diffusion, osmomis and active transport.docx

7/28/2019 Diffusion, osmomis and active transport.docx

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Diffusion, Osmosis and Active Trasport

For plants to say alive, chemicals (small molecules) must be able to move easily in and out of

the cell. The movement may be:

From one part of a cell to another part. Into and out of a cell From one cell to another cell

For the organism, it is an advantage that the movement does not require energy (expenditure

of energy). The movement of molecules without spending energy will happen only in the

conditions i.e. favorable conditions.

Diffusion

Diffusion is a kind of movement without spending energy.

Definition: Diffusion is the movement of molecules from a region of higher concentration to a

region of its lower concentration, down a concentration gradient until it reaches equilibrium.

Example of diffusion in plants:

The movement of carbohydrates during photosynthesis. Carbon dioxide in solution(dissolved in water), moves from the surrounding mesophyll cells inside the leaf and

getting into the chloroplast.

The movement of water vapor during transpiration. Water moves from mesophyll cellsand got out through stoma.

Example of diffusion in animals:

The movement of oxygen into blood, in lungs (air sacs) during respiration. During the same process, the movement of carbon dioxide from the cells into the blood.

Osmosis

Dilute solutions which have a relatively large number of molecules are said to have a high water

potential. Concentrated solutions, which have a fewer water molecules, are said to have a low

water potential.

Definition: Osmosis can be defined as the passage of water molecules from a region of high

water potential to a region of lower water potential, through a semipermeable membrane.


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Osmosis in plants:

Naturally, all cell membranes are partially permeable. The cell sap of root hair cells hasrelatively low water potential. Soil water has a relatively high water potential. So, the

water molecules move into the vacuole of root hair cells. Because of this, the water

potential in the root hair cell is increasing.

Again, the same osmosis causes the movement of water molecules into the next cellsand it continues towards the center of the root and towards the center of the stem

(xylem vessel). From xylem vessels, the water got transported throughout the stem and

leaf.

Effects of osmosis on plant cells

Cell placed in a relatively diluted solution will take up the water and increases in size. Sothe cell membrane pressurizes the cell wall outwardly. The condition of the cell is turgid

and pressure responsible for turgidity is turgor pressure.

Cell placed in a normal neutral solution, the cell will be unchanged. Cells placed in a highly concentrated solution will loss water by osmosis. Because

continuous loss of water. The cytoplasm got pulled toward the center (shrinking) and

cells became flaccid.

Diagram of cell in solutions

Effects of osmosis on animal cells

Animal cells placed in a solution of lower water potential lose their shape and turgidity as watermoves out of their cytoplasm. A red blood cell shrinks in size and its membrane becomes

unevenly creased.

Active transport

If only diffusion and osmosis is the way of transport, the organism cannot transport anything

when there is an equal distribution of materials/molecules. Also, the molecules which are

having high concentration inside the cells may also diffuse out. No overcome organisms are

using another kind of transport called active transport.

Definition: Active transport is an energy consuming process where substances are transported

against the concentration gradient.


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Examples of active transport

In plants, if the plants need ions/minerals even the soil surrounding the plant may haveless ion concentration by spending extra energy; the plant will take up the ions or

minerals.

In the small intestine of an animal when digested food is getting absorbed by villi is anexample of active transport.

diffusion, osmomis and active transport.docx

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