Chapter Exercises (Page 248 - 250)
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1. Various parts of a cell are given below. Write them in the appropriate places in the following diagram.
Nucleus, Chloroplast, Cell membrane, Cytoplasm, Cell wall, Nucleoid.Category Cell Parts Only in Animal Cell Cell membrane, Cytoplasm, Nucleus Only in Plant Cell Cell membrane, Cytoplasm, Nucleus, Cell wall, Chloroplast Only in Bacterial Cell Cell membrane, Cytoplasm, Cell wall, Nucleoid Common to all three cells Cell membrane, Cytoplasm -
2. Visali took two test tubes and marked them A and B. She put two spoonfuls of sugar solution in each of the test tubes. In test tube B, she added a spoonful of yeast. Then she attached two incompletely inflated balloons to the mouth of each test tube. She kept the set-up in a warm place, away from sunlight.
(i) What do you predict will happen after 3-4 days? She observed that the balloon attached to test tube B was inflated. What can be a possible explanation for this?Answer: C. Yeast produced a gas inside the test tube B which inflated the balloon.
(ii) She took another test tube, $1/4$ filled with lime water. She removed the balloon from test tube B in such a manner that the gas inside the balloon did not escape. She attached the balloon to the test tube with lime water and shook it well. What do you think she wants to find out?She wants to test and confirm whether the gas produced by yeast respiration and fermentation in test tube B is carbon dioxide, which turns lime water milky. -
3. A farmer was planting wheat crops in his field. He added nitrogen-rich fertiliser to the soil to get a good yield of crops. In the neighbouring field, another farmer was growing bean crops, but she preferred not to add nitrogen fertiliser to get healthy crops. Can you think of the reasons?
Beans are leguminous plants that have root nodules containing Rhizobium bacteria. These bacteria naturally trap atmospheric nitrogen and convert it into usable compounds for the plant, enriching the soil with nitrogen. Therefore, the farmer growing beans did not need to add external nitrogen fertilisers.
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4. Sneha dug two pits, A and B, in her garden. In pit A, she put fruit and vegetable peels and mixed it with dried leaves. In pit B, she dumped the same kind of waste without mixing it with dried leaves. She covered both the pits with soil and observed after 3 weeks. What is she trying to test?
She is trying to test the effect of carbon-rich dry leaves along with nitrogen-rich kitchen waste (proper moisture and C:N ratio) on the rate and efficiency of decomposition by microorganisms into compost/manure.
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5. Identify the following microorganisms:
(i) I live in every kind of environment, and inside your gut.Bacteria (such as gut bacteria/Lactobacillus)
(ii) I make bread and cakes soft and fluffy.Yeast (Fungi)
(iii) I live in the roots of pulse crops and provide nutrients for their growth.Rhizobium bacteria -
6. Devise an experiment to test that microorganisms need optimal temperature, air, and moisture for their growth.
Take bread slices under different conditions: one moist slice kept at room temperature (optimal air, moisture, and temperature), one completely dry slice, one moist slice kept inside a refrigerator (low temperature), and one airtight sealed container. Observe mold growth over a few days to conclude that moisture, warm temperature, and air are essential for microbial growth.
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7. Take 2 slices of bread. Place one slice in a plate near the sink. Place the other slice in the refrigerator. Compare after three days. Note your observations. Give reasons for your observations.
Observation: The bread slice left near the sink shows fungal growth (mold), whereas the slice in the refrigerator remains mostly unchanged. Reason: Microorganisms like fungi require moisture and warm temperatures to grow and multiply. The refrigerator's low temperature inhibits microbial growth.
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8. A student observes that when curd is left out for a day, it becomes more sour. What can be two possible explanations for this observation?
1. The Lactobacillus bacteria continue to feed on the remaining lactose sugar and multiply, producing more lactic acid.
2. Keeping the curd exposed in a warm environment accelerates bacterial activity and acid production. -
9. Observe the set-up given in Fig. 1.15 and answer the following questions.
(i) What happens to the sugar solution in flask A?The sugar solution undergoes fermentation by yeast, releasing carbon dioxide gas and producing a slight alcohol smell.
(ii) What do you observe in test tube B after four hours? Why do you think this happened?The lime water in test tube B turns milky. This happens because the carbon dioxide gas produced by yeast in flask A passes into the lime water and reacts with it to form insoluble calcium carbonate.
(iii) What would happen if yeast was not added in flask A?No fermentation would take place, no carbon dioxide gas would be produced, and the lime water in test tube B would remain clear.
