Class 9 Science Chapter 5 The Fundamental Unit Of Life

 1. Who discovered cells, and how?

Solution:

In 1665, Robert Hooke discovered cells while examining a thin slice of cork through a self-designed microscope. He observed that the cork resembled the structure of a honeycomb consisting of numerous tiny compartments. The minuscule boxes are referred to as cells.

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

Solution:

Cells form the structure of an entity. A group of cells form a tissue, further an organ and ultimately an organ system. They perform fundamental functions and life processes such as respiration, digestion, excretion etc., in both unicellular and multicellular entities. They perform all the activities independently. Hence, cells are referred to as structural and fundamental units of life.

3. Why is the plasma membrane called a selectively permeable membrane?

Solution:

The plasma membrane is called as a selectively permeable membrane as it permits the movement of only certain molecules in and out of the cells. Not all molecules are free to diffuse.

4. Why are lysosomes known as suicide bags?

Solution:

When there is damage to the cell and when revival is not possible, lysosomes may burst, and the enzymes digest their own cell. Consequently, lysosomes are known as suicide bags.

5. Where are proteins synthesised inside the cell?

Solution:

Protein synthesis in cells takes place in ribosomes. Hence, ribosomes are also referred to as protein factories. Ribosomes are particles that are found attached to the rough endoplasmic reticulum.

6. 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

7. 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.

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

Solution:

If the plasma membrane ruptures or breaks down, then molecules of some substances will freely move in and out of the cells.

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

Solution:

Mitochondria are known as the powerhouse of the cell. It is because it releases the energy required for different activities of life. Mitochondria releases energy in the form of ATP (Adenosine triphosphate).

10. How does an Amoeba obtain its food?

Solution:

Through the process of endocytosis, an Amoeba obtains its food. As its cell membrane is flexible enough, food particles are engulfed, forming a food vacuole girdling it, which is assisted by the pseudopodia. Amoeba secretes digestive enzymes to bring about digestion of the engulfed particle once the food is trapped.

11. What is osmosis?

Solution:

The process of movement of a water molecule from a region of higher concentration to a region of lower concentration through a semipermeable membrane is known as osmosis.

BIOLOGY CLASS IXth NOTES FOR CBSE SCHOOLS EXAMINATIONS PICKED BY THE PROFESSIONAL ACADEMIC TEACHERS OF THE SIDDIQUI ACADEMY®.