Cell Number, Shape and Size - Class 8 Notes

Organisms show Variety in Cell Number, Shape, and Size: Human beings consist of trillions of cells. Single-celled organisms are known as unicellular organisms—for example- bacteria, protists, and yeast. Multi-cellular organisms consist of more than one cell. Examples are humans, cows, dogs, and so on. Cells provide shape to the body which can be rounded, spherical, or elongated. In some organisms, the size can be as small as 0.0001mm, and large in some organisms up to six to twelve inches.

Number of Cells

Human beings consist of trillions of cells. Unicellular organisms consist of single cells whereas multicellular organisms consist of more than one cell. Every living organism starts its life from a single cell, that is a fertilized egg and then it further divides into thousands and then millions. Unicellular organisms are capable of performing all required functions similar to multicellular organisms. Unicellular organisms like amoeba capture the food digest it and then excretes it out. These organisms also grow and reproduce. In multi-cellular organisms, these similar functions are performed by a group of special cells known as tissues and later on these tissues form the organs.

Shape and Structure of the Cell

There are different types of cells, shapes, and sizes from which the living organisms are made. The shape of an animal cell is rounded, spherical, or elongated whereas plant cells are rectangular and rigid in shape. Some of the cells are long and pointed on both ends such are spindle shape cells which help in movement. Some also consist of long and branched-like nerve cell which is used to transfer and receive the signals. Muscle cells are small. The cell membrane provides the shape to the animal and plant cells. The cell wall provides the additional covering to the cell membrane. This cell wall is present in the plant cells which provides shape and rigidity to the cell.

Cell Size

The size of the cell are variable. In some organisms it can be small as 0.0001mm and can be large in some organisms up to six to twelve inches. Majority of the cells can't be seen through naked eyes special microscopes are there to see those cells. Unicellular organisms are seen through the microscopes like the bacteria whereas single cell like the egg are large.

Functions of the Cell

Cell performs many important functions which helps the body in the growth and development. Some of the functions are mentioned below:

• Cell provides shape and structure to body to take the useful nutrients from the food and convert those nutrients into energy.
• It facilitates the growth during mitosis.
• It helps in the process of reproduction.
• It helps in the generation of energy from the nutrients and permits the transportation of different substances.

Answer:

All Living organisms consists of cell which helps to perform all its function. It is called the building block of all living things. Cell is known as the functional and structural unit of life.

2. Write about the Shape of the Cell ?

Answer:

Animal cell is rounded, spherical or elongated in shape whereas plant cells are rectangular and rigid in shape. Some of the cells are long and pointed on both ends such are spindle shape cells which helps in movement. Some also consists of long and branched like nerve cell which is used to transfer and receive the signals.

3. What is the Function of the Cell ?

Answer:

Cell provides structure and support to the body to take the useful nutrients from the food and convert those nutrients into energy. Cell also helps in the process of reproduction.

4. Write about the Variety in Cell Number ?

Answer:

Single celled organisms consists of single cell whereas the multicellular organisms consist of more than one cell. Every living organism starts its life from a single cells, that is a fertilized egg and then it further divides into thousands and then millions.

5. Write about the size of a cell ?

Answer:

Size of the cell are variable. In some organisms it can be small as 0.0001mm and can be large in some organisms up to six to twelve inches.