Biology Class 9 : Chapter 5 - The Fundamental Unit of Life

In this page you get NCERT Solution Class 9 Science (Biology) Chapter 5 The Fundamental Unit of Life being given. Science have three parts. Science (Biology) Class 9th has been set by the CBSE Board. The speciality of this page is that here you can download pdf of NCERT Solution Class 9 Science (Biology). I expect that the given Class 9 Science (Biology) Solution Chapter 5 The Fundamental Unit of Life will be immensely useful to you.

Chapter - 5

The Fundamental Unit of Life

Page 59

Question 1. Who discovered cells, and how?

Answer: Robert Hooke discovered cells in 1665 while examining a thin slice of cork through a self-designed microscope. He saw that the cork resembled the structure of a honey comb consisting of many little compartments. These small boxes are called cells.

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

Answer: A cell is capable of independently carrying out all necessary activities of life. So, they are called basic or functional unit of life.

Page 61

Question 1. How do substances like CO₂ and water move in and out of the cell? Discuss.

Answer: CO₂ moves by diffusion and H₂O move by osmosis through cell membrane.

Question 2. Why is the plasma membrane called a selectively permeable membrane?

Answer: It is called selectively permeable membrane because it allows the entry and exit of some substances, not all.

Page 63

Question 1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Answer: Prokaryotic cell

1. Size generally small.

2. Nuclear region.

Is poorly defined due to absence of a nuclear membrane and know as nucleoid.

3. Single Chromosome.

4. Membrane bound cell organelles absent.

Eukaryotic cell

1. Size generally large.

2. Nuclea rregion.

Well defined and surrounded by a nuclear membrane.

3. More than one chromosome.

4. Membrane bound cell organelles present.

Page 65

Question 1. Can you name the two organelles we have studied that contain their own genetic material?

Answer: The two organelles which have their own genetic material are:

1. Mitochondria   2. Plastids

Question 2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?

Answer: The cell will not be able to revive and lysosomes will digest it.

Question 3. Why are lysosomes known as suicide bags?

Answer: When the cell gets damaged, lysosomes may burst, and the enzymes digest their own cell. Therefore lysosomes are known as suicide bags.

Question 4. Where are proteins synthesised inside the cell?

Answer: The proteins are synthesised in the ribosomes that are also known as protein factories. 

Exercises

Question 1. Make a comparison and write down ways in which plant cells are also different from animal cells.
Answer:
Plant Cell
1. Plant cells have cell wall.
2. They contain chloroplast.
3. They do not have centriole.
4. Vacuole is large and present in centre of the cell.
5. Nucleus is present in the side of the plant cell.

Animal Cell
1. Animal cells don’t have a cell wall.
2. They don't have chloroplasts.
3. Centriole is present in them.
4. Vacuole is small.
5. Nucleus is present in the centre of the animal cell.


Question 2. How is prokaryotic cell different from a eukaryotic cell?
Answer: The following are the differences between prokaryotic and eukaryotic cells.




Question 3. What would happen if the plasma membrane ruptures or breaks down?
Answer: If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out of the cells. As plasma membrane acts as a mechanical barrier, exchange of material from its surroundings through osmosis or diffusion in a cell won't take place. Consequently, the cell would die due to the disappearance of the protoplasmic material.


Question 4. What would happen to the life of a cell if there was no Golgi apparatus?
Answer: The Golgi apparatus consists of stacks of membrane-bound vesicles whose functions are as follows:
• storage of substances
• packaging of substances
• manufacture of substances
Without the golgi apparatus, the cells will be disabled from packing and dispatching materials that were produced by the cells. The golgi apparatus is also involved in the formation of cells. Hence, in the absence of golgi apparatus, cells will not be produced.


Question 5. Which organelle is known as the powerhouse of the cell? Why?
Answer: 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) molecules, essential for numerous chemical activities of life. Hence ATP is often referred to as 'energy currency of the cell’.


Question 6. Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer: Lipids and proteins are synthesised in the ER [Endoplasmic Reticulum],


Question 7. How does an Amoeba obtain its food?
Answer: 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 food is trapped.

Question 8. What is osmosis?
Answer: 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.


Question 9. 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.
Answer: (i) Water accumulates in the hollowed portions of B and C as a difference in the water concentration is observed. Thereby, endosmosis occurs as the cells act as a semipermeable membrane.
(ii) Potato A is essential in this experiment as it is significant to compare different scenarios seen in potato cups B, C and D. The potato A in this experiment clearly shows that the potato cavity on its own cannot bring about water movement.
(iii) Cup in A does not show any change in the water flow concentration for osmosis to occur, which requires the concentration to be higher than the other. Cells in cup D are dead, thus there is no existence of a semipermeable membrane for water flow. Consequently, 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: There are two ways in which a cell divides:
• Mitosis
• Meiosis
Mitosis is the type of cell division that is involved in the growth and repair of body whereas meiosis is a type of cell division which results in the formation of gametes.