Cell theory

Cell Theory
- all organisms are made at least one cell.
- the CELL is the basic unit of life.
- all cells come from pre-existing cells.
- cells carry genetic information in the form of DNA or RNA.
- these genetic information are passed down from parent cell to daugther cell.

Prokaryotic Cells
- these are cells with no nucleus.
- they have no membrane-bound organelles.
- they have cell walls. (different from plant cell walls.)
- example : red blood cells are single-celled organelles.

Eukaryotic Cells
- these are cells with a nucleus.
- there are membrance-bound organelles present.
- example : protists, fungi, plants and animals.
- only plant and fungi cell walls are different from others. (chitinous and cellulose cell walls respectively.)

Living things with just one cell are known as unicellular organisms. Most things are multicellular, that is, they are made up of more than 1 cell.

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Pit-like structures in plant cells have 2 different names. If a pit contains enzymes, it is celled a lysosome. If it does not have enzymes, it is called a vacuole.

- cytoplasm is a jelly-like substance that contains many tiny structures. chemical reactions take place in the cytoplasm where new substances are made with energy.
- vacuoles allow support, metabolism, storage, and waste disposal. (plants only.)

Plants store their excess glucose as starch; animals store their excess glucose as glycogen in the liver and muscles.

- the cell membrane is a partially permeable layer which controls the movements of substances in and out of the cell. as it is partially permeable, it only allows certain substances to pass through, but not others as their molecular structure may be too big to pass through the cell membrane.
- the plasma membrane has 2 layer of phospholipid molecules. there are no bonds between these molecules, with protein molecules interspersed in between. phospholipid molecules are made up of fatty acid tails and polar heads. the fatty acid tails are hydrophobic (anti-water), while the polar heads are hydrophilic (pro-water). the plasma membrane gies protection, information, nutrients, and helps in waste disposal. it is made of fat, protein and phosphorus molecules.
- the cell wall is made up of a thick layer of cellulose. it supports a plant cell, gives it a regular shape, and holds it together with other plant cells.