Page No: 59
1. Who discovered cells, and how?
Answer
An English Botanist, Robert Hooke discovered cells in 1665. While examining a thin slice of cork under a microscope, he noticed that the thin slice of cork resembled the structure of a honey comb consisting of many hexagonal compartments known as 'cells'.
2. Why is the cell called the structural and functional unit of life?
Answer
Cells are called the structural and functional unit of life because all the living organisms are made up of cells. All the functions taking place inside the body of organisms are performed by cells.
Page No. 61
1. How do substances like CO2 and water move in and out of the cell? Discuss.
Answer
Substances such as carbon dioxide move in and out of cells by the process of diffusion. In this process, there is a spontaneous movement of substances from a region of higher concentration to a region of their lower concentration.
Movement of water occurs by the process of osmosis. In this process, there is spontaneous movement of water from a region of higher concentration to a region of lower concentration across a selectively permeable membrane.
2. Why is the plasma membrane called a selectively permeable membrane?
Answer
Plasma membrane permits the entry and exit of selected materials in and out of the cell. It also prevents movement of some other materials. Hence, it is called a selectively permeable membrane.
Page No: 63
1. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
| Prokaryotic cell | . | Eukaryotic cell |
| 1. | Size: generally small ( 1-10 µm) 1 µm= 10-6 m | 1. | Size: generally large (5-100 µm) |
| 2. | Nuclear region: _____________________________ and is known as ________. | 2. | Nuclear region: well-defined and surrounded by a nuclear membrane |
| 3. | Chromosome: single | 3. | More than one chromosome |
| 4. | Membrane-bound cell organelles are absent | 4. | _________________________________ |
Answer
| Prokaryotic cell | | Eukaryotic cell |
| 1. | Size: generally small ( 1-10 µm) 1 µm== 10-6 m | 1. | Size: generally large (5-100 µm) |
| 2. | Nuclear region: poorly defined because of the absence of a nuclear membrane, and is known as nucleoid | 2. | Nuclear region: well-defined and surrounded by a nuclear membrane |
| 3. | Chromosome: single | 3. | More than one chromosome |
| 4. | Membrane-bound cell organelles are absent | 4. | Membrane-bound cell organelles such as mitochondria, plastids, etc., are present |
Page No: 65
1. Can you name the two organelles we have studied that contain their own genetic material?
Answer
Mitochondria and plastids
2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer
If the organisation of a cell is destroyed, it will stop performing basic functions and will ultimately die. Lysosomes present inside the cell will burst to release enzyme which will digest the cell.
3. Why are lysosomes known as suicide bags?
Answer
Lysosomes are called suicide bags because in case of disturbance of their cellular metabolism they digest their own cell by releasing own enzymes.
4. Where are proteins synthesized inside the cell?
Answer
In the Ribosome inside the cell.