Cell Wall

2. Cell Wall • Most commonly found in plant cells • Supports, protect and controls the movement of materials in and out of the cell • It is a barrier between cell and its environment • Gives rigidity to the cell

3. Cell Wall • There are several layers in plant cell walls:

4. Cell Wall The middle lamella, a layer rich in pectins. This outermost layer forms the interface between adjacent plant cells and glues them together. 2) The primary cell wall, generally a thin, flexible and extensible layer formed while the cell is growing. 3) The secondary cell wall, a thick layer formed inside the primary cell wall after the cell is fully grown. It is not found in all cell types.

5. Cell Wall • Some cells, such as the conductiong cells in xylem, possess a secondary wall containing lignin, which strengthens and waterproofs the cell. • Cell walls are found in plants, bacteria, fungi, algae, and some Achaea. • Animals and protozoa do not have cell walls.

6. Cell Wall • The cell wall provides these cells with structural support and protection, in addition to acting as a filtering mechanism. • A major function of the cell wall is to act as a pressure vessel, preventing over-expansion when water enters the cell.

7. Cell Surface Membrane • Also called plasma membrane • Outer boundary of the cell • Partially permeable • Surrounds the nucleus • Composed of two layers • Numerous openings for nuclear traffic

8. Cell Surface Membrane • Separates the interior of all cells from the outside environment. • Molecules can pass the cell surface embrane by 3 main ways. • The way the moleules cross the cell membrane depends on the size of the molecules, and on wether the molecules are already concentrated either on the inside or outside of the cell.

9. Cell Surface Membrane • If a molecule is small enough to fit through a special protein channel in the cell surface membrane, it will be able to move across the membrane [either by passive transport or active transport]. • If, however, the molecule is too big to fit through any pore in the channel, then it will have to enter or exit the cell through endocytosis or exocytosis.

10. Cell Surface Membrane • As mentioned before, large molecules cross the cell membrane through exocytosis or endocytosis. • Exocytosis occurs when a substance is exiting the cell. Firstly, the substance moves into a vesicle, which joins with the cell surface membrane, and becomes part of it. After which, the vesicle releases the substance to the outside of the cell. • Endocytosis occurs when a substance is entering the cell. In endocytosis, the cell surface membrane pinches in, forming a vesicle that contains material from outside the cell.

11. Fun Facts  • The cell wall is rigid and strong, preventing the cell from bursting as it absorb water by osmosis • Cell membranes are 7.5 nm thick • The fibres of the cell wall are laid in different direction to add strength • Mature cells add substances to the orimary cell wall for additional strength or to make it waterproof. That is thesecondary cell wall • When the cell matures and stops growing, it strengthens the wall

12. Video!  http://www.youtube.com/watch?v=j5Qway4LAkk&feature=related

13. Questions?

14. Quiz Time!!! 

15. Question : The molecules crossing the cell membrane depends on what? (2 answers) Answer: 1.) Size of molecules 2.) Whether they are already concentrated either on the side or outside of the cell

16. Question : Cell membrane is _______ permeable Answer: Partially

17. Question: What is the function of the cell wall? (2 answers) Answer: 1.) Supports, protect and controls the movement of materials in and out of the cell 2.) Gives rigidity to the cell