Cell Structure and Organisation

Cell surface membrane: It is a partially permeable membrane made up of lipids and proteins. It controls the substances entering or leaving the cell and holds the cytoplasm of the cell together and separates it from other cells.

Cytoplasm: It is the location where most cell activities occur due to the presence of enzymes and organelles which carry out various functions in the cell. Excess sugars in plants are also stored in the cytoplasm as insoluble starch granules.

Nucleus: It controls all activities in the cell-like cell growth and repair of worn-out parts and is essential for cell division. Cells without a nucleus have short life-span and are unable to reproduce.

Chromatin: It is a network of threadlike structures that controls cell activities like cell division. It is also made up of deoxyribonucleic acid (DNA) which carries hereditary information. Chromatin threads condense, coil and shorten to form chromosomes when the cell is dividing.

Centrioles: Centrioles help in cell division. They are absent in most plant cells and found only in animal cells. They also occur in pairs.

Cell wall: Cell wall is made of cellulose and protects the cell from injury and gives the plant cell a fixed shape. It is also fully permeable. It provides support by preventing cell from absorbing too much water and keeping it from bursting.

Chloroplasts: Chloroplasts are oval structures that contain chlorophyll for light-dependent stage of photosynthesis.

Rough endoplasmic reticulum: Ribosomes are required to synthesize polypeptides. The RER transports proteins to the Golgi apparatus for secretion out of the cell.

Ribosomes: They are needed to synthesise proteins in the cell. Ribosomes attached to the ER make proteins that are usually transported out of the cell. Ribosomes lying freely in the cytoplasm make proteins that are used within the cytoplasm of that cell.

Smooth endoplasmic reticulum: SER does not have ribosomes. It synthesises substances such as fats and steroids and is involved in detoxification.

Golgi apparatus: It chemically modifies substances made by the ER. The GA stores and packages the substances in vesicles for secretion out of the cell. Mitochondria: Mitochondria perform aerobic respiration. They oxidise food to release energy, which is used for growth and reproduction.

Vacuoles: Vacuoles store substances within the cell. Animal cells have many small vacuoles containing water and food substances temporarily. Plant cells have a large central vacuole containing cell sap. Cell sap is surrounded by tonoplast.

Which structures can be seen under the light microscope?

• Nucleus
• Cell membrane
• Cellulose cell wall
• Cytoplasm
• Large central vacuole/ small numerous vacuoles
• Starch grains

Describe how proteins synthesised by ribosomes are transported out of the cell. [5]

• In the Golgi apparatus, proteins are stored, chemically modified and packaged. It is pinched off from the Golgi apparatus into secretory vesicles and then move towards the cell membrane and fuse with the cell membrane, thus, secreting out of the cell.

Plant Cell vs Animal Cell

Plant Cell	Animal Cell
Cell wall present	Cell wall absent
Chloroplasts present	Chloroplasts absent
Centrioles absent	Centrioles present
A large central vacuole	Numerous small vacuoles

Both have a nucleus

Both have cytoplasm

Both have cell membrane