1.5. OSMOSIS
When two solution of different concentration are separated by a semi permeable membrane.
Water flows from the less concentrated solution to the more concentrated solution into the semi-permeable membrane until both solutions have the same concentration ratio. If one solution is stronger than the other it is said to be hypertonic. A solution that is weaker than the other is said to be hypotonic to the other.
Definition of osmosis: osmosis is defined as the movement of water molecules from a lower solution (weaker solution) to a higher concentrated solution (stronger solution) through a semi permeable membrane or selectively permeable membrane.
A semi-permeable membrane allows certain types of particle to pass through it but does not allow other to pass.
A solution of lighter concentration is said to have a higher osmotic concentration or ineptly of strong solution. A solution of higher concentration is said to be a lower concentration and weak solution. A weak solution a higher osmotic potential than a stronger potential.
1.5.1. OSMOTIC POTENTIAL
The osmotic potential of a solution Is measured by a tendency of water molecules to diffuse out of it. A very concentrated solution with fewer molecules of water has a lower osmotic potential and a very dilute solution with more molecules of water has a higher osmotic potential.
Pure water (distilled water) which is the weakest solution has the highest possible osmotic potential
1.5.2. Demonstration of osmosis
1.5.2.1. IN NONE LIVING TISSUES
REQUIREMENTS:
cellophane paper, beaker, thistle funnel, strong sugar solution, rubber band, distilled water, clamp and retort stand.
PROCEDURE:
The mouth of thistle funnel is covered with cellophane paper and some strong sugar solution is poured into a funnel in an upside-down position, this is placed in a beaker of distilled water. The stem of the funnel is clamp onto the retort stand.
The level of the sugar solution on the stem of the funnel is marked. The apparatus is allowed to stay for about twelve hours before it is observed.
RESULTS:
After twelve hours the level of the sugar is stemmed on the funnel has risen.
DIAGRAM:
FIG: Apparatus to carry out osmosis using cellophane paper.
RESULTS:
After twelve hours, the level of the sugar in the stemmed of the funnel has risen
EXPLANATION:
The cellophane paper acts as a selectively permeable membrane (semi permeable membrane) and water molecules have passed through it from the distilled water in to strong solution by osmosis.
CONCLUSION:
Water molecules move from a les concentrated solution or a weaker solution in to a more concentrated solution through a selectively permeable membrane.
1.5.2.2. IN LIVING TISSUES
Requirements:
Potatoes tuber, Beaker, water, some strong sugar solution.
Procedure:
peel a large potatoes tuber and cut a hole in it. Make the bottom of the tuber flat so that it can stand in a beaker. Place the potatoes tuber in a beaker which is half full of distilled water and mark the level of water in the beaker. Put the strong sugar solution in the hole of the potatoes tuber and allow the experiment to stand for twelve hours.
Diagram:
Results:
Absorption of water and mineral salt in plants is carried out by root hairs. The root hairs are extremely narrow tubes which grow out.
The root hairs contain cell sap in vacuum. Which has a higher osmotic pressure than soil water. In this way, soil water moves into the root hair cell and the cell sap becomes more dilute followed by an increase in the osmotic potential relative to the next root hair cell.
Under these circumstances, the root hair cell less to the cell next to it. The same sequence goes from one cell to the next until the water reaches the xylem vessel and starts moving upward towards the leaf. When the root hairs do this, they give rise to root pressure within the root. The entry of water into a new root near cell is controlled by osmotic pressure and turgor pressure. The total force with which the plant absorb water from the environment is called suction pressure.
1.5.2.3. EXPERIMENT TO SHOW THAT THE XYLEM CONDUCTS WATER UPWARD.
Aim:
To show that the xylem conducts water upward
Requirements:
Uprooted plant, red ink, container, razor blade.
Procedure:
Uproot a plant, wash away the soil from the root and place the plant in a container of red ink for 12 hours. After this remove the plant from the red ink and make a cross section of the root, the stem and the leaf.
Diagram:
Results:
It will be noticed that there are red ink marks along the xylem vessels of the root, the stem, and the leaf.
Explanation:
The red ink moves from the container through the xylem of the root stem and leaf.
Conclusion:
This shows that the xylem tissue conducts water upward.
1.5.2.1. EXPERIMENT TO SHOW ROOT PRESSURE.
Aim:
To show root pressure in plants
Requirements:
Potted plant, clamp and retort stand, plastic paper, a glass tube, rubber band.
Procedure:
A potted plant is attached to a clamp and a retort stand and a plastic paper is tied around the port of the plant in order to prevent the evaporation of soil water in the pot.
The stem of the potted plant is cut at a point and a pass tube is attached at the point using a rubber band.
Diagram:
Results:
Water rises to a certain height in the glass tube. This height is the maximum root pressure
Explanation:
Because the root developed pressure the water in the root was false up the xylem vessel into the glass tube.
Conclusion:
This shows that the root develops room pressure.
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