Chap 2 : The Invisible Living World: Beyond Our Naked Eye

In-Text Questions and Answers

This section covers the questions asked within the paragraphs of the chapter.

Question (Page 2): You might have seen some people using reading glasses. How does it help them see better? Answer: Reading glasses use a special curved glass called a lens. This lens bends light in a way that makes letters and small things look bigger and clearer, helping people to see better.

Question (Page 2): Do you know which scientific discovery helped us see the tiny world for the first time? Answer: The scientific discovery that helped us see the tiny world for the first time was the invention of the microscope.

Question (Page 4): What similarities do you find in Fig. 2.3c (onion cells) and Fig. 2.3d (a brick wall)? Answer: Both the onion cells and the brick wall are made of small, repeating units. Just like bricks are the basic units of a wall, cells are the basic units of the onion peel. Both are arranged closely together without any big spaces in between.

Question (Page 4): What do you think the body of an animal is made of? Answer: The body of an animal, just like a plant, is also made up of cells. All living beings are made of cells.

Question (Page 5): What similarities and differences did you observe between the cells of onion peel in Activity 2.2 and human cheek cells in Activity 2.3? Answer:

Similarities: Both onion cells and human cheek cells have three main parts: a cell membrane on the outside, a nucleus in the center, and cytoplasm filling the space in between.
Differences: Onion cells have an extra, strong outer layer called the cell wall, which human cheek cells do not have. This cell wall gives plant cells a more fixed, rectangular shape.

Question (Page 6): Does the shape and structure of a cell relate to its function? Answer: Yes, the shape and structure of a cell are directly related to the job it does. For example, a nerve cell is very long with branches to carry messages quickly over long distances in the body. A muscle cell is spindle-shaped and flexible, which helps it contract and relax to cause movement.

Question (Page 11): But where did these microbes come from? Answer: These microbes came from the surroundings. Microorganisms are present everywhere—in the air, water, and soil. They can easily land on food that is left outside.

Question (Page 11): But why do microorganisms not infect the pickles and murabbas? Answer: Microorganisms do not infect pickles and murabbas because these foods contain a high amount of salt or sugar. Salt and sugar act as preservatives, which stop the microbes from growing.

Question (Page 13): Now, think what would have happened if microorganisms did not exist on Earth? Answer: If microorganisms did not exist, our planet would be covered in waste. Dead plants and animals would not decay or break down. The nutrients from this waste would not return to the soil, so new plants would not be able to grow well.

Question (Page 13): What are the other problems which you think can be solved with the help of microorganisms? Answer: Besides cleaning up pollution like oil spills, microorganisms can help solve other problems. They can be used to:

Create medicines like antibiotics.
Treat sewage and clean wastewater.
Make biofuels, which are a cleaner source of energy.
Improve farming by making soil more fertile naturally.

Activity Questions and Answers

This section provides the answers to questions asked in the chapter’s activities.

Activity 2.1: Let us observe

Question: Do you notice something interesting? Answer: Yes. When looking through the round-bottom flask filled with water, the letters on the book appear larger than they really are. This is because the flask of water acts like a magnifying glass.

Question: Were you able to see the details of its body more clearly? Answer: Yes, when using a real magnifying glass to look at an ant, I was able to see the details of its body, like its legs, antennae, and body segments, much more clearly.

Activity 2.2: Let us study a cell

Question: What similarities do you find in Fig. 2.3c and Fig. 2.3d? Answer: Both the onion cells (Fig. 2.3c) and the brick wall (Fig. 2.3d) are made of small, basic units that are arranged neatly without any gaps. This shows how cells are the “building blocks” of living things, just like bricks are the building blocks of a wall.

Activity 2.3: Let us investigate

Question: What similarities and differences did you observe between the cells of onion peel in Activity 2.2 and human cheek cells in Activity 2.3? Answer:

Similarities: Both types of cells have a cell membrane, cytoplasm, and a nucleus.
Difference: The onion cell has a hard outer layer called a cell wall, which the human cheek cell does not have.

Activity 2.7: Let us do

Question: Do you observe any difference in the contents of the container? Answer: Yes. After 2-3 weeks, the peels of fruits and vegetables have disappeared. They have turned into a dark-coloured, soil-like material.

Question: But how did the peels of fruits and vegetables turn into manure? Answer: The peels turned into manure because of the action of microorganisms like bacteria and fungi present in the soil. These microbes break down the vegetable waste into simple, nutrient-rich manure.

Activity 2.8: Let us perform

Question: Did you find any change in the volume, smell, or texture of the dough? Answer: Yes. The dough in bowl A (with yeast) has risen and increased in volume. It has also become soft and fluffy and has a slightly different smell. The dough in bowl B (without yeast) did not change.

Question: Why does this happen? What is the role of yeast? Answer: This happens because yeast is a living microorganism. When it gets food (sugar) and warmth, it respires and releases carbon dioxide gas. This gas gets trapped in the dough, creating bubbles that make the dough rise and become fluffy.

Question: Why did we add sugar and warm water to the flour? Answer: We added sugar as food for the yeast. We added warm water because yeast grows and multiplies well in warm conditions, which helps the process happen faster.

Activity 2.9: Let us prepare

Question: Write your predictions and observations in Table 2.4. Answer: Here are the completed predictions and observations for the table.

	Change in the appearance of milk	Change in the colour of milk	Possible reason
	Bowl A (Warm Milk)	Bowl B (Cold Milk)	Bowl A
Prediction	The milk will become thick and set like curd.	The milk will remain liquid.	The colour will stay white but may look thicker.
Observation	The milk has turned into thick curd and smells a little sour.	The milk has not turned into curd; it is still liquid.	The colour is white and the texture is thick.

Exercises: Keep the Curiosity Alive

This section covers the exercises at the end of the chapter.

1. Question: Various parts of a cell are given below. Write them in the appropriate places in the following diagram. (Nucleus, Cytoplasm, Chloroplast, Cell wall, Cell membrane, Nucleoid) Answer:

Only in Animal Cell: (None from the list)
Only in Plant Cell: Chloroplast
Only in Bacterial Cell: Nucleoid
Common to Animal and Plant cells: Nucleus
Common to Plant and Bacterial cells: Cell wall
Common to all three cells (Animal, Plant, Bacterial): Cell membrane, Cytoplasm

2. Question: (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:

Prediction: The balloon on test tube B (with yeast) will inflate, while the balloon on test tube A (without yeast) will not.
Explanation: The correct explanation is (c) Yeast produced a gas inside the test tube B which inflated the balloon. The yeast used the sugar for food and released carbon dioxide gas during respiration.

(ii) She took another test tube, 1/4 filled with lime water… What do you think she wants to find out? Answer: She wants to find out what gas was produced by the yeast. By shaking the gas from the balloon with lime water, she is testing for the presence of carbon dioxide. If the gas is carbon dioxide, it will turn the clear lime water milky.

3. Question: A farmer was planting wheat crops… In the neighbouring field, another farmer was growing bean crops, but she preferred not to add nitrogen fertiliser… Can you think of the reasons? Answer: The farmer growing bean crops did not need to add nitrogen fertiliser because beans are legume plants. Legume plants have special bumps on their roots called root nodules. Inside these nodules live bacteria called Rhizobium, which can take nitrogen directly from the air and give it to the plant. This process makes the soil naturally rich in nitrogen.

4. Question: 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… What is she trying to test? Answer: She is trying to test if mixing dried leaves with the vegetable waste helps in making manure faster or better. The dried leaves can help provide air pockets and a better environment for the microorganisms to break down the waste.

5. Question: Identify the following microorganisms: (i) I live in every kind of environment, and inside your gut. Answer: Bacteria

(ii) I make bread and cakes soft and fluffy. Answer: Yeast

(iii) I live in the roots of pulse crops and provide nutrients for their growth. Answer: Rhizobium bacteria

6. Question: Devise an experiment to test that microorganisms need optimal temperature, air, and moisture for their growth. Answer:

Take four slices of bread.
Bread 1 (Control): Sprinkle a little water on it, and keep it in a warm, open place (like a kitchen counter). This has moisture, air, and a warm temperature.
Bread 2 (Test for Temperature): Sprinkle a little water on it and place it inside a refrigerator. This has moisture and air, but a cold temperature.
Bread 3 (Test for Air): Sprinkle a little water on it and seal it tightly in an airtight plastic bag. Keep it in a warm place. This has moisture and warmth, but very little air.
Bread 4 (Test for Moisture): Keep a dry slice of bread in a warm, open place. This has air and warmth, but no moisture.
Observation: After a few days, mould (a microorganism) will grow best on Bread 1. There will be very little or no growth on the other three slices. This shows that microorganisms need the right amount of warmth, air, and moisture to grow.

7. Question: 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. Answer:

Observation: The slice of bread near the sink will have fuzzy, black or green patches of mould growing on it. The slice in the refrigerator will look almost the same as before, with no mould.
Reason: The area near a sink is usually warm and moist, which are perfect conditions for mould (a microbe) to grow. The refrigerator is very cold. This cold temperature slows down the growth of microorganisms, so the bread stays fresh for longer.

8. Question: A student observes that when curd is left out for a day, it becomes more sour. What can be two possible explanations for this? Answer:

More bacterial activity: The Lactobacillus bacteria that made the curd continue to grow and multiply in the warm temperature outside. As they multiply, they produce more lactic acid, which makes the curd taste more sour.
Contamination: Other types of bacteria and microbes from the air may have entered the curd. Their growth can also spoil the curd and produce other substances that make it taste even more sour.

9. Question: Observe the set-up given in Fig. 2.15 and answer the following questions. (i) What happens to the sugar solution in flask A? Answer: The yeast in flask A will feed on the sugar and start the process of fermentation. During this process, the sugar will be converted into alcohol and carbon dioxide gas.

(ii) What do you observe in test tube B after four hours? Why do you think this happened? Answer: After four hours, the lime water in test tube B will turn milky. This happens because the carbon dioxide gas produced by the yeast in flask A travels through the tube and bubbles into the lime water, causing the chemical reaction that makes it milky.

(iii) What would happen if yeast was not added in flask A? Answer: If yeast was not added, there would be no fermentation. No carbon dioxide gas would be produced, and therefore, the lime water in test tube B would remain clear.

Projects: Discover, Design, and Debate

This section gives information related to the project-based questions.

1. Question: Find out about the Biogas Program initiated by the Ministry of New and Renewable Energy, Government of India. Answer: The Government of India, through the Ministry of New and Renewable Energy, runs a program to promote biogas plants, especially in rural areas. This program helps people build their own small biogas plants. These plants use animal waste (like cow dung) and farm waste to produce biogas (mostly methane gas). This gas can be used for cooking and lighting, which saves money and is cleaner than burning wood. The leftover slurry is an excellent, nutrient-rich manure for farms.

2. Question: With the help of your parents and teachers, list some traditional food items from your area that utilise the process of fermentation. Answer: Many traditional Indian foods are made using fermentation. Some common examples are:

Idli and Dosa: The batter is fermented using bacteria like Lactobacillus and yeast, which makes it rise and gives it a slightly sour taste.
Dhokla: The batter made from gram flour is fermented to make it light and spongy.
Bhatura: The dough for bhatura is often fermented with yeast to make it soft and puffy.
Jalebi: The batter for this sweet is fermented before being fried.
Curd (Dahi): Milk is fermented by Lactobacillus bacteria to make curd.

The microorganisms break down the sugars in the food, making them easier to digest and adding to their flavour and nutritional value.

3. Question: Study the different parts of a macro fungus mushroom using a magnifying glass and microscope/foldscope. Answer: This is a discovery activity. Here is how you can approach it:

With a Magnifying Glass: Get a fresh mushroom. You can easily see its main parts: the cap (the top umbrella-like part), the gills (the lines on the underside of the cap), and the stem or stalk that holds the cap up.
With a Microscope: If you have access to a microscope, a teacher can help you prepare a slide. You could try to scrape some of the gills to see the tiny spores, which are like the seeds of the mushroom. You could also take a very thin slice of the stem or cap to see the network of thread-like structures that make up the mushroom’s body.
Learning about Cultivation: You can ask a local farmer or search online to learn how mushrooms are grown. It involves preparing a special compost (food for the mushroom), adding mushroom spawn (the “seeds”), and keeping it in a dark, moist, and cool place until the mushrooms grow.