The Invisible Living World: Beyond Our Naked EyeClass 8 Science NCERT Solutions
9 Solutions
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Solution 1 of 9
Q1Keep the curiosity alive
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
Solution
The diagram should be labeled as follows:
- Outermost layer: Cell membrane
- If it is a plant cell, the layer outside the cell membrane: Cell wall
- The fluid inside the cell: Cytoplasm
- The central structure: Nucleus
- If it is a plant cell, the green structure: Chloroplast
- If it is a bacterial cell, the region with genetic material: Nucleoid
Q2Keep the curiosity alive
Aanandi 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 testtube B was inflated. What can be a possible explanation for this?
(a)
Water evaporated in test tube B and filled the balloon with the water vapour.
(b)
The warm atmosphere expanded the air inside the test tube B, which inflated the balloon.
(c)
Yeast produced a gas inside the test tube B which inflated the balloon.
(d)
Sugar reacted with warm air, which produced gas, eventually inflating the balloon.
(ii)
She took another test tube, 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?
Solution
(i)
After 3-4 days, the balloon attached to test tube B will inflate because (c) Yeast produced a gas inside the test tube B which inflated the balloon.
(ii)
She wants to find out if the gas produced by the yeast is carbon dioxide. Carbon dioxide turns lime water milky.
Q3Keep the curiosity alive
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?
Solution
The farmer growing bean crops did not add nitrogen fertilizer because bean plants have root nodules that contain Rhizobium bacteria. These bacteria can trap nitrogen from the air and convert it into a form that plants can use. Wheat crops do not have this ability and therefore require nitrogen-rich fertilizer.
Q4Keep the curiosity alive
Snehal 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?
Solution
Snehal is trying to test the effect of dried leaves (which provide carbon) on the decomposition of fruit and vegetable peels by microorganisms. She is likely trying to see if the addition of dried leaves speeds up the decomposition process and improves the quality of the resulting manure.
Q5Keep the curiosity alive
Identify the following microorganisms:
(i)
I live in every kind of environment, and inside your gut.
(ii)
I make bread and cakes soft and fluffy.
(iii)
I live in the roots of pulse crops and provide nutrients for their growth.
Solution
(i)
Bacteria
(ii)
Yeast
(iii)
Rhizobium
Q6Keep the curiosity alive
Devise an experiment to test that microorganisms need optimal temperature, air, and moisture for their growth.
Solution
To test the conditions needed for the growth of microorganisms, you can set up the following experiment:
- Take three slices of bread.
- Keep one slice in a warm, moist place (like a closed container with a few drops of water), open to air.
- Keep another slice in a refrigerator (low temperature), in a closed container with a few drops of water.
- Keep the third slice in a dry place (no moisture), open to air, at room temperature.
- Observe the bread slices over several days for any signs of mold growth.
The bread slice in the warm, moist place, open to air, will show the most mold growth, demonstrating that microorganisms need optimal temperature, air, and moisture to grow.
Q7Keep the curiosity alive
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.
Solution
Observation: After three days, the bread slice near the sink will likely have mold growth, while the bread slice in the refrigerator will show little to no mold.
Reason: The bread slice near the sink has access to moisture, warmth, and microbes from the environment, all of which support mold growth. The refrigerator's low temperature inhibits the growth of microorganisms, so the bread slice stored there remains relatively free of mold.
Q8Keep the curiosity alive
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?
Solution
Two possible explanations for why curd becomes more sour when left out for a day are:
- Increased bacterial activity: The bacteria (Lactobacillus) in the curd continue to multiply and produce more lactic acid. Lactic acid is responsible for the sour taste, so increased production leads to a more sour flavor.
- Warmer temperature: At room temperature, the bacteria are more active than at refrigerated temperatures. This increased activity leads to faster fermentation and more lactic acid production.
Q9Keep the curiosity alive
Observe the set-up given in Fig. 2.15 and answer the following questions.
(i)
What happens to the sugar solution in flask A?
(ii)
What do you observe in test tube B after four hours? Why do you think this happened?
(iii)
What would happen if yeast was not added in flask A?
Solution
(i)
The yeast in flask A will break down the sugar solution through fermentation, producing carbon dioxide gas and alcohol.
(ii)
After four hours, the lime water in test tube B will turn milky. This is because the carbon dioxide gas produced by the yeast in flask A is bubbled through the lime water, causing it to react and form calcium carbonate, which makes the lime water milky.
(iii)
If yeast was not added to flask A, there would be no fermentation. As a result, no carbon dioxide gas would be produced, and the lime water in test tube B would not turn milky.