1st PUC Biology Question Bank Chapter 11 Transport in Plants

Karnataka 1st PUC Biology Question Bank Chapter 11 Transport in Plants

1st PUC Biology Transport in Plants One Marks Questions and Answers

Question 1.
Define diffusion.
Answer:
The movement of molecules or ions of gases, liquids or solids from a region of their higher concentration to a region of their lower concentration is known as diffusion.

Question 2.
Define osmosis.
Answer:
It is a special type of diffusion in which only the solvent or water molecules move from a region of their higher concentration to a region of their lower concentration through a semi permeable membrane.

Question 3.
Define imbibition.
Answer:
Imbibition is a special kind of diffusion which involves movement of water molecules along a diffusion gradient from a region of higher concentration on to a suitable solid matrix (adsorption).
or
It is the adsorption of water molecules by hydrophilic colloids.

Question 4.
What type of osmosis takes place in a living cell that is immersed in a hypotonic solution?
Answer:
Endosmosis.

Question 5.
What type of osmosis is involved during plasmolysis?
Answer:
Exosmosis.

Question 6.
What is turgor pressure?
Answer:
Due to endosmosis the volume of cytoplasm increases, and applies a pressure on the cell membrane. This pressure is called turgor pressure.

Question 7.
What is wall pressure?
Answer:
The pressure exerted by the cell wall on the protoplast which is equal and opposite to turgor pressure is known as wall pressure.

Question 8.
What is a hypertonic solution?
Answer:
It is a solution whose solute concentration is more than the solute concentration of the cell sap.

Question 9.
Define water potential.
Answer:
Water potential is defined as the difference in the free energy of water molecules in pure water, and the free energy of water in a solution.

Question 10.
Why does a wooden door swell during humid weather?
Answer:
It is due to imbibition.

Question 11.
What is the value of water potential of pure water?
Answer:
Zero.

Question 12.
Which is the actual part of the root system that absorbs water?
Answer:
Root hair region.

Question 13.
What is ascent of sap?
Answer:
It is the upward movement of water along with dissolved salts, from the roots to other aerial parts of the plant through xylem.

Question 14.
Which is the most convincing theory that explains ascent of sap?
Answer:
Transpiration pull theory or cohesion tension theory.

Question 15.
Who proposed mass flow hypothesis?
Answer:
Ernst Munch.

Question 16.
Name the tissue that is involved in the translocation of solutes?
Answer:
Phloem.

Question 17.
Define transpiration.
Answer:
It is the phenomenon by which excess water is eliminated, in the form of vapours through the aerial parts of the plant body.

Question 18.
Name the process by which plants lose water in the form of liquid through water stomata?
Answer:
Guttation.

Question 19.
What is epithem?
Answer:
Group of loosely arranged cells found below the H20 cavity in the hydathode is called epithem.

Question 20.
Define translocation of solutes.
Answer:
It is the movement or transport of organic solutes or products of photosynthesis from the mesophyll of the leaves (source) to roots, and other parts (sink) through phloem.

Question 21.
What is endosmosis?
Answer:
Influx of water when a plant cell is placed in a hypotonic solution is called endosmosis.

Question 22.
What is exosmosis?
Answer:
Out flux of water when a plant cell is placed in a hypertonic solution is called exosmosis.

Question 23.
What are imbibants?
Answer:
Imbibants are hydrophilic colloidal substances which can absorb or imbibe water, e.g: Lignin, Pectin etc.

Question 24.
What is plasmolysis?
Answer:
Plasmolysis is the phenomenon of cell shrinkage, when the cell is placed in a hypertonic solution.

Question 25.
What is deplasmolysis?
Answer:
Deplasmolysis is a phenomenon in which a plasmolysed cell regains its original size and shape due to endosmosis, when it is placed in a hypotonic solution.

Question 26.
Mention the different types of transpiration?
Answer:
1. Stomatal transpiration
2. Cuticular transpiration
3. Lenticular transpiration.

Question 27.
What is guttation?
Answer:
The loss of water in liquid form through specialized structures called water stomata or hydathodes is called guttation.

Question 28.
What is vein loading?
Answer:
The process of transporting sugar molecules actively into the sieve tubes of the veins in the leaf lamina is called vein loading.

Question 29.
What are anti transpirants?
Answer:
Anti transpirants are the substances that prevent the process of transpiration without affecting any other physiological functions. e.g: Low viscosity waxes, ABA, Phenyl mercuric acetate.

Question 30.
Why do fresh grapes shrink, when they are soaked in a strong salt solution?
Answer:
When fresh grapes are kept in a petri dish filled with concentrated sugar solution, exosmosis occurs, and the grapes shrink due to loss of water.

Question 31.
Differentiate between the following:
(a) Diffusion and Osmosis.
(b) Transpiration and Evaporation.
(c) Osmotic Pressure and Osmotic Potential
(d) Imbibition and Diffusion.
(e) Apoplast and Symplast pathways of movement of water in plants.
(f) Guttation and Transpiration.
Answer:
(a) It is the movement of water molecules (solvent) from the region of their higher concentration to a region of their lower concentration, through a semipermeable membrane. The process of osmosis mainly depends on the solute concentration of the cell.

(b) Evaporation and transpiration are the two different types of naturally occurring process in the atmosphere.

• Transpiration Evaporation:
  Transpiration makes the surface of leaves and young stems wet and protects them from sunburn.
• Evaporation:
  Evaporation provides dryness to the free surface.

Evaporation is loss of water on cells surface due to heat.

(c) Osmotic pressure is the pressure due to which movement of water molecules takes place from region of their higher concertration to the region of their lower concentration. Osmotic potential is a hydrostatic pressure developed on the region of lower concentration to prevent the entry of H₂O by osmosis.

(d) Imbibition : Imbibition is a special kind of diffusion which involves movement of water mólecules along admision gradient from a region of higher concentration on to a suitable solid matrix (adsorption).
or
It is the adsorption of water molecules by hydrophilic colloids.

Diffusion:
The movement of molecules or ions of gases, liquids or solids from a region of their higher concentration to a region of their lower concentration is known as diffusion.

(e) The apoplastic pathway is one of the two main pathways for water transport in plants, the other being symplastic pathway. In apoplastic transport, water and minerals flow in an upward direction via the apoplast to the xylem in the root. … Transport velocity is higher in the apoplast than the symplast.

(f)

Transpiration	Guttation
1. Transpiration is universal phenomenon which occurs in all plants.	1. Guttation occurs only in herbs, especially in the members ofthe family graminae.
2 It occurs through stomata, cuticle or lenticels.	2. It occurs through hydathodes or water sto­mata.
3. Amount of water lost is enormous.	3. Water lost is negligible.
4. Transpired water is pure, and is in the form of vapour.	4. Guttated water contains nitrogenous wastes, amino acids etc. It is impure, and is in the form of droplets.

Question 32.
What happens when a pressure greater than the atmospheric pressure is applied to pure water or a solution?
Answer:
If a pressure greater than atmospheric pressure is applied to pure water or a solution, its water potential increases.

Question 33.
How is the mycorrhizal association helpful in absorption of water and minerals in plants?
Answer:
By increasing the surface area for absorption.

Question 34.
In a passive transport across a membrane, when two protein molecules move in opposite directions, and are independent of each other, it is called….
Answer:
Independent diffusion.

Question 35.
Osmosis is a special kind of diffusion in which water diffuses across the cell membrane. The rate, and direction of osmosis depends upon both…
Answer:
Pressure, and concentration gradient.

Question 36.
A flowering plant is planted in an earthern pot, and irrigated Urea is added to make the plant grow faster, but after some time the plant dies. This may be due to…
Answer:
Exosmosis.

Question 37.
How does most of the water move within the root?
Answer:
Passively through apoplast (upto cortex), and to a lesser through symplast (from endodermis onwards) before entering the lumen of xylem.

1st PUC Biology Transport in Plants Two Marks Questions and Answers

Question 1.
Distinguish between osmosis and diffusion.
Answer:

Osmosis	Diffusion
1. It is the movement of only water molecules from the region of their higher concentration to their region of lower concentration through a semi permeable membrane.	1. It is the movement of molecules or ions from a region of higher concentration to a region of lower concentration.
2. Semi permeable membrane is required.	2 Semi permeable membrane is not required.

Question 2.
Differentiate between turgor pressure and wall pressure.
Answer:

Turgor pressure	Wall pressure
Due to endosmosis the volume of wall increases, the tonopiast of the vacuole pushes the cytoplasm towards the cell wall. This pressure exerted on the cell wall by the proto plast in the turgid cell is known as turgor pressure.	The cell wall also exertes a pressure on the proto plast which is equal and opposite to the turgor pressure. This pressure is called wall pressure.

Question 3.
Differentiate between endosmosis and exosmosis.
Answer:

Endosmosis	Exosmosis
1.  The entry of water into the cell when it is surrounded by a hypotonic solution is called endosmosis. 2.   Due to this, the cell swells and becomes turgid.	1.  The movement of water from the cell when it is surrounded by a hypertonic solution is called exosmosis. 2.   Due to this, the cell shrinks, and becomes flaccid.

Question 4.
Differentiate between plasmolysis and deplasmolysis.
Answer:

Plasmolysis	Deplasmolysis
It is the phenomenon in which a plasmolysed cell beomes flaccid, due to exosmosis when it is surrounded by a hypertonic solution.	It is a phenomenon in which a plasmolysed cell regains its original size and shape, due to endosmosis, when it is surrounded by a hypotonic solution or pure water.

Question 5.
Mention any four factors which influence the rate of transpiration in plants.
Answer:
Leaf surface, stomata, wind velocity, Light, temperature etc

Question 6.
Sketch and label the Dicot Stomatal apparatus
Answer:

Question 7.
Give any four differences between transpiration and guttation.
Answer:

Transpiration	Guttation
1. Transpiration is universal phenomenon which occurs in all plants.	1. Guttation occurs only in herbs, especially in the members of the family graminae.
2 It occurs through stomata, cuticle or lenticels.	2. It occurs through hydathodes or water sto­mata.
3. Amount of water lost is enormous.	3. Water lost is negligible.
4. Transpired water is pure, and is in the form of vapour.	4. Guttated water contains nitrogenous wastes, amino acids etc. It is impure, and is in the form of droplets.

Question 8.
Write any four significant points of osmosis.
Answer:
(a) It is the cell to cell movement of water in plants.
(b) It brings about opening and closing of stomata.
(c) Many plant movements like seismonasty are due to osmosis.
(d) Absorption of water by root hair is due to osmosis.

Question 9.
Define water potential. Mention its components.
Answer:
Water potential can be defined as the difference between the free energy of water molecular in pure water, and energy of water in a solution. The components of water potential are:
(a) Solute potential.
(b) Pressure potential.

Question 10.
Write any two significances of diffusion in plants.
Answer:
(a) In the plants exchange of gases occur by diffusion.
(b) Cell to cell movement of water takes place by diffusion.

Question 11.
Write any four significances of Transpiration?
Answer:
(a) Transport of water within the plant body.
(b) It has cooling effect on the plant.
(c) Responsible for ascent of sap.
(d) Helps in the absorption of water.

Question 12.
What are the factors affecting the rate of diffusion?
Answer:
(1) Nature of the diffusing particle.
(2) Nature of the disparting medium.
(3) Temperature.

Question 13.
What are porins? What role do they play in diffusion?
Answer:
Porins are proteins that form huge pores in the outer membranes, and help to facilitate diffusion.

Question 14.
Describe the role played by protein pumps during active transport in plants.
Answer:
They help in active transport of ions across the cell membranes.

Question 15.
What role does root pressure play in water movement in plants?
Answer:
Upward water movement in a plant:
The upward movement of water with dissolved salts from the roots to the aerial parts through xylem is called as Ascent of sap. It is unidirectional.

Mechanism:
Root Pressure:-
Due to osmotic entry of water into the xylem elements an hydrostatic pressure is developed, which is called as root pressure. his responsible for pushing up water, to small heights in
the stem. Thus in herbaceous plants it is responsible for transport of water.

Question 16.
Why is solute potential negative? Explain Ψ_w = Ψ_s + Ψ_p
Answer:
Water potential of pure water is taken as zero. Addition of solute particles reduces water potential.
Ψ_w = Ψ_s + Ψ_p
Therefore, solute potential is always less than zero is negative.
Ψ_w = Water potential Ψ_s = Solute potential, Ψ_p= Pressure potential (Turgor pressure)

Question 17.
Differentiate between apoplast and symplast pathways of water movement. Which of these need active transport?
Answer:
(a) Differences between apoplast, and symplast pathway. The apoplast route is the fully permeable route in which the water movement occurs in passive diffusion. Whereas, the symplast is a selectively permeable route in which the water movement occurs by osmosis. Active transport is needed during symplast pathway.

Question 18.
What causes the opening, and closing of guard cells of stomata, during transpiration?
Answer:
Presence of glucose and enough water (turgid) in the guard cells makes stomata to open. Presence of starch and carbonic acid in the guard cells will close the stomata.

1st PUC Biology Transport in Plants Three Marks Questions and Answers

Question 1.
Briefly describe water potential. What are the factors affecting it?
Answer:
It is defined as the difference in the free energy of water molecules in pure water to the liee energy of water in a solution.

• Water potential of pure water
• Water potential) decrees with dating of solutes, there by water potential is always a negative integer for a solution.
• Water potential in a solution is determined by two factors, namely:

(a) Solute potential.
(b) Pressure potential.
Osmotic potential is the amount by which water potential is reduced due to the addition of solute particles.
Pressure potential is a positive potential developed due to turgor pressure.

Question 2.
What essential role does the root endodermis play during mineral absorption in plants?
Answer:
Unlike water, all minerals cannot be passively absorbed by the roots. Therefore most minerals must enter the root by active absorption into the cytoplasm of epidermal cells.

Transport proteins of endodermal cells are control points, where a plant adjusts the quantity, and types of solutes that reach the xylem. It is important to note that the root endodermis is because of the layer of suberin that has the ability to actively transportions in one direction only.

Question 3.
Explain why xylem transport is unidirectional, and phloem transport is bi-directional.
Answer:
Xylem transport is Unidirectional : The force for xylem transport is generated by transportation transport occurs only in the aerial parts, mostly those having leaves. It creates a negative pressure or tension in the xylem channels that cause the upward movement of sap. Xylem transport is, therefore, unidirectional or in the upward direction only.

Phloem transport is Bidirectional :
Pholem transport is based upon the development of positive pressure in the region where nutrients are loaded. The movement is towards the sink region where there is less Turgot pressure, and a mechanism to offload the nutrients.

Positive or high turgor pressure develops in the area of food manufacture. transport location occurs both towards roots (for storage, and consumption), and towards growing points of the shoot (for consumption). Pholem transport is, therefore, bidirectional, both towards the upper side as well as towards lower side.

1st PUC Biology Transport in Plants Five Marks Questions and Answers

Question 1.
Explain the Transpiration pull theory of ascent of sap. Add a note on its merits of demerits.
Answer:
It is one of the most successful physical theories of ascent of sap. Dixon and Jolly proposed this theory. According to this theory, ascent of sap is due to three factors namely,
(a) Cohesive force of water
(b) Adhesion of water molecules to the walls of the xylem vessel
(c) Transpiration pull
A strong inter molecular force of attraction exists between water molecules. Thus water molecules are bound to each other forming a continuous column of water.

There is a force of attraction between water molecules on the inner walls of xylem elements. Therefore water molecules are attached to the wall of xylem. It is called adhesion.

Due to adhesive and cohesive properties of water, a continuous column of water is present in xylem. TrAnswer:piration at the leaf surface force the mesophyll cells of the leaves to draw water from the neighbouring xylem elements. This creates a suction force known as TrAnswer:piration pull. This suction force pulls the water column in the xylem upwards. Thus ascent of sap is due to combined effect of adhesive, and cohesive properties of water and trAnswer:piration pull.

Merits:
1. The ascent of sap is directly proportional to the rate of transpiration.
2. It is a physical process, and does not need energy.
3. Strong cohesive, and adhesive forces are sufficient to prevent the rupture of water column in xylem vessels.

Demerits:
1. Presence of air bubble breaks the continuity of water column.
2. Ascent of sap continues even in the absence of transpiration, as at night times.
3. Strength of water column is thoughtful against two opposing forces such as gravitation force and transpiration tension.

Question 2.
Explain mass flow hypothesis?
Answer:
According to Munch, food materials are translocated from the source (leaves) to sink (roots) enmass, through turgor pressure gradient that occurs between leaves and roots. The mechanism of translocation can be explained as follows:

1. Sugars are formed in the mesophyll cells during photosynthesis, and are loaded into the phloem sieve elements of veins. This is called vein loading.

2. The osmotic potential in the phloem becomes more negative, and as a result water is drawn into phloem elements from xylem cells.

3. Turgor pressure increases in the sieve tubes of leaves, and at the same time the turgor, pressure of roots becomes less. So a turgor pressures gradient occurs between mesophyll cells and root cells.

4. As a result, food molecules in solution form, are translocated from leaves to roots.

5. In the roots the food is consumed, and in the fruits it is converted into insoluble starch. So osmotic potential and turgor pressure in the roots and storage organs. decreases.

6. Thus turgor pressure gradient continues between leaves, and roots, and translocation of food also continues.

Munch conducted a physical experiment to demonstrate the mass flow. He took two osmometers A and B, with concentrated sugar solution in A and B filled with dilute solution. These are connected by a ‘U’ tube C. At B are immersed in a rough containing water.

Now water enters into ‘A’, due to high osmotic pressure and this creates turgor pressure. This results in mass flow of sugar solution from A to B through ‘C’ until equilibrium is attained and maintained. He compared osmometer A to leaves, B to roots, C to phloem, and water in vessels to xylem vessels. This clearly explains the mass flow hypothesis.

Question 3.
Explain the factors influencing the rate of transpiration?
Answer:
The important external factors that influence the rate of transpiration are:
1. Light: Light directly increases the rate of transpiration by inducing the opening of stomata. Starch is formed in the guard cells in the presence of light. Starch gets converted into sugars which absorb water into the guard cells. Guard cells become turgid, and stoma opens, and the rate of transpiration increases. When there is no light the stomata gets closed, and the rate of transpiration decreases.

2. Temperature: When temperature increases, the atmospheric humidity decreases and rate of transpiration increases and when temperature decreases, transpiration decreases.

3. Atmospheric humidity: It is the amount of water vapour present in the atmospheric air. When the atmospheric humidity is more, the rate of transpiration is less, and when atmospheric humidity is less the rate of transpiration is more.

4. Wind velocity: Plants produce a cloud of water vapour just above the leaves which reduces the rate of transpiration. When wind velocity removes the water vapour around the plant, then the rate of transpiration increases. But a very high wind velocity tends to close the stomata, and the rate of transpiration decreases.

5. Availability of soil water: When there is less soil water, the rate of water absorption is less, and rate of transpiration is also less.

Question 4.
(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.
Answer:
(a) The shrinkage of protoplasm of a cell due to loss of water by exosmosis is called plasmolysis and the cell is said to be plasmolysed. As a result the cell becomes flaccid. Suppose a cell is sorrounded by a solution which is more concentrated (hypertonic) than the cell sap, water molecules diffuse out of the cell through the membrane (exosmosis).

The solution of higher concentration than that of the cell sap is called a hypertonic solution. As a result the cell sap looses water and the cell becomes flaccid. The protoplasm shrinks. The extent of shrinkage of the cytoplasm depends upon the concentration of the surrounding solution.

If is slightly more concentrated than the cell sap, incipient plasmolysis is observed. If the cell in incipient plasmolysis is placed in hypertonic solution for some more time, it enters into evident plasmolysis and further into final plasmolysis.

(b) Plant cell absorbs water by endosmosis and become turgid.

Question 5.
Describe transpiration pull model of water transport in plants. What are the factors influencing transpiration? How is it useful to plants?
Answer:
Plants absorb water, and mineral ions from the soil through roots. These substances are subjected for bulk movement through the conducting or vascular tissues of plants for aerial parts of the plants which is called as translocation.

How do plants. absorb water?
Plants absorb water by the root hairs in two distinct pathways namely, apoplast pathway, and symplast pathway.

In apoplast pathway, movement of water occurs excipsively through the intercellular spaces, and the walls of the cells. This can take place only upto the endodermis, because the suberised casparian strip will block further movement of water. In symplast pathway, movement of water takes place through the interconnected protoplasts through cytoplasm, and plasmodesmatal connections. This is the most accepted pathway.

Question 6.
Discuss the factors responsible for transpiration in plants.
Answer:
The important external factors that influence the rate of transpiration are:
1. Light:- Light directly increases the rate of transpiration by inducing the opening of stomata. Starch is formed in the guard cells in presence of light. Starch gets comerted into sugars which absorb water into guard cells. Guard cells become turgid and stoma opens and the rate of transpiration increases. When there is no light stomata are get closed and the rate of transpiration decreases.

2. Temperature:- When temperature increases atmospheric humidity decreases and rate of transpiration increases and when temp decreases transpiration decrease.

3. Atmospheric humidity:- It is the amount of water vapor present in the atmospheric air when atmospheric humidity is more the rate of transpiration is less and when atmospheric humidity is less the rate of transpiration is more.

4. Wind velocity:- Plants produce a cloud of water vapor just above the leaves which reduces the rate of transpiration. When wind velocity removes the water vapour around
the plant, then the rate of transpiration increases, high wind velocity tends to close stomata and the rate of transpiration decreases.

5. Availability of soil water:- When there is less soil water, the rate of water absorption is less and rate of transpiration is also less.

Question 7.
Explain pressure flow hypothesis of translocation of sugars in plants.
Answer:
In Plants, the mechanism explained for the translocation of sugars from source to sink is referred to the pressure flow hypothesis. Glucose generated by photosynthesis at the source is converted to sucrose which is moved to the phloem sieve tube cells through the companion cell by active transport.

The remaining transport in the phloem is carried out by the differences in the osmotic pressure, which facilitates the transport from higher pressure to lower pressure regions of the sink. Again by active transport, the sucrose is transported from phloem to the cells of the sink where it will be stored for long.

1st PUC Biology Transport in Plants Text Book Questions and Answers

Synopsis:

• W_ater is regarded as an universal solvent.
• All life activities take place in the protoplasm which contains about 90% water.
• Water is aptly called‘fluid of life’.

Some of the important functions of water are:

• It is the hydrogen donor for photosynthesis.
• It maintains a constant temperature.
• It helps in movement of salts, and other soliites.
• It is essential for germination of seeds, and spores.
• It is responsible for elongation of cells during growth.
• It provides turgidity to the cells of the plant body. _x
• It helps in opening, and closing of stomata.

Movement of water, salts, and other solutes takes place due to physiological processes like diffusion, osmosis, and imbibition.

Diffusion: 
It is the movement of molecules (gas, liquid or solids) from a region of their higher concentration to a region of lower concentration.

Significance:

• Respiratory gases (O₂ and CO₂) are exchanged with the atmosphere by diffusion
• Transpiration occurs by diffusion through stomata.
• Cell to cell movement of substances occurs by diffusion.

Facilitated Diffusion:

This is somewhat comparable with diffusion, since the solute moves along the concentration gradient, and no energy is needed. But the most important distinguishing feature is that facilitated diffusion occurs through specific carrier proteins for the transport.

Specific carrier proteins for the transport of glucose, galactose, etc have been identified. These carriers are called as porins. Those porins which help in conduction of water are called Aquaporins.

Water Potalcial:
It is defined as the difference in the free energy of water molecules in pure water to tree energy of water in a solution.

• Water potential of pure water is zero.
• Water potential decreases with addition of solutes, therefore water potential is always a negative integer for a solution.
• Water potential in a solution is determined by two factors, namely:

(a) Solute potential.
(b) Pressure potential.
• Osmotic potential is the amount by which water potential is reduced due to the addition of solute particles.
• Pressure potential is a positive potential developed due to turgor pressure.

Osmosis:
It is the movement of water molecules (solvent) from the region of their higher concentration to a region of their lower concentration, through a semipermeable membrane,
• The process of osmosis mainly depends on the solute concentration of the cell.

Types of Osmosis:
(a) Endosmosis: It is the entry of water into the cell when it is surrounded by a hypotonic solution. Due to this, the cell swells and becomes turgid.
(b) Exosmosis: It is the movement of water from the cell when it is surrounded by a hypertonic solution. Due to this the cell shrinks and becomes flaccid.

Significance of osmosis :
1. Absorption of water by root hairs takes place by osmosis.
2. Cell to cell movement of water in plants is due to osmosis.
3. Due to osmosis, the cells become turgid.
4. Opening and closing of stomata is due to osmosis in guard cells.

Plasmolysis :

It is a phenomenon in which the cell shrinks or becomes flaccid due to exosmosis when it is surrounded by a hypertonic solution.

Deplasmolysis :

It is a phenomenon in which a plasmolysed cell regains its original size, and shape due to endosmosis when it is surrounded by a hypotonic solution.
Based on the solute concentration, die solutions are classified into three types:

• Hypotonic solution: It is a solution whose solute concentration is less than the solute concentration of the cell sap.
• Hypertonic solution: It is a solution whose solute concentration is more than the salute concentration of the cell sap.
• Isotonic solution: It is a solution whose solute concentration is equal to the solute concentration of the cell sap.

Imbibition :

• It is the adsorption of water molecules by hydrophilic colloids like cellulose, pectin, lignin etc.
  present on the surface of cell.
• The substance that imbibes water is known as imbibant
• The pressure produced due to imbibition is known as imbibitional pressure

Long Distance Transport Of Water:

– Plants absorb water, and mineral ions from the soil through roots. These substances are subjected for bulk movement through the conducting or vascular tissues of plants for aerial parts of the plants which is called as translocation.

How do plants, absorb water?
Plants absorb water by the root hairs in two distinct pathways namely, apoplast pathway, and symplast pathway.

In apoplast pathway, movement of water occurs exclusively through the intercellular spaces, and the walls of the cells. This can take place only upto the endodermis, because the suberised casparian strip will block further movement of water.

In symplast pathway, movement of water takes place through the interconnected protoplasts through cytoplasm, and plasmodesmatal connections. This is the most accepted pathway.

Structure of root hair:
Root hairs are unicellular and arise from some of the epiblema cells. These cells enclose a large vacuole surrounded by thin cytoplasm which extends into root hair. There is a single nucleus in the cytoplasm at the tip of the root hair. The root hair is covered by a thin, and permeable cell wall made-up of cellulose and Pectin.

• The total amount of water present in the soil is called holard.
• The water available to the plants for absorption is called Chesard.
• Soil water which cannot be absorbed by the plant is Echard.
• The path of absorption of water in roots is as follows :

Root hairs → Epiblema → Cortex → Endodermis (Passage cells) → Pericycle → Xylem

 

Mechanism of absorption of water:
It occurs by two different mechanisms. Namely,
(I) Active absorption: It is of two types:

(a) Active osmotic absorption of water: Here absorption of water occurs along the concentration gradient ie, from the region of higher water potential to the region of lower water potential.

(b) Active non osmotic absorption : It occurs against the concentration gradient. It requires the expenditure of ATP.

(2) Passive absorption: It is absorption of water by root hairs due to some other activity taking place in the plant like transpiration. The suction force created due to loss of water in transpiration results in entry of water into the roots from the soil.

Upward water movement in a plant:
The upward movement of water with dissolved salts from the roots to the aerial parts through xylem is called as Ascent of sap. It is unidirectional.

Mechanism:
Root Pressure:-
Due to osmotic entry of water into the xylem elements an hydrostatic pressure is developed, which is called as root pressure. It is responsible for pushing up water, to small heights in the stem. Thus in herbaceous plants it is responsible for transport of water.

Transpiration pull theory or cohesion Tension theory:

• This is the most accepted theory.
• This theory was proposed by Dixon and Jolly.
• According to this theory, ascent of sap is due to three factors namely.

(i) Cohesive property of water
(ii) Adhesion of water molecules to the walls of the xylem vessels.
(iii) Transpiration pull

– A strong inter molecular force of attraction exists between water molecules. Thus water molecules are bound to each other forming a continuous column of water.
– There is a strong force of attraction between water molecules, and the inner wall of xylem elements. Therefore water molecules are attached to the wall of xylem. This is called adhesion.
– Due to the adhesive and cohesive properties of water, a continuous column of water is created in xylem.
– Transpiration at the leaf surface forces the mesophyll cells of the leaves to draw water from the neighboring xylem elements. This creates a suction force called as ‘Transpiration pull’ which pulls the water column in the xylem, upwards. Thus ascent of sap is due to combined effect of adhesive, and cohesive properties of water and transpiration pull.

Loss of water in plants:
Loss of water in plants takes place by three ways namely transpiration, and guttation.
Transpiration is loss of water in the form of water vapours from the aerial parts of the plant body.

Types:
(1) Cuticular Transpiration – loss of water through cuticles on the leaf surface.
(2) Lenticular Transpiration – loss of water through lenticels
(3) Stomatal Transpiration – loss of water through stomata.

Dicot Stomatal Apparatus:

Dicot stomatal apparatus includes
(a) Stoma – a minute opening present between the guard cells.
(b) Guard cells – Specialised epidermal cells surrounding the stoma. These are two in number and are kidney shaped. Their outer walls are thin, and elastic but inner walls are thick, and less elastic.

Factors affecting transpiration :
The external factors that affect transpiration are:
(a) Temperature
(b) Sunlight
(c) Wind velocity
(d) Humidity.

Internal factors includes:
(a) Number and distribution of stomata.
(b) Orientation of the leaves.

Transpiration and photosynthesis:
Photosynthesis is controlled by the availability / supply of water which in turn is controlled by the rate of transpiration.
If the rate of transpiration is more, the guard cells become flaccid, and close the stomata, there by reducing the supply of carbon dioxide for photosynthesis. C₄ plants have evolved for minimising water loss, and maximising the availability of carbon dioxide.

Uses of Transpiration :
(1) It creates transpiration pull which is responsible for passive absorption of water, and ascent of sap.
(2) It cools the leaf surface, and prevents overheating of plant parts.
(3) Supplies water for photosynthesis.
(4) It is responsible for maintaining the shape, and structure of plant cells, and plant organs.

Uptake of mineral ions:
Till 1900, scientists had to opinion, that minerals enter the root in a dissolved form along with water. But later it was known that majority of,the minerals cannot enter the root by passive absorption along with water because,
(i) Minerals occur in the soil as charged particles (ions) which cannot move across the cell membranes.
(ii) The concentration of minerals in the soil is usually lower than the concentration in the root.

Note : Only about 5% of the minerals enter passively. The bulk (95%) of the minerals will enter by an active transport with the help of specific carrier proteins in the membranes.
The cell membrane of endodermal cells acts as a barrier, and regulate the movement of ions selectively.

Transport of mineral ions :
Once the mineral ions enter xylem, they are transported to all the other parts along with water.
(i) Consumption of ions is more in the apical, and lateral meristems, young leaves, flowers, fruits, and seeds.
(ii) Minerals are transported by diffusion and active transports. Further, minerals can be remobilised from older parts to young leaves, and other parts.

Extra information :
Guttation:-

• Guttation is defined as loss of water in liquid form, through hydathodes along the margin of leaves.
• Guttation occurs in leaf tips, and leaf margins where the veins end.
• The cause of guttation is mainly root pressure.

Structure of hydathode:

Hydathodes are present at the margin of the leaves where the veins end.
Each hydathode is composed of a water pore which remains permanently open. This pore leads to a small cavity followed by a group of loosely arranged cells called epithem. These cells are in close contact with the veins.
– Water lost through guttation contains dissolved substances like mineral salts, sugars, nitrog-enous wastes amino acids etc. So water lost through guttation is not pure.

Translocation Of Solutes:

• It is a process by which products of photosynthesis are transported from leaves to other parts of the plant body.
• Phloem is the pathway of translocation of organic solutes.
• The movement is multi directional.
• The sieve tubes of the phloem carry the organic solutes prepared during photosynthesis.

Composition of phloem sap:
It contains Sugars, Amino acids, and Vitamins.

Munch’s Mass flow hypothesis:

• Mass flow theory is also called pressure flow hypothesis.
• It is mainly based on the assumption that an extreme concentration gradient exists between the sources and sink.
• Organic solutes enter the sieve tubes from the mesophyll cell during translocation.
• Due to this, a high DPD gradient develops and water from surrounding cells enters the sieve tube cells and this creates a hydrostatic pressure.

This pressure is mainly responsible for the movement of food material ie, organic solutes move en-mass towards less concentration gradient ie, the root system where it is used for ATP production or stored as reserve food material.

1st PUC Biology Question Bank with Answers