This is the diffusion of water molecules from a weak solution to a strong solution cross semi- permeable membrane.
Osmotic pressure.
If sufficient external pressure is applied to the surface of the strong sugar solution the entry of water by osmosis will be prevented. This external pressure prevents osmosis when it is sufficient to stop the movement of water molecules diffusion into the strong sugar solution. The pressure that is just sufficient to prevent the entry of eater by osmosis into a solution is known as the osmotic pressure of that solution.

Osmotic Pressure and Osmotic Potential
Osmotic pressure varies according to the amount of dissolved material in a solution that is according to the strength of a solution. The stronger the solution, the greater is the osmotic pressure. Water flows across a semi permeable membrane from a solution with a weak osmotic pressure to one with a stronger osmotic pressure until both are equal. However, there are circumstances in which strong solutions are prevented from taking in water by osmosis. Under these conditions it is more accurate to describe the solution as having an osmotic potential rather than an osmotic pressure. Osmotic pressure is measured in kilo Pascals

Osmosis in plants cells
All living cells whether from plants or animals are surrounded by a semi-permeable membrane This is the cell membrane. In plants, however the wall of cellulose surrounds the cell membrane. The cellulose has no osmotic properties. It is freely permeable to all liquid and dissolved substances but the fact that it stretches very little limits the size to which plants cells can swell when they take in water by osmosis. if you have a solution A which is stronger than B that means A is hypertonic to B, B is hypotonic to A and if they are equal in strength they are isotonic.
What happens to one plant cell under various osmotic conditions?
In A, the liquid inside the cell called cell sap has higher osmotic pressure than the surrounding fluid (hypertonic to the surrounding fluid). The cell sap has a lower osmotic pressure than the surrounding fluid (is hypotonic to the surrounding fluid). The cell sap has a lower osmotic pressure than the surrounding fluid (is hypotonic to the surrounding fluid). The cell sap osmotic pressure is equal to the osmotic pressure of the surrounding fluid (isotonic)
N.B
The cell wall is freely permeable and just slightly elastic and the cell membrane is semi-permeable

In A the surrounding fluid which has a weaker osmotic pressure will pass through the semi permeable membrane of the cell to the cell sap with a higher osmotic pressure by osmosis. This and will result into formation of a uniform mixture with the solution level in the cell being greater than that in the surrounding fluid. The vacuole expands.
The water from the cell sap will pass through the semi permeable membrane of the cell to the surrounding fluid by osmosis and will form a uniform mixture with the solution level in the cell being less than in the surrounding fluid. The vacuole will shrink.
The water molecules will be in constant motion but since the cell sap is isotonic to the surrounding fluid, osmosis will not take place.
Experiment:
Aim: To demonstrate osmosis in living tissues;
Apparatus and materials; Knife, potatoes, Bunsen burner, water, petri dish
Method
-Cut three half potatoes peel them thoroughly and cut cavities in them.
-Immerse one of then in boiling water for about ten minutes to kill the cytoplasm
-Place each of them in a petri dish of water and place some salt (sodium chloride) in the cavities of the boiled potato and also in one of the raw ones.
Expected observation;
In A water in the petri dish reduced and a #solution# was formed in the sodium chloride. In B it remains the same and so does in C
Deduction
Osmosis takes place only in living tissues.

Experiment B; to demonstrate rigidity and plasmoylsis;
Apparatus; A large potato, cork borer
Procedure
-Prepare two cylinders of potato tissue by pushing a cork borer into a large potato and the core of tissue extracted by pushing with the flat end of the pencil and the end trimmed with a razor blade or scapal.
-Cut the cylinders into two equal pieces of four centimetres each. Place one cylinder in a test tube of solution A and the other in a test tube of solution B. After forty minutes remove the cylinders and measure again.
Expected observation; Solution A was less concentrated than the cell sap. Osmosis took place and water was taken into the cylinder. The cell became turgid.
Solution B was more concentrated than the cell sap Osmosis took place and water was taken from the potato cylinder. The cell became deflated and thus flaccid (plasmolysis)
As the cell absorbs more and more water by osmosis the vacuole enlarges because it takes up most of the water and it pushes the contents against the cell wall. That force by which the vacuole pushes the cell contents against the cell wall is called turgor pressure and it goes on increasing as more and more water comes in until when the cell wall cannot stretch anymore. When the cell becomes inflated due to turgor pressure it is said to be turgid. And when the cell wall is fully stretched then it said to be fully turgid

WALL PRESSURE
This is the inward force, which is exerted by the cell wall, and which is opposed to the outward turgor pressure and when the two forces are equal then the cell stops inflating.
N.B
When a cell is fully turgid, it does not necessary mean that the cell sap is equal to the surrounding in concentration
Turgidity is important in plants especially in young plants or plants with herbaceous stems. It provides support that is when the cells are turgid the stem is strong.

Water uptake by Plants:
Osmotic pressure in the cell sap is higher than the osmotic pressure in surrounding water. The water enters the root hair by osmosis and the cell sap in the root hair is diluted. The cell sap in the epidermis has a higher osmotic pressure than that in the root hair by osmosis and become diluted. The first cortical cell has a higher osmotic pressure than the epidermal cell water from the epidermal cell will enter the first cortical cell by osmosis making it dilute. And this goes on up to the last cell nearest to the xylem.
Xylem is a dead tissue. Water does not move from the cortex to the xylem by osmosis. It moves from the last cortical cell to the xylem by simple diffusion. There are some forces through which water moves through xylem up to the leaves