BIOLOGY

CHAPTER-1 TRANSPORT OF FOOD AND MINERALS IN PLANTS

INTRODUCTION

By the process of osmosis, water and minerals are absorbed from the soil by

roots and transported to various parts of the plants through xylem tissues.

Minerals needed by plants are taken up in the inorganic form, such as

nitrates, phosphates. The loss of water in vapour form from the leaf into the

atmosphere is called transpiration. This creates a suction which pulls water

from xylem cells. Thus, transpiration helps in the upward movement of cell

sap or water and minerals from roots to leaves.

ABSORPTION OF WATER BY PLANTS

Root is typically non-green, underground part of the plant. It does not

possess nodes, leaves and buds, but it is branched extensively. Root is well

suited to its function of absorption of water from soil, both morphologically

and anatomically.

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https://www.youtube.com/watch?v=BVZaUnMiOwM

MOVEMENTS OF MOLECULES

Three types of movements of molecules are seen:

1. Diffusion- It is the movement of gases, liquids or solids from the region of

higher concentration to that of lower concentration. It is a physical

process.

2. Osmossis- It is a special form of diffusion which involves only the

movement of water molecules from the region of their higher

concentration to the region of their lower concentration through a

semipermeable membrane.

3. Active transport- Whenever the substances like ions,salts and minerals

move from the region of their lower concentration to the region of their

higher concentration, they use energy in the form of ATP(Adenosine

triphosphate) from the cell. This process is called active transport.

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https://www.youtube.com/watch?v=eDeCgTRFCbA

A root hair with its semipermeable membrane acts as an osmotic system

through which the movement of the water molecules takes place.

Root pressure- The pressure developed in the root which helps in pushing

the sap upwards.

Root hair zone is the region of water absorption. The inside of root has

higher concentration than soil solution. Root hairs are in contact with soil

interspaces having capillary water. The root hairs pick up water that is

transferred inward due to still higher osmotic concentration since the root

hair cells have vacuole which contains a high concentrated solution of cell

sap in it. It reaches the cells surrounding xylem channel. Salt accumulated in

basal part of xylem channel causes osmotic entry of water and creates

positive pressure known as root pressure.

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https://www.youtube.com/watch?v=sUh9io7B3QM

CONDUCTION OF SAP

The upward movement of the water or sap from roots towards the top of the

plant is called conduction or ascent of sap. It occurs through tracheids and

vessels of the xylem tissue.

To undersatnd better click the link given below

https://www.youtube.com/watch?v=cnk3BJDBqIo

There are many forces which can be suggested for the rise of cell

sap:

Capillary force- Xylem tissues function as fine capillary tubes through which

water rises up by capillary action.

Root pressure- The pressure developed in the root due to continuous inflow

of water into it and responsible for pushing the sap upward.

Transpiration pull- Loss of water from the leaves develop a force which pulls

water from the roots to the top of the plant. The pull so set up is called

transpiration pull. It is very important in case of tall trees.

Turgor pressure- On absorption of water, a plant cell becomes swollen or

turgid. The protoplasm of this turgid cell presses the cell wall outside with a

force called turgor pressure. It keeps leaves, flowers, fruits of the plant

expanded. Decrease in turgor pressure of the cell leads to wilting.

Importance of water to the plants

1. Water is used by the plant in producing food by the process of

photosynthesis .

2. Plant absorb minerals and gases dissolved in water.

3. Water helps in the transportation of the substances from one region to

another in the plants.

4. It provides turgidity to plant cell which is essential for the maintenance of

support, form and growth of the plant cell.

5. Water is a major components of protoplasm (about 90%).

6. It is a general solvent of living system where various vital activities of life

are carried out.

7. It cools the plant by causing evaporation from the surface of leaves.

8. Water controls the opening and closing of stoma in leaf.

Some terms related to osmosis:

Endosmosis – Inflow of water/solvent molecules from an external dilute

solution into a cell.

Exosmosis – Withdrawal of water/solvent molecules from a cell into an

external concentrated solution.

Plasmolysis – Shrinkage of protoplasm of a cell from its wall due to the loss

of water by exosmosis when placed in the concentrated solution.

Deplasmolysis - Swelling of a plasmolysed cell to retain its original volume

when placed in pure water. This happens due to endosmosis.

TRANSPIRATION

Plants continuously absorb water through their roots which is sent up

through the stem to all parts of the plants, including the leaves. Only a little

amount of water is retained in the plant utilized by it in photosynthesis. The

rest of it gets evaporated into the atmosphere as water vapour through the

stomata present in the epidermis of leaves. This creates a suction pressure

which pulls up water from xylem of the roots to the stem and then to the

leaves. Water molecules are pulled up due to their tendency of remaining

joined (cohesion). Transpiration can be defined as the loss of water in the

form of vapours from the aerial exposed parts of the plants.

To undersatnd better click the link given below

https://www.youtube.com/watch?v=U4rzLhz4HHk

Factors affecting the rate of transpiration

1. Sunlight- In daylight, the stomata of the leaves are open. This allows the

water vapour in the leaves to diffuse out into the atmosphere. At night,

when the stomata close, transpiration is greatly reduced.

2. Temperature – Increase in temperature increases the capacity of the air

for more water vapour and thus the rate of transpiration increases.

Whereas with decrease in temperature, the rate of transpiration slows

down.

3. Humidity- A humid air contains a great deal of water vapours. It can

accept very little of water vapours from the plants and so transpiration

slows down. In dry air, the diffusion of water vapours from the leaf to the

atmosphere will be rapid.

4. Air movements - When the air is still, the region round a transpiring leaf

will become saturated with water vapours so thet no more water vapour

can escape from the leaf. In these conditions,transpiration would slow

down. In moving air, the water vapour will be swept away from the leaf

as fast as it diffuses out. This will speed up transpiration.

Potometer- It is an apparatus which is used to measure the rate if water loss

from a shoot under natural or artificial condition. It is normally used to

compare the rates of transpiration of the same shoot under different

conditions by timing the movement of air bubble over a given distance on

the scale.

Significance of transpiration

1. Cooling effect-A leaf exposed to direct sunlight will absorb heat and its

temperature may rise to a level which could kill the cytoplasm. Water

evaporating from a leaf absorbs its latent heat and thus cools the leaf.

2. Conduction of minerals- It helps in carrying minerals absorbed by the

roots to all the parts of the plant along with the water column.

3. Ascent of sap- It sets up a transpiration pull which helps in the upward

movement of the water from roots to top of the plant.

Disadvantages of transpiration

It has some disadvantages also. A lot of energy is wasted in absorbing and

lifting of extra water which is lost through transpiration. It causes the wilting

and shedding of leaves. It reduces the amount of water availability which

further limits the growth of seeds and fruits. Transpiration has more

disadvantages than advantages. But plants cannot check it. Therefore it is

regarded as ‘necessary evil’ to the plants.

CONDUCTING TISSUES

Complex tissue helps in transportation of organic materials, water and

minerals up and down the plants that is why it is known as conducting or

vascular tissue. The conducting tissues are of two types:

(A) Xylem

(B) Phloem

Xylem

It is a vascular and mechanical tissue. Xylem cells are thick walled. They are

found in the form of tubular passages. Xylem consists of four types of cells

called xylem elements. These are:

Tracheids- Single-celled elongated angular dead cells;walls thick due the

deposition of lignin. They are mainly found in lower vascular plants .

Vessels or tracheae- Much elongated multicellular tubes; the cell wall of

vessels is moderately thick; lignified and lumen is wide. They are found in the

xylem of angiosperms.

Xylem or wood parenchyma-They are living parenchymatous cells with thin

cellulose wall.

Xylem sclerenchyma or wood fibres- They are long, narrow cells tapering at

both the ends. These are dead cells with lignified walls.

Except xylem parenchyma, all other xylem elements are dead. Vessels are

the most important cells of all the four types of xylem elements. The

transverse walls between the vessel elements are partially or fully dissolved

to form continuous channels or water pipes.

The rings present in the trunk of an old tree are the xylem rings. By counting

the number of rings, we can determine the age of a tree.

Functions of Xylem

1. The main function of xylem is the upward movement of water and

dissolved minerals from the roots to different parts of shoots.

2. Tracheids, vessels, and xylem sclerenchyma provide mechanical strength

to the plant body.

3. Xylem parenchyma stores food and helps in conduction of water.

Phloem

It is a living conducting or vascular tissue. It contains tubes, like xylem, but it

performs no mechanical function. Phloem consists of four elements or cells.

These are:

(A) Sieve tubes

(B) Companion cells

(C) Phloem parenchyma

(D) Phloem fibres

Sieve tubes- These are slender, tube like structures made up of elongated,

thin-walled cells placed end to end. The end walls of sieve tube cells are

perforated by numerous pores and are called sieve plates. The nucleus of

sieve tubes degenerates on maturity.

Companion cells- These are thin walled and elongated cells attached to the

lateral sides of the sieve tubes. These cells are living and have large

elongated nucleus.

Phloem parenchyma- They are thin walled living cells. They store food and

help in the lateral transportation of food.

Phloem fibres- These are sclerenchymatous fibres which provide mechanical

strength to the plant.

Functions of Phloem

1. It helps in the transportation of organic food to all the parts of a plant.

2. Phloem parenchyma helps in the lateral conduction and the storage of

food.

3. Phloem fibres are used by man for making ropes and rough clothes.

To undersatnd better click the link given below

https://www.youtube.com/watch?v=1X0cEgPH7p4

https://www.youtube.com/watch?v=CmBDVIUB19g

NUTRIENTS IN PLANTS

Plants nutrients are inorganic raw materials that the plants absorb from

surronunding and utilise the same in buildings up their organic matter.

Plants nutrients and their sources :

1. Air - Carbon, oxygen

2. Water - Hydrogen

3. Soil -(i) Nitrogen, phosphorus, potassium, calcium, magnesium, sulphur.

(ii) Iron, manganese, boron, zinc, copper, molybdenum, chlorine.

Macronutrients – They are those essential elements which are present in

plants in easily detectable quantities more than 1 ppm of plant body ( 1 part

per million or 1 mg per g of dry weight ). These are nitrogen, phosphorus,

potassium, calcium, magnesium, sulphur.

Importance of Macronutrients – Macronutrients take part in synthesis of

organic molecules and development of osmotic potential.

Micronutrients – They are those essantial elements which are present in

plants in small quantity, less then 1 ppm or 1mg/g of dry matter. These are

iron, manganese, boron, zinc, copper, molybdenum, chlorine.

Importance of Micronutrients – Micronutrients are involved in functioning

of enzymes.

Deficiency diseases caused by lace of these essential nutrients:

1. Chlorosis – Yellowing of leaves can be seen and they die due to

deficiency of nitrogen.

2. Maturity may be delayed due to deficiency of phosphorus.

3. Due to deficiency of potassium brown spotting on plant leaves can be

seen on the edges of leaves.

4. Stem gets cracked due to deficiency of boron.

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WORKSHEET-1

A. Name the following: 1. The membrane which allows the solvent to pass through it but not the

solute.

2. The process by which solid, liquid and gases move from a place of

higher concentration to a place of lower concentration.

3. The upward movement of water and minerals from roots towards the

top of the plant.

4. The pull which helps in conduction of water in case of tall trees.

5. The tissue which helps in conduction of water and minerals in the plant.

6. An apparatus used to measure the rate of transpiration.

7. An antitranspirant.

8. A plant having hydathodes.

9. The tissue which helps in conduction of food in plants.

10. Name the disease caused due to deficiency of nitrogen nutrient in

plants.

B. Choose the correct answer: 1. Ascent of sap occurs due to:

a) Root pressure

b) Transpiration pull

c) Capillary force

d) All of these

2. The pressure developed in the root due continuous inflow of water in

it:

a) Turgor pressure

b) Root pressure

c) Transpiration pull

d) None of these

3. The upward movement of cell sap in the plants is called:

a) Conduction

b) Absorption

c) Transpiration

d) Diffusion

4. The tissue which helps in conduction of water and minerals in the plant:

a) Phloem

b) Xylem

c) Vein

d) Seive tube

5. Movement of molecules from a region of higher concentration to lower

concentration through a membrane:

a) Diffusion

b) Active transport

c) Osmosis

d) All of these

WORKSHEET-2 A. Select the odd one out by giving suitable category: 1. Osmosis, Diffusion, Active transport, Transpiration pull

2. Conduction, Translocation, Transpiration, Ascent of sap

3. Root pressure, Transpiration pull, Turgor pressure, Capillary force

4. Stomata, Xylem, Lenticel, Hydathodes

5. Sunlight, Temperature, Humidity, Hydathodes

6. Nitrogen, Phosphorus, Potassium, Copper

7. Tracheids, Trachea, Xylem parenchyma, Sieve plates

B. Fill in the blanks: 1. ______ tissue is involved in transportation of water in plants.

2. The young growing tip of the root is protected by ______.

3. ______ occurs through a semipermeable membrane.

4. A plant cell becomes _____ on absorbing water from soil.

5. Root hairs absorb _____ from the soil by active transport.

6. Upward movement of water takes place through _____.

7. _____ system of plants absorb water and minerals from the soil.

8. ______ is the inflow of water molecules from an external solution into

a cell.

9. A plasmolysed protoplasm swells when it is placed in _____ water.

10. Sunken stomata _____ the rate of transpiration.

C. Write true or false and correct the incorrect statements: 1. Osmosis plays an important role in the absorption of water by plants.

2. A semipermeable membrane allows the passage to only solvent

molecules through it.

3. Root hairs do not help in absorption of water and minerals.

4. Water is responsible for developing turgor pressure in the soil.

5. Movement of molecules from the region of lower to that of higher

concentration is called diffusion.