Plant Water Relation : Notes : Class 12th Biology Chapter 6 : Maharashtra State Board New Syllabus

 Plant Water Relation

Chapter Notes & Explaination 

Based on Maharashtra State Board (HSC) New Syllabus - Reduced Syllabus

Q) Why water is considered as 'Elixir of Life' ?

Answer : Water is considered as 'Elixir of life' because :- 

1) It constitutes almost 90 to 95% of most plant cells and tissues.

2) I helps plants to maintain turgidity and shape.

3) It is best transporting medium for dissolved minerals and food molecules.

4) It is an essential raw material for photosynthesis.

→ Properties of Water :- 

1) Best solvent for most solutes & medium for biochemical reactions that occur in cells.

2) Inert inorganic compound with neutral pH, so it is best transporting medium for dissolved minerals and food molecules.

3) High specific heat, High heat of fusion & High heat of vaporization, therefore, it acts as thermal buffer. (due to hydrogen bonding between water molecules).

4) High surface tension, high adhesive and cohesive forces lead to easy rise in capillaries.

→ Water Absorbing Organ :- 

ROOT :- 

Main Function : - Water and Mineral Absorpion.

Mode of Absorption :- 

1) From Soil ( Terrestial Plants )

2) From water vapours from air ( Epiphytic Plants) 

Epiphytic Plants have epiphytic roots which contain Velamen Tissue to absorb moisture from surrounding air.

Structure of Roots : - 

Four Divisible Regions of Root : -

1) Maturation Zone 

2) Absorption Zone

3) Cell Elongation Zone

4) Meristematic Zone

Absorption Zone 

Root Hairs : - Epidermal cells (epiblema cells) form unicellular hair like cytoplasmic extensions called root hairs.

Structure of Root Hairs : - 

1) Each root hair may be 1 to 10 mm long and tube like.

2) It is colorless, unbranched, short lived (ephemeral) and very delicate.

3) It has large central vacuole, surrounded by thin film of cytoplasm, plasma membrane and thin cell wall (two layered)

4) Cell wall : Outer- Pectin , Inner - Cellulose

5) Cell Wall is freely permeable. Plasma Membrane is selectively permeable.

Water Absorption :-

Rhizosphere :-  Micro-environment surrounding the root from which plants absorb water.

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 Types of Water that occur in soil : -

1) Gravitational Water :  Water which percolates deep in soil due to gravity.

2) Hygroscopic Water : Water absorbed by fine soil particles.

3) Combined Water : Water present in form of hydrated oxides of silicon, aluminium, etc.

4) Capillary Water : Water held in pores present between neighbouring soil particles due to capillarity. 

Capillary water is available for absorption for plants.