Absorption of water and Minerals by roots

 Importance of water

Among the different substances needed for the life activities, water is the most important component. a large part of the Protoplasm is composed of water. plants in general have more water than animals. depending on their habitat, different types of plants have different amount of water in their body.

Organism             % of water  

                         By body weight

Land plant                   40-80%

Woody plant               40-50%

Herbaceous                 70-80%

Aquatic plants            75-98%

Animals                        60-80%

Water is required by the organisms mainly for the following purpose:

1 water serves as a solvent for many substances.

2 it participates in different metabolic reaction.

3 it facilitates exchange of gases between the organism and atmosphere by dissolving them.

4 it helps in movement of substances into and out of the cell.

5 it it helps in heat loss.

6 it helps in opening and closing of stomata by providing turgidity to them.

7 water is used as raw material for the process of photosynthesis.

Absorption of water and Minerals by roots

8  water is given out in the form of water vapour through stomata, lenticels and cuticle during transpiration, does help in regulation of temperature and creating a suction Force for the sap.

9 it helps in transportation of minerals from the roots to upward part of the plant and prepared food from the upper parts to the lower part of the plant.

Importance of minerals

Mineral element are obtained from the soil these are found as salts for free ions in the soil and are essential for normal functioning and growth of plant the mineral element which are required for normal growth of plant include nitrogen, phosphorus, potassium, calcium, iron, copper ,magnesium ,manganese, zinc, molybdenum, chloride and Boron etc.        N P K are most for normal growth and development of plants hence called Essential elements.

The process involved in absorption of water

Imbibition 

Imbibition is the process of absorption of water molecules by dry hydrophilic colloids due to surface. Imbibition occurs along the diffusion gradient.

Maximum imbibition occurs in agar agar protein, pectin, cellulose etc.

Examples of imbibition

1 swelling of dry seeds during germination 2 absorption of water by wooden doors and windows during rainy season causing them to swell.

 3 kneading of flour.

Diffusion

Diffusion is a physical phenomenon. it may be defined as the movement of molecules of a substance (solid , liquid or gas) from area of their higher concentation to area of their low concentration when they are in direct contact.

Demonstration of diffusion

Diffusion can be demonstrated by dropping a crystal of potassium permanganate into water contained in a beaker .The crystal dissolves, and gradually the purple colour of potassium permanganate spreads until finally it is distributed evenly in the water. Initially they are more concentrated at one place. This fact causes movement of the molecules Awaye from the Crystal. In other words, there is a net movement of molecules away from the vicinity of the Crystal. This is diffusion. The diffusion will occur whenever a difference in consideration exists. Mor concentration gradient will cause more Rapid diffusion. The diffusion take place usually along the concentration gradient. Rate of the diffusion depends mainly on size, temperature and concentration of molecules.

Importance of diffusion to organisms

1 plants

.   the movement of substances into and out of the cell is made possible by the diffusion.

.  it allows exchange of materials among cells.

. Roots absorb water and Minerals from the soil due to diffusion.

. In plants, opening and closing of stomata is directly based on the diffusion.

. The raw materials required for photosynthesis enter the photosynthetic cells of leaves is due to this process.

Animals

. Formation of urine in Kidneys.

. Distribution of substances by blood to different part and tissues of the body eg level of sugar in blood.

. Transport of hormones in the body of animals.

Membranes

Membranes are thin sheet of liquid or solid materials. these are the following types:

1 Impermeable:

They do not allow the passage of solute or solvent molecules through them; such as rubber sheet. 

2 permeable:

They allow movement of solute as well as solvent molecules across them, for example cell wall of cellulose.

3 semi-permeable:

These membranes allow the passage of water molecules but do not allow solute molecules to move across them,eg Cello phane egg membrane,  goat bladder and parchment paper. 

4 selectively permeable or differentially permeable:

These membranes allow passage of of water molecules and some selected solute molecules as well,e.g, plasma membrane. 

Osmosis

Definition:

Osmosis is a special kind of diffusion where by water molecules move through a semipermeable membrane from region of their higher concentration to region of their lower concentration. The movement of water molecules continuous until their concentration becomes equal on two side of the semi permeable membrane.

Demonstration of osmosis

Take distilled water in a beaker and 20% sugar solution in a thistle funnel whose mouth is covered with a semipermeable membrane such as cellophane or goat's bladder. Mark initial level of the solution on the tube of the funnel and then immerse the Funnel in the beaker containing water.

Absorption of water and Minerals by roots

Leave this experimental setup can undisturbed for about 15 minutes and thereafter, observe the level of the solution in the tube of the funnel. You will find that the level of the solution in the tube has been raised. This has become possible due to movement of water from the beaker to the sugar solution in the funnel through the semipermeable membrane ( cellophane or goat's bladder).