Topic 2 [Organisation of the Organism]
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Cells are the basic unit of life, as all living organisms are made out of cells. Cells exist in various shapes and sizes. There are smaller components called organelles within a cell and each organelle performs a specific function inside the cell or for the cell.
Cell Membrane:
- Also known as the plasma membrane.
- It is selectively permeable (Only allows some substances to pass through).
- The cell membrane is made of two layers. It had a hydrophilic (Love water) head and a hydrophobic (Hate water) tail. Two layers of the head and tail connected together (Note that the tails are pointing towards each other) are called the phospholipid bilayer.
Function of Cell Membrane:
1. Separate a cell from its' external environment
2. Controls the exchange of molecules between the cell and its' external environment
Cell Wall: (Only present in plant cells and fungus)
- A rigid cellulose layer surrounding the plasma membrane of plant cells.
- In fungus, the cell was is made of chitin.
Function of Cell Wall:
- To provide support and protection for the cell
- To prevent the cell from bursting in a dilute solution
Cytoplasm:
- Between the cell membrane and the nucleus.
- Containing organelles, salts, dissolved gases, nutrients, enzymes, and other organic molecules.
Function of Cytoplasm:
- Gives shape to the cell (Especially for animal cells, who do not have cell wall).
- Supports and protects the cell organelles
- Provides a medium for all cellular metabolic reactions to occur.
Nucleus:
- Bound by the nuclear membrane.
- Containing chromosomes.
**The nucleus contains chromosomes. The chromosomes contain DNA.**
Function of the Nucleus:
- Controls all cell activities
Ribosome:
- Small, dot-like organelles found in large numbers in all cells.
Two types of Ribosomes:
1. Attached to the Rough Endoplasmic Reticulum.
2. Occur freely in the cytoplasm.
Function of Ribosomes:
- To synthesise all types of proteins.
Rough Endoplasmic Reticulum:
- A flat, sealed sac of membrane.
- Ribosomes attached on its' surface.
- Present in all cells.
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