Class 8 Science

Cell: Structure

Parts of Cell:

Following are the main parts of a cell:

Cell Membrane: Cell membrane is also called plasma membrane. It makes the boundary of a cell. It is composed of protein and lipid. It is porous and allows various materials to pass through it. Cell membrane is semi-permeable in nature which means it allows selected materials to pass through it.

  • Cell membrane separates the contents of the cell from external environment.
  • Cell membrane provides protection to the cell.
  • Cell membrane facilitates exchange of materials between cell and external environment.

Cell Wall: Cell wall is present in plant cells and in bacteria. Cell wall in plants is made up of cellulose. Cell wall gives additional strength and protection to plant cells.

animal cell

Cytoplasm: A jelly-like substance is present between the cell and nucleus. It is called cytoplasm. Different cell organelles are present in the cytoplasm. Examples of cell organelles are; mitochondria, Golgi body, ribosomes, lysosomes, chloroplast, etc.

Nucleus: This is a spherical structure which is present inside the cell; usually at the centre of the cell. Nucleus is surrounded by a double membrane called nuclear membrane. A dot-like structure; called nucleolus is present inside the nucleus. Nucleus contains chromosomes which are thread-like structures. Genes are present on chromosome. They are responsible for transferring characters from parents to their offspring.

  • Nucleus controls the function of a cell.
  • Nucleus controls inheritance of characters, i.e. transfer of characters from one generation to the next generation.

Nucleus contains genetic materials. But genetic materials may or may not be organized in the form of nucleus. Based on this, organisms are divided into two groups, viz. prokaryotes and eukaryotes.

Prokaryotes: When genetic materials are not organized in the form of nucleus, the organism is called prokaryote. In other words, nucleus is absent in prokaryotes. Bacteria and blue green algae are examples of prokaryotes.

Eukaryotes: When genetic materials are organized in the form of nucleus, the organism is called eukaryote. In other words, nucleus is present in eukaryotes. Organisms; other than bacteria and blue green algae; are eukaryotes. Animals, plants, fungi, etc. are eukaryotes.

Protoplasm: The fluid inside the cell is called protoplasm. Protoplasm is composed of cytoplasm and nucleoplasm. The fluid between cell membrane and nucleus is called cytoplasm. The fluid inside the nucleus is called nucleoplasm.

Vacuoles: Some fluid-filled bag-like structures can be seen inside a cell. These are called vacuoles. Vacuoles are very large and conspicuous in plant cells but are very small in animal cells. Vacuoles may be absent in most of the animal cells.

Plastids: Plastid is an important cell organelle and is found in plant cells only. Plastids perform some important functions in cells. Chloroplast is a type of plastid. It contains a green pigment called chlorophyll. It imparts green colour to leaf and carries out photosynthesis.

Difference Between Plant Cell and Animal Cell
Plant CellAnimal Cell
Cell wall is present.Cell wall is absent.
Chloroplast is present.Chloroplast is absent.
Vacuoles are large.Vacuoles are much smaller or absent.