Complete the journey of food through the alimentary canal by filling up the boxes with appropriate parts—
Food → Mouth → ............... → Stomach → ............... → ............... → Anus
Answer
Food → Mouth → Oesophagus (Food pipe) → Stomach → Small intestine → Large intestine → Anus
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
Iodine gives a blue-black colour when it reacts with starch. The observations are:
- Test tube A (pieces of chapati): The contents turn blue-black because chapati contains starch.
- Test tube B (chewed chapati): There is no change in colour, or only a very light blue-black colour appears. Saliva breaks down starch into simple sugars while chewing, so little or no starch remains.
- Test tube C (boiled and mashed potato): The contents turn blue-black because potato contains starch and it has not been mixed with saliva.
What is the role of the diaphragm in breathing?
- To filter the air
- To produce sound
- To help in inhalation and exhalation
- To absorb oxygen
Answer
To help in inhalation and exhalation
Reason — The diaphragm is a dome-shaped muscle present below the lungs. During inhalation, it moves downwards, increasing the space inside the chest so that air enters the lungs. During exhalation, it moves upwards, reducing the space inside the chest and pushing air out of the lungs.
Match the following.
| Name of the part | Functions |
|---|---|
| (i) Nostrils | (a) fresh air from outside enters |
| (ii) Nasal passages | (b) exchange of gases occurs |
| (iii) Windpipe | (c) protects lungs |
| (iv) Alveoli | (d) tiny hair and mucus help to trap dust and dirt from the air we breathe |
| (v) Ribcage | (e) air reaches our lungs through this part |
Answer
| Name of the part | Functions |
|---|---|
| (i) Nostrils | (a) fresh air from outside enters |
| (ii) Nasal passages | (d) tiny hair and mucus help to trap dust and dirt from the air we breathe |
| (iii) Windpipe | (e) air reaches our lungs through this part |
| (iv) Alveoli | (b) exchange of gases occurs |
| (v) Ribcage | (c) protects lungs |
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 Anil the following questions:
- Is breathing a physical process or a chemical process? (Breathing is a physical process, while respiration is a chemical process.)
- Which process releases energy by breaking down glucose? (Respiration releases energy, while breathing only moves air in and out.)
- Does only inhaling and exhaling of air give us energy?
Through these questions, Anil will understand that breathing only involves taking air in (inhalation) and giving air out (exhalation), whereas respiration uses oxygen to break down food and release energy inside the body. So, the two processes are not the same.
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
Anu's statement, "We inhale air," is correct.
We do not inhale pure oxygen; we inhale air, which is a mixture of gases. Therefore, Anu's statement is the most accurate. Tanu's statement is incorrect, the air contains oxygen but it is not rich in oxygen, and Shanu's statement is incorrect, because we do not inhale only oxygen.
We often sneeze when we inhale a lot of dust-laden air. What can be possible explanations for this?
Answer
Tiny hairs and mucus in the nasal passages trap dust and dirt from the air we breathe in. When a large amount of dust enters the nose, it irritates the inner lining of the nasal passages and triggers sneezing. Sneezing helps expel dust and other foreign particles from the respiratory passage.
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
Two possible explanations are:
- Anusha may have run faster or done more vigorous exercise than Paridhi. More physical activity needs more energy, so her body needs more oxygen. To take in more oxygen, she breathes faster.
- Paridhi may be more physically fit and have better stamina than Anusha. So Paridhi's breathing rate returns to normal more quickly, while Anusha continues to breathe faster.
Yadu conducted an experiment to test his idea. He took two test tubes, A and B, and added a pinch of rice flour to the test tubes, half-filled with water and stirred them properly. To test tube B, he added a few drops of saliva. He left the two test tubes for 35–45 min. After that, he added iodine solution into both the test tubes. Experimental results are as shown in Fig. 9.15. What do you think he wants to test?
Answer
Yadu wants to test the action of saliva on starch, that is, whether saliva can break down starch.
Rice flour contains starch. In test tube A, which has no saliva, starch remains present and iodine gives a blue-black colour. In test tube B, saliva breaks down the starch into simple sugars, so iodine does not give a blue-black colour. This shows that saliva helps break down starch into simple sugars.
Rakshita designed an experiment taking two clean test tubes, A and B and filled them with lime water as shown in the figure. In test tube A, the surrounding air that we inhale was passed on by sucking air from the pipe, and in test tube B, the exhaled air was blown through the pipe (Fig. 9.16). 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 the air we inhale.
She can confirm her findings as follows: lime water turns milky when it reacts with carbon dioxide. In test tube B (exhaled air), the lime water turns milky, while in test tube A (inhaled air), the lime water does not change. This shows that exhaled air contains more carbon dioxide than the air we inhale.