Cell Structure and Function

Cell Theory
- All living things are made up of cells.
- Cells are the smallest working units of all living things.
- All cels come from pre-existing cells through cell division.

Definition of cells
A cell is the smallest that is capable of performing life functions.

Two types of Cells
- Prokaryotic
- Eukaryotic

Prokaryotic
- Do not have organelles (specialized structures in cells) surrounded by membranes
- Few internal structures
- One-celled organisms eg. bacteria

Eukaryotic
- Contain organelles surrounded by membranes
- Most living organisms eg plant, animal, fungi

Cell Parts

Organelles - specialized structures in the cell

SURROUNDING THE CELL

Cell Wall

- Most commonly found in plant cells & bacteria

- Surrounds the cell membrane

- Rigid structure that maintains the shape, supports & protects cells

Cell membrane
- Selectively/partially permeable membrane of cell that controls movement of substances in and out of the cell.
- Permeable to small molecules and small proteins only

INSIDE THE CELL

Nucleus
- Contain chromatins that control cell activities
- Chromatins contain DNA which is genetic material
- DNA contain instructions for traits & characteristics and to carry out the cell's function
- Separated from cytoplasm by nuclear membrane

Cytoplasm
- Gel-like mixture
- Surrounded by cell membrane
- Contains organelles

Mitochondria
- Referred to as the "powerhouse" of the cell.
- The food we eat is transformed into energy (ATP) for the cell and our bodies.

Endoplasmic Reticulum
- An interconnected network of tubes and vesicles
- Synthesis of proteins, fats, steroid
- Transports materials around in cell
- Smooth type: lacks ribosomes
- Rough type (in picture) : ribosomes embedded in surface

Ribosomes
- Each cell contains thousands
- Make proteins
- Found on endoplasmic reticulum & floating throughout the cell

Golgi Bodies
- Works closely with the ER
- Primary function is to process and package complex molecules such as proteins and fats that are made by the cell
- Bring these products to the surface of the cell where they can be secreted
- Other secretions include hormones, antibodies and enzymes

Lysosome
- Contain digestive enzymes
- Digest excess or worn-out organelles, food particles and engulf bacteria or viruses
- Also help repair worn-out plasma membrane
- They also provide sugars, amino acids and bases which are the foundation of macromolecules
- Cell breaks down if lysosome explodes

Vacuoles
- Membrane-bound sacs for storage, digestion, and waste removal.
- Central large vacuole-help plant cells maintain shape
- Food vacuoles: formed by phagocytosis
- Contractile vacuoles (in freshwater protist): pump excess water out of the cell

Chloroplast
- Usually found in plant cells
- Contains green chlorophyll
- Where photosynthesis takes place
- Converts light energy into chemical energy in glucose

Difference in plant cell and animal cell
- Chloroplast appears in the plant cell while it does not appear in the animal cell
- The plant cell has a large central vacuole while the animal cell has many mini vacuoles.
- The plant cell has a cell wall but an animal cell does not have a cell wall. Therefore, the plant cell has a fixed shape while the animal cell has an irregular shape.