The living contents of the eukaryotic cells are divided into nucleus and cytoplasm. It is a colorless, transparent and semifluid substance. Cytoplasm is found around the nucleus. It contains water, proteins, carbohydrates, lipids and other substances. Cytoplasm maintains the life of a cell. All chemical process takes place in the cytoplasm. These living contents (nucleus and cytoplasm) collectively form protoplasm.
The cytoplasm has two parts:
a. Organelles and Insoluble Products
It contains different cell organelles like mitochondria, Golgi bodies, endoplasmic reticulum, lysosomes etc. It also contains insoluble waste and storage products.
The soluble part of the cytoplasm is called cytosol. It forms the ground substances of the cytoplasm. Chemically, it has about 90% water. It contains all fundamental molecules of the cells. These molecules are present in two forms:
- True Solution: the small molecules and ions from a true solution.
- Colloidal Solution: some large molecules from a colloidal solution. The colloidal solution is present in two forms.
- Sol: It is the part of cytoplasm present in the peripheral region. It is more transparent and less viscous and also known as “Sol”.
The non-viscous colloidal solution is called sol. It is present in liquid form. For example, Milk.
- Gel: It is the part of cytoplasm present in the central region. It is less transparent and more viscous and also known as “Gel”.
The viscous colloidal solution is called gel. It is present in the form of semi-solid. For example, Butter.
Functions of Cytoplasm
Cytoplasm performs following functions:
- It acts as a storage house. Most of the important compounds like starch are stored in the cytoplasm.
- Some metabolic processes like glycolysis (breaking or glucose) take place in the cytoplasm.
- The cytoplasm contains several cell organelles like Mitochondria, Golgi-bodies, Endoplasmic Reticulum and Lysosomes etc. These cell organelles perform many important functions of the cells.
- Cytoplasm shows streaming movements. This is an active mass movement of cytoplasm. Many free floating organelles like mitochondria move in the cytoplasm due to these streaming movements.
What is Cell Wall?
The outermost boundary in most of the plant cells is called Cell Wall. The plant and prokaryotes have different types of cell walls. The plant cell wall is different from the cell walls of prokaryotes. These walls have different structures and chemical compositions.
The cell wall is secreted by the protoplasm of the cell. The thickness of the cell wall is different in different types of the cells. The cell wall is composed of three basic layers: primary wall, secondary wall, and middle lamella.
1. Primary Wall
The primary wall is mainly composed of cellulose. Primary Wall also contains some pectin and hemicelluloses. It is a true cell wall. It develops in the newly growing cells. The cellulose molecules are arranged in a criss-cross manner.
It is produced on the outer side of the plasma membrane in a young plant cell. Primary Wall is thin and elastic. It is made up of cellulose.
2. Secondary Wall
The secondary wall is formed on the inner surface of the primary wall. It is much thick and rigid. Chemically, it is composed of inorganic salts, silica, waxes, cutin, lignin, etc.
It is produced in an old cell on the inner side of the primary wall. Due to the secondary wall, the cell wall becomes stronger and non-elastic.
3. Middle Lamella
It is present between the walls of two adjacent cells in their attachment.
Cell Wall of Prokaryotes and Fungi:
Cellulose is absent in the cell wall of prokaryotes. Their wall is composed of peptidoglycan or murein. The cell wall of fungi contains chitin.
Functions of Cell Wall
- It gives definite shape to plant cells.
- It keeps the cell rigid.
- All types of materials can pass through it. So, it does not act as a barrier for the passing material.
- Cell wall is a protective layer around the cell.
- It is a permeable membrane. It allows water and other substances to pass. So, it helps in the diffusion process.