Why do most plants, bacteria and fungi have cell walls while animal cells don't?

Well, animal cells don't have cell walls because, um, they have to be flexible. You can see this best in muscle cells: they contract and relax, so the animal can move!





Animals typically maintain an internal environment that is isotonic with respect to the cell interior.





Plants and fungi don't. The external environment is hypotonic. Water pushes into plant cells -- until the cell is constrained rigidly by its membrane against its cell wall with physical pressure. Without the cell wall, the cell would burst.


Why do most plants, bacteria and fungi have cell walls while animal cells don't?
Plant cells (for example) have cellulose cell walls which provide structure. They are not as complex as animal cells. Animal cells have cell membranes that are complex structures made of different layers which selectively allow certain ions or substances (e.g. proteins) in and out. Different kinds of animal cells have different functions depending on where they are in the body. For instance nerve cells in mammals have complex membranes round them which have evolved to allow the passage of ions such as sodium and potassium which cause the electrochemical process of neural transmission to take place. Specific areas of these cells can act as 'binding sites' where molecules of neurotransmitter such as noradrenalin (norepinephrine in USA) or dopamine can be accepted, so that information is passed to the next cell. There is nothing as complicated as this in plant cells.





Within animal cells, with their own complex outer cell membranes, you'll find other membranes around different kinds of cellular organelles such as mitochondria, the nucleus and several other structures that have important functions.





The outer cell membrane of each animal cell acts as a 'wall' but it is a dynamic structure that, itself, has many functions.Why do most plants, bacteria and fungi have cell walls while animal cells don't?
Plants- Cellulose is meant to give lot of rigidity-- thats what cell wall is made of. Here giving rigidity is the function. Plants dont move.





Cell membrane are made of fatty acids or lipids which give special permeability-- It is not highly rigid but rather fluid like surface which can reorganize itself easily and in continuous motion- This helps in flexibility motion and movement. If they have cell walls made of cellulose then the cells will break on movement. But membrane can reorganize.
Plant cells have cellulose cell walls which provide structure. They are not as complex as animal cells. Animal cells have cell membranes that are complex structures made of different layers which selectively allow certain ions or substances (e.g. proteins) in and out. Different kinds of animal cells have different functions depending on where they are in the body.
Cell walls mainly function as a supporting mechanism for cells who have it.





As for animal cells, they who wholly supported by other structures such as bones and muscles.
anamal calls have cell walls
because they need to be flexible