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Tag: Chapter 5 Class 9th Science NCERT Solutions

  • Class 9th Science Chapter-5 Exercises

    Exercise – Chapter 5: The Fundamental Unit of Life

    Question 1

    Make a comparison and write down ways in which plant cells are different from animal cells.

    Answer:

    Feature Plant Cell Animal Cell
    Cell wall Present Absent
    Plastids

    Present (chloroplasts, etc.)

    		 Absent
    Vacuole Large central vacuole Small or absent
    Shape

    Usually regular (rectangular)

    		 Usually irregular (rounded)
    Mode of nutrition Autotrophic Heterotrophic

    Question 2

    How is a prokaryotic cell different from a eukaryotic cell?

    Answer:

    Prokaryotic Cell Eukaryotic Cell
    No true nucleus True nucleus present
    Nuclear membrane absent

    Nuclear membrane present
    Single chromosome More than one chromosome
    Membrane-bound organelles absent

    Membrane-bound organelles present
    Smaller in size Larger in size

    Question 3

    What would happen if the plasma membrane ruptures or breaks down?

    Answer:

    If the plasma membrane ruptures, the cell contents will leak out, and the entry and exit of substances cannot be controlled.
    As a result, the cell will die.

    Question 4

    What would happen to the life of a cell if there was no Golgi apparatus?

    Answer:

    If the Golgi apparatus is absent:

    • Proteins and lipids will not be modified, packaged, or transported

    • Secretion from the cell will stop

    As a result, the cell will not function properly and may die.

    Question 5

    Which organelle is known as the powerhouse of the cell? Why?

    Answer:

    Mitochondria are known as the powerhouse of the cell because they produce energy in the form of ATP, which is required for all cellular activities.

    Question 6

    Where do the lipids and proteins constituting the cell membrane get synthesised?

    Answer:

    • Proteins are synthesised on ribosomes of rough endoplasmic reticulum (RER)

    • Lipids are synthesised in the smooth endoplasmic reticulum (SER)

    Question 7

    How does an Amoeba obtain its food?

    Answer:

    Amoeba obtains its food by endocytosis.
    It surrounds the food particle with pseudopodia, forming a food vacuole, where digestion takes place.

    Question 8

    What is osmosis?

    Answer:

    Osmosis is the movement of water molecules through a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.

    Question 9

    Potato Osmosis Experiment

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

    Answer:
    Sugar (B) and salt (C) create a hypertonic solution inside the potato cup.
    Water moves from the surrounding dilute solution into the cup by osmosis, so water gathers inside.

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

    Answer:
    Potato A acts as a control to show that osmosis does not occur without a solute inside the potato cup.

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

    Answer:

    • A: No solute is present, so no concentration difference exists.

    • D: Boiling destroys the living cells and the selectively permeable membrane, so osmosis does not occur.

    Question 10

    Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?

    Answer:

    • Mitosis is required for growth and repair of the body

    • Meiosis is involved in the formation of gametes

  • Class 9th Science Chapter-5 In-Text Questions

    Answers to In-Text Questions

    Chapter 5: The Fundamental Unit of Life

    Page No. 51 

    Question 1:

    Who discovered cells, and how?

    Answer:
    Cells were discovered by Robert Hooke in 1665. He observed a thin slice of cork under a self-designed microscope and noticed small box-like compartments, which he named cells.

    Question 2:

    Why is the cell called the structural and functional unit of life?

    Answer:
    The cell is called the structural unit of life because all living organisms are made up of cells.
    It is called the functional unit of life because all vital life processes such as respiration, nutrition, growth, and reproduction take place within cells.

    Page No. 53 

    Question 1:

    How do substances like CO₂ and water move in and out of the cell? Discuss.

    Answer:

    • Carbon dioxide (CO₂) moves in and out of the cell by diffusion.
      It moves from a region of higher concentration to lower concentration across the plasma membrane.

    • Water moves in and out of the cell by osmosis, which is the movement of water through a selectively permeable membrane from a region of higher water concentration to lower water concentration.

    Thus, diffusion helps in gaseous exchange, while osmosis helps in the movement of water across the cell membrane.

    Question 2:

    Why is the plasma membrane called a selectively permeable membrane?

    Answer:
    The plasma membrane is called selectively permeable because it allows some substances (like gases and water) to pass through it while preventing the movement of other substances.
    This property helps the cell to maintain its internal environment.

    Page No. 55 

    Question:

    Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

    Prokaryotic Cell Eukaryotic Cell
    1. Size: generally small (1–10 µm)

    1. Size: generally large (5–100 µm)
    2. Nuclear region: not well defined and not surrounded by a nuclear membrane

    2. Nuclear region: well defined and surrounded by a nuclear membrane

    3. Chromosome: single chromosome

    		 3. More than one chromosome

    4. Membrane-bound cell organelles: absent

    		 4. Present

    Answer (in words, for exams):

    • Prokaryotic cells have a poorly defined nuclear region, single chromosome, and lack membrane-bound organelles.

    • Eukaryotic cells have a well-defined nucleus, more than one chromosome, and membrane-bound organelles present.

    Page No. 57 

    Question 1:

    Can you name the two organelles we have studied that contain their own genetic material?

    Answer:
    The two organelles that contain their own genetic material (DNA) are:

    1. Mitochondria

    2. Plastids (chloroplasts)

    Question 2:

    If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

    Answer:
    If the organisation of a cell is destroyed, the cell will not be able to perform its vital functions.
    As a result, the cell will die.

    Question 3:

    Why are lysosomes known as “suicide bags” of the cell?

    Answer:
    Lysosomes contain powerful digestive enzymes.
    When a cell is damaged or old, lysosomes may burst and digest the cell itself, leading to cell death.
    Hence, lysosomes are called the “suicide bags” of the cell.

    Question 4:

    Where are proteins synthesised inside the cell?

    Answer:
    Proteins are synthesised on ribosomes, which are present:

    • On the rough endoplasmic reticulum (RER)

    • Freely in the cytoplasm