Cell organelles-plasma membrane

Question 1 What are cell organelles?
Question 2 What is plasma membrane?
Question 3 Why plasma membrane is  called as semi-permeable membrane?
Question 4 Define the term diffusion?
Question 5 Define osmosis?
Question 6 How carbon dioxide and oxygen undergoes diffusion?
Question 7 What are hypotonic solution.Give example?
Question 8 What are the three major functional regions of the cell?
Question 9 What are hypertonic solution.Give example?
Question 10 What are isotonic solution.Give example?
Question 11 What are endocytosis?
Question 12 What is exocytosis?
Question 13 What is a cell wall?
Question 14 Give the functions of cell wall?
Question 15 Define the term plasmolysis?
Cell Organelles

Each cell has got certain specific component within it called cell organelle.Each cell organelle perform specific function.

Structural Organisation of cell
All cells have 3 major functional regions:
1)Plasma membrane
Plasma Membrane
The outermost covering of cell that separates the contents of cell from its external environment is called plasma membrane.
It permits the entry and exit of some material in and out of the cell therefore it is called selective-permeable membrane.
Diffusion:It is the spontaneous movement of molecules from the region of higher concentration to a region of lower concentration.

For Ex:Substances like carbon dioxide,oxygen move across the cell membrane by this process.

1)Carbon dioxide(Cellular waste,excreted out)
Cell (high Concentration) ———–>  outside cell(Low concentration)
By diffusion Carbon dioxide moves out of cell from High concentration to low concentration.
2) oxygen(Needed for respiration)
Cell(Low concentration)————> Outside cell(high concentration)
By diffusion oxygen moves into the cell from a region of high concentration to region of low concentration.
Osmosis:The passage of water from a region of high concentration to a region of low concentration through semi-permeable membrane.
The movement of water across plasma membrane is affected by substances dissolved in it.
What will happen if we put plant cell or animal cell into sugar or salt solution.
1)If the medium surrounding the cell has higher water concentration than cell ie outside solution is very dilute,the cell will gain water by osmosis(Hypotonic solution)will come into cell as a result of cell swells.
2)If the medium has lower concentration of water outside the cell ie concentrated solution,the cell will lose water by osmosis (hypertonic solution).Water move across and thus cell shrink.
3)If the medium has exactly same concentration inside and outside,there will be no net movement of water across membrane(isotonic solution).The amount of water going in and out will be same so cell will be of same size.
Remove shell of an egg by placing it in dilute HCl.A thin outer skin now encloses the egg.
1)Put this egg in pure water.The egg swells because water enters by osmosis.
2)Put another similar egg in concentrated salt solution.The egg will shrink because water moves out of the egg.
1)Put dried raisins in water and leave for sometime.The raisins gain water and swell.
2)Put dried raisins in concentrated solution of salt or sugar,it loses water and shrinks.
Endocytosis:It is the ingestion of material by the cell through plasma membrane.
For Ex: Amoeba
Cell wall
In plants there is a rigid cell wall which lies outside the plasma membrane.It is made up of cellulose.
Functions of Cell wall
1)When water enter the cell by osmosis,plant cell expand.The cell wall is strong enough to resist this expansion.
2)The inter cellular connections allow exchange of material between the living cell organism.
3)It provide mechanical strength to the cell.
4)It is permeable to water and substance in solution.
Plasmolysis: When a living cell looses water through osmosis,there is shrinkage of protoplasm away from cell wall.This is called plasmolysis.
When the concentration of water molecule inside the cell is higher than outside,the cell will shrink away.Water will move by osmosis from higher water potential(inside)to lower water potential(outside).

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