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Cells
Reproduction
A cell is the basic structure of all life. Every living organism is made up of at least one cell..
Some organisms (eg amoeba) have only one cell (these are called single cellular organisms) but most have many cells (eg human) and these are called multicellular organisms.
[remember an organism is the name given to ANY living thing, animal or plant, whatever it's size]
 ANIMAL CELL (Amoeba x1000) |
 PLANT CELL (Leaf cell x 750) |
Definitions:
Cell membrane: The living outer layer to the cell. The membrane is selective about which substances enter and leave the cell.
Nucleus: Controls the function and behaviour of the cell. Contains the genetic information (genes). The genes are grouped into packages called chromosomes.
Cytoplasm: The liquid contents of the cel (excluding the nucleus). Contains structures for carrying out respiration (these are called mitochondria).
Chloroplasts: Where photosynthesis is carried out. Chlorosplasts contain a green chemical called chlorophyll which is needed for photosynthesis to take place.
Large vacuole: A cavity in the cytoplasm of a plant cell. It contains cell sap. It helps keep the cell rigid. Some cells ( animal and plant) also contain a smaller vacuole that helps regulate the water content of the cell.
Cell wall: A structure made odf cellulose that surrounds a plant cell and helps it keep its shape.
The body is made up of ORGANS.
Each organ has a particular job to do (eg the HEART pumps blood).
The organs are made up of groups of similar cells called TISSUE. eg a piece of liver, made up of liver cells, is called liver tissue.
In order of size: CELLS ------> TISSUE -----> ORGAN --------> ORGANISM
[Of course some organisms, like the amoeba, do not have organs as they are only a single cell to start with]
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Examples of some cells in a human
A: Sperm cell |
A single cell multiplies by dividing in two
This is called binary fission and is a type of asexual
reproduction.
