Cell Structure and Functions
Cells within the body of a multi-cellular organism differ in shape, size and function, but have three basic parts - cell membrane, cytoplasm and nucleus.
1. Cell Membrane or Plasma Membrane
It is a thin delicate membrane enclosing the cell. It forms outermost covering in animal cell and inner to cell wall in plant cell. Cell membrane is selectively permeable, so allows only selected substances to pass in and out of the cell. It protects cell from injury and maintains shape of cell.
2. Cytoplasm
It is translucent, homogeneous, colloidal semi fluid filling the space between plasma (cell) membrane and nucleus. Cell organelles are present in it. Cytoplasm helps in manufacture and distribution of substances within the cell and in exchange of materials between different cell organelles.
3. Nucleus
It is small, located in or near the centre of the cytoplasm. Nucleus is bound by a nuclear membrane. Network of chromosomes is present as chromatin. One or more rounded nucleolus are present in the nucleus. Nucleus coordinates the activities of the entire cell and contains the genetic material or DNA.
Protoplasm: Protoplasm is the living substance of the cell. The nucleus and cytoplasm together form the protoplasm.
Cell Organelles found in Cytoplasm
4. Endoplasmic reticulum (ER)
It is irregular network of double membranes in the cytoplasm. Ribosomes may be present on endoplasmic reticulum. It gives rigidity to the cell and helps in the synthesis and transport of various proteins and fats within the cell to the outside.
5. Ribosomes
Ribosomes are granules either scattered freely in the cytoplasm or attached to the endoplasmic reticulum. They are sites for protein synthesis.
6. Mitochondria
They are minute sausage shaped or rod shaped granular bodies scattered in the cytoplasm. They carry out cellular respiration. They are called powerhouse of cell because energy gets released and stored in them during respiration.
7. Golgi Bodies
Stacks of flattened sacs or small vesicles generally located near the nucleus. Similar structures in a plant cell are called dictyosomes. They help in the secretion and storage of substances such as enzymes, hormones, etc.
8. Lysosomes
Lysosomes are small vesicles or sacs containing digestive enzymes, which destroy and digest the worn out cell parts. They help to rapidly destroy and digest damaged cells and their parts, hence these also known as suicide bags. They clean up the cell debris.
Parts other than Organelles
The vacuoles and granules are the non-living parts of a cell.
9. Vacuoles
These are fluid filled membrane-bound spaces. Large-sized vacuoles are in plants and smaller and fewer ones in animals. They help in storage of water and other substances.
10. Granules
These are small particles, crystals or droplets. Granules containing starch, fat, etc. serve as food for the cell.
Parts found in Plant Cell only
11. Cell wall
It is outer, rigid, protective, supportive and semi-transparent covering of a plant cell made of cellulose. It provides a definite shape and rigidity to the cell. It protects the plasma membrane and internal structures.
12. Plastids
Plastids are of three types - chloroplasts, chromoplasts and leucoplasts. Chloroplasts are green. They possess photosynthetic pigment - chlorophyll and carotenoids. Chromoplasts contain yellow, orange or red coloured pigment. Leucoplasts are colourless plastids.
Chloroplasts help in photosynthesis. Chromoplasts provide colour to the flowers and the fruits. Leucoplasts help in the storage of food.
Parts found in Animal Cell only
13. Centrosome
It is a small body lying above the nucleus. It consists of two small granules called centrioles. It participates in cell division and help in spindle formation during cell division.
Difference Between Plant and Animal Cell
| Feature | Plant Cell | Animal Cell |
| Size | Larger | Smaller |
| Shape | Rectangular | Oval |
| Vacuoles | Large and central | Small and scattered |
| Golgi bodies | Diffused & are called dictyosomes | Well-developed & present near nucleus |
| Centrosome | Absent | Present |
| Plastids | Present | Absent |
| Storage of reserve food | In the form of starch or oil | in the form of glycogen |