The Invisible Living World: Beyond Our Naked Eye — Hard

Q1. The yolk of an ostrich egg is described in the chapter as the largest known cell in the living world. Which statement about it is correct?

• A. It is a multicellular structure formed by many yolk cells joined together.
• B. It is a single cell about 130 to 170 mm in diameter, nourished by extra non-cellular material.
• C. It is a tissue made up of cells of the digestive system.
• D. It is the smallest cell ever measured under an electron microscope.

Q2. Consider three statements about the schematic drawings of an animal cell and a plant cell in Fig. 2.5 of the chapter: I. The plant cell shows a cell wall outside the cell membrane. II. Both cells show a nucleus and cytoplasm. III. The animal cell shows a chloroplast. The correct statements are

• A. II and III only
• B. I and II only
• C. I and III only
• D. All three

Q3. Assertion (A): Fungal cells cannot make their own food through photosynthesis. Reason (R): Fungal cells have a cell wall but lack chloroplasts. Choose the correct option

• A. Both A and R are true, but R is NOT the correct explanation of A.
• B. A is true, R is false.
• C. Both A and R are true, and R is the correct explanation of A.
• D. A is false, R is true.

Q4. When we swallow food, a group of muscle cells in the food pipe contract and relax in a wave-like manner to push food to the stomach. This wave-like movement is possible mainly because muscle cells in the food pipe are

• A. Thin, flexible, and spindle-shaped
• B. Long and branched like neurons
• C. Rectangular with a rigid cell wall
• D. Spherical and arranged in clusters

Q5. Three statements about the stomach are given: I. Muscle cells in the stomach wall help churn the food. II. Other cells in the inner lining of the stomach produce digestive juices and acid. III. All cells in the stomach are exactly the same in shape and function. The correct statements are

• A. II and III only
• B. I and III only
• C. All three
• D. I and II only

Q6. The life of complex multicellular organisms begins with a single cell, the egg, which has an amazing ability to

• A. Stay as one cell throughout life
• B. Divide repeatedly to form a complete organism made of many cells
• C. Convert directly into a tissue without becoming an organ
• D. Live independently outside the parent's body for years

Q7. In the digestive system of a Class 8 student, different types of tissues — muscle, lining, blood — work together to form the stomach. Going by the chapter, the stomach is best classified as

• A. A single cell
• B. A tissue
• C. An organ
• D. An organism

Q8. While observing pond water in Activity 2.4, Aanandi notes: 'I see a single-celled organism that is moving and constantly changing its shape — it has no fixed boundary.' She has most likely seen

• A. Amoeba (a protozoan)
• B. Algae (a green plant-like microbe)
• C. Bread mould (a fungus)
• D. A virus

Q9. Table 2.1 describes Paramecium as a single-celled organism that 'moves from one place to another with the help of specialised structures.' Which point is closest to this description?

• A. Paramecium uses chlorophyll to make food.
• B. Paramecium has many cells joined together.
• C. Paramecium cannot move on its own.
• D. Paramecium has specialised structures on its body that help it move.

Q10. Three statements compare bacterial cells with cells of yeast, protozoa, plants, and animals: I. Bacterial cells have a cell membrane. II. Bacterial cells have a well-defined nucleus enclosed by a nuclear membrane. III. Bacterial cells have a nucleoid region instead of a well-defined nucleus. The correct statements are

• A. II and III only
• B. I and III only
• C. I and II only
• D. All three

Q11. Activity 2.9: lukewarm milk in bowl A with a spoon of curd forms curd in a few hours; cold milk in bowl B does not. The Lactobacillus bacterium does the following in bowl A

• A. Produces alcohol from milk sugar like yeast does.
• B. Feeds on lactose, multiplies, and ferments milk producing lactic acid that sours the curd.
• C. Releases nitrogen that thickens the milk.
• D. Photosynthesises and turns the milk green.

Q12. In Activity 2.7, fruit and vegetable peels mixed with soil disappear after 2-3 weeks and turn into a dark, nutrient-rich material. The process that breaks down the complex substances of these peels into simpler substances is called

• A. Decomposition
• B. Fermentation
• C. Photosynthesis
• D. Nitrogen fixation

Q13. Three statements about biogas are given: I. Biogas is produced by bacteria and fungi living in an oxygen-free environment. II. Biogas is a mixture mainly of carbon dioxide and a high proportion of methane. III. Biogas can be used for cooking, heating, generating electricity, and even running vehicles. The correct statements are

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q14. A farmer in Bihar plants wheat one season and beans the next season in the same field, without adding nitrogen fertiliser before the bean crop. The most likely reason is

• A. Beans do not grow in nitrogen-rich soil.
• B. Rhizobium bacteria in bean root nodules trap nitrogen from air for the plant, making fertiliser unnecessary.
• C. Wheat removes all microbes from the soil; beans add them back.
• D. Bean roots release nitrogen fertiliser directly into the soil.

Q15. Apart from making the dough fluffy, yeast also produces a small amount of another substance during respiration that gives the dough its slightly different smell. This substance is

• A. Lactic acid
• B. Alcohol
• C. Methane
• D. Glucose