Differentiate between the following: (a) Diffusion and Osmosis(b) Transpiration and Evaporation(c) Osmotic Pressure and Osmotic Potential(d) Imbibition and Diffusion(e) Apoplast and Symplast pathways of movement of water in plants.(f) Guttation and Transpiration.

Question

Philoid · Accepted Answer

(a) Diffusion and Osmosis

Diffusion	Osmosis
1. It is the movement of particles, molecules or ions from the region of their higher free energy to the region of their lower free energy.	1. It is the movement of solvent or water from the area of its higher free energy or chemical potential to the area of its lower free energy or chemical potential through a semi-permeable membrane.
2. It can occur in any medium.	2. It occurs only in the liquid medium.
3. The diffusing molecules may be solids, liquids or gases.	3. It involves the movement of solvent molecule only.
4. It does not require a semi-permeable membrane.	4. A semi-permeable membrane is required for the operation of osmosis.
5. It is purely dependent upon the free energy of the diffusing substance.	5. It depends upon the free energy or chemical potential of the solvent present on the two sides of the semi-permeable membrane.

(b) Transpiration and Evaporation

Transpiration	Evaporation
(i) This is a physiological process that occurs in plants.	(i) This is a physical process that occurs from any free surface.
(ii) It involves living tissues.	(ii) It may involve both living and non-living surfaces.
(iii) It is controlled by environmental factors as well as by plant factors such as osmotic pressure of the cells, thickness of cuticle, number and position of stomata, etc.	(iii) It is influenced only by environmental factors.
(iv) It moistens the surface of leaves and young stems and protects them from the burning Sun.	(iv) It causes dryness of free surfaces.
(v) It is comparatively a slow process.	(v) It is comparatively a faster process.

(c) Osmotic Pressure and Osmotic Potential

Osmotic pressure	Osmotic potential
1. The maximum pressure, which is developed in a solution, when it is separated from its pure solvent by a semi-permeable membrane, is called osmotic pressure.	1. The confined solution has osmotic pressure, but it does not literally exert any pressure. The pressure is exerted only when it is confined by a membrane. Thus, the term osmotic potential is preferred to the term osmotic pressure.

(d) Imbibition and Diffusion

Imbibition	Diffusion
1. Imbibition is a type of diffusion by which movement of water takes place along a diffusion gradient. An adsorbent is required for imbibition to occur. Swollen seeds produce a large pressure developed by imbibition	1. It is the movement of particles, molecules or ions from the region of their higher free energy to the region of their lower free energy.
2. It occurs in solids	2. It can occur in any medium.
3. Dry plant material or seeds act as adsorbent to imbibe water and swell	3. The diffusing molecules may be solids, liquids or gases.
4. The two factors involved in imbibition are,(i) water potential gradient between the surface of the adsorbent and the liquid imbibed and(ii) Affinity between the adsorbent and the imbibed liquid	4. It does not require a semi-permeable membrane. It is purely dependent upon the free energy of the diffusing substance.

(e) Apoplast and Symplast pathways of movement of water in plants.

Apoplast	Symplast
1. The apoplastic movement of water occurs exclusively through the intercellular spaces and the walls of the cells.	1. In symplastic movement, the water travels through the cells – their cytoplasm;
2. Movement through the apoplast does not involve crossing the cell membrane.	2. Water has to enter the cells through the cell membrane,
3. This movement is dependent on the gradient.	3. Movement is again down a potential gradient.
4. The apoplast does not provide any barrier to water movement and water movement is through mass flow.	4. intercellular movement is through the plasmodesmata.

(f) Guttation and Transpiration.

Guttation	Transpiration
Due to root pressure water is pushed to a small height in the stem this excess of water collects in the form of droplets around special openings of veins. Such water loss in liquid phase is known as guttation.	Transpiration is the evaporative loss of water by plants. The water is lost through the stomata of the leaf.