The Fundamental Unit of Life

Science

NCERT

1   Who discovered cells and how?

Solution :

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?

Solution :

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. All cells vary in their shape, size, and activity they perform. In fact, the shape and size of the cell is related to the specific functions they perform.

3   How do substances like $CO_2$ and water move in and out of the cell? Discuss.

Solution :

The cell membrane is selectively permeable and regulates the movement of substances in and out of the cell. $\\$ $\textbf{Movement of CO 2 : }$$\\$ $CO_2$ is produced during cellular respiration. Therefore, it is present in high concentrations inside the cell. This $CO_2$ must be excreted out of the cell. In the cell’s external environment, the concentration of $CO_2$ is low as compared to that inside the cell. Therefore, according to the principle of diffusion, $CO_2$ moves from a region of higher concentration (inside the cell) towards a region of lower concentration (outside the cell). Similarly, $O_2$ enters the cell by the process of diffusion when the concentration of $O_2$ inside the cell is low as compared to its surroundings.$\\$ $\textbf{Movement of water:}$$\\$ 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.

4   Why is the plasma membrane called a selectively permeable membrane?

Solution :

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.

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

Solution :

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