JAC Board Class 9th Science Solutions Chapter 5 The Fundamental Unit of Life
JAC Class 9th Science The Fundamental Unit of Life InText Questions and Answers
Page 59
Question 1.
Who discovered cells and how?
Answer:
Robert Hooke discovered cells in 1665. He observed the cells in thin slices of cork. They appeared like small compartments when viewed under the microscope.
Question 2.
Why is the cell called structural and functional unit of life?
Answer:
A cell is capable of carrying out all the life functions such as nutrition, excretion, respiration, etc Hence, a cell is called the functional unit of life. Additionally, the cell is the smallest unit of life and all the living beings are made up of cells. Therefore, a cell is called the structural unit of life.
Page 61
Question 1.
How do substances like CO, and water move in and out of the cell? Discuss.
Answer:
Substances move in and out of the cell because of diffusion. Diffusion is the random movement of particles in order to attain concentration equilibrium. The movement of water molecules through a semi – permeable membrane is called osmosis. It is important to note that plasma membrane is a semi – permeable membrane. Water always moves from its higher concentration to its lower concentration.
Question 2.
Why is the plasma membrane called a selectively permeable membrane?
Answer:
Plasma membrane allows passage to some selected substances. Hence, it is called a selectively permeable or semi- permeable membrane.
Page 63
Question 1.
Fill in the gaps in the following table illustrating difference between prokaryotic and eukaryotic cells.
| Prokaryotic cell | Eukaryotic cell |
| (a) Size: generally small (1 – 10µm) | (a) Size: generally large (5 – 100µm) |
| (b) Nuclear region ……………. ………………… …………………and known as …. ………………… |
(b) Nuclear region: well – defined and surrounded by a nuclear membrane. |
| (c) Chromosome: single | (c) More than one chromosome. |
| (d) Membrane bound cell organelles absent. | (d) …………… ………………. ………………. |
Answer:
- Prokaryotic cell (b): Nuclear region is poorly defined due to absence of a nuclear membrane and is known as nucleoid.
- Eukaryotic cell (d): Membrane bound cell organelles are present.
Page 65
Question 1.
Can you name the two organelles we have studied that contain their own genetic material?
Answer:
Mitochondria and chloroplast contain their own genetic material.
Question 2:
If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer:
Various parts of a cell are responsible for various functions. They work in tandem
to continue life in the cell. In case, the organisation of a cell is destroyed due to some physical or chemical influence, the cell will die.
Question 3.
Why are lysosomes known as suicide bags?
Answer:
Lysosomes contain digestive enzymes. In case of a rupture in lysosomes, the enzymes are released in the cytoplasm and end up digesting the contents of the cell. This results in cell death. Due to this, lysosomes are also known as suicide bags of cells.
Question 4.
Where are proteins synthesised inside the cell?
Answer:
The proteins are synthesised in the ribosomes present on RER (rough endoplasmic reticulum). They are also known as protein factories.
JAC Class 9th Science The Fundamental Unit of Life Textbook Questions and Answers
Question 1.
Make a comparison and write the ways in which plant cells are different from animal cells.
Answer:
| Plant cell | Animal cell |
| (a) Plant cells have cell wall. | (a) Animal cells don’t have a cell wall. |
| (b) They contain chloroplast. | (b) They don’t have chloroplasts. |
| (c) They do not have centrioles. | (c) Centriole is present in them. |
| (d) Vacuole is large and present in centre of the cell. | (d) Vacuoles are numerous and small. |
| (e) Nucleus is present at the periphery of the plant cell. | (e) Nucleus is present in the centre of the animal cell. |
Question 2.
How is a prokaryotic cell different from a eukaryotic cell?
Answer:
| Prokaryotic cell | Eukaryotic cell |
| (a) Cell size is generally small (1 – 10µm). | (a) Cell is , generally large (5 – 100µm). |
| (b) Nuclear region, called nucleoid, is not surrounded by a nuclear membrane. | (b) Nuclear material is surrounded by a nuclear membrane. |
| (c) Nucleolus is absent. | (c) Nucleolus is present. |
| (d) Membrane bound cell organelles are absent. | (d) Cell organelles bounded by membrane are present. |
| (e) Cell division by fission or budding (no mitosis). | (e) Cell division by mitosis or meiosis. |
Question 3.
What would happen if the plasma membrane ruptures or breaks down?
Answer:
Plasma membrane provides a container for the cell organelles and cytoplasm. Moreover, plasma membrane also protects the contents of a cell from external environment. In case the plasma membrane ruptures or breaks down, the cell contents would be exposed to the external environment. This would prove lethal for the cell and the cell would cease to exist.
Question 4.
What would happen to the life of a cell if there was no Golgi apparatus?
Answer:
If Golgi apparatus is not present, the packaging and transport of materials would cease to happen. Various substances would not be transformed into useful materials of the cell. Plasma membrane will also be affected The secretory activities of the cell would also cease to occur. Hence, the cell will eventually die off.
Question 5.
Which organelle is known as the powerhouse of the cell? Why?
Answer:
Mitochondrion is known as the powerhouse of the cell. The reason for this is the fact that cellular respiration takes place in mitochondria and the energy released after that, gets stored in mitochondria in the form of ATP. As ATP instantly provides energy, they are called energy currency of the cell.
Question 6.
Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer:
Lipids are synthesised in the endoplasmic reticulum (smooth ER). Protein is synthesised in ribosomes which are usually present on the rough ER.
Question 7.
How does Amoeba obtain its food?
Answer:
Amoeba obtains its food through a process called phagocytosis. The cell membrane of amoeba is projected into numerous finger – like outgrowths called pseudopodia Amoeba surrounds a food particle by pseudopodia and makes a food vacuole after engulfing the food.
Question 8.
What is osmosis?
Answer:
Osmosis is the process of movement of water molecules from a region of higher water concentration, through a semi – permeable membrane, to a region of lower water concentration.
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:
1. Explain why water gathers in the hollowed portion of B and C.
2. Why is potato A necessary for this experiment?
3. Explain why water does not gather in the hollowed out portions of A and D.
Answer:
- Water gathers in the hollowed portion of potato B and C because: Living plasma membrane of potato cells act as semi – permeable membrane. There is higher concentration of water in trough than the hollowed portions of B and C. So water, by the process of osmosis, moves into the hollowed portions of potato cups B and C.
- Potato cup A is kept empty to act as control set – up.
- potato is necessary because
- (a) As the potato cup A is empty, water does not gather in hollowed out portions of A.
- (b) In the potato cup D, the potato cell membrane lose semi – permeability due to boiling. So, no water movement occurs from the trough into the potato cup D.
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:
Growth and repair of body – Mitosis. Formation of gametes – Meiosis.