11-TRANSPORT IN PLANTS

CHAPTER NO. 11 TRANSPORT IN PLANTS

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INTRODUCTION:TRANSPORTATION is an important phenomenon which will take place in all

the higher organisms.In plants, materials of transport mainly include gases,

water, hormones, minerals, organic material etc. through diffusion, active

transport. In this chapter we will learn about various means of transport in

plants.

MEANS OF TRANSPORT IN PLANTS

1. DIFFUSION:It is an important process in the life of a plant. Movement by this process is passive and may be from cell to cell or from one part of the plant to the cell.Diffusion process does not result in the expenditure of energy and movement

of molecules takes place in random fashion.

The substance move from higher concentration region to lower concentration

region. It is a slow process and occurs most likely in liquid and gases. In

plants, diffusion is the only means of transport for gases. The rate of diffusion

depends on the gradient of concentration, pressure, temperature and permeability of membrane separating them. Following figure shows the diffusion of water vapor from higher concentration to lower concentration.

2.FACILITATED DIFFUSION:Presence of gradient is important for the process of diffusion and its rate depends on the size of substance.It is important to note that smaller substance diffuse faster as compared to larger ones.Along with size, the rate of diffusion also depends on solubility in lipids and the major constituent of the membrane.The substances with hydrophilic moiety are difficult to pass via membrane and therefore, its movement is facilitated.In this, the site is provided by membrane protein at which such molecules are able to cross the membrane.The concentration gradient is already present for molecules to diffuse even if facilitated by protein and this process is referred as facilitated diffusion.In this process, special protein helps the substance move across the

membrane without the use of energy of ATP.

It does not cause net transport of molecules and the rate of transport is

maximized when all the protein transporters are being used.Facilitated diffusion is the passive process and includes three type of

transport protein namely Uniport, Symport and Antiport.“The Uniport proteins carry a single solute across the membrane.

Symport proteins translocate two different solutes simultaneously in the

same direction.Antiport proteins exchange to solute by transporting one into the cell and one out of the cell.” All of these types are explained via figure below:

3.ACTIVE TRANSPORT:Active transport use energy in the form of ATP in the process of pumping molecules against the concentration gradient. The ATP donates a phosphate to a particular gateway molecule which then pumps the desired molecule across membrane, even if goes opposite concentration gradient.Thus, the energy of ATP is used to drive the pump. Following figure shows

the active transport in cell:

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:-

(a) MCQ

1. Choose the correct statement/statements. Pumps in active transport are

A. Lipids that bind molecules to pass them through the membrane.

B.Transport molecules uphill.

C. These are specific transporters.

D. These are

sensitive to inhibitors.

(a) A and C

(b) A, B and D

(c)B, C andD

(d) C and D

2. Two types of molecules cross the membrane in the same direction, it is

called as:

(a) Uniport

(b) Symport

(d) Multiport

3. Diffusion rate is affected by:

(a) temperature

(b) membrane permeability

(d) all of these

4. Which of the following is true about diffusion?

(a) There is no expenditure of energy.

(b) Molecules move in Brownian motion.

lower concentration.

(d) Diffusion depends on the type of living system.

5. Membrane protein is responsible for:

(a) Water molecule

(b) Transpiration of H2O

(d) Passive transport

(B) TRUE/FALSE:-

1. Transport over longer distances proceeds through the vascular system (the xylem and the phloem) and is called transpiration.

2. Diffusion rates are affected by the gradient of concentration, the

permeability of the membrane separating them, temperature and pressure.

3. When a molecule moves across a membrane independent of other molecules, the process is called uniport.

(C) FILL IN THE BLANKS:-

1 Water channels-made up of 8 different types of ............

2 lons are absorbed from the soil by both ............ and ............ transport.

PART: B SHORT ANSWER TYPE QUESTIONS:-

1 Name a molecular movement that is highly selective requiring special membrane proteins without needing any energy.

2. What are the different means of Transportation in plants?

PART: C LONG ANSWER TYPE QUESTION:-

1. Write a comparison between diffusion, facilitated diffusion and active

transport.

ANSWER KEY

PART: A VERY SHORT ANSWER TYPE QUESTIONS:-

A) MULTIPLE CHOICE QUESTIONS:

1. (c) Pumps in active transport are proteins that bind molecules to pass

Them through the membrane.

2. (b) In symport two types of molecule cross the membrane in Same direction.

3. (d) diffusion rate is affected by temperature, pressure, concentration

gradient and membrane permeability

4. (d) Diffusion is a slow process, it is not dependent on the living systems.

5. (c)membrane protein act as carrier molecule for active transport.

B) TRUE/FALSE:

1. False. Transpiration is a process of loss of water in the form of vapour's

from aerial part's of plant.

2. True.

3. True.

C)FILL IN THE BLANKS:

1. aquaporins

2. active and passive

PART: B SHORT ANSWER TYPE QUESTIONS:-

1. Facilitative diffusion

2. Active Transport, Diffusion and Facilitative diffusion

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INTRODUCTION:Plants lack both interstitial fluid as well as a regular circulation system. Even then they have to move various types of substances not only to short

distance but also to very long distances such as water from roots to tops of

plants or photosynthates from leaves to tips of roots. Substances move for

short distance through diffusion and active transport. Long distance transport occurs through vascular systems xylem and phloem.

PLANT WATER RELATIONS Water is a major component of all living cells, a medium in which all substances are dissolved and undergo various types of reactions. Water is itself a reactant as well as a product. It is a medium for transport. Water is

essential for cell growth and cell turgidity. The amount of water absorbed by

plant is very high.

IMBIBITION The absorption of water by the solid particles of an adsorbent causing it to enormously increase in volume without forming a solution is called imbibition. Solid substances or adsorbents which take part in imbibition are called imbibants. The liquid which is imbibed is known as imbibate.

Imbibition plays an important role in absorbing and retaining water-

i) Absorption of water by young cells is mostly through imbibition.

ii) Water is absorbed by germinating seeds through imbibition.

iii) Breaking of the seed coat in germinating seed is due to greater

imbibitional swelling of the seed kernel as compared to seed covering.

DIFFUSION Diffusion is defined as the movement of particles of different substances from the region of their higher concentration to region of their lower

concentration. Diffusion is a dependent upon the number of particles per

unit volume, density of medium, distance through which diffusion is to occur, temperature and pressure. Diffusion will be more rapid when the difference in concentration is larger. Gases diffuse more rapidly than liquids.e.g. Open a bottle of perfume in one corner of the room soon order of the perfume will be felt throughout the room.

DIFFUSION PRESSURE The pressure exerted by density of particles to diffuse from the area of its higher concentration to region of its lower concentration is called diffusion pressure. It depends upon the density, permeability of medium, temperature and diffusion pressure gradient.

IMPORTANCE:

I) Diffusion keeps the cell wall of the internal plant tissues moist.

ll) It is means of spreading of ions and other substances throughout the protoplast.

lll) Exchange of gases between the plant interior and outside air occurs

through diffusion.

IV) Aroma of flowers is due to diffusion of volatile aromatic compound to attract pollinating animals.

MEMBRANE PERMEABILITY Membrane permeability is the ability of a membrane to allow passage of gases, liquids, solutes through it. It is a dependent upon two factors:-

nature of membrane and nature of passing substance. On the basis of their permeability membranes are of four types

i) IMPERMEABLE-Which do not allow the passage of substances through them e.g- suberised cell wall, cutinized cell wall.

ii) PERMEABLE MEMBRANE-These allow the passage of substances through them e.g- cellulose cell wall.

iii) SEMIPERMEABLE MEMBRANE-These are those membranes which permit the movement of solvent molecules through them but prevent the movement of solute particles e.g- egg membrane,animal bladder.

iv) DIFFERENTIALLY PERMEABLE MEMBRANE-These are normally semipermeable but allow selective passage of solute through

them e.g- plasmalemma, tonoplast.

OSMOSIS Diffusion of water from its pure state or dilute solution into a

solution or stronger solution when the two are separated by a semipermeable membrane is termed as osmosis.

The movement of solvent or water molecules from the region of their higher diffusion pressure or free energy to the region of

their low diffusion pressure or free energy across a semipermeable membrane.

OSMOTIC PRESSURE It is maximum pressure which can develop in an osmotically

active solution when it is separated from its pure solvent by a semipermeable membrane under ideal conditions of osmosis that do not allow dilution of solution.

It is also defined as the pressure required to completely stop the entry of water into an osmotically active solution across a

semipermeable membrane.

IMPORTANCE

i) Entry of soil water into root is carried by osmosis.

ii) Osmosis performs cell to cell movement of water.

iii) The Soft organs like leaves,flowers,fruits and stems are

able to keep themselves stretched and swollen due to the rigidity of their cells which is dependent upon osmosis.

iv) Stomata open and close only in response to increase or decrease of osmotic pressure of the guard cells in relation

to nearby epidermal cell.

v) Osmotic pressure has been found to protect the plants against drought and frost injury.

DIFFUSION PRESSURE DEFICIT The reduction in the diffusion pressure of water in a

solution over its pure state is called diffusion pressure deficit.DPD=OP-WP

Where DPD is diffusion pressure deficit,OP-Osmotic pressure,WP-Water pressure

WATER POTENTIAL It is the difference in free energy or chemical potential for

unit molal volume of water in a system and that of pure water at the same temperature and pressure.

PLASMOLYSIS Shrinkage of the protoplast of a cell from its wall under the

influence of a hypertonic solution is called plasmolysis.DE-PLASMOLYSIS

The swelling up of plasmolysed protoplast under the influence of hyportonic solution or water is called deplasmolysis.

IMPORTANCE OF PLASMOLYSIS:

) Plasmolysis proves that the cell membrane is semipermeable.

ll) It shows that the cell wall is elastic as well as permeable.

lll) Plasmolysis can be shown only by living cells. It can therefore determine whether a cell is living or dead.

LET US KNOW WHAT WE HAVE LEARNT!

PART:A VERY SHORT ANSWER TYPE QUESTIONS:

(I) MCQs:

1. Difference between osmotic pressure is:

a)DPD

b) osmotic potential

c)solute potential

d)transpiration pull

2. Osmotic concentrations of a cell kept in water is chiefly regulated by:

a)vacuoles

b)plastids

c)ribosomes

d) mitochondria

3.Opening and closing of stomata due to:

a) plasmolysis

b) imbibition

c) osmosis

d) deplasmolysis

4. What will happen if a plant cell is kept in hypotonic solution for sometime

a) exosmosis

b)endosmosis

c)aandb

d)none of above

5. The instrument used for measuring osmotic pressure is called

a) osmometer

b) anemometer

c) ammeter

d)voltmeter

(Il) TRUE /FALSE:

1. Osmotic pressure is required to completely stop the entry of water into an

osmotically active solution across a semipermeable membrane.

2. Diffusion is the movement of substances from a region of lower concentration to

region of higher concentration.

3. Plant imbibants are hydrophobic in nature.

(Ill) FILL UPS:

1. The movement of water out of the cell is called..........

2. Raisins swell due to the process of...........

3. DPDis the........

ANSWER KEY: PART-A

MCQs:

1.a HINT-DPD=OP-WP so it is difference in osmotic pressure of water in

solvent and its form.

2.a HINT-Vacuoles are covered by membrane called tonoplast which allow

passage of solvent particles.Tonoplast is differential semipermeable

membrane which allow passage of some solute particles.

3.c HINT- Endosmosis and exosmosis are responsible for opening and closing

of stomata.Due to endosmosis the cells become turgid ,so stomata closed.Due to

exosmosis the cells become flaccid ,so stomata open.

4.5 HINT-The cell swell up due to entry of water into the cell due to

endosmosis.When we placed cell in hypotonic solution the water enters the cell

from outside.

5.a HINT-Osmometer is used to measure osmosis.

TRUE/FALSE:

1. True

HINT-Osmotic pressure is the pressure required to stop the process of

osmosis.

2. False

HINT-Diffusion is movement of substances from region of higher

concentration to region of low concentrations.

3. False

HINT-imbibants are hydrophilic in nature.

FILL UPS:

1. Endosmosis

2. Plasmolysis

3. Diffusion pressure deficit

PART: B SHORT ANSWER TYPE QUESTIONS:

1. What is diffusion? Also give importance of diffusion.

2. Differentiate between endosmosis and exosmosis.

3. What are the factors affecting osmotic pressure?

PART: C_ _LONG ANSWER TYPE QUESTIONS:

1. What is osmosis? Also define osmotic pressure. Give the importance of osmosis

2. |) Define diffusion pressure deficit and water potential.

ii) Differentiate between plasmolysis and deplasmolysis.

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INTRODUCTION:Water absorption occurs in plants through roots, which are often extensive and grow rapidly in the soil. The Zone of rapid absorption is characterized

by presence of roots hairs.

ABSORPTION OF WATER BY PLANTS:Water is absorbed purely by diffusion.Root hairs greatly increase the surface area for absorption.Once water is absorbed by the root hairs, it can move deeper into root hairs by two distinct pathways:

Apoplast pathway

Symplast pathway

APOPLASTPATHWAY; 2

1. The APOPLAST is the system of adjacent cell walls that is continuous

throughout the plant, except at the casparian strips of the endodermis in

the roots.

2. The Apoplastic Movement of water Occurs through the intercellular

spaces and the walls of the cells.

3. As water evaporates from the intercellular spaces, the atmosphere,

tension develop in the continuous stream of water in the APOPLAST,hence mass flow of water occurs due to the adhesive and cohesive properties of water.

SYMPLAST PATHWAY:

1. The SYMPLASTIC system is the system of interconnected protoplasts.

2. Neighbouring cells are connected through cytoplasmic strands that extend through the structure called Plasmodesmata.

3. During Symplastic Movement, the water travels through the cytoplasm and intercellular movement is through the Plasmodesmata.

4. The inner boundary of the cortex, the Endodermis is impervious to water

because of a band of suberised matrix called the Casparian Strip.

5. Water molecules are unable to penetrate the layer, so they are directed to

wall region and the water then moves through the Symplast and again crosses a membrane to reach the cells of the xylem.

6. Once inside the xylem, water is again free to move between cells as well

as through them.

MYCORRHIZAL ASSOCIATION Some plants have additional structures associated with them that help in water (and mineral) absorption. A MYCORRHIZA is a Symbiotic association of a fungus with a root system. In mycorrhizal association large numbers of fungal hyphae (associated with the young roots) extends to sufficient distance into the soil and have a large surface area. These hyphae are specialized to absorb both water

and minerals and provide them to the root; in turn the roots provide sugars and N- containing compounds to the mycorrhiza. Some plants have an_ obligate

association with the mycorrhizae. For example, Pinus seeds cannot germinate and

establish without the presence of mycorrhizae.

TYPES OF WATER ABSORPTION IN PLANTS:

Plants typically absorb water by the following two methods:

1. Active absorption of water

2. Passive absorption of water

1. ACTIVE ABSORPTION OF WATER:

This type of water absorption requires the expenditure of metabolic energy by the

root cells to perform the metabolic activity like respiration.

2. PASSIVE ABSORPTION OF WATER:

Passive absorption of water from the soil into plant is due to the more negative

water potential in the Xylem than in the soil water. It can occur independently of

any activity of roots. Its take place due to forces developed as a result of

transpiration i.e. Transpiration Pull.

ASCENT OF SAP:The upward movement of water and dissolved mineral salts from roots

upwards to the leaves and other aerial parts is called Ascent of Sap.

CASUATIVE FORCES OF ASCENT OF SAP:

1. Capillary action of the xylem tracheids.

2. Imbibition of the cell wall of xylem.

3. Transpiration Pull and Forces of Adhesion.

4. Root pressure.

ROOT PRESSURE: The pressure generated in the root due to continuous inward movement of water through cell to cell osmosis is called root pressure, It pushes the water upwards through root and stem.

GUTTATION: Loss of water in its liquid phase is known as Guttation.

TRANSPIRATION PULL & COHESION WATER THEORY:

1. This theory was originally proposed by Dixon and Joly (1894) and greatly

supported and elaborated by Dixon (1914, 1924).

2. According to this theory, there is a continuous column of water from root

through the stem and into the leaves.

3. Water molecules remain attached to one another by a strong mutual force of attraction called cohesion force. This is due to the hydrogen bonds formed amongst adjacent water molecules.

4. There is another force called adhesion force between the walls of treachery elements and water molecules. Thus, the three physical properties of water i.e., cohesion, adhesion and surface tension mainly account for the transpiration driven ascent of xylem sap.

5. As the water is lost from the leaf surface by transpiration osmotic

pressure of the leaf cells increases. As a result, the cells develop low water potential and water from the leaf veins (xylem) moves into leaf cells. The xylem vessels, in turn, draw water from xylem of main stem.

6. A negative (pulling) pressure is thus exerted by all the leaves on the

stem. The combined pressure, called transpiration pull, is strong enough to pull up the column of water to great heights.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A_ VERY SHORT ANSWER TYPE QUESTIONS:

(a) MCQs:

1. Xylem translocates:

(a) Water, minerals salts, some nitrogen and hormones

(b) Water only

(d) Water, minerals and some organic

Nitrogen only

2. Roots Pressure develops due to:

(a) Active absorption

(b) Low osmotic potential in soil

(d) Increase in transpiration

3. Upward movement of water in plant is called:

(a) Sucking

(b) Translocation

(d) all of these

4. Root pressure occurs when there is:

(a) less transpiration and less absorption.

(b) More transpiration and more absorption.

(d) None of above

5. The structure through which ascent of sap take place:

(a) Tracheary elements

(b) Pholem

(d) Passive transport

(b) TRUE/FALSE:

1. Metabolic energy of cell is utilized in passive absorption of water.

2. Water moves from one cell to another cell through plasmodesmata.

3. The area of young roots where most absorption takes place is the root hair

zone.

(c) FILL THE BLANKS:

1. Metabolic energy of the cell is utilized in_s absorption of water.

2. Plasmodesmata connections help ins

PART: B_ SHORT ANSWER TYPE QUESTIONS:

1. The given diagram represents the result of an experiment conducted on two freshly taken leafy shoots of herbaceous plant .The lower ends of the shoot are dipped in ordinary water

a) What is the aim of this experiment?

b) Some parts of stem in both the shoots have been removed. Name the conducting tissue in shoot A and B that have been removed.

2. How is mycorrhizal association helpful in absorption of water and minerals

in plants?

3. Given here is a diagrammatic representation of a part of the cross section of the root in root hair zone.

a) Name the parts indicated by the guidelines 1 to 5

b) Is the root hair cell unicellular and multicellular?

c) Name the process that is responsible for the entry of water molecules from

the soil into A1 and Then A2

d) What pressure is responsible for the movement of water in the direction

indicated by arrows?

e) How does this pressure set up?

PART:C LONG ANSWER TYPE QUESTIONS:

1. Describe the mechanism of absorption of water by plants?

ANSWER KEY: PART -A&B

A) MULTIPLE CHOICE QUESTIONS:

1 (A). Hint: xylem is associated with translocation of mainly water ,minerals

salts,some nitrogen and hormones

2 (A). Hint: Root pressure occurs in the xylem of some vascular plants when the soil

moisture level is high either at night or when transpiration is low during the day.

Root pressure is caused by active absorption of mineral nutrient ions into the root xylem.Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential.

3 (C).

4 (C). Hint: Plants when the soil moisture level is high either at night or when

transpiration is low during the day

5 (A). Hint: The ascent of sap in the xylem tissue of plants is the upward movement of

water and mineral from the root to the upper part of the plant body.

B) TRUE/FALSE:

1. False; Hint: Active absorption refers to the absorption of water by roots with the

help of adenosine triphosphate, generated by the root respiration. As the root cells

actively take part in the process, it is called active absorption.

2. True; Hints :Plasmodesmata (PD) are intercellular channels that span the plant

cell wall and serve as cytoplasmic bridges to facilitate efficient exchange of

signalling molecules between neighbouring cells.

3. True; Hint : Roots hairs Increasing the surface area of these hairs allows plants

to be more efficient in absorbing nutrients.

C) FILL IN THE BLANKS:

1. Active

2. Movement of substance between cells

PART:B SHORT ANSWER TYPE QUESTIONS:

1. a) to show that ascent of sap occurs through xylem tissue.

b) A) Phloem B) Xylem

2. Mycorrhizae are able to create a massive connection between the roots of a

plant and with the surrounding soil, which allows the fungus to uptake nutrients

such as nitrogen and phosphorus for the plant and increase the surface area of the

roots

3. a) 1) roots hair cell 2) soil particle 3) Xylem

4) cortical cell

5) Nucleus

b)Unicellular c) Endosmosis d)Rootpressure — e) by cell to cell osmosis

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INTRODUCTION:Transpiration is the biological process by which water is lost in the form of water vapours from the aerial parts of the plants.During the process of transpiration, water molecules in the plant tissues are removed from the aerial parts of the plants. Only a small

amount of water absorbed by the plants is utilized in growth and development. The rest is eliminated in the form of transpiration.Stomatal transpiration is the evaporation of water from the stomata of the plants. Most of the water from the plants is transpired this way. The

water near the surface of the leaves changes into vapor and evaporates when the stomata are open.

OPENING AND CLOSING OF STOMATA:

Stomata consist of a pair of guard cells with an aperture in between.It remains open during the daytime and is closed at night.

The reason for the opening and closing of this structure is the turgidity of guard cells. The interior wall of the guard cells present towards the aperture is dense and flexible.The stomata open when the turgidity of the guard cells increases. The

exterior walls bulge out, and the interior walls form a crescent shape.The orientation of the micro fibrils in the guard cells also plays an important role in the opening of the stomata. The radial orientation of the micro fibrils makes it easier for the stomata to open.The stomata close when the turgidity of the guard cells decreases due to the water loss and the interior walls form a crescent shape retrieve their original shape.

In dicots, the lower side of leaves have more stomata while in monocots,

both the sides have an equal number of stomata

Some plant factors include number and distribution of stomata affect

transpiration.

ASCENT OF SAP:When water evaporates through the leaves, a pull is created through

the xylem, and water moves back to the leaves. This is known as the

transpiration pull.The ascent of sap that is driven by transpiration depends on the

following properties of water:

COHESION - This is the mutual attraction between molecules of water.ADHESION The attraction of water molecules towards the cell surfaces.

SURFACE TENSION - The molecules of water are more attracted to each other in the liquid phase than in the gas phase.

SIGNIFICANCE OF TRANSPIRATION IN PLANTS:

1. Transpiration helps in the conduction of water and minerals to different parts of the plants.

2. Due to the continuous elimination of water from the plant body, there is

a balance of water maintained within the plant.

3. It maintains osmosis and keeps the cells rigid.

4. A suction force is created by transpiration that helps in the upward

movement of water in the plants.

5. Certain hydrophilic salts are accumulated on the surface of the leaves,

which keeps the leaves moist.

6. It maintains the turgidity of the cells and helps in cell division.

7. Optimum transpiration helps in the proper growth of the plants.

8. The cooling effect of a tree is due to the evaporation of water from its

leaves.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

(A) MCQs:

1. Loss of water from plants in the form of water vapor is called:

a) Surface tension

b) Cohesion

c) Ascent of sap

d) Transpiration

2. Which of the following statement is INCORRECT for transpiration?

a) It occurs by stomata, lenticels, and cuticle

b) Water comes out as water vapor

c) It occurs in all plants

d) Root pressure is involved

3. Transpiration occurs from: -

(a) leaves

(b) stems

(d) roots

4. Stomata open during the daytime because the guard cells

(a) photosynthesize

(b) are thin walled

(d) have to help in gaseous exchange

5. Of the processes which occurs in leaves, the one which may lower their temperature is

(a) respiration

(b) photosynthesis

(d) hydrolysis

(B) TRUE/FALSE:

1. Transpiration helps to cool the body of the plant.

2. Excessive transpiration results in the wilting of the leaves.

3. Atmospheric humidity promotes transpiration from a green plant.

(C) FILL IN THE BLANKS:

1. The leaves have more on their lower surface.

2. Transpiration is reduced if the air is .

ANSWER KEY: PART -A

(A) MCQs:

Answer 1: (d) Explanation: Transpiration is the process by which aerial part of the plant (mainly leaves) loses water in the form of water vapor.

Answer 2: (d) Explanation: Transpiration is a universal process that occurs in all plants. It does not involve root pressure but the water comes out from a plant in the form of water vapor.

Answer 3: (c) all aerial parts.

Answer 4: (a) photosynthesize

Answer 5: (c) transpiration

(B) TRUE/FALSE:

ANS 1. TRUE

ANS 2. TRUE (When the rate of transpiration far exceeds the rate of absorption of water by roots, the cells lose their turgidity. Hence, excessive transpiration results in wilting of the leaves.)

ANS 3. FALSE (Corrected statement Atmospheric humidity reduces transpiration from a green plant.)

(C) FILL IN THE BLANKS:

1. STOMATA

2. HUMID

PART: B SHORT ANSWER TYPE QUESTIONS:

1. Define cohesion.

2. How is transpiration important to the plants?

PART: C LONG ANSWER TYPE QUESTION:

1. How does the opening and closing of stomata regulate the transpiration

process?

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INTRODUCTION:Plant body requires minerals for the proper functioning of all the organs.The supply of carbon is from carbon dioxide of atmosphere. Rest of the minerals are picked up from the soil and trans located to other parts of the body for growth and other activities in plants. Requirement of hydrogen is full-filled by mean of passive water absorption.

MINERAL ABSORPTION: - In plants entry point of minerals is roots. Minerals are

present in the soil in ions form.

FACTORS AFFECTING MINERAL UPTAKE IN PLANTS:

1. Minerals ions which are charged particles.

2. Concentration of minerals in the soil (mostly lower) as compare to roots.

3. Minerals ions cannot directly cross the cell membrane.Based on above factors two types of mineral absorption is responsible, as all mineral cannot be passively absorbed.

MECHANISM OF MINERAL ABSORPTION:-

A) Passive Absorption

B) Active Absorption

PASSIVE ABSORPTION:In passive absorption movement of mineral ions into roots occurs by simple diffusion and rate of diffusion depends on potential gradient.

VARIOUS THEORIES OF PASSIVE ABSORPTION:

MASS PLOW TREOR'Y: - Under this theory ions are absorbed by root along with mass flow under transpiration pull. But it fails to explain salt accumulation.

ION EXCHANGE THEORY: - Mineral ions adsorbed on the surface of the

membrane of root cells may be exchanged with same charged particle from external

soil solution. e.g. Kt may be exchanged with H* adsorbed on the surface of root

cells .

DONNAN EQUILIBRIUM:-This theory explains the passive accumulation of ions that are non-diffusible, which may be present on one side of the membrane. Unlike diffusible ions, the membrane is not permeable to non-diffusible ions, such ions are called fixed ions.

All the passive absorption is without use of cellular energy.

ACTIVE ABSORPTION:-The movement of ions from soil to interior of root is against the concentration gradient and requires active transport. Specific ions pumps occur in the membrane of root hairs. It uses the energy provided by ATP molecule.

Enzyme called ATPase on plasma membrane uses energy to pump proton across

the membrane.These ions pump are proteins and act as control point and check quantity and types of solutes that reach the xylem.

Apart from it root endodermis has layer of suberin having ability to actively transport ions in one direction only.

It uses the energy provided by ATP molecules. Enzyme called ATPase on plasma

membrane uses energy to pump proton across the membrane.This establishes an electro chemical proton gradient that provides energy.

In xylem sap NITROGEN travel as inorganic ions, as well as organic form of

amino acids. Small amount of PHOSPHOROUS and SULPHUR are passed in xylem as organic compounds.Mineral elements pass up xylem in both organic and inorganic form.From xylem, ions are distributed in to young leaves, developing flowers, fruits,and seeds, apical and lateral meristem.Minerals are unloaded by mean of simple diffusion.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

1) MCQs:

1 Xylem translocates

a) water only

b) water and mineral salt only

c) water, mineral salts and nitrogen

d) water, mineral, organic N2, harmones

2 The active transport takes energy from;

a) Glucose

b) ATP molecule

b) Do not use energy

d) none of the above

3 lons exchange method is a type of absorption;

a) Active

b) Passive

c) both

d) none

4 Enzyme present in plasma membrane that facilitates active absorption;

a) ATPase

b) transcriptase

c) amylase

d) all the above

5) Passive mineral uptake by roots system is due to:

a) Force created in roots

b) Osmotic force in shoot

c) High respiratory activity in root

d) Tension in sap due to transpiration

2) TRUE / FALSE:

1. Concentration of ions is more in root interior than in the soil.

2. Only Active mineral uptake takes place.

3. Active transport involves some transport proteins called Porins.

3) FILL UPs:

1. Metabolic energy of the cells is used in .................. adsorption of mineral.

2. ...........enzyme is used in active transport.

3. Transport proteins present in ..................cell of roots.

ANSWER KEY: PART -A

1) MCQs:

1. d Hint; xylem translocate all water soluble material , ions ,organic

nitrogen and hormones.

2. b Hint; ATP molecule is driving force for active transport

3. b Hint; it is a passive absorption because it does not require energy

4.a_ Hint; ATPase is used to hydrolyse ATP molecule to give energy.

5. d Hint; it is transpiration pull which create tension in sap which in

turn increase mineral uptake.

2) TRUE/FALSE:

1. True; Hint; With this active transport going on to uptake of

mineral.

2. False; Hint; Both active and passive transport is present.

3. True; Hint; Porins are present root epidermal cells.

3) FILL UPs:

1. ACTIVE

2. TRANS MEMBRANE ATPase.

3. ENDODERMAL

PART: B SHORT ANSWER TYPE QUESTIONS:

1. What is Donnan’s equilibrium?

2. Why most of mineral up taken by active transport?

3. Difference between active and passive transport of mineral.

PART: C LONG ANSWER TYPE QUESTION:

1. Give the detail mechanism of mineral uptake by plants.

A116

INTRODUCTION

TRANSPORT IN PLANTS: Plants need to move molecules over a long distance . Water taken up by the roots has to reach all parts of the plant.The food synthesised by the leaves has also to be moved all parts

including the root tips embedded deep inside the soil.In rooted plants, transport in xylem is uni-directional from root to stem.Organic and minerals nutrients however undergo multidirectional transport. Organic compounds synthesised in the photosynthetic leaves are exported to all other parts of the plant including storage organs. From

the storage organs they are later re-exported.

PHLOEM TRANSPORT: Food is transported by the vascular tissue phloem from a source to a sink that is the leaf and sink, the part that store the food. The source and sink may be reversed depending on season or

the need. The direction of movement in the phloem is bi-directional means upward and downward. So the food in phloem sap can be transported in any required direction. Mostly the phloem sap is water and sucrose but other sugars, hormones and amino acids are also transported.

MASS FLOW HYPOTHESIS:The theory behind Mass flow hypothesis which is also called as pressure flow hypothesis describes the movement of sap via phloem, proposed by

the German physiologist Ernst Munch in 1930.A highly concentrated organic sugar especially sugar in the cells of phloem from a source like a leaf forms a diffusion gradient which draws water in the cells from adjacent xylem. This develops turgor pressure in the phloem which is also called as hydrostatic pressure.Phloem movement occurs by mass flow from sources of sugar to sugar sinks. The phloem movement is bidirectional but unidirectional in xylem

cells. Due to this multidirectional flow, it is not uncommon for sap in the

sieve-tubes besides to move in opposite direction based on the fact that

sap cannot travel easily between adjacent sieve tubes.The movement of minerals and water via xylem is driven mostly by

negative pressure and movement via phloem is driven by hydrostatic pressure. This process is called as TRANSLOCATION and accompanied by a process known as phloem loading and unloading.Cells in sugar sources load a sieve tube by osmosis developing pressure that pushes the sap low. The cells deliver solutes out of the elements of sieve-tube and produce opposite effects. The sugar gradient from source

creates pressure flow via sieve tube towards the sink.GLUCOSE is formed by photosynthesis in the cells of mesophyll and someglucose is utilized in the cells during respiration. The left over glucose istransformed into non-reducing sugar.

SUCROSE is delivered to the neighbour cells of minute veins of the leaves.

Sucrose diffuses from neighbour cells to the elements of sieve tube via

plasmodesmata. Hence, the amount of sucrose rises in the elements of sieve tube.

Water travels from the close xylem to the leaf vein by osmosis and raises

the hydrostatic pressure of the elements of sieve tube. The Hydrostatic pressure shifts the sucrose along with other substances

via the cell of sieve tube towards the sink.In storage sinks, sucrose is eliminated into Apoplast before entering the sink’s Symplast.The water travels out of the cells via osmosis and lowers the hydrostatic pressure in them.Hence, a gradient of pressure is developed as a result of the entry of sugar at source and elimination of sucrose at the sink.

The phloem sugar is eradicated by the cortex of root and stem and utilized

by cellular respiration. The starch is insoluble and does not exert any

osmotic effect. Ultimately, pure water is left and drawn into xylem vessels

by transpiration pull.

TURGOR GRADIENT HYPOTHESIS:It is generally believed that an Osmotically generated pressure gradient drives the phloem mass flow. So far, this widely accepted Munch theory has required remarkably few

adaptations. Recently, a possible shortcoming of the Munch theory has

been pointed out, suggesting that the Munch pressure flow is more suitable for herbs than for trees. Estimation of the phloem resistance indicates that a point might be

reached in long sieve tubes where the pressure required to drive the

Munch flow cannot be generated.

Therefore, the relay hypothesis regained belief as it implies that the sieve

tubes are shorter than the plant’s axial axis.In the source phloem, three different loading strategies exist which

probably result from evolutionary advantages.Passive diffusion seems to be the most primitive one, whereas active

loading strategies substantially increase the growth potential.Along the transport phloem, a leakage-retrieval mechanism is observed.Appreciable amounts of carbohydrates are lost from the sieve tubes to feed the lateral sinks, while a part of these lost carbohydrates is subsequently reloaded into the sieve tubes. This mechanism is probably involved to buffer short-term irregularities in phloem turgor and gradient.As phloem of higher plants has multiple functions in plant development,

reproduction and growth, the fundamental understanding of the mechanisms behind phloem transport should be elucidated to increase our ability to influence plant growth and development.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

A)MCQs:

1. All the following are sink except

a. Fruit

b. Seed

c. Leaves

d. Rhizome

2. The movement of photosynthate through phloem is always

a. From source to sink

b. From sink to source

c. Bi-directional

d. None of these

3. Phloem loading is the transfer of sugar from

a. Source to sink

b. Leaves to sieve tube

c. Fruit to seed

d. All of these

4. The process of transferring sugar from sieve tube to sink is called

a. Photosynthate transfer

b. Source sink transfer

c. Phloem loading

d. Phloem unloading

5. The long distance transport of photosynthate from one region to

another in higher plants is called

a. Xylem translocation

b. Phioem translocation

c. Apoplast

d. Symplast

B) TRUE/ FALSE:

1. Food and various other substances are transported in plants

through diffusion.

2. The main function of phloem is translocation of food.

3. Phloem transport in uni-directional.

C) FILL UPS:

1. For transport of food in plants it requires

2. Transport of food material in plants takes place through

3. The transport system in plants are made up of

4. Munch hypothesis is based on

ANSWER KEY: PART-A

MCQ’s

1. C (leaves)

2. A. (from source to sink)

3. D. (All of these)

4. D.( phloem unloading)

5. B. (phloem translocation)

TRUE /FALSE:

1. [EY (Plants have their unique vascular system which helps them to transport food and water throughout the plant body.)

2. EEE (Phiocem is elongated, tubular shape with thin-walled sieve tubes vascular tissue. Its function is the transportation of food and nutrients such as sugar from leaves to other parts of the plant. This

movement of substances is called translocation.)

3. [EE (it is bi-directional. both in upward and downward directions.)

FILL UPS:

1. ATP and phloem (When food like glucose or sucrose it transferred to

phloem tissue, using ATP, the concentration of water molecules decreases in that area this results in movement of water into the

cells due to osmosis.)

2. Sieve tubes (The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.)

3. Vascular tissue(Plants do not move much and have many dead cells in their tissues. Therefore, they do not need much energy. So, they have transport systems slower than those of animals. In plants, the

transport system consists of tube like passages made up of vascular tissue.)

4. Translocation of food due to Turgor Pressure (TP) gradient. Munch

hypothesis is based on the movement of phloem sap along a turgor pressure gradient. The mass flow of organic solutes takes place from the site of higher concentration, (source) to the site of lower concentration (sink).

PART: B SHORT ANSWER TYPE QUESTIONS:

1. Explain the process of translocation of food materials in plants.

2. If food is transported to various parts of the plant through phloem?

3. Food synthesized in the leaves is transported to other parts by which

means?

ANSWER KEY: PART-B

1. Translocation occurs through part of vascular tissue known as phloem that also transports carbohydrates, amino acids and other substances such as plant hormone which are made in tips of roots

and shoots to the storage and growing organs.

2. Transportation of food requires living tissue. Sieve tubes in phloem tissue are living cells and are involved in transportation of sugars.

3. Translocation is the movement of organic nutrients from the region of source or supply to the region of sink or utilization. Phloem is the pathway for this translocation.

PART: C LONG ANSWER TYPE QUESTIONS:

1. Explain which the source is and sink in phloem translocation.

2. Explain mass flow hypothesis experiment.

A117

INTRODUCTION

TRANSPORT IN PLANTS:Transport in plants is of utmost importance as:Plants need to take up water, minerals and carbon dioxide, and

transport them to the leaves for photosynthesis.They then move the products of photosynthesis to where they're

needed in the plant.Means of Transport

As studied earlier, there are varied means of transport in plants like Diffusion, Facilitated Diffusion, Osmosis, Active Transport.In this assignment, now we shall study about various differences that has

come under this chapter.

LET US KNOW WHAT WE HAVE LEARNT!

PART:A VERY SHORT ANSWER TYPE QUESTIONS:

A) MCQs:

1. If the atmospheric pressure is low, the rate of transpiration will:

a. Increase

b. Decrease

c. Stay unchanged

d. Can't be determined

2. The main function of guard cells is to help with:

a. Transpiration

b. Guttation

c. Transcription

d. None of the above

3. The movement of water across a semi permeable membrane is:

a. Osmosis

b. Active transport

c. Facilitated diffusion

d. Pinocytosis

4. Transpiration is a phenomenon pertaining to:

a. Activated transport

b. Diffusion

c. Osmosis

d. Facilitated diffusion

5. Symplastic movement is slower than Apoplastic movement because:

a. Molecule has to enter through cell membrane

b. It is down the gradient

c. As it involves cytoplasmic through streaming always

d. All of the above

B) TRUE/ FALSE:

1. When placed in water, raisins swell up as a result of Endosmosis.

2. Facilitated diffusion involves a carrier protein.

3. In osmosis, there is movement of solute molecules.

C) FILL Ups:

1. During Transpiration, there is loss of water as

2. Osmosis is limited only to the medium.

3. Apoplast involves components of a cell.

ANSWER KEY: PART -A

A) MCQs:

1. (a) Increase, due to more outward water movement.

2. (a) As guard cells help in opening and closing of stomata.

3. (a) Osmosis

4. (b) Diffusion

5. (a) Molecule has to enter through cell membrane

B) TRUE/ FALSE:

1. True; Because due to hypertonic medium inside, water molecules move

inside.

2. True; Carrier protein is a characteristic feature of facilitated diffusion, as it helps in quick transfer.

3. False; Semi-permeable membrane does not allow solute molecules due to their size.

C) FILL UPs:

1. water vapour

2. liquid

3. non-living

PART: B— SHORT ANSWER TYPE QUESTIONS:

1. Write difference between Active and passive transport.

2. Enlist difference between Symplast and Apoplast patyhways.

3. Write difference between Diffusion and facilitated diffusion.

PART: C- LONG ANSWER TYPE QUESTIONS

1. Explain the difference between osmosis & diffusion.

118

INTRODUCTION:In the chapter TRANSPORT IN PLANTS; you have studied that, plants transport various substances like gases, minerals, water, hormones and organic solutes to short or long distances as water and minerals from roots to tips of stem and otherorgans of plants. The food prepared in leaves also transported to the tip of the root and all other organs of the plant.

Long distance transport occurs through vascular system, Xylem and Phloem

called translocation through mass flow.

Now in this topic, let's revise diagrams related to transport in plants.

FACILITATED DIFFUSION:Passive transport of molecules along their concentration gradient across the biological membrane with the help of special proteins. In these, special proteins help to move substances across membranes without expenditure of ATP energy.UNIPORT: Movement of particles of a solute across a membrane irrespective of the particles of other solutes.

SYMPORT: Two or more molecules cross the membrane in the same direction.

ANTIPORT: Two or more molecules move in the opposite direction across the membrane.

2. OSMOSIS: It refers specifically to the diffusion of water across a differentially

or selectively permeable membrane from higher concentration of water (HYPOTONIC) to its lower concentration (HYPERTONIC). As pure water has higher water potential, in osmosis water moves from higher water potential to lower water potential.

PLASMOLYSIS: The process in which the water moves out of the cell and the cell

membrane of the plant cell shrinks away from its cell wall.Cells swell in HYPNOTIC solutions and shrink in HYPERTONIC solutions.

HOW DO PLANTS ABSORB WATER?

Plants absorb water through roots by the process of diffusion. Water can move

deeper into root layers by two distinct pathways.

APOPLAST PATHWAY: System of adjacent cell wall that is continuous through out the plants except at casparian strips of the endodermis of the root.

SYMPLAST PATHWAY: System of interconnected protoplasts.

TRANSPIRATION & TRANSPIRATION PULL:It is evaporative loss of water by plants mainly through stomata. Since the thin film of water over the cells is continuous, transpiration results in pulling of water

molecule by molecule, into the leaf, from the xylem.Also, because of lower concentration of water vapour in the atmosphere as compared to the sub stomatal cavity and intercellular spaces, water diffuses into the surrounding air, this creates a “pull”, called TRANSPIRATION PULL.

MASS FLOW HYPOTHESIS:Translocation of sugars from source (green leaves) to sink occurs by pressure flow mechanism. The movement of sugars in the phloem begins at the source where sugars are loaded into a sieve tube. Loading of phloem sets up a water potential gradient that facilitates the mass movement in the phloem.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A- VERY SHORT ANSWER TYPE QUESTIONS:

-MCQs:

1. Transpiration is regulated by the movements of:

a) Parenchyma

b) Guard cells

c) Epithelial cells

d) None of the above

2. Transport of food materials in higher plants occurs through:

a) Flowers

b) Companion cells

b) Tracheids

d) Sieve elements

3. The movement of materials from the leaves to other tissues of the plant is

called:

a) Tropic movement

b) Guttation

c) Transpiration

d) Translocation

4. Movement of water that occurs exclusively through intercellular spaces

and the walls of the cells is:

a) Apoplast

b) Symplast

d) Tonoplast

d) Both ‘a’ and ‘b’

5. Acell when kept in a sugar solution gets dehydrated then the solution is:

a) Hypotonic

b) Hypertonic

b) Isotonic

d) None of the above

A. TRUE / FLASE:

1. Imbibition is a special type of diffusion when water is absorbed by solids-

colloids- causing them to increase in volume.

2. Cells swell up in hypertonic solutions.

3. The apoplast system is the system of interconnected protoplasts.

B. FILL UPs:

1. Transpiration occurs through tiny pores called............

2. The upward movement of sap that contains water and minerals is

called... ....... of sap.

ANSWER KEY: PART-A

A. MCQs:

Ans. 1 (b) The immediate cause of opening and closing of stomata is the change

in the turgidity of guard cells.

Ans. 2 (d) Phloem tissues is composed of sieve tube cells which form long

columns which are loaded with sugar at the source.

Ans. 3(d) Transport of soluble food from leaves to other plant parts is referred to as translocation.

Ans. 4(a) The apoplast is the system of adjacent cell walls that is continuous —.

throughout the plant except at the casparian strips.

Ans. 5(b) As compared to hypertonic sugar solution cell has high concentration of water so movement of water is from cell to sugar solution thus the cell loses water and becomes dehydrated.

B. TRUE / FLASE:

1. True

2. False: Cells dehydrate in hypertonic solution due to higher concentration of

water inside the cell.

3. False: The system of interconnected protoplast is Symplastic system.

C: FILL UPs:

1. Stomata

2. Ascent

PART B : SHORT ANSWER TYPE QUESTIONS

1. What is transpiration?

2. Draw a diagram showing pathway of water movement in the root.

PART C: LONG ANSWER TYPE QUESTIONS

1. Explain mass flow hypothesis with the help of a diagram.

A119

RECAPITULATION:In this chapter of “Transport in Plants”, we leamt about;

1) Means of transport in plants i.e. Diffusion, active and passive transport.

2) Plant water relation i.e. Water potential, osmosis, plasmolysis and imbibition.

3) Transport of water and minerals-From soil into roots and then to leaves.

4) Transpiration, its types and mechanism.

5) Phloem transport -Flow from source to sink

“LETS US KNOW WHAT WE HAVE LEARNT”

PRACTICE QUESTIONS WITH SOLUTION (N.C.E.R.T)

Q.1. What are the factors affecting the rate of diffusion?

Ans.1. Factors affecting the rate of diffusion are:

Gradient of concentration Permeability of membrane Temperature Pressure

Q.2. What are porins? What role do they play in diffusion?

Ans.2. The porins are proteins that form large pores in the outer membranes of the

plastids, mitochondria and some bacteria. The large pores allow passive transport

of small sized protein. Hence, they promote diffusion.

Q.3. Describe the role played by protein pumps during active transport in

plants.

Ans.3. In plant cells, protein pumps are used to transport the substances against the concentration gradient, i.e., from a region of lower concentration to a region of higher concentration. The protein pumps are made up of specific proteins called trans- membrane proteins. These pumps first make a complex with the substance to be

transported across the membrane, using the energy derived from ATP. The substance

finally gets liberated into the cytoplasm as a result of the dissociation of the protein—substance complex.

Q.4. Explain why pure water has the maximum water potential.

Ans.4. Water potential refers to the tendency of water molecules to move from one part to the other during various cellular processes. Pure water has the maximum water potential because they have the kinetic energy of their own and they remain in constant random motion.

Q.5. Differentiate between the following:

(a) Diffusion and Osmosis

(b) Transpiration and Evaporation

(d) Imbibition and Diffusion

(e) Apoplast and Symplast pathways of movement of water in plants

(f) Guttation and Transpiration

Q.6. Briefly describe water potential. What are the factors affecting it?

Ans. 6. Water potential is the tendency of the water to move from one area to other

due to osmosis, gravity and mechanical pressure. Itis denoted by the Greek letter

Psi or ¥ and its units are expressed in Pascals (Pa).The water potential of pure water is always taken as zero at standard temperature and pressure.Water potential (Yw) is expressed as the sum of solute potential (Ws) and pressure potential (Yp).

Factors affecting water potential:

Solute potential

Pressure potential

Matric potential

Pressure

Temperature

Gain/oss of water

Q.7. What happens when a pressure greater than the atmospheric pressure is applied to pure water or a solution?

Ans.7. When a pressure greater than the atmospheric pressure is applied to pure

water or a solution then its water potential increases. This happens due to the increased pressure potential on increasing pressure. Pressure can be built in a plant cell, when water diffuses in it. This makes the cell wall turgid. This pressure is termed as pressure potential and has a positive value.

Q.8. (a) With the help of well-labelled diagrams, describe the process of

plasmolysis in plants, giving appropriate examples.

(b) Explain what will happen to a plant cell if it is kept in a solution having

higher water potential.

Ans.8. a) Plasmolysis can be defined as the shrinkage of the cytoplasm of a plant

cell, away from its cell wall and toward the centre. It occurs because of the

movement of water from the intercellular space to the outer-cellular space. This happens when the plant cell is placed in a hypertonic solution (i.e., a solution having more solute concentration than the cell cytoplasm). This causes the water to move out of the cell and toward the solution. The cytoplasm of the cell shrinks and the cell is said to be plasmolysed. This process can be observed in an onion peel kept in a highly concentrated solution.

(b) When a plant cell is placed in a solution having higher water potential, the water diffuses into the cell. The entry of water in the plant cell exerts pressure on the rigid cell wall. This is called turgor pressure. The pressure cause enlargement of the cell but the rigidity of cell wall prevents the cell from bursting.

Q.9. How is the mycorrhizal association helpful in absorption of water and

minerals in plants?

Ans.9. Mycorrhiza is a symbiotic association of fungi with the root systems of some plants. The fungal hyphae either form a dense network around the young roots or they penetrate the cells of the roots. The large surface area of the fungal hyphae is helpful in increasing the absorption of water and minerals from the soil. In retum, they get sugar and nitrogenous compounds from the host plants.

Q.10. What role does root pressure play in water movement in plants?

Ans.10. Root pressure is the positive pressure that develops in the roots of

plants by the active absorption of nutrients from the soil.When the nutrients are actively absorbed by root hairs, water (along with minerals) increases the pressure in the xylem. This pressure pushes the water up to small heights. Root pressure can be observed experimentally by cutting the stem of a well-watered plant on a humid day. When the stem is cut, the solution oozes from the cut end.

Q.11. Describe transpiration pull model of water transport in plants. What are

the factors influencing transpiration? How is it useful to plants?

Ans.11.Transpiration is the loss of water in the form of water vapors from aerial

parts of plants. In tall trees, the water rises with the help of the transpiration pull generated by transpiration.

This is called the cohesion-tension model of water transport (proposed by

Dixon and Joly in 1894). According to this model, the water is mostly pulled from

roots to leaves due to the driving force of transpiration from the leaves.

The water molecules remain attached with one another by cohesion force.

The water molecule does not break in vessels and tracheid due to adhesive force

between their walls and water molecules.

On account of tension created by transpiration, the water column of a plant is pulled up passively from roots to great heights.Factors affecting transpiration pull are:

Temperature

Humidity

Light

Wind speed

Location of stomata

Number and distribution of stomata.

Importance of transpiration pull:It has a cooling effect on plants.Transpiration pull exerts ascent of sap which helps in the distribution of mineral salts.It helps in retaining shape and structure by keeping the cells turgid.Transpiration helps in the removal of excess water absorbed by the plants.It provides water for photosynthesis.

Q.12. Discuss the factors responsible for ascent of xylem sap in plants.

Ans.12.The factors that responsible for the ascent of sap are:

1. Cohesion — This is a mutual attraction between water molecules.

2. Adhesion — An attraction of water molecules to polar surfaces of the xylem

cells.

3. Surface Tension — The water molecules are attracted to each other in the liquid

phase more than to water in the gas phase.

Q.13. What essential role does the root endodermis play during mineral

absorption in plants?

Ans.13.The endodermal cells have many transport proteins embedded in their

plasma membrane that control the quantity and types of various solutes reaching

the xylem. Minerals need to be actively absorbed by the epidermal cells. The root

endodermis has a layer of suberin which has the ability to actively transport ions in

one direction only.

Q.14. Explain why xylem transport is unidirectional and phloem transport bi-

directional.

Ans.14.Water moves only in the upward direction when absorbed by roots

through the xylem. Hence water transport is unidirectional. Food is transported by

the phloem tissue. Food is synthesized in leaves and required by both roots

and shoot system thus phloem sap moves upwards as well as downwards

making food transport bidirectional so that it can reach other plant parts.

Q.15. Explain pressure flow hypothesis of translocation of sugars in plants.

Ans.15. Pressure flow hypothesis is the most accepted theory for the translocation

of sugar from source to sink. Glucose is prepared at the source(LEAVES) by

photosynthesis which is converted into disaccharides sucrose which further moves

into companion cells and then into sieve tube cells by active transport. Loading of

phloem at source creates a water potential gradient that facilitates the mass

movement in the phloem. Sieve tube cells of phloem form along column with holes

in their wall called sieve plates. Cytoplasmic strands pass through the hole in the sieve plates to form a continuous filament. Hydrostatic pressure developed in sieve tube cells moves the sap in the phloem. At the sink, incoming sugar is actively moved out of the phloem as complex carbohydrates. The loss of solute produces a high water potential in the phloem and water passes out and returming into the xylem.

Q.16. What causes the opening and closing of guard cells of stomata during

transpiration?

Ans.16. The cause for the opening and closing of the stomata is the change in

the turgidity of the guard cells. When guard cells become turgid, their thin, outer walls get extended and thick,inner walls become slightly concave to cause the

stomatal aperture to open. When water is lost, guard cell loses water, and flat

elastic inner walls regain their original snape, thus guard cells become flaccid, and

the stomata close.

A120

RECAPITULATION:Plants obtain a variety of inorganic elements and salts from their

surroundings especially from water and soil.The movement of these nutrients from environment into the plants is known as transportation.Transport can occur through diffusion, facilitated diffusion or by active transport.Water and minerals are transported through xylem.Organic materials are transported to other parts of plant by phloem.

SIMPLE DIFFUSION:-It is movement of the particles from their higher concentration to lower concentration. It is a slow process and no energy expenditure takes

place in this process.

FACILITATED DIFFUSION -In facilitated diffusion special proteins help to move substances across membrane without expenditure of ATP energy. Transport rate reaches a maximum when all of the proteins transporters are being used.

ACTIVE TRANSPORT:-Active transport uses energy to pump molecules against a

concentration gradient. Active transport is carried out by membrane-proteins. These pumps can transport substances from a low

concentration to a high concentration.

OSMOSIS:-The movement of a water molecules from a solution with a high concentration of a water molecules to a solution with a low concentration of water molecules through a differentially or semi-permeable membrane is known as osmosis.

Plasmolysis occurs when water moves out of cell and the cell membrane of a plant cell shrinks away from its cell wall.This occurs when the cell is placed in a solution that is hypertonic to the protoplasm of cell.

APOPLAST PATHWAY OF WATER MOVEMENT:-The apoplastic movement of water occurs through the intercellular spaces and the walls of the cells. Movement through the apoplast does not involve crossing the cell membranes. This movement is dependent

on the gradient.

SYMPLAST PATHWAY OF WATER MOVEMENT:-During symplastic movement, the water travels through the cells- their Cytoplasm; intercellular movement is through plasmodesmata.Water has to enter the cells through the membrane; hence the

movement is relatively slower.

TRANSPIRATION:-Transpiration is the loss of water in the form of water vapours from plant mainly through stomata. Besides the loss of water vapours in transpiration, exchange of gases in the leaf also occurs through stomatal pores. Transpiration is affected by several external factors; temperature,light, humidity, wind speed.

Evaporation from the leaf sets a pressure gradient between outside air and the air spaces of leaf. The gradient is transmitted into the photosynthetic cells and the water-filled xylem in the leaf vein.

PHLOEM TRANSPORT: THE PRESSURE FLOW OR MASS FLOW

HYPOTHESIS:Food primarily sucrose, is transported by vascular tissue phloem from a source to a sink.Source is the area where nutrients are available in plenty either due to Synthesis or previous storage.

Sink has nutrients in low concentration either due to their consumption or conversion into insoluble stage (storage).The most accepted model for phloem translocation is originally

proposed by E.Munch.Pressure-flow mechanism is based on the mass transfer of solutes from source to sink along a hydrostatic (turgor) pressure gradient.Translocation of solutes in the phloem is closely linked to the flow of water in the transpiration stream and a continuous recirculation of water in the plant.

The loading of sugar into the sieve elements adjacent to a source cell causes the osmotic uptake of water from the nearby xylem elements.

The uptake of water increases the hydrostatic (turgor) pressure in the

sieve element.The pressure is lowered at the sink end when sugar is unloaded into the receiver cell and the water returns to the xylem.This pressure differential causes a flow of water from the source region

to the sink.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

1) MCQs:

1) All the following involves osmosis except which case?

(a) Water entering from soil into root hair

(b) Water passing from root hair to an adjacent cell

(d) Water entering a mesophyll cell from the xylem vessel.

2) The shrinkage of the protoplast of a cell from its cell wall under the

influence of a hypertonic solution is known as:

(a) endosmosis

(b) exosmosis

(d) deplasmolysis

3) The non-living continuum that occurs in plants is called:

(a) apoplast

(b) symplast

(d) both (1) and (2)

4) The transport of sugars and other organic molecules within a plant is:

(a) transpirational pull

(b) guttation

(d) assimilation

5) Transport of food material in higher plants takes place through:

(a) Companion cells

(b) Transfusion tissue

(d) Sieve elements

2) TRUE/FALSE:

1. The apoplastic movement of water occurs through intercellular spaces and walls of cells.

2. Facilitated diffusion uses energy for transport of substances.

3. Plasmolysis occurs when cell is placed in hypertonic solution with respect to the protoplast of cell.

C) FILL UPs:

1. Most accepted model for translocation of food is

2. The loss water in the form of water vapours from plant leaves is known as

3. Active transport uses energy to pump a molecules the concentration gradient.

ANSWER KEY: PART-A

1) MCQs:

1. (c) Water passing up an xylem vessel element to xylem vessel element

2. (c) plasmolysis

3. (a) apoplast

4. (c) translocation

5. (d) sieve elements

2) TRUE/FALSE:

1. True

2. False: In facilitated diffusion special proteins help to move the substances across the membrane without the use of energy.

3. True

3) FILL UPs:

1. Mass flow hypothesis

2. Transpiration

3. Against

PART: B SHORT ANSWER TYPE QUESTIONS;

1. How diffusion is different from facilitated diffusion?

2. Differentiate between apoplast and symplast pathway.

3. What is transpiration? What are the factors influencing rate of transpiration?

PART: C LONG ANSWER TYPE QUESTIONS:

1. Explain mass flow hypothesis of translocation of sugars in plants.

A121

INTRODUCTION:Mineral Nutrition is defined as the naturally occurring inorganic nutrient found in the soil and food that is essential for the proper functioning of plant body. Minerals are vital elements necessary for the body. Both the plants and

animals require minerals essential.

Nutrients which are required by plants in very small amounts are termed as

Micronutrients. Some of them are Boron, Copper, Iron & Molybdenum.Nutrients which are required by plants in larger amounts are termed as Macronutrients. Some of them include sulfur, nitrogen, carbon, phosphorus,calcium, potassium and magnesium.

METHODS TO STUDY THE MINERAL REQUIREMENTS OF PLANTS:In 1860, Julius von Sachs, a prominent German botanist, demonstrated,

for the first time, that plants could be grown to maturity in a defined nutrient solution in complete absence of soil. This methods of growing plants in a nutrient solution is known as Hydroponics.These methods require purified water and mineral nutrient salts. Can you explain why this is so essential?In hydroponics carefully prepared standardized nutrient solutions are used for growing plants. These nutrients are taken up by the roots of

the plants. It is essential to purify the water we use and remove any minerals present in it. This is because the preparation of standard nutrient solution has a fixed concentration of minerals and any minerals if present previously and not removed from the water will cause an error in proper resolution. Hence purification of water and minerals is required for obtaining maximum optimum growth of plants

After a series of experiments in which the roots of the plants were immersed in nutrient solutions and wherein an element was added /substituted / removed or given in varied concentration, a mineral solution

suitable for the plant growth was obtained. By this method (Hydroponic),essential elements were identified and their deficiency symptoms discovered.

HYDROPONICS: Is the art of gardening without soil. Hydroponics is a Latin word meaning “WORKING WATER”. In the absence of soil , water goes to work providing nutrients, hydration and oxygen to plant of life.Hydroponics has been successfully employed as a technique for the

commercial production of vegetables such as tomato, seedless, cucumber. It must be emphasized that the nutrient solutions must be adequately aerated to obtain the optimum growth.

What are the six types of hydroponic systems?

1. Nutrients Film Technique

2. Deep water Culture

3. Wick system

4. Ebb and Flow

5. Drip Recover System

6. Aeroponics

THE MAIN ADVANTAGES OF USING HYDROPONICS METHOD ARE:

1. Conservation of water and nutrients.

2. No more use of fertilizers, pesticides, and other chemicals.

3. It can be grown anywhere as it requires very less space for growing and

involves a soil-free condition.

4. It minimizes the loss of nutrients and has a lot more accurate control over

the nutrients required by the plants.

5. Plant growth is completely dependent on the nutrient solution provided.Thus, there is controlled plant growth.

THE DISADVANTAGES ASSOCIATED WITH HYDROPONICS ARE:

1 It is a supplement to traditional growing methods which requires high

technical knowledge and training before starting the process.

2 It is a time-consuming process.

PART: A VERY SHORT ANSWER TYPE QUESTIONS:

A) MCQs:

1. The form of hydroponics that does not require a growing medium at all is:

(a) Aquaculture

(b) Static solution culture

(Medium culture

(d) Aeroponic

2. Plants with larger roots can be cultivated with which of the following types

of hydroponics?

(a) Ebb and flow system

(b) Drip system

(d) None of these

3. Hydroponics is a method of cultivation of plants without the use of:

(a) water

(b) air

(d) sunlight

4. Which of the following is not true about hydroponics?

(a) Requires high investment

(b) Technical knowledge required

(d) Plants through hydroponics cannot be cultivated everywhere

5. Salts and water in hydroponic plants are absorbed by:

(a) Leaves

(b) Stem

(d) Outer Layer of plants

B) TRUE / FALSE:

1. Hydroponic technique for the commercial production of vegetables such as tomato, seedless, cucumber.

2. Hydroponic technique essential elements were identified and their deficiency symptoms discovered.

C) FILL THE BLANKS:

1. Hydroponics is a method of cultivation of plants without the use of

2. Salts and water in hydroponic plants are absorbed by

ANSWER KEY: PART -A

A) MCQs:

1. ANS. D) Aeroponics is the process of growing plants in an air or mist

environment without the use of soil or an aggregate medium.

2. ANS. C) Nutrient film technique (NFT) is a hydroponic technique where in a very shallow stream of water containing all the dissolved nutrients required for plant growth is re-circulated past the bare roots of plants in a watertight gully, also known as channels.

3. ANS. C) The process of growing plants in sand, gravel, or liquid, with added nutrients but without soil.

4. ANS. D)

5. ANS. C) The primary functions are anchorage of the plant, absorption of

water and dissolved minerals and conduction of these to the stem, and storage of reserve foods.

B) TRUE / FALSE:

1. TRUE Hydroponics can regulate pH optimum for a particular crop,control soil borne pathogens, avoid problems of weeding and obtain consistently better yield. Hydroponics has been successfully

employed as a technique for the commercial production of vegetables such as tomato, seedless cucumber

2. TRUE

C) FILL THE BLANKS:

1. SOIL

2. ROOTS

PART:B SHORT ANSWER TYPE QUESTIONS:

Q. 1. Hydroponic methods require purified water and mineral nutrient salts.

Can you explain why this is so essential?

Q 2 What is main advantage of using hydroponics method?

PART:C LONG ANSWER TYPE QUESTIONS:

Q. 1. Explain methods to study the mineral requirements of plants?

A122

INTRODUCTION:MINERAL NUTRITION is defined as the naturally occurring inorganic nutrients found in soil and food that is essential for the proper functioning of animal and plant body.A large number of inorganic elements are essential for all the life processes and should be taken in our diet in adequate amount.It is study of source, mode of absorption, distribution and metabolism of various minerals by plants for their growth, development, structure,physiology and reproduction.

MINERALS IN PLANTS Julius von Sachs, a German botanist, was the first to grow plants to maturity in a nutrient solution in the complete absence of soil. This technique of growing plants in a soil-free, nutrient solution is ‘Hydroponics’. The essential minerals were identified by adding or omitting an element in the nutrient solution or using varying concentrations. Today, hydroponics is commercially used as a technique to grow tomatoes, lettuce, and seedless cucumbers.

ESSENTIAL MINERAL ELEMENTS:So far, 105 elements have been discovered, of which more than 60 exist in plants.How do we know which minerals are essential for plants and which are not?There are certain criteria to determine this. Let's learn what they are.

CRITERIA FOR ESSENTIALITY:The plant can not complete its life cycle or produce seeds in the absence of the element.The requirement for the element must be specific and not replaceable by another element. This means the deficiency of one element cannot

be compensated by supplying any other element.The element must have a direct role in the metabolism of the plant.According to the above-mentioned criteria, only a few mineral elements were found to be absolutely necessary for plant growth and

development. Based on the quantity in which these minerals are required, they are further classified as follows:

MACRONUTRIENTS:These are present in plant tissues in large (macro) amounts (i.e. more than 10mmole/kg of dry matter). Macronutrients include carbon, hydrogen,

nitrogen, oxygen, sulphur, phosphorus, calcium, potassium and magnesium.

MICRONUTRIENTS:These are needed in small (micro) amounts (i.e. less than 10m mole/kg of dry matter). Therefore, they are also called trace elements.Micronutrients include iron, copper, manganese,

molybdenum, chlorine, nickel, zinc and boron.All the 17 elements mentioned above are essential elements. In addition to these,elements such as sodium, silicon, selenium and cobalt are also important for higher plants.

CLASSIFICATION OF ESSENTIAL -

MINERAL ELEMENTS:Essential mineral elements can also be classified as follows based on their diverse functions:

As components of biomolecules and hence structural elements of cells. Examples — carbon, hydrogen, nitrogen and oxygen.

As components of energy-related chemical compounds in plants.Examples — phosphorus in ATP and magnesium in chlorophyll.

As activators or inhibitors of enzymes.

Examples -Zinc is an activator of Alcohol Dehydrogenase while molybdenum activates Nitrogenase during nitrogen metabolism.

As elements that can alter the osmotic potential of a cell.Example— Potassium is very important in the opening and closing of stomata.

DEFICIENCY SYMPTOMS OF ESSENTIAL ELEMENTS:

When a plant gets limited amounts of an essential mineral, its growth becomes

retarded. The concentration of the essential element below which the growth

of a plant is retarded is the ‘critical concentration’. Below this concentration,

the plant is said to be deficient in that particular element.Deficiencies are indicated by morphological changes in plants. These are called ‘deficiency symptoms’. These symptoms differ from mineral to mineral and disappear when sufficient levels are provided.

PLANTS SHOW THE FOLLOWING TYPES OF

DEFICIENCY SYMPTOMS:CHLOROSIS; (loss of chlorophyll), due to lack of N, K, S, Fe, Mg, Mo,Mn and Zn.NECROSIS; (tissue death, particularly leaf tissue) due to lack of Ca,Mg, K and Cu.INHIBITION OF CELL DIVISION; due to lack of N, K, S, and Mo.

DELAYED FLOWERING due to low levels of N, S, Mo.

Deficiency of one element can cause multiple symptoms or same symptoms

can be caused by the deficiency of multiple elements. Mineral deficiencies that

affect crop yield are provided through fertilizers. Macro and micronutrients are

important parts of fertilizers.

TOXICITY OF MICRONUTRIENTS:There is a narrow range of concentration at which the micronutrients are optimum.Just like a little less than the critical concentration leads to deficiency, little more can cause toxicity.The mineral concentration that reduces the dry weight of plant tissue by 10% is considered toxic.The excess of one element may inhibit the uptake of another element. For example, the excess of manganese may cause deficiencies of iron, calcium and magnesium.

ABSORPTION OF ELEMENTS:The mechanism of absorption of mineral elements involves two phases: The first phase involves the rapid uptake of ions into the ‘free space’ or

‘outer space’ of cells called the ‘APOPLAST’. This usually occurs through

ion channels; Trans membrane proteins that act as selective pores and is therefore passive (does not need energy).The second phase involves the slow uptake of ions into the ‘inner space’of plants called the ‘SYMPLAST’. This uptake requires energy and

therefore is an active process. The entry of ions into cells is ‘influx’ and exit

of ions from ceils is ‘efflux’.To sum up mineral elements are pulled up from the soil along with water through the xylem. Soil acts as a reservoir for minerals. In addition to minerals,soil also provides water and air; and holds beneficial microbes like nitrogen- fixing bacteria.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A- VERY SHORT ANSWER TYPE QUESTION:

(a) MULTIPLE CHOICE QUESTIONS:

1. Which of following is not caused by deficiency of mineral nutrition?

(a)Necrosis

(b)Chlorosis

(c)Etiolation

(d)Shortening of internodes

2. Phosphorus is a structural element in:

(a)Fat

(b)Starch

(c)Nucleotide

(d)Carbohydrates

3. Necrosis means:

(a)Yellow spots on leaves

(b)Death of tissues and decomposition

(c)Darkening of green colour in leaves

(d) None of the above

4. Zn, Mo, Fe, Cu, are:

(a)Trace elements

(b)Non-essential elements

(c)Micro-nutrients

(d) None of the above

5. The process of growth of plants by suspending their roots:

(a)Osmosis

(b)Hydroponics

(d)Aeroponics

(B) TRUE/FALSE:

1. Essential minerals are necessary for normal growth and reproduction

in plants.

2. Carbon is a trace element.

3. Copper is needed for synthesis of Auxin.

(C) FILL IN THE BLANKS:

1. Deficiency of causes chlorosis in older leaves.

2. Sulphur is present in and amino acids.

3. plays an important role in opening and closing of stomata.

(A) MULTIPLE CHOICE QUESTIONS:

1. (c) Etiolation

HINT- Necrosis, Chlorosis, Shortening of internodes are deficiency symptoms but etiolation means growth of plants without sunlight.

2. (c) Phosphorus

HINT- Phosphorus is important important constituent of nucleotides.

3. (b) Death of tissues and decomposition

HINT- Necrosis means cell injury which results in premature death of cells in living tissue by destruction of a cell through own enzymes.

4. (a) Trace elements

HINT- These are required in small amount.

5. (b) Hydroponics

HINT- Plants grow to maturity in a nutrient solution in the complete absence of soil.

(B) TRUE/FALSE:

1. True.

2. False (Carbon is macro nutrient)

3. False (Zinc is needed)

(C) FILL IN THE BLANKS:

1. Magnesium

2. Cysteine and Methionine

3. Potassium

PART: B SHORT ANSWER TYPE QUESTIONS:

1. Define Macronutrients and macronutrients with example.

2. What do you mean by Critical concentration?

3. Name kind of deficiency symptoms of minerals?

PART: C LONG ANSWER TYPE QUESTION:

1. What are criteria of essentiality of minerals?

A123

INTRODUCTION:In the previous topics we have discussed about various minerals,elements required by plants, for growth and development.Unlike water, all minerals cannot be passively absorbed by roots.

The two factors account for this:

(1) Minerals are present in the soil as charged particles (ions) which cannot

move across cell membranes and.

(ii) Concentration of minerals in the soil is usually lower than the conc. of

minerals in the root.Therefore, most minerals must enter the root by active absorption into the cytoplasm of epidermal cells. This needs energy in the form of ATP.The active uptake of ions is partly responsible for the water potential

gradient in roots, and therefore for the uptake of water by osmosis.Some ions also move into epidermal cells passively.

So lons are absorbed from the soil by both passive and active transport.Much of the studies on mechanism of absorption of elements by plants has been carried out .These studies revealed that the process of absorption can be demarcated into two main phases:

APOPLASTIC PATHWAY: In this first phase, an initial rapid uptake of ions into the free space, outer space of cell, along the concentration gradient. i.e. apoplast is passive .The passive movement of ions into apoplast usually occurs through ion

channels, the trans membrane proteins that function as selective pores.«The movement occurs in apoplast route is the fully permeable route.

SYMPLASTIC PATHWAY: In this second phase of uptake, the ions are taken in slowly into the inner space i.e. the symplast of the cells against the concentration gradient. The entry or exit of ions to and from the symplast requires the expenditure of metabolic energy, which is an active process.The symplast is a selectively permeable route which is bounded by the

plasma membranes. It contains the complete network of the cytoplasm of plant cells that are connected by plasmodesmata.

SYMPLAST is considered as the living part of the plant tissue without the

presence of cell wall and intercellular spaces in it.

FLUX: The movement of ions is usually called flux.The inward movement of ions into the cell is called influx.The outward movement of ions into the cell is called outflux.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A_ VERY SHORT ANSWER TYPE QUESTIONS:

A) MULTIPLE TYPE QUESTIONS:

1.Statement A: Minerals are present in the soil in the form of charged particles.

Statement B: Concentration of minerals is lower in root than in soil.

a) Both the statements are true

b) Both the statements are false

c) Statement A is true but Statement B is false

d) Statement B is true but Statement A is false

2. Statement A: The process of absorption of minerals is divided into 2

phases.

Statement B: One phase of absorption is passive while the other is active.

a) Both the statements are true

b) Both the statements are false

c) Statement A is true but Statement B is false

d) Statement B is true but Statement A is false

3. Statement A: The outward movement is influx.

Statement B: The inward movement is efflux.

a) Both the statements are true

b) Both the statements are false

c) Statement A is true but Statement B is false

d) Statement B is true but Statement A is false

4. The space between cell wall between plasma membrane is known as:

a) Inner space

b) Apoplast

c) Symplast

d) Semipermeable route

5. A transport of ions which require expenditure of energy is:

a) diffusion

b) Active process

c) Passive process

d) Apoplast process

B) FILL UPS:

1. The movement of ions out of cell is called...

2. The process of absorption of elements can be demarcated into...........

phases.

3. Apoplast is also called................... space.

C) TRUE/FALSE :

1. Passive movement of ions require energy.

2. Symplastic pathway is an active process.

3. Apoplastic pathway is rapid.

ANSWER KEY: PART -A

A) MCQs:

1. Answer - c Explanation: Minerals are present as charged ions in the soil which

can be easily transported to the plant in the same form or after conversion to a

more stable form. The concentrations of minerals are always more in the root than

in the soil. The root extracts the minerals required from the soil with the help of

active absorption.

2. Answer - a Explanation: The process of absorption of minerals is demarcated

into two main phases. The first is the uptakes of ions into the outer space of cell-the apoplast via passive process. The second phase is the slow uptake of ions

into the inner space of cell-the symplast via active process.

3. Answer - b Explanation: The movement of ions is called flux. The inward movement into the cells is influx. The outward movement is called efflux. Both the

processes are active in nature.

4. Answer - b Explanation: The space between cell membrane and cell wall is

called apoplast.

5. Answer - b Explanation : The transport of ions which requires expenditure of

energy is called active transport.

B) FILL IN THE BLANKS:

1. Efflux

2. Two

3. Outer or free space

C) TRUE/FALSE:

1. False, Passive movement of ions do not require energy.

2. True

3. True

PART: B- SHORT ANSWER TYPE QUESTIONS:

1. What is apoplastic pathway?

2. What is active transport?

3. Define Influx.

PART: C - LONG TYPE QUESTION ANSWERS:

1. Write difference between both phases of transport of elements.

124

INTRODUCTION:In plants the substances that would need to be transported are:

Water, mineral nutrients, organic nutrients and plant growth regulators.Over small distances these substances move by diffusion and by cytoplasmic

streaming supplemented by active transport.

Special long distance transport systems become necessary to move substances across long distances and at much faster rate.

TRANSLOCATION OF SOLUTES IN PLANTS:

Transport over long distances proceeds through the vascular system, i.e.

the xylem and the phloem.Water and minerals, and food are generally moved by a mass flow or bulk flow system.Mass flow is the movement of substances in bulk or en masse from one point to another as a result of pressure differences between the two points.The bulk movement of substances through the conducting or vascular

tissues of plants is called translocation.

The higher plants have highly specialized vascular tissues:

Xylem: Xylem is associated with translocation of mainly water, mineral

salts, some organic nitrogen and hormones from roots to aerial parts of the

plant.

Phloem: Phloem is associated with translocation of a variety of organic

and inorganic solutes mainly from leaves to other parts of plant.

TRASLOCATION OF MINERAL IONS:lons are absorbed from the soil into the cytoplasms of epidermal cells by both passive and active transport.The absorbed mineral elements move laterally from epidermis to xylem through cortex, endodermis and pericycle by two pathways i.e. apoplastic

pathway and symplastic pathway The apoplastic pathway involves movement of minerals by simple diffusion from cell to cell through their primary cell walls.

The cell walls of endodermal cells possess a waxy thickening the casparian

strip (a band of suberised matrix) which block the passage of solutes from

one side of endodermis to other side via cell wall route.

Minerals can enter

the pericycle and xylem by passing through protoplast of endodermal cells.

Movement of solute is APOPLASTIC in cortex and pericycle but SYMPLAST in endodermis.

The symplastic pathway involves the movement of minerals through the

protoplast of cortex, endodermis and pericycle and finally released into the

xylem. The cell to cell movements of ions takes place through plasmodesmata.

After the ions have reached xylem, they are further transported upwards through xylem along with the transpiration stream to all the upper parts of the plant.The chief sinks for mineral elements are the growing regions of the plants such as apical and lateral meristems, young leaves,

developing flowers, fruits, seeds and the storage organs. Unloading of mineral ions occurs at the fine vein endings through diffusion and active uptake by these cells.Mineral ions are frequently remobilised from older, senescing parts. Older dying leaves export much of their mineral content to younger leaves and

other parts.Elements most readily mobilised are phosphorus, sulphur, nitrogen and

potassium.Some elements of structural components like calcium are not remobilised.Some of the nitrogen travels as inorganic ions, much of it is carried in

organic form as amino acids and related compounds. Similarly, small amount of phosphorus and sulphur are carried as organic compounds.Small amount of exchange of materials does takes place between xylem

and phloem.

PHLOEM TRANSPORT: FLOW FROM SOURCE TO SINK

Food, primarily sucrose, is transported by the vascular tissue, phloem from

a source to a sink.Usually the source, the part of the plant which synthesizes the food, i.e, the leaf and sink, the part that needs or stores the food.But the source and sink may be reversed; the direction of transport in phloem varies depending upon the developing stages, season or needs of

plants.During germination, the food moves upward from seeds to young leaves

until they begin to form food.Similarly the sugar stored in roots may be mobilised to become a source of food in the early spring when the buds of trees need energy for growth and development of photosynthetic apparatus, so act as sink.So the direction of movement in the phloem is bi-directional as it can beupwards and downwards. Whereas in xylem the movement is always upwards i.e. unidirectional from roots to upward parts. Food in phloem sap can be transported in any required direction from a source of sugar to a sink able to use, store or remove the sugar. Phloem sap is mainly water and sucrose but other sugars, hormones and amino acids are also transported or translocated through phloem.

THE PRESSURE FLOW OR MASS FLOW HYPOTHESIS:

The most accepted mechanism used for the translocation of sugars from source to sink is called pressure flow hypothesis. The pressure flow hypothesis, also known as the mass flow hypothesis was first proposed by the German physiologist Ernst Munch in 1930 and later elaborated by Crafts(1938) and

others.The Munch's hypothesis postulated the movement of protoplasm en masse

along a turgor pressure gradient, induced by a maintained gradient of water potential.The mass flow of organic solute (translocation) takes place from the

sources of food materials to the site of utilization through phloem along the

concentration gradient i.e. from the site of higher concentration to the site

of lower concentration.

As glucose is prepared at the source by the process of photosynthesis. It is converted to sucrose, a disaccharide. The sugar is then moved in the form of sucrose into the companion cells and then into the living phloem sieve tube cells by active transport.This process of loading at the source produces a hypertonic condition in the phloem.

Water in the adjacent xylem moves into the phloem by osmosis.As osmotic pressure builds up, the phloem sap will move to the areas of lower osmotic pressure, i.e, the sink.At the sink, active transport is necessary to move the sucrose out of the

phloem sap into the cells which will use the sugar by converting it into energy, starch or cellulose.As the sugars are removed the osmotic pressure decreases and water moves out of the phloem and goes to the Xylem.The mass flow hypothesis can be explained by a simple experiment:

The two bulbs A and B made up of semi permeable membranes are connected by glass tube as shown in figure.The bulb A contains concentrated sugar solution and bulb B contains dilute sugar solution.Both the bulbs are kept in a vessel containing water. The OP of bulb A is high as compared to B.The water enters into bulb A and its turgor pressure is increased.This increase in turgor pressure causes mass flow of sugar solution to bulb B under the influence of turgor pressure gradient.

This movement will continue till the solution in both the bulbs attains the

same concentration.

In the living plants, the carbohydrates are synthesized in mesophyll cells of leaves.Consequently the OP of these cells is increased.Cells then absorb water from neighboring cells.

The turgor pressure of mesophyll cell also increased.This allows some of the cell contents to pass into the sieve tubes.

On the other end, in the parts like roots and storage organs, cells either

consume food material or they convert it into insoluble sugar forms.This transformation results decrease in OP.

With the result their turgor pressure also decreased.In this way, a turgor pressure gradient is formed between supply site and

consumption site and with this gradient a mass flow of solute takes place.

LET US KNOW WHAT WE HAVE LEARNT!

PART:A VERY SHORT ANSWER TYPE QUESTIONS:

(A) MCQs:

1. The form of sugar transported through phloem is:

(a) Glucose

(b) Fructose

(d) Ribose

2. Which of the following is not correct in mass flow hypothesis?

(a) As hydrostatic pressure in the phloem sieve tube increases, pressure flow stops

and sap is accumulated

(b) The sugar is moved directionally

(d) Loading of the phloem sets up a water potential gradient that facilitates the mass movement in the phloem

3. The transportation in the vascular tissue, phloem, from a source to a sink is

(a) Unidirectional

(b) Bi-directional

(d) None of these

4. Most accepted mechanism for the translocation of sugar from source to sink:

(a) Action theory

(b) Pressure flow hypothesis

(d) Electro -osmotic theory

5. Munch hypothesis is based on

(a) Translocation of food due to imbibition force.

(b) Translocation of food due to TP gradient and imbibition force.

(d) None of these

(B) TRUE/FALSE:

1. Food and various other substances are transported in plants through diffusion.

2. Translocation through phloem is unidirectional.

3. Mass flow is the movement of substance in bulk as a result of pressure difference.

(C) FILL IN THE BLANKS:

1. Translocation of solutes primarily takes place through ;

2. For translocation of sugar, the glucose prepared at the source by photosynthesis is

converted into .

3. blocks the passage of solutes from one side of the endodermis to the

other side via cell wall route.

(&) MOGs:

Ans. 1: (c) sucrose Explanation: For translocation of sugar, the glucose prepared at the source by photosynthesis is converted into sucrose (a disaccharide).

Ans. 2: (a) As hydrostatic pressure in the phloem sieve tube increases, pressure

flow stops and sap is accumulated Explanation: As hydrostatic pressure in the

phloem sieve tube increases, pressure flow begins and sap moves through

phloem.

Ans. 3: (b) bi-directional Explanation: As source sink relationship is variable, the

direction of movement in phloem can be upwards or downwards.

Ans. 4: (b) Pressure flow hypothesis Explanation: Munch’s mass flow or

pressure flow hypothesis

Ans. 5: (c) Translocation of food due to turgor pressure (TP) gradient Explanation: Translocation occurs en masse along a turgor pressure gradient induced by a maintained gradient of water potential. The mass flow of organic solute takes place from site of higher concentration to site of lower concentration.

Ans. 1: False Explanation: Plants have their unique vascular system which helps

them to transport food and water throughout the plant body. Xylem is responsible

for transport of water and minerals, while phloem is responsible for transport of

food and other substances.

Ans. 2: False Explanation: Translocation through phloem can be either upward

or downward depending upon the plant needs. For example, in the spring, sugar

stored in root or stem tissue would be transported to the buds which need

energy to grow. Translocation through xylem is unidirectional.

Ans. 3: True Explanation: The movement of a substance in bulk as a result of

pressure difference is named mass flow.

Ans. 1: Phioem

Ans. 2: Sucrose