Class 9 Science Exploration Cell the Building Block of Life Excercise 

1. Differentiate between the following pairs of terms based on the clues given in parentheses:

(i) Cell membrane and cell wall (permeability)

(ii) RER and SER (structure)

(iii) Chloroplasts and chromoplasts (pigments)

2. Two similar animal cells are placed in two different solutions:

Cell X is placed in pure water.

Cell Y is placed in a concentrated salt solution.

24

Exploration | Grade 9

Cell: The Building Block of Life

Cells are observed after some time. Cell X swells, and Cell Y shrinks. Which statement provides the correct explanation for the above observations?

(i) Salt molecules moved into Cell Y, causing it to shrink.

(ii) Water moved into Cell X and more water moved out of Cell Y than the salt solution entered in it.

(iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.

(iv) Solute movement caused osmosis in both cells.

3. Look at the diagram of a cell in Fig. 2.20. Identify the parts labelled from (a) to (g) and correctly match them with their functions given below:

(i) Controlling all the activities of a cell.

(ii) Site of cellular respiration.

(iii) Storage organelle that also provides rigidity to the cell.

(iv) Separates the cell contents from surroundings.

(v) Provides structural rigidity to the cell.

(vi) Packs and stores materials received from ER.

(vii) Helps in manufacturing food.

Fig. 2.20

(1)

4. Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories?

Option Present in the plant cells

(n)

(b)

(c)

Absent in the animal cells

Leucoplast

(11)

Mitochondria

Cell wall

18

(iii)

Cell wall

(iv)

Ribosome

Golgi apparatus

Lysosome

23

(d)

(e)

(४)

:

Endoplasmic reticulum

5. Two students, Renu and Rohit, were having a discussion on the plastids. Renu emphasised that all parts of the plants, even roots, contain plastids. However, Rohit did not agree with the statement and told her that plastids are absent in plant roots since the roots are underground and do not need to perform photosynthesis. Who is correct? Justify your answer.

6. Mitochondria and chloroplasts are two important organelles in a plant cell. Discuss how these two organelles are structurally and functionally similar to each other, and different from each other.

7. Which of the following pairs of cell organelles contains DNA?

(i) Chloroplasts, Ribosomes

(ii) Mitochondria, Nucleus

(iii) Golgi bodies, Ribosomes

(iv) Nucleus, Lysosomes

8. A researcher carried out an experiment in which she took two carrots of similar size. She placed one carrot in plain water and the other carrot in concentrated salt solution (l'ig. 2.21). After 24 hours she recorded her observations.

Fig. 2.21: Experimental

set-up having carrol (a) in plain water, and (b) in salt solution

(i) What hypothesis does she want to test through this experiment?

(ii) What would you suggest for the improvement of this experiment?

(iii) Why does the carrot in plain water stay stiff and crunchy, but the carrot in concentrated salt solution become rubbery and limp?

9. Indicate the presence or absence of following structures in bacterial and animal cells:

Structures in a cell

Bacterial cell

Animal cell

Chromosome

Nucleus

Mitochondria

Golgi complex

Chromoplasts

10. Carry out the following experiment:

Take four peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Place each of the potato cups in a beaker containing water (lig. 2.22). Now, set up the experiment as follows:

(a) Keep Cup A empty.

(b) Add one teaspoon sugar in Cup B.

(c) Add one teaspoon salt in Cup C.

(d) Add one teaspoon sugar in the boiled potato in Cup D.

Observe the four potato cups at least two hours and answer the following questions:

(1) Explain why water gathers in the hollowed portion of Cup B and Cup C.

(ii) Why is Cup A necessary for this experiment?

(iii) Explain why water does not gather in the hollowed portions of Cups A and D.

Fig. 2.72: Experimental set-up

11. Identify the pair that incorrectly matches the cell organelle with its function.

(i) Ribosome-Protein synthesis

(ii) SER Lipid and cellulose synthesis

(iii) Lysosome Digestion of foreign agents

12. What outcome do you expect, if all the mitochondria are removed from a eukaryotic cell?

13. Which phenomenon inhibits the formation of tumors in the human body? Can plants also develop tumors? Explain.

26 Exploration | Grade 9

Cell: The Building Block of Life

14. The cell membrane of a cell is made up of proteins and lipids. Which cell organelles help in the synthesis of cell membrane? Write the path of these compounds from their site of synthesis to the cell membrane and show this through a labelled diagram.

15. What would happen if gametes are formed by mitotic divisions?

Answers

1. Differentiate between the following pairs

(i) Cell membrane and Cell wall (Permeability)

Cell membrane Cell wall

Selectively permeable (allows only certain substances to pass). Freely permeable (allows most substances to pass).

(ii) RER and SER (Structure)

Rough Endoplasmic Reticulum (RER) Smooth Endoplasmic Reticulum (SER)

Ribosomes are present on its surface, giving it a rough appearance. Ribosomes are absent, so it appears smooth.

(iii) Chloroplasts and Chromoplasts (Pigments)

Chloroplasts Chromoplasts

Contain green pigment chlorophyll. Contain red, yellow, or orange pigments (carotenoids).

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2. Correct explanation

Correct answer: (iii)

Water moved into Cell X and moved out of Cell Y through the cell membrane.

Reason:

Cell X was placed in pure water (hypotonic solution), so water entered the cell by osmosis, causing it to swell.

Cell Y was placed in a concentrated salt solution (hypertonic solution), so water moved out of the cell by osmosis, causing it to shrink.

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3. Match the cell parts with their functions

Function Cell organelle

(i) Controlling all the activities of a cell Nucleus

(ii) Site of cellular respiration Mitochondrion

(iii) Storage organelle that also provides rigidity Vacuole

(iv) Separates the cell contents from surroundings Cell membrane

(v) Provides structural rigidity Cell wall

(vi) Packs and stores materials received from ER Golgi apparatus

(vii) Helps in manufacturing food Chloroplast

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4. Correct option

Correct answer: (iii)

Present in plant cells: Cell wall

Absent in animal cells: Cell wall

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5. Who is correct? Justify.

Renu is correct.

Justification: Plant roots also contain plastids, but they are usually leucoplasts, not chloroplasts. Leucoplasts store food such as starch, oils, and proteins. Since roots grow underground and do not receive sunlight, they generally lack chloroplasts for photosynthesis.

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6. Similarities and differences between mitochondria and chloroplasts

Similarities

Both are double membrane-bound organelles.

Both contain their own DNA and ribosomes.

Both can replicate independently inside the cell.

Both are involved in energy conversion.

Differences

Mitochondria Chloroplasts

Present in both plant and animal cells. Present only in plant cells and algae.

Site of cellular respiration. Site of photosynthesis.

Release energy in the form of ATP. Prepare food using sunlight.

Do not contain chlorophyll. Contain chlorophyll.

7. Which pair contains DNA?

Correct answer: (ii) Mitochondria and Nucleus.

Explanation: Both the nucleus and mitochondria contain their own DNA. Chloroplasts also contain DNA, but ribosomes, Golgi bodies, and lysosomes do not.

8. Carrot Experiment

(i) Hypothesis: The experiment tests that water moves into or out of plant cells by osmosis, depending on the concentration of the surrounding solution.

(ii) Improvement:

Use carrots of the same size and weight.

Measure the weight/length before and after the experiment.

Repeat the experiment several times for accuracy.

(iii) Explanation:

Carrot in plain water: Water enters the cells by osmosis, making them turgid (stiff and crunchy).

Carrot in concentrated salt solution: Water moves out of the cells by osmosis, making them flaccid (rubbery and limp).

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9. Presence or Absence of Structures

Structure Bacterial Cell Animal Cell

Chromosome Present Present

Nucleus Absent Present

Mitochondria Absent Present

Golgi complex Absent Present

Chromoplasts Absent Absent

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10. Potato Cup Experiment

(i) Water collects in Cups B and C because sugar and salt create a concentrated solution, so water enters the potato cup by osmosis.

(ii) Cup A acts as the control to compare the results.

(iii)

Cup A: No sugar or salt is present, so there is no concentration difference; therefore, no osmosis occurs.

Cup D: The potato is boiled, so its cell membrane is damaged. Without a selectively permeable membrane, osmosis cannot occur.

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11. Incorrectly matched pair

Answer: (ii) SER – Lipid and cellulose synthesis

Reason: SER synthesizes lipids, but cellulose is synthesized at the plasma membrane by cellulose-synthesizing enzymes, not by SER.

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12. What if all mitochondria are removed?

The cell will not be able to produce sufficient ATP (energy) through cellular respiration. As a result:

Cellular activities will stop.

The cell will eventually die.

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13. Tumor Formation

Phenomenon that prevents tumors: Contact inhibition.

Can plants develop tumors? Yes. Plants can develop tumors such as crown gall disease, usually caused by bacteria. However, these tumors generally do not spread throughout the plant like cancer in animals.

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14. Cell Membrane Synthesis

Organelles involved:

SER: Synthesizes lipids.

RER: Synthesizes membrane proteins.

Golgi apparatus: Modifies, packages, and transports them.

Vesicles: Carry them to the cell membrane.

Path:

Proteins: RER → Golgi apparatus → Vesicles → Cell membrane

Lipids: SER → Golgi apparatus → Vesicles → Cell membrane

Simple labelled diagram:

RER ───►

          \

           ► Golgi Apparatus ───► Vesicles ───► Cell Membrane

          /

SER ───►

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15. What would happen if gametes were formed by mitosis?

If gametes were formed by mitosis, they would have the same (diploid, 2n) number of chromosomes as body cells. After fertilization, the zygote would have double the normal chromosome number (4n), and the chromosome number would keep increasing in every generation. Therefore, gametes are formed by meiosis.

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16. Case Study (Visible questions answered)

(i) Why did adding salt, sugar, or jaggery help preserve the products?

They create a hypertonic environment, causing water to move out of microorganisms by osmosis, preventing their growth.

(ii) Which process is involved?

Osmosis (specifically exosmosis in microbial cells).

(iii) How did this benefit the farmer?

Reduced post-harvest losses.

Increased income through value-added products.

Reduced food wastage.