IN TEXT QUESTIONS:

(IN TEXT QUESTIONS: ( Page  59)

1: Who discovered cells and how.

Ans: Cells were discovered in 1665 by an English Botanist, Robert Hooke. He used a primitive microscope to observe cells in a cork slice.

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

Ans: Cells constitute various components of plants and animals. A cell is the smallest unit of life and is capable of all living functions. Cells are the building blocks of life. This is the reason why cells are referred to as the basic structural and functional units of life.

 

(IN TEXT QUESTIONS) ( Page  61)

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

Ans: The cell membrane is selectively permeable and regulates the movement of substances in and out of the cell.
Movement of CO₂:  CO₂ is produced during cellular respiration, it is present in high concentrations inside the cell. This CO₂ must be excreted out of the cell. In the cell’s external environment, the concentration of CO₂ is low as compared to that inside the cell. Therefore, according to the principle of diffusion, CO₂ moves from a region of higher concentration (inside the cell) towards a region of lower concentration (outside the cell). Similarly, O₂ enters the cell by the process of diffusion when the concentration of  O₂ inside the cell is low as compared to its surrounding.
Movement of Water: Water moves from a region of high concentration to a region of low concentration through the plasma membrane. The plasma membrane acts as a semi-permeable membrane, and this movement of water is known as osmosis. However, the movement of water across the plasma membrane of the cell is affected by the amount of substance dissolved in water.

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

Ans: The cell membrane or the plasma membrane is known as a selectively permeable membrane because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.

(IN TEXT QUESTIONS) ( Page  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.	______________________________________________________________________________________

Ans::

	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

 

(IN TEXT QUESTIONS) ( Page  65)

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

Ans: Mitochondria and Plastids are the two organelles that contain their own genetic material. Both these organelles have their own DNA and ribosomes.

2: If the organization of a cell is destroyed due to some physical or chemical influence, what will happen

Ans: Cell is the smallest unit of life, which is capable of all living functions. If the organization of a cell is destroyed due to some physical or chemical influence, then the ability of the cell to perform all living functions such as respiration, nutrition, excretion, etc. would be affected.

3: Why are lysosomes known as suicide bags

Ans: Lysosomes are membrane-bound vesicular structures that contain powerful digestive enzymes. These enzymes are capable of breaking down any foreign food particle or microbes entering the cell. Sometimes, lysosomes can cause self-destruction of a cell by releasing these digestive enzymes within the cells. Hence, they are also known as ‘suicidal bags’.

4: Where are proteins synthesized inside the cell

Ans: Ribosomes are the site for protein synthesis. Ribosomes are very small structures found either in a free state, suspended in the cytoplasm, or attached to the surface of the endoplasmic reticulum. They are composed of ribonucleic acids and proteins.