NCERT Solution For Class 9 Science Chapter 5

The Fundamental Unit of Life

NCERT Solution For Class 9 Science Chapter 5

Exercise-5.1 Page: 59

Who discovered cells, and how?

Solution:

Robert Hooke used a self-made microscope to study a small slice of cork in 1665, when he made the discovery of cells. It occurred to him that the cork looked like the design of a honeycomb, with its many small chambers. We call the little boxes that they are called cells.

NCERT Solution For Class 9 Science Chapter 5

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

Solution:

An entity is made up of its cells. A collection of cells becomes a tissue, then an organ, and finally an organ system. In both unicellular and multicellular organisms, they carry out essential bodily activities and processes as respiration, digestion, excretion, etc. Every task is completed by them on their own. As a result, cells are referred to as the basic and structural building blocks of life.

Exercise-5.2.1 Page: 61

How do substances like CO₂and water move in and out of the cell? Discuss.

Solution:

CO2 diffuses through space. While the concentration of CO2 in the outer environment is relatively lower, the waste products of the cell build up in high concentrations within the cell. Within the cell, CO2 diffuses from a location of higher concentration to a region of lower concentration due to the difference in concentration levels between the interior and exterior of the cell.
Through the cell membrane, H2O diffuses by osmosis. Until equilibrium is attained, it passes through a selectively permeable membrane from a region of higher concentration to a region of lower concentration.
NCERT Solution For Class 9 Science Chapter 5

Why is the plasma membrane called a selectively permeable membrane?

Solution:

Because it only allows specific chemicals to enter and exit cells, the plasma membrane is referred to as a selectively permeable membrane. Not every molecule can diffuse freely.

Exercise-5.2.2-5.2.4 Page: 63

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

Prokaryotic Cell

Eukaryotic Cell

1. Size: Generally small (1-10 μm)

1 μm = 10^-6m

2. Nuclear region:

______________________________

and known as ___________________

3. Chromosome: single

4. Membrane-bound cell organelles absent.

1. Size: Generally large (5-100 μm)

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

3. More than one chromosome.

4. ______________________________

______________________________

Solution:

Prokaryotic Cell

Eukaryotic Cell

1. Size: Generally small (1-10 μm)

1 μm = 10^-6m

2. The nuclear region is poorly defined due to the absence of a nuclear membrane and is known as the nucleoid.

3. There is a single chromosome.

4. Membrane-bound cell organelles absent.

1. Size: Generally large (5-100 μm)

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

3. There is more than one chromosome.

4. Membrane-bound cell organelles present.

Exercise-5.2.5 Page: 65

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

Solution:

Plasmids and mitochondria are the two organelles that possess genetic material of their own.
NCERT Solution For Class 9 Science Chapter 5

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

Solution:

When there is damage to the cells and they cannot be revived, the cells are broken down by enzymes and lysosomes. Lysosomes are sometimes referred to as “suicide bags” for this reason.

Why are lysosomes known as suicide bags?

Solution:

Lysosomes may burst, allowing the enzymes to devour their own cell when there is cell damage and revival is not possible. As a result, suicide sacks are another name for lysosomes.

NCERT Solution For Class 9 Science Chapter 5

Where are proteins synthesised inside the cell?

Solution:

In cells, ribosomes are where protein synthesis occurs. For this reason, ribosomes are sometimes called “protein factories.” Attached to the rough endoplasmic reticulum are particles known as ribosomes.

Exercise Page: 67

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

Solution:

The following table depicts the differences between plant cells and animal cells.

Characteristic	Plant Cell	Animal Cell
Cell Wall	Present	Absent
Shape of Cell	With distinct edges, the shape is either rectangular or square-shaped.	Round and irregular shape
Nucleus	Present. It lies on one side of the cell	Present. It lies in the centre of the cell
Lysosomes	Rarely present	Always present
Plastids	Present	Absent
Structure of Vacuoles	Single or a few large vacuoles that are centrally located	Presence of numerous and small vacuoles

NCERT Solution For Class 9 Science Chapter 5

How is a prokaryotic cell different from a eukaryotic cell?

Solution:

The following are the differences between prokaryotic and eukaryotic cells.

Prokaryotic Cell

Eukaryotic Cell

1. Size: Generally small (1-10 μm)

1 μm = 10^-6m

2. The nuclear region is not well defined as the nuclear membrane is absent and is referred to as the nucleoid.

3. There is a single chromosome.

4. Membrane-bound cell organelles absent.

1. Size: Generally large (5-100 μm)

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

3. There is more than one chromosome.

4. Membrane-bound cell organelles present.

NCERT Solution For Class 9 Science Chapter 5

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

Solution:

A rupture or breakdown of the plasma membrane will allow certain substances’ molecules to freely enter and exit cells. Osmosis or diffusion cannot carry out material exchange from the surrounding environment into a cell because the plasma membrane functions as a mechanical barrier. The protoplasmic substance would eventually vanish, causing the cell to perish.

NCERT Solution For Class 9 Science Chapter 5

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

Solution:

The Golgi apparatus is made up of stacks of vesicles that are joined by membranes and serve the following purposes:
• Keeping items stored
• Material packaging

• Production of substances

The Golgi apparatus prevents the cells from packaging and distributing materials that they have created. The development of cells also involves the Golgi apparatus. Therefore, there cannot be cell production in the absence of the Golgi apparatus.

NCERT Solution For Class 9 Science Chapter 5

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

Solution:

The powerhouse of the cell is referred to as the mitochondria. It does so by releasing the energy needed for various life tasks. Adenosine triphosphate (ATP) molecules, which are necessary for many of the chemical processes involved in living, are released from mitochondria. Consequently, ATP is frequently described as the “energy currency of the cell.”

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

Solution:

The endoplasmic reticulum (ER) is where proteins and lipids are synthesized.

7. How does an Amoeba obtain its food?

Solution:

An amoeba gets its food by a mechanism called endocytosis. Food particles are absorbed by it and form a food vacuole surrounding it, helped by the pseudopodia, since its cell membrane is sufficiently flexible. As soon as the food particle is captured, the amoeba secretes digestive enzymes to initiate the process of breaking down the particle.

NCERT Solution For Class 9 Science Chapter 5

NCERT Solution For Class 9 Science Chapter 5

8. What is osmosis?

Solution:

Osmosis is the term used to describe the flow of a water molecule across a semipermeable membrane from an area of higher concentration to one of lower concentration.

Carry out the following osmosis 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. Put each potato cup in a trough containing water. Now,

(a) Keep cup A empty

(b) Put one teaspoon sugar in cup B

(c) Put one teaspoon salt in cup C

(d) Put one teaspoon sugar in the boiled potato cup D.

Keep these for two hours. Then observe the four potato cups and answer the following:

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

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

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

Solution:

(i) When a difference in the concentration of water is seen, water collects in the hollowed sections of B and C. Thus, while the cells function as a semipermeable membrane, endosmosis takes place.
(ii) In order to compare the many conditions witnessed in this experiment, Potato A is crucial.

B, C, and D potato cups. As demonstrated by Potato A in this experiment, the potato cavity on its

Water does not move on its own.

(iii) Cup in A shows no indication of a shift in the water flow concentration necessary for osmosis to take place, which

demands more concentration than the other. Because the cells in cup D are dead, there isn’t

existence of a water-flowing semipermeable membrane. Osmosis does not happen as a result.
NCERT Solution For Class 9 Science Chapter 5

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

Solution:

A cell can divide in one of two ways:
• Meiosis and mitosis

The process of cell division known as mitosis is important in the development and repair of the body, whereas the process known as meiosis leads to the creation of gametes.

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