Are you looking for easy-to-understand science notes and NCERT solutions? In this post, you will get simple, step-by-step answers to Class 7 Science chapter "Life Processes in Animals" questions about how our body digests food and breathes air. We have also explained common school lab experiments, like testing starch with iodine and checking carbon dioxide with lime water, in very easy language. Read below to clear all your doubts and score well in your school exams!
Life Processes in Animals - NCERT Exercise
Q1. 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 → Anus
Q2. 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. In test tube A, Sahil will observe a blue-black color change because unchewed chapati contains starch, which reacts positively with iodine.
In test tube B, Neha will observe no blue-black color change (the solution will retain the light brown color of iodine). This happens because the chewing process mixes saliva with the chapati, and the salivary amylase enzyme breaks down the starch into sugars, leaving no starch to react with the iodine.
In test tube C, Santushti will observe a deep blue-black color change because boiled and mashed potato contains a high amount of intact starch that reacts readily with the iodine solution.
Q3. What is the role of the diaphragm in breathing? (i) To filter the air (ii) To produce sound (iii) To help in inhalation and exhalation (iv) To absorb oxygen
Answer. (iii) To help in inhalation and exhalation
Q4. Match the following:
Answer.
(i) Nostrils matches with - (a) fresh air from outside enters
(ii) Nasal passages matches with - (d) tiny hair and mucus help to trap dust and dirt from the air we breathe
(iii) Windpipe matches with - (e) air reaches our lungs through this part
(iv) Alveoli matches with - (b) exchange of gases occurs
(v) Ribcage matches with - (c) protects lungs
Q5. 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: "Where does the process take place—is it just a physical exchange of gases in the lungs, or does it happen inside every single cell of our body to release energy?" She can also ask: "Does breathing require enzymes and produce energy in the form of ATP, or is that a chemical process unique to cellular respiration?" These questions help point out that breathing is merely a mechanical organ-level process, whereas respiration is a biochemical cellular process.
Q6. 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's statement is the most accurate because we do not isolate and breathe pure oxygen from our surroundings; instead, we breathe the atmospheric air around us, which contains a high concentration of oxygen (around 21 percent) compared to the air we exhale. Anu is technically correct that we breathe air, but Tanu provides the necessary detail regarding its composition during inhalation. Shanu is incorrect because our respiratory system cannot selectively pull only pure oxygen molecules out of the atmosphere.
Q7. We often sneeze when we inhale a lot of dust-laden air. What can be possible explanations for this?
Answer. Sneezing is a protective reflex mechanism of our body to expel foreign particles. When we breathe in air filled with dust, these particles bypass the hair and mucus in our nasal passage and irritate the sensitive lining of our nasal cavity. This irritation sends a signal to the brain, which triggers a sudden, forceful expulsion of air to clear out the unwanted dust particles and protect the lungs.
Q8. 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. One possible explanation is that Anusha may have run at a higher speed or put in more physical effort during the workout, which required her muscles to generate more energy and consume oxygen at a faster rate. A second explanation is that Paridhi might have a higher physical fitness level or greater lung capacity from regular exercise, allowing her body to recover more efficiently and maintain a lower breathing rate compared to Anusha.
Q9. 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 effect of saliva on starch present in food. Specifically, he is demonstrating how the enzyme salivary amylase breaks down complex starch molecules into simple sugars, which prevents the starch-iodine reaction from turning blue-black in test tube B.
Q10. 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 a higher concentration of carbon dioxide than inhaled atmospheric air. She can confirm her findings by observing the speed and intensity of the color change in the lime water. The lime water in test tube B, where exhaled air is blown, will turn milky very quickly because exhaled air is rich in carbon dioxide. In contrast, the lime water in test tube A will take much longer or show very minimal change because the surrounding air contains a much lower percentage of carbon dioxide.