BIOLOGY [2 Mark Question Answer]

All multicellular animals begin their life with a single cell, which divides and redivides to fonn many cells, leading to growth in size. This process goes on during the life of an organism. Hence, cell division fonns the basis of growth. Cell division also forms the basis of reproduction in living organisms. It leads to formation of two daughter cells from a parent cell in unicellular organisms. In higher living organisms, cell division leads to formation of male and female gametes and sexual reproduction takes place leading to birth of young ones.

Any function performed by an organism is due to the activity of the cells in its body. They are the basic unit of living organisms and mast by present for life to exist. They can exist independently (as in unicellular organisms like bacteria) or can divide and multiply to make multicellular organisms like man. Thats why they are called the building blocks of life they make up all living things.

CELL WALL is non living structure present outside the plasma membrane of plant cell. It is formed of cellulose.Functions of cell wall :

• Cell wall gives a definite shape to the cell.
• It also provides strength and rigidity to the cell.
• It provides protection to the plant cell.
• It allows the materials to pass in and out of the cell.

Nucleus controls all activities of the cell. It is called the control centre of the cell. It helps in cell division and its stores all genetic information of the cell and without it, a cell won’t be able to function. Hence, nucleus is the most important part of a cell.

Cell theory was given by Schleiden and Schwann in the year 1838-1839. It was refined further by Rudolf Virchow. The main postulates of cell theory are :

• All living beings are made up of one or more cells.
• Cells are the basic structural and functional unit of all living beings.
• All cells are basically alike in chemical composition and metabolic processes.
• New cells arise by division of pre existing cells. (Rudolf Virchow)

All living organisms, unicellular or multicellular “are made up of cells. Microscope makes it possible to see inside the cells’ that make up all living organisms. Without microscope we could not see or understand, how life works. So the invention of microscope made it possible to see the basic component of life.

Three kinds of plastids are present in plants – chromoplasts, chloroplasts and leucoplasts. Among above three, chromoplasts are of different colours which provide different colours yellow to papaya, green to spinach and red to edible part of watermelon.

Cell division is a process by which a cell divides, forming two new cells. It is the basis of growth and reproduction of an organism. The life of all multicellular organisms begin with single cell. This cell divided and redivides, there by forming a cluster of many cells. So cell division is necessary for growth.

A cell is called the structural unit of life because all living organism irrespective of their size, shape and complexity are made up of cells and functions performed by organism is the result of the activity of the cells in its body.