Ch.6 Plant Water Relation

 

Prof.Dr.Sadhana Nikam
Vice Principal
Rashtriya Jr. College, Chalisgaon
Biology Subject
Notes of XII Science
CH.6 Plant Water Relation

 INTRODUCTION
* Plant obtain variety of substances like water,minerals, nutrients, food and gases like O2
and CO2 

 *Water is considered as ‘elixir of life’

6.1   Properties of Water:
Q. Describe Properties of Water(2 Mks)
1. Water occur in liquid form at room temperature.
2. Water is best solvent for most of solutes.
3. Water is inert inorganic  compound  with neutral pH.
4. Water is best aqueous  medium  for  all  biochemical  reactions
in the cells.
5. Water has high specific heat,high heat of vaporization and high heat of fusion.
6. Water molecules have good adhesive and cohesive forces of attraction.

6.2 Water absorbing organ
Root :
1. Root is the main organ of water and mineral absorption.
2. Terrestrial plants absorb water in the form of liquid from the soil.
3. Epiphytic plants like orchids absorb water vapours from the air
with the help of velamen tissue of epiphytic roots.
Q. Enlist  different  zones  of  a Typical root (2 Marks)
4. Typical root is divisible into four different regions as
a. Zone of Cell Division ( Meristematic  zone)
b. Zone of Cell Elongation
c. Zone of Root hair
d. Zone of Maturation

Q. In which part root hairs are present (1 Mark)
In Zone of absorption (zone of root hair) unicellular hair like extensions called root hairs are present.
Structure of Root hair :
Q.Describe Structure of root hair( 3 Marks)
1. Root hair is cytoplasmic extension of epiblema cell.
2.Each root hair is tube like with length of 1 to 10 mm. long
3. It is colourless, unbranched, short lived and very delicate.
4. Root hair has a large central vacuole surrounded by thin layer of cytoplasm.
5. Root hair is covered by inner plasma membrane and outer cell wall.
6. Outer layer is composed of pectin and inner layer is made up of cellulose.
7. Cell wall is freely permeable and plasma membrane is selectively permeable.
Figure : Text book  page

6.3 Water available to roots for absorption :
Q. From which part Plants absorb water(1Mark)
Plants absorb water from the Rhizosphere.
Q. What is Rhizosphere (1 Mark)
Rhizosphere is the microenvironment surrounding the root.
Q.In which form Water present in the soil (2 Marks)
Water present in the soil occur as gravitational (free) water,hygroscopic water, combined water and capillary water.
Q. What is gravitational  water(1 Mark)
Water percolates  deep  in  the  soil due  to gravity is  called
Gravitational  water.
Q. What is hygroscopic  water (1 Mark)
Water absorb  and  hold  by  fine  soil  particles  is called  Hygroscopic  water.
Q. Define Combined  water (1 Mark)
Water present in the form of hydrated oxides of silicon and aluminium is called  Combined  water.

Q. What is capillary water (1 Mark)
Some amount of water held in pores present between the
neighbouring  soil  particles  due to capillary  is  called  capillary  water.
Q. Which water is available for absorption  for  plants(1 Mark)
Only  capillary  water is  available  for  absorption  for  plants.

According to Reduced syllabus of XII th during 2020-2021