SCIENCE CLASS- 7
CHAPTER-9 (Life Processes in Animals)
Let Us Enhance Our Learning
1. Complete the journey of food through the alimentary canal by filling up the boxes with appropriate parts.
Answer:
Food → Mouth → Oesophagus (Food Pipe) → Stomach → Small Intestine → Large Intestine → Rectum → Anus
2. Sahil placed some pieces of chapati in test tube A. Neha placed chewed chapati in test tube B, and Santushti took boiled and mashed potato in test tube C. All of them added a few drops of iodine solution to their test tubes—A, B, and C, respectively. What would be their observations? Give reasons.
Answer:
Test Tube A: The chapati will turn blue-black because chapati contains starch, and iodine gives a blue-black colour in the presence of starch.
Test Tube B: The chewed chapati may show no blue-black colour or only a light blue-black colour. This is because saliva has already started breaking down the starch into sugars.
Test Tube C: The boiled and mashed potato will turn blue-black because potato contains a large amount of starch.
3. What is the role of the diaphragm in breathing?
Answer:
(iii) To help in inhalation and exhalation
The diaphragm moves downward during inhalation, increasing the space in the chest cavity and allowing air to enter the lungs. During exhalation, it moves upward and helps push air out of the lungs.
4. Match the following.
| Name of the Part | Function |
|---|---|
| (i) Nostrils | (a) Fresh air from outside enters |
| (ii) Nasal passages | (d) Tiny hair and mucus help trap dust and dirt |
| (iii) Windpipe | (e) Air reaches our lungs through this part |
| (iv) Alveoli | (b) Exchange of gases occurs |
| (v) Rib cage | (c) Protects lungs |
5. Anil claims to his friend Sanvi that respiration and breathing are the same process. What question(s) can Sanvi ask him to make him understand that he is not correct?
Answer:
Sanvi can ask:
- Does breathing only involve taking in and giving out air?
- Is energy released during breathing?
- Does respiration occur inside body cells where food is broken down to release energy?
- If breathing and respiration are the same, why is breathing called a physical process while respiration is called a chemical process?
These questions will help Anil understand that breathing and respiration are different processes.
6. Which of the following statements is correct and why?
Anu: We inhale air.
Shanu: We inhale oxygen.
Tanu: We inhale air rich in oxygen.
Answer:
Tanu is correct.
We do not inhale pure oxygen. We inhale air, which contains many gases. Air contains about 21% oxygen along with nitrogen, carbon dioxide, water vapour, and other gases. Therefore, it is correct to say that we inhale air rich in oxygen.
7. We often sneeze when we inhale a lot of dust-laden air. What can be possible explanations for this?
Answer:
Dust particles entering the nose irritate the nasal passages. The tiny hairs and mucus in the nose try to trap these particles. Sneezing is a protective reflex that helps remove dust, dirt, and other unwanted particles from the respiratory tract, keeping the air passages clean.
8. Paridhi and Anusha of Grade 7 started running for their morning workout. After they completed their running, they counted their breaths per minute. Anusha was breathing faster than Paridhi. Provide at least two possible explanations for why Anusha was breathing faster than Paridhi.
Answer:
Possible reasons are:
- Anusha may have run faster or covered a longer distance than Paridhi.
- Anusha may have lower physical fitness and therefore required more oxygen.
- She may have become tired more quickly.
- Her body may have needed more oxygen to release energy after exercise.
9. Yadu conducted an experiment using rice flour and saliva. What do you think he wants to test?
Answer:
Yadu wanted to test whether saliva breaks down starch into simpler sugars.
Rice flour contains starch. In test tube A, where saliva was not added, iodine would give a blue-black colour showing the presence of starch. In test tube B, saliva breaks down the starch into sugars, so the blue-black colour would not appear or would appear very faintly. This demonstrates the digestive action of saliva on starch.
10. Rakshita designed an experiment using lime water and inhaled/exhaled air. What do you think she is trying to investigate? How can she confirm her findings?
Answer:
Rakshita is trying to investigate whether exhaled air contains more carbon dioxide than inhaled air.
Carbon dioxide turns lime water milky. If the lime water in test tube B (through which exhaled air is passed) turns milky faster than the lime water in test tube A, it confirms that exhaled air contains a higher amount of carbon dioxide. This observation proves that carbon dioxide is released during respiration.