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Why can't all the cells of a multicellular organism be the same?

Because no one cell can provide the best conditions for all functions.


What is cell differentiation?

All cells in an organism are initially identical. As it matures, each cell takes on it's own individual characteristics that suit it to the function that it will perform when it is mature. E.g the cell becomes specialised in structure to suit the role that it will carry out.


How does cell differentiate?

Every cell contains the genes needed for it to develop into any one of the many different cells in an organism. But only a few of these genes are switched on in any one cell.

Different genes are switched on and off in each type of differentiated cell.


What else, aside from the shape, differs between different types of differentiated cells?

The numbers of each of their organelles.


What is a tissue?

A collection of similar cells that perform a specific function.


Give two examples of tissues.

Epithelial tissue:
Found in animals
Consist of sheets of cells
Line surfaces of organs and often have a protective/secretory function

Occurs in plants
Made up of a number of cell types
Used to transport water and mineral ions throughout the plant and also give mechanical support.


What is an organ?

A combination of tissues that are coordinated to perform a variety of functions althought they often have one predominant major function.


Give two examples of organs.

The stomach
-churns and mixes contents of stomach
-epithelium to protect the stomach wall and produce secretions
-connective tissues to hold together the other tissues

A leaf
-palisade mesophyll made up of palisade cells which carry out photosynthesis.
-spongy mesophyll adapted for gaseous diffusion.
-epidermis to protect the leaf and allow gaseous diffusion.
-phloem to transport organic materials away from the leaf
-xylem to transport water and ions into the leaf


It is not always easy to determine...

Which structures are organs

Veins and arteries are organs but capillaries are not. They all have the same major function. Capillaries are made up of one tissue whereas arteries and veins are made up of many tissues.


What are organ systems?

Organs working together as a single unit to perform particular functions more efficiently.


Name some organ systems:

Digestive system - digests and processes foods
Respiratory system - used for breathing and gas exchange
Circulatory system - pumps and circulates blood