BIOLOGY TRANSPORTATION IN PLANTS

BIOLOGY TRANSPORTATION IN PLANTS

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Transportation in Plants

Transportation in plants is the process in which a substance is absorbed or synthesized in one part of the

plant and is transported to the other part of the plant.

Transport of Water and Minerals

Need for Water Water is required by the plant for various purposes.

Photosynthesis Water is one of the raw materials required to carry out

photosynthesis.

Transportation Transportation of minerals and sugar from roots to other

parts of the plant body.

Cooling Water is used to cool the plant by evaporation through

leaves when it is hot outside.

Need for Minerals Minerals are required as constituents of the cell and are also required for the synthesis of different

compounds and enzymes.



Characteristics of Roots for Absorbing Water

The root system of plants consists of the main root, which gives out lateral roots.

The lateral roots bear a large number of fine outgrowths called root-hairs.

A root hair is a long protuberance of a cell.

The ability of roots to draw water from the soil is dependent on the following factors:

The root hairs cover a large surface

area. More the surface area, the greater

is the absorption.

The cell membrane is semi-permeable.

The vacuoles present in the root hair

cells contain cell sap. The water

concentration in cell sap is lower than the

concentration of water in soil.



Experiment to show only Roots absorb Water

Take four test tubes and mark them A, B, C and D.

Fill water in test tubes A, B and C up to about three-quarters. Add only a little amount of water in test

tube D.

Fix a cork on the mouth of test tube A. Take three small-sized plants with their roots intact.

Wash their roots under tap water and insert them in test tubes B, C and D in a manner that the roots get

dipped fully in water in test tube B and C but remains above the water level in test tube D.

In test tube C, add pink dye to water.

Pour a few drops of oil in B and C to prevent the loss of water by evaporation.

Mark the levels of water in the four test tubes and leave the set up. Observe the change in the water

levels after 24 hours.

Observation:

Test Tube Observation Conclusion

A

Water level remains

unchanged.

No loss of water



B

Water level falls. Water was absorbed by

the roots of the plant

dipped in it.

C

Water level falls.

The veins of the leaves

have taken up the pink

colour of the dye.

Water was absorbed by

the roots of the plant

dipped in it and it is

transported to leaves.

D

The leaves wilt. Leaves of the plant

experience a loss of water

due to transpiration and

this loss is not replaced by

the absorption of water by

roots.



Osmosis

Absorption of water occurs through root hairs by the process of osmosis.

Osmosis is the movement of water molecules from a region of high concentration of water molecules to a

region of low concentration of water molecules across a semi-permeable membrane.

Semi-permeable Membrane

A semi-permeable membrane is a membrane that allows only selective materials to pass through it.

Raisins swell up in water and grapes shrink in thick syrup.

Put some raisins in bowl containing water and some grapes in another bowl

containing thick syrup of sugar. Observe the changes after 10-12 hours.

After 10-12 hours raisins swell up and the grapes shrink. The raisins absorb water

because they are placed in water while grapes lose water because they are kept in a

strong sugar solution. In both the cases, water movement takes place by osmosis.

The gain or loss of water is through the peel which acts as a semi-permeable

membrane.



Absorption of Mineral Salts by Roots

Roots not only absorb water from the soil but also mineral salts.

Depending on the concentration of minerals, two mechanisms are involved in their absorption:

Diffusion Diffusion is the free movement of molecules of a substance from the region of its higher concentration to

the region of its lower concentration, until their concentration in both the regions is equal.

If the concentration of mineral outside the cell is higher than the cytoplasm of root hair cell, then the

mineral salts enter by the process of diffusion.

Diffusion Osmosis

Movement of a substance from its

higher concentration to lower

concentration when the two are in

direct contact.

No membrane is involved.

Direct contact between the two

substances is necessary.

It occurs in gases as well as in

liquids.

Diffusion of water molecules

across a semi-permeable

membrane from a more dilute

solution to a less dilute solution.

Osmosis takes place across a

semi-permeable membrane.

Two solutions are separated by a

semi permeable membrane.

Only water, a liquid can move

from its high concentration to low

concentration region across a

semi-permeable membrane.



Active Transport Active transport involves the transportation of particles against a concentration gradient i.e. from a region

of low concentration to a region of high concentration.

Nutrients which cannot pass through the cell membrane of the roots cells easily are transported by

active transport.

Such substances are ions such as nitrates, sulphates, potassium, zinc, manganese, etc.

Active transport involves expenditure of energy. The energy utilized here is in the form of ATP.

Vascular Bundles

Vascular bundles constitute of xylem and phloem.



1. Xylem It conducts water upwards in a plant.

It is located in the centre of the plant body.

Xylem chiefly consists of tracheids and vessels.

2. Phloem It conducts manufactured food from leaves to different parts of the plant.

The food in phloem can move in upwards as well as in downward direction.

Phloem chiefly consists of sieve tube cells and companion cells.

Together, xylem and phloem constitute of conducting tissues and are known as vascular tissues.

Experiment to show that xylem carries water and phloem carries manufactured food in the plant.

Procedure:

Take a pot containing a small, woody plant.

Of the main stem, remove the outer bark for about 4 to 6 inches vertically.

Make sure the central core of the stem is not removed.

Water the pot well and leave it in bright sunlight.

Observation:

After a few days, leaves on the top appear very fresh and healthy. This indicates that water from

the soil has reached the leaves through xylem located in the core of the stem.

Just above the cut region, a small bulge can be seen on the stem. This is because the bark which

was removed earlier is the location of phloem tissue. Due to its removal, the food prepared in the

leaves cannot go all down, but accumulates above the cut.

Conclusion:

The experiment proves that xylem located in the core of the stem conducts water while the phloem

located in the outer region of the stem conducts food.



Root Pressure

It is the pressure developed in the roots due to continuous inflow of water.

Root pressure helps in pushing the plant sap upwards.

Due to root pressure water enters the xylem vessels.

Root Pressure

Process of Conduction of Water and Minerals

Water enters the root hairs through osmosis and mineral ions enter the root cells by active transport.

Both, water and minerals move upward from cell to cell through the cortex of the root by osmosis.

From the cortex, water and minerals are brought to the xylem.



Ascent of Sap

The sap which contains water and dissolved minerals move upwards from the root cells to xylem. The

upwards movement of sap is called the ascent of sap.

Transpiration

Transpiration is the loss of water in the form of water vapours from the aerial parts of a plant.

Transpiration occurs through openings called stomata.



During transpiration, water evaporates from the mesophyll cells of the leaves and escapes through the

open stomata.

Water loss through evaporation lowers the concentration of water inside the mesophyll cells. Due to

this, water enters the mesophyll cells from the neighbouring xylem vessels through osmosis.

More water is pulled upwards through the xylem vessels in stem, from the roots to replace the

water loss.

Therefore the pull is created by transpiration i.e. transpiration pull causes water and dissolved minerals

to move up through the stem.

Factors Affecting the Rate of Transpiration

Sunlight In day time, stomata remain open. Therefore, the rate of transpiration is faster.

During dark, the stomata are closed. Hence transpiration hardly occurs at night.

Temperature Increase in temperature increases the rate of transpiration.

Transpiration is faster on hot summer days than in cold winters.

Velocity of wind Transpiration increases with the blowing wind.

When the wind is blowing faster the water vapours from the leaves are

removed faster.

Humidity Transpiration is reduced if the air is humid.

Air cannot hold any water molecules when it is already laden with moisture.

Significance of Transpiration

Cooling Effect Maintaining Concentration of Cell Sap

During transpiration, water gets evaporated from

the plants.

The heat required for this evaporation is obtained

from the plant itself (latent heat).

Therefore, the plant is able to cool itself when it is

hot outside.

Transpiration ensures the maintenance of the

concentration of cell sap.

If there is no transpiration, then the

absorption of water by roots will make the cell

sap more dilute.



Experiments to Demonstrate Transpiration:

Experiment 1: To demonstrate transpiration.

Procedure:

Take a small sized, well-watered plant.

Cover the plant with a transparent polythene bag completely and tie its mouth around the base of

the stem.

Keep the plant in sunlight and note the change after a few hours.

Observation:

Drops of water appear on the inner side of the polythene bag.

Inference:

The plant gives off water vapour which saturates and condenses on the inner surface of the

polythene bag.



Experiment 2: To demonstrate that the plants lose water through its leaves.

Procedure:

Take a small sized, well-watered plant having a few branches.

Place a polythene bag over its one branch (consider this branch as A) as shown in the figure. Tie the

bag at the base of the stem with a rubber band.

From its other branch, remove all the leaves and cover it with another polythene bag as shown

in figure. (Consider this branch as B).

Place the plant in sunlight for 4-6 hours.

Observation:

Drops of water appear on the inner side of the polythene bag used to cover branch A.

No water drops appear on the polythene bag used to cover branch B.

Inference:

Most of the water gets evaporated from the plant through its leaves.



Experiment 3: To demonstrate that leaves lose more water from their lower surface.

Procedure:

Fold strips of dry cobalt chloride paper on both the surfaces of a leaf of a well-watered potted plant.

Cover the two strips by glass slides tied together by elastic bands. This is to hold the strip in position.

Remove the paper after 1-2 hours and observe the changes in the cobalt chloride paper.

Observation:

The cobalt chloride paper attached to the lower surface of the leaf turns pinker than the one attached

to the upper surface of the leaf.

Inference:

Leaves lose more water from the lower surface. This is because the lower surface of the leaves have

more number of stomata.

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BIOLOGY TRANSPORTATION IN PLANTS