CHAPTER 6 :- PLANT WATER RELATION

Introduction:-

1. Plant physiology is a branch of botany dealing with study of various functional processes of plant.

2. Water is essential for all physiological activities of plant.

3. Water constitutes anywhere from from about 60-95% of protoplasm & hence it is described' as "Liquid of Life".

4. In many metabolic processes water takes part directly as a reagent.

5. It helps maintaining turgidity of cell.

6. It is needed for transport of materials into the plant and-within the plant body,

7. Proper hydration of protoplasm is essential for the activity of enzymes which in turn controls various physiological processes.

8. Water is the universal solvent i.e. it provides the medium in which most substances are dissolved.

Physiological Components of Cell

1. A plant cell has 3 physiological compartments - cell wall, protoplast and central vacuole.

Two membranes separate these compartments, tonoplast around central Vacuole and plasmalemma around protoplast but below the cell wall. Both are selectively permeable.

2. Central vacuole contains an osmotically active fluid called cell sap.

3. Plant cell forms a living component called symplast with the help of plasmodesmata which functions as cytoplasmic bridge between adjacent cells.

4. A nonliving continuum of space amongst adjacent cell walls is called apoplast.

5. It occurs in many vascular plants.

Permeability

1. Permeability is the degree of diffusion of gases, liquids and dissolved substances through a membrane.

2. Some membranes which are impermeable to some substances (e.g. solutes) and permeable to other substances (e.g. water) are called semipermeable.

3. Some membranes allow some substances (e.g. water) to pass through them much more readily than the others.

4. There are called selectively permeable or differentially permeable. 

5. Molecules move in and out of living cells by diffusion and osmosis (in fact, osmosis is a special type of diffusion). Osmosis (Nollet, 1748)

Types of membranes :-

i. Permeable: which allow all solutes and solvents to pass through them are called permeable membranes. eg. cellulosic ceil walls and lignified cell walls 

ii. Impermeable: which do not allow any solute or solvent to pass through them are called impermeable membranes, eg. cutinized cell wall and suberized cell walls, 

iii. Semipermeable: which allow solvents but no solute to pass through them are called semipermeable memebranes. eg. parchment membrane, copper ferrocyanide membrane, 

iv. Selectively permeable: which allow all solvents and few selected solutes to pass through them are called selectively or differentially permeable membranes, eg. all biological membranes, plasma membrane, tonoplast and all membranes surrounding different types of organelles.