tiger and the lion must tear flesh to eat it, so they need sharp and pointed canines. A cow is a herbivore and has to grind plant food rather than tear it, so its canines are neither sharp nor pointed.
In simple words: Tearing flesh needs sharp teeth, grinding plants does not.

Teacher's Note:
1. Link the shape of the teeth to the food.
2. This is called an adaptation to the diet.

Question 13. The gastric glands present in our stomach produce hydrochloric acid which activates the enzyme pepsin to digest proteins. Then, why is it that our stomach does not get digested/damaged by the action of the acid?
Answer:
The inner wall of the stomach is protected by a slippery layer of mucus. This mucus lining protects the stomach from the corrosive action of the acid.
In simple words: A mucus coat shields the stomach wall from its own acid.

Teacher's Note:
1. Name the protective substance: mucus.
2. Without mucus the acid could damage the wall.

Question 14. Although fibres are indigestible by human body, why is it advisable to have breakfast cereal that is high in fibre?
Answer:
Fibre (roughage) cannot be digested, but it adds bulk to the food passing through the digestive tract. This helps the waste to move easily through the bowel. Too little fibre in the diet leads to constipation.
In simple words: Fibre adds bulk and keeps the bowel moving.

Teacher's Note:
1. Mention constipation as the problem avoided.
2. Fibre is found in cereals, fruits and vegetables.