The Fundamental Unit Of Life

Q57. What would happen if the plasma membrane ruptures or breaks down? 

Ans. This is the outermost covering of the cell that separates the contents of the cell from its external environment. The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. In case of rupturing of the plasma membrane, the protoplasmic contents will get dispersed in the surrounding medium and thus cell will disintegrate. Consequently, the cell would die due to the disappearance of the protoplasmic material.

Q58. Following are a few definitions of osmosis. Read carefully and select the correct definition.

(a) Movement of water molecules from a region of higher concentration to a region of lower concentration through a semi- permeable membrane.

(b) Movement of solvent molecules from its higher concentration to lower concentration.

(c) Movement of solvent molecules from higher concentration to lower concentration of solution through a permeable membrane.

(d) Movement of solute molecules from lower concentration to higher concentration of solution through a semi-permeable membrane.

Ans. (a) Movement of water molecules from a region of higher concentration to a region of lower concentration through a semi- permeable membrane.

Explanation:

Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.

Q59. Name the organelles which show the analogy written as under

(a) Transporting channels of the cell _______

(b) Power house of the cell _______

(c) Packaging and dispatching unit of the cell _______

(d) Digestive bag of the cell _______

(e) Storage sacs of the cell _______

(f) Kitchen of the cell _______

(g) Control room of the cell _______

Ans. (a) Endoplasmic reticulum

(b) Mitochondria

(c) Golgi apparatus

(d) Lysosome

(e) Vacuoles

(f) Chloroplasts

(g) Nucleus

Q60. The cell organelle involved in forming complex sugars from simple sugars are

(a) endoplasmic reticulum

(b) ribosomes

(c) plastids

(d) Golgi apparatus.

Ans. (d) Golgi apparatus

Explanation:

The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. Its functions include the storage, modification and packaging of products in vesicles. In some cases, complex sugars may be made from simple sugars in the Golgi apparatus.

Q61. Differentiate between nucleus and nucleoid.

Ans. 

Q62. Write a short note on plastids.

Ans. Plastids are present only in plant cells. There are two types of plastids – chromoplasts (coloured plastids) and leucoplasts (white or colourless plastids). Plastids containing the pigment chlorophyll are known as chloroplasts. Chloroplasts are important for photosynthesis in plants. Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll. Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules are stored.

Q63. Why is endocytosis found in animals only?

Ans. The flexibility of the cell membrane also enables the cell to engulf in food and other material from its external environment. Such processes are known as endocytosis. Amoeba acquires its food through such processes. This is possible only when plasma membrane is in direct contact with external environment. It occurs only in animal cells. In plant cells, a cell wall is present over the plasma membrane. Therefore, their plasma membrane cannot perform endocytosis.

Q64. Which out of the following is not a function of vacuole?

(a) Storage

(b) Providing turgidity and rigidity to the cell

(c) Waste excretion

(d) Locomotion

Ans. (d) Locomotion

Explanation:

In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell. Many substances of importance in the life of the plant cell are stored in vacuoles. These include amino acids, sugars, various organic acids and some proteins. In single-celled organisms like Amoeba, the food vacuole contains the food items that the Amoeba has consumed. In some unicellular organisms, specialised vacuoles also play important roles in expelling excess water and some wastes from the cell.

Q65. Make a comparison and write down ways in which plant cells are different from animal cells.

Ans. 

Q66. How is a prokaryotic cell different from a eukaryotic cell?

Ans. 

Q67. How is a bacterial cell different from an onion peel cell?

Ans. 

Q68. What are the consequences of the following conditions?

(a) A cell containing higher water concentration than the surrounding medium.

(b) A cell having low water concentration than the surrounding medium.

(c) A cell having equal water concentration to its surrounding medium.

Ans. (a) If the medium has a lower concentration of water than the cell, meaning that it is a very concentrated solution, the cell will lose water by exosomosis. The cell will ultimately shrink.

(b) If the medium surrounding the cell has a higher water concentration than the cell, meaning that the outside solution is very dilute, the cell will gain water by endosmosis and the cell will ultimately swell up.

(c) If the medium has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrane.

Q69. How do substances like CO₂ and water move in and out of the cell? Discuss.

Ans. Some substance like CO₂ (which is cellular waste and requires to be excreted out by the cell) accumulates in high concentrations inside the cell. As soon as there is a difference of concentration of CO₂ inside and outside a cell, CO₂ moves out of the cell, from a region of high concentration, to a region of low concentration outside the cell by the process of diffusion.

Water moves in and out of the cells by osmosis.  Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.