Question Bank — The Invisible Living World: Beyond Our Naked Eye

QUESTION BANK

Chapter: The Invisible Living World: Beyond Our Naked Eye
(CBSE Class 8 – NCERT Curiosity, Chapter 2)

Section A — MCQs (10 questions, 1 mark each)

1. Which scientist first used the term “cell” after observing a thin slice of cork?
   (a) Antonie van Leeuwenhoek (b) Robert Hooke (c) Louis Pasteur (d) Alexander Fleming

2. The outermost layer in an onion peel cell that is absent in human cheek cells is:
   (a) Cell membrane (b) Cytoplasm (c) Cell wall (d) Nucleus

3. Assertion (A): Yeast is added to dough to make it soft and fluffy.
   Reason (R): Yeast respires and releases carbon dioxide that forms bubbles in the dough.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

4. Microorganisms that can be seen only under a microscope are collectively called:
   (a) Macro-organisms (b) Microorganisms (c) Multicellular organisms (d) Tissue

5. The part of the cell that controls all its activities and regulates growth is:
   (a) Cytoplasm (b) Cell membrane (c) Nucleus (d) Vacuole

6. Assertion (A): Rhizobium bacteria increase soil fertility without the addition of chemical fertilisers.
   Reason (R): Rhizobium lives in root nodules of legumes and converts atmospheric nitrogen into a form usable by plants.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

7. In Activity 2.2, safranin is used while preparing the onion peel slide because it:
   (a) Kills the cells (b) Makes the cells pink and increases visibility (c) Removes water (d) Prevents drying

8. Which of the following is a correct sequence of levels of organisation in a living body?
   (a) Organ → Tissue → Cell → Organism (b) Cell → Tissue → Organ → Organ system → Organism
   (c) Tissue → Cell → Organ system (d) Organism → Organ system → Cell

9. Bacteria that help convert milk into curd belong to the group:
   (a) Protozoa (b) Fungi (c) Lactobacillus (d) Algae

10. The large empty-looking space present in most plant cells but usually absent or very small in animal cells is:
    (a) Nucleoid (b) Chloroplast (c) Vacuole (d) Mitochondria

Section B — Very Short Answer (6 questions, 2 marks each)

1. State two differences between the shape of a muscle cell and a nerve cell. How does each shape help the cell perform its function?

2. What is the function of the cell membrane? Why is it described as porous?

3. Name the two scientists who made important contributions to the discovery of cells and microorganisms. Mention one contribution of each.

4. Why do gardeners collect dry leaves and plant waste in pits? What role do microorganisms play in this process?

5. List any two conditions required for the growth of microorganisms as mentioned in the chapter.

6. What is the difference between a unicellular and a multicellular organism? Give one example of each from microorganisms.

Section C — Short Answer (5 questions, 3 marks each)

1. Draw a neat labelled diagram of a plant cell showing at least five parts. Label the parts that are present only in plant cells.

2. Describe the step-by-step procedure of preparing a temporary mount of an onion peel as given in the chapter. Why is glycerin used?

3. Explain how microorganisms help in cleaning the environment. What would happen if microorganisms did not exist on Earth?

4. Differentiate between plant cell and animal cell on the basis of: (i) outermost covering, (ii) large vacuole, (iii) chloroplasts. Give one reason for each difference.

5. How do yeast and Lactobacillus help in the preparation of different food items? Give one example for each.

Section D — Long Answer (3 questions, 5 marks each)

1. Describe the levels of organisation in the body of a living organism with a labelled flow diagram. Explain how a single cell (egg) gives rise to a complete multicellular organism. (Diagram compulsory)

2. (a) Draw a labelled diagram of the experimental set-up used to show the effect of yeast on dough.
   (b) Explain the observations after 4–5 hours and the role of yeast, sugar and warm water in the process.

3. What are microorganisms? Describe any four different types of microorganisms observed in pond water or soil suspension with one identifying feature of each. How do these microorganisms show diversity in shape and structure?

Section E — Case/Source-Based (2 questions, 4 marks each)

Case 1

A student performed an activity using two bowls of flour dough. In bowl A, yeast and sugar were added before kneading with warm water. In bowl B, only sugar and warm water were added. Both bowls were covered and kept in a warm place. After 5 hours, the dough in bowl A had risen and become fluffy while the dough in bowl B remained unchanged.

(i) Name the microorganism responsible for the change in bowl A.
(ii) Which gas is released during the process and how does it make the dough fluffy?
(iii) Why was sugar and warm water added to the flour?
(iv) What would happen if the same activity was performed by keeping the bowls in a refrigerator? Give reason.

Case 2

A farmer grows beans and peas in his field every alternate season with wheat. He does not add nitrogen fertiliser to the soil when growing beans and peas but still gets a good yield. The roots of these plants show small swellings called nodules.

(i) Name the microorganism present in the root nodules.
(ii) How does this microorganism help the plant and the soil?
(iii) Why does the farmer prefer to grow legumes in rotation with other crops?
(iv) What would happen to soil fertility if only wheat was grown continuously without legumes?

Section F — HOTS and Application (4 questions, 3 marks each)

1. Predict-and-justify: What would happen if all microorganisms suddenly disappeared from the Earth? Explain at least three consequences with reasons.

2. Analyse an unexpected observation: In Activity 2.7, a student observed that fruit and vegetable peels mixed with dried leaves turned into dark-coloured manure faster than peels kept without dried leaves. Give a possible scientific reason for this observation.

3. Apply to an unfamiliar real-life situation: A bakery owner wants to make soft bread quickly during winter when the temperature is very low. Suggest two changes he should make in his usual method of dough preparation and justify why each change is necessary.

4. Compare two situations: Situation X: Curd is prepared by adding a spoonful of curd to lukewarm milk and keeping it in a warm place. Situation Y: The same amount of curd is added to cold milk and kept in a refrigerator. In which situation will curd form faster? Justify your answer by comparing the conditions required by the microorganism involved.