शनिवार, 29 जुलाई 2017


(Page No. 59)
1. Who discovered cells, and how?

Ans. In 1665, an English scientist named Robert Hooke discovered cells. When he saw honey comb like structure while observing thin slice of cork under his self-designed microscope.

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

Ans. All living organisms are made up of cells so cell is the basic building unit of a living organism and all the activities performed by a living organism are sum total of activities performed by its cells hence cell is called the structural and functional unit of life.

(Page No.61)

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

Ans. The exchange of gases  between cells takes place by diffusion process.

Diffusion is defined as movement of a substance from a region of higher concentration to lower concentration.  is formed inside cell due to respiration and it accumulates in the cell so its concentration is high in the cell as compared to the surroundings. On the other hand is utilized inside cell during respiration and therefore its concentration decreases inside the cell while remains comparatively high in the surroundings. As a result diffuses out and diffuses into the cell.

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

Ans. Plasma membrane is a highly specific structure. It is made up of lipids and proteins who selectively allow the entry of substance into cell and exit of some other substances from the cell i.e. selectively permeable.

(Page No.63)

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


(Page No.65)

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

Ans. Chloroplast and Mitochondria.

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

Ans. If the organisation of a cell is destroyed due to some physical or chemical influence then such cell would not survive any more as all components of that cell are digested up by its lysosomes.

3. Why are lysosomes known as suicide bags?

Ans. Lysosomes are cell organelles filled with hydrolytic(digestive) enzymes. When a cell is damaged, its lysosomes may burst out and its enzymes digest up its own cell. Due to this, we can say that lysosomes are suicide bags.

4. Where are proteins synthesised inside the cell?

Ans. Ribosomes are the sites for protein synthesis inside the cell.

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