Thinking Process

Osmosis is special type of diffusion of water molecules across a semipermeable membrane from a region of higher concentration to that of a lower concentration. The net direction and rate of osmosis depends on pressure and concentration gradient.

Answer

(d) Reverse osmosis is not an active process. A process (in organisms) is considered active when its completion requres energy in from of ATP. And as reverse osmosis dose not consume ATP, it is a passive process, though external pressure is applied in order to carry out osmosis in a reverse direction (lower to higher). Rest of the options are true for reverse osmosis.

• (a) It is used for water purification: This statement is correct. Reverse osmosis is indeed used for water purification, so it does not apply as an incorrect statement.

• (b) In this technique, pressure greater than osmotic pressure is applied to the system: This statement is also correct. Reverse osmosis involves applying pressure greater than the osmotic pressure to reverse the natural flow of water, so it does not apply as an incorrect statement.

• (c) It is a passive process: This statement is correct. Reverse osmosis is considered a passive process because it does not require energy in the form of ATP, so it does not apply as an incorrect statement.

Answer

(d) Chlorophyll content will not affect the rate of transpiration.

Options (a), (b) and (c) all affect the rate of transpiration.

(a) Temperature increass the rate of transpiration.

(b) Light quality and intensity also affect the rate of this phenomenon.

(c) Wind speed higher the wind speed, more will be the rate of transpiration.

Answer

(a) In dorsiventral leaf, the number of stomata will be more on lower surface. This feature enhances gas exchange between leaf surface and the atmosphere for the processes of photosynthesis and respiration.

Whereas in isobilateral leaf, stomata are uniformly distributed on both the surfaces.

• (b) In isobilateral leaf, stomata are uniformly distributed on both the surfaces, so the number of stomata on the lower surface is not more than the upper surface.
• (c) Both (a) and (b) cannot be correct because in isobilateral leaves, the stomata are evenly distributed on both surfaces, unlike dorsiventral leaves where they are more on the lower surface.
• (d) None of these is incorrect because option (a) is correct for dorsiventral leaves.

Thinking Process

Glucose is the first product of photosynthesis in plant and also is the source of energy for every cell. Plants cannot transport it to the other cell as such because it is an reactive molecule.

Answer

(c) Sucrose a disaccharide sugar is transported through phloem. It comprises of 2 units of glucose joined by $\alpha-1-4$ linkage. It is the most inactive form of sugar so used in the transport of food.

Glucose because of presence of $\mathrm{CHO}$ group is reactive sugar.

Fructose is founds in fruits and ribose is present in nucleic acids.

• Glucose because of presence of $\mathrm{CHO}$ group is reactive sugar.
• Fructose is found in fruits.
• Ribose is present in nucleic acids.

Answer

(a) Guttation occurs when root pressure is high and rate of transpiration is low and there is high humidity in the air.

The other given conditions do not fovour guttation.

• (b) Guttation does not occur when the root pressure is low and the rate of transpiration is high because low root pressure is insufficient to force water out through hydathodes, and high transpiration would lead to water loss through stomata rather than guttation.

• (c) Guttation does not occur when the root pressure equals the rate of transpiration because this balance would not create the necessary pressure differential to force water out through hydathodes.

• (d) Guttation does not occur when both root pressure and the rate of transpiration are high because high transpiration would lead to water loss through stomata, reducing the likelihood of guttation through hydathodes.

Thinking Process

Imbibition is a physical phenomenon. Water is absorbed by the surface of seed and other biological materials.

Answer

(c) Swelling of seed in soil is an example of imbibition. Imbibition is a type of diffusion process along the concentration gradient enabling the solid to absorb water and increase in volume. When seed is put in the soil it absorbs water which activate enzymes present in seed and this induces the seed germination.

The other options, i.e., uptake of water by root hair is an example of absorption, exchange in of gases stamata is an example of diffusion and opening of stomata is an example of turgor pressure or turgidily.

• Uptake of water by root hair is an example of absorption.
• Exchange of gases in stomata is an example of diffusion.
• Opening of stomata is an example of turgor pressure or turgidity.

Answer

(c) Senescence is the programmed death of a plant. Translocation of nutrients to different parts of the plant are withdrawn at the time of senescence.

• (a) Accumulated: During senescence, nutrients are not accumulated in the dying parts of the plant. Instead, they are mobilized and translocated to other parts of the plant where they can be reused.

• (b) Bound to cell wall: Nutrients are not bound to the cell wall during senescence. The process involves the breakdown of cellular components and the movement of nutrients away from the senescing tissues.

• (d) None of these: This option is incorrect because the correct process during senescence is the translocation of nutrients, as stated in option (c).

Answer

(c) Water potential of pure water at standard temperature is zero. It is the highest value of water potential.

• Option (a) 10: Water potential is a measure of the potential energy in water and is typically expressed in units of pressure (such as megapascals, MPa). The value of 10 does not correspond to any standard measure of water potential for pure water at standard temperature.

• Option (b) 20: Similar to option (a), the value of 20 does not correspond to any standard measure of water potential for pure water at standard temperature. Water potential is not typically expressed in such arbitrary numerical values without units.

• Option (d) None of these: This option is incorrect because the correct answer is provided in option (c), which states that the water potential of pure water at standard temperature is zero.

Thinking Process

Symbiosis is a phenomenon in which two organisms are associated with each other in such a way that both of them derive benefit from each other.

Answer

(c) Mycorrhiza associated with roots of plants helps in both absorption of water and minerals from the soil. The other options are incorrect.

• Option (d) Both B and C is incorrect because mycorrhiza does not play a role in the translocation of nutrients within the plant. Translocation is primarily the function of the plant’s vascular system (xylem and phloem), not the mycorrhiza.

• Option (a) Only A is incorrect because mycorrhiza not only aids in the absorption of water but also significantly enhances mineral nutrition by increasing the surface area for nutrient uptake.

• Option (b) Only B is incorrect because mycorrhiza assists in both mineral nutrition and water absorption, not just mineral nutrition alone.

• Option (d) Both B and C is incorrect because mycorrhiza does not facilitate gaseous exchange. Gaseous exchange is primarily managed by the stomata in the leaves and other parts of the plant, not by the mycorrhiza.

Answer

(b) Movement of water will take place from chamber A to B. It is not the solute which will move from chamber $A$ to $B$. The is because osmosis is a process in which solvent molecules moves from a region of higher concentration to a region of lower concentration through a semi-permeable membrane.

• (a) Movement of solvent molecules will take place from chamber A to B: This statement is actually correct. In osmosis, solvent molecules (typically water) move from an area of higher solvent concentration (lower solute concentration) to an area of lower solvent concentration (higher solute concentration) through a semipermeable membrane.

• (c) Presence of a semipermeable is a pre-requisite for this process to occur: This statement is also correct. Osmosis specifically requires a semipermeable membrane that allows only solvent molecules to pass through while blocking solute molecules.

• (d) The direction and rate of osmosis depends on both the pressure gradient and concentration gradient: This statement is correct as well. The process of osmosis is influenced by both the concentration gradient of the solvent and the pressure gradient across the semipermeable membrane.

Answer

(a) The correct matched sequence of the two columns is as follows.

Leaves - Transpiration

Seed - Imbibition

Roots - Absorption

Aspirin - Anti-transpirant

Plasmolysed cell - $\quad$ Negative osmotic potential

• Option (b):

  • Leaves (iii) Negative osmotic potential: Incorrect because leaves are primarily involved in transpiration, not in creating negative osmotic potential.
  • Seed (ii) Transpiration: Incorrect because seeds are involved in imbibition, not transpiration.
  • Roots (iv) Imbibition: Incorrect because roots are primarily involved in absorption, not imbibition.
  • Aspirin (i) Anti-transpirant: Correct.
  • Plasmolysed cell (v) Absorption: Incorrect because plasmolysed cells are associated with negative osmotic potential, not absorption.

• Option (c):

  • Leaves (i) Anti-transpirant: Incorrect because leaves are primarily involved in transpiration, not in acting as anti-transpirants.
  • Seed (ii) Transpiration: Incorrect because seeds are involved in imbibition, not transpiration.
  • Roots (iii) Negative osmotic potential: Incorrect because roots are primarily involved in absorption, not in creating negative osmotic potential.
  • Aspirin (iv) Imbibition: Incorrect because aspirin is an anti-transpirant, not involved in imbibition.
  • Plasmolysed cell (v) Absorption: Incorrect because plasmolysed cells are associated with negative osmotic potential, not absorption.

• Option (d):

  • Leaves (v) Absorption: Incorrect because leaves are primarily involved in transpiration, not absorption.
  • Seed (iv) Imbibition: Correct.
  • Roots (iii) Negative osmotic potential: Incorrect because roots are primarily involved in absorption, not in creating negative osmotic potential.
  • Aspirin (ii) Transpiration: Incorrect because aspirin is an anti-transpirant, not involved in transpiration.
  • Plasmolysed cell (i) Anti-transpirant: Incorrect because plasmolysed cells are associated with negative osmotic potential, not acting as anti-transpirants.

Thinking Process

Plants have plastids as an cell organelles. They are of three types chromoplasts, chloroplasts and leucoplasts (amyloplast).

Answer

(a) Amyloplasts are the colourless plastids which store starch but not the protein granules. Other pairs are correctly matched.

• Elaioplasts store oils or fats, which is correctly matched.
• Chloroplasts contain chlorophyll pigments, which is correctly matched.
• Chromoplasts contain coloured pigments other than chlorophyll, which is correctly matched.

Thinking Process

The movement of substances across the limiting membrane in a living cell is a highly specific and regulated phenomenon. This regulation is done mainly by membrane proteins.

Answer

Proteins.

The movement of hydrophilic substances are facilitated by transporters which are chemically proteins. These proteins form porins, which are huge pores in the outer membranes of the plastids, mitochondria and some bacteria. These porins allow the small molecules to pass through the membrane.

Answer

Antiport This process facilitates transport of molecules in both the directions across the membrane and their movement is independent of each other.

Thinking Process

Osmosis is an important biological phenomenon in the living world. It is governed by number of factors.

Answer

The rate and direction of osmosis depends upon both the pressure gradient and concentration gradient.

Answer

The plant dies due to exosmosis. As the solution outside the plant is an hypertonic solution, and the plant celsl are hypotonic in nature, so there is a gradual movement of water from plant cell to outside urea solution leading to plasmolysis of root cells and plant dies gradually.

Thinking Process

Seeds usually have colloid substances which absorb and adsorb lot of water when it is available to them and show significant swelling and increase in size.

Answer

Due to imbibition of water by seed materials (starch and protein), pushes the seedlings out of the soil, thus the seed swells and imbibition pressure increases inside the seed, which contributing for germination of seeds.

Answer

Transpiration pull is the physiological phenomenon which is responsible for the upward movement of water in trees of height up to $20 \mathrm{~m}$. As the water molecules transpire from stomata, it pulls water molecules up ward to the leaf from the continuous chain of water molecules carried by xylem.

This transpiration from leaf creates a pressure gradient between the atmosphere and sub-stomatal cavity and intercellular spaces of leaf. This gradient is transferred to photosynthetic cells and then on to xylem of leaf vein.

It results in a force called “transpirational pull” that can lift water upto $130 \mathrm{~m}$ high, through a xylem column.

Answer

The transport takes place by the cell membrane because cell membrane is semi-permeable and composed of lipids that are arranged in bilayer structure along with proteins and carbohydrate.

The lipid soluble molecules pass readily across lipid bilayer of cell membrane whereas movement of other molecules of small size is facilitated by porins, pores made up of proteins. While cell wall does not helps in transport of substances because it $CO_2$ and not $C_2$.

Cell wall is basically a non-living rigid structure forming outer covering over plasma membrane and it provides shape, mechanical strength and protection to the plant cell from damages and infection.

Answer

Half, The evolution of the $C_{4}$ or plants photosynthetic system is probably one of the strategies for maximising the ability of $CO_{2}$ while minimising water loss. $C_{4}$ plants are twice as efficient as $C_{3}$ plants in terms of fixing carbon in the form of glucose, but lose only half as much water as $aC_{3}$ plant for the same amount of $C_{2}$ fixed.

Thinking Process

Xylem and phloem are complex permanent tissues found in vascular plants (gymnosperms and angiosperms).

Answer

Xylem is involved in the one way transport of water and minerals from soil to root $\rightarrow$ stem $\rightarrow$ leaves. Several forces act in this mechanism like imbibition, root pressure and finally transpiration pull. There is continuous loss of water at the body surface of plants. Thus, it is a unidirectional process.

Phloem’s main function is to transport food from source to sink where source implies with the part of plant responsible for synthesising food and sink to those parts and organs that needs or consumes food for their growth and development. These source and sink parts of a plants may vary in different phases of its growth, thus the food need to travel in both upwards and downward direction. So, phloem shows bidirectional movement of substances.

Thinking Process

Facilitated diffusion involves special proteins that help in moving substances across membranes without the expenditure of energy, i.e., ATP.

Answer

I. Uniport In this process, there is movement of a molecule across a membrane, i.e., of other molecules.

II. Antiport In this process, there is a movement of two types of molecules in opposite direction.

III. Symport In this process, there is a movement of more than one molecule across the membrane in the same direction, at one time.

Ans.

Active Transport It uses energy to pump molecules against a concentration gradient. Hence, different proteins in the membrane play a major role in active transport.

Carrier protein involved in active transport is very specific in what it carries across the membrane.

Facilitated Transport In facilitated transport special proteins help in movement of substances across the membrane without the expenditure of ATP. Facilitated transport is very specific as it allows cell to select substances for uptake.

Simple Diffusion It is a physical phenomenon which involves the movement of water from higher concentration to lower concentration. It is not a selective process and do not require energy.

Answer

Water potential is a measure of free energy associated with water per unit volume $\left(\mathrm{JM}^{-3}\right)$. The water potential of pure water $\left(\Psi_{w}\right)$ at atmospheric pressure is zero. The unit of water potential is bars or Pascal $(1 \mathrm{mPa}=10$ bars $)$.

Solute Potential The addition of solutes reduce water potential (to a negative value). This reduces the concentration of water. Hence, solutions have a lower water potential than pure water, the magnitude of this lowering due to dissolution of a solute is called solute potential or $\Psi_{s}$.

Answer

If some solute is dissolved in pure water, solution has fewer free water molecules and the concentration of water decreases, reducing its water potential.

Hence, all the solutions have a lower water potential than pure water. The magnitude of this lowering is due to dissolution of solute is called solute potential or $\Psi_{s} . \Psi_{s}$ is always negative. The more the solute molecules, the lower (more negative) is the solute potential $\psi_{\mathrm{s}}$ water potential of a cell is affected by both solute and pressure potential.

The relationship can be illustrated as

$$ \begin{aligned} & \Psi_{w}=\Psi_{s}+\Psi_{p} \\ \text{Where, } \quad \quad & \Psi_{w}=\text { water potential } \\ & \Psi_{s}=\text { solute potential, } \\ & \Psi_{p}=\text { pressure potential } \end{aligned} $$

Thinking Process

Onion is a modified stem which is called bulb. The leaves become thick, flashy, scaly and store food materials. The epidermis in them is very thin and good object to study the water related experiments.

Answer

(a) Onion peel when placed in salt solution, shrinks as water from cells cytoplasm moves out of the cell i.e., hypertonic solution.

(b) When it is placed again back in distilled water, cell regains it’s shape and absorbs water and become turgid (full of water) i.e., hypertonic solution.

Answer

Difference between apoplast pathway and symplast pathway is as follows

Thinking Process

The responsibility of absorption of water and minerals is more specifically the function of the root hairs that are present in millions in the root hair zone.

Answer

Most of the water flow in the root occur via the apoplast pathway since, the cortical cells are loosly packed and hence offer no resistance to water movement, which is through mass flow. This mass flow of water occurs due to adhesive and cohesive properties of water.

However, symplast pathway is also involved in the movement of water molecules within the root (i.e., via endodermis to xylem).

Answer

Casparian strip is found in the endodermis. The walls of this layer are impervious to water because of the presence of suberin. So, it does not allow movement of water across the endodermis, rather is forced to enter the symplast pathway through cell membranes and reaches the xylem.

Answer

Difference between guttation and transpiration is as follows

Thinking Process

Loss of water in the form of water vapours from the surface of leaves of plant is called transpiration.

Answer

Transpiration a Necessary Evil

The plant continuously lose water in the vapour form from its body surfaces. It creates a transpiration pull to absorb more and more water from soil through roots.

If the plant does not get water in soil, even then loss through transpiration is not stopped, so plant shows wilting sometimes it leads to the physiological wilting (non-recoverable) and plant dies. So, the transpiration is necessary evil.

Thinking Process

Water is a chemical substance which has chemical formula $H_{2} O$. Two hydrogen atoms attach to $O_{2}$ with covalent bonds.

Answer

The three physical properties of water that helps in ascent up to xylem are as given

Thinking Process

No living being (plant or animal) can survive without water.

Answer

If gardener forgets to water the plants, it will start it wilting (a physiological state of plant in which plant leaves droop down). If watered in time, the plant may recover and become normal.

But in second condition, if watering is delayed, the plant will not recover as if it reaches at physiological wilting stage, it will not recover and dies.

Answer

Facilitated diffusion’s is the mechanism which is highly selective passive process. In facilitated diffusion special proteins help in movement of substances across the membrane without expenditure of ATP energy because facilitated diffusion cause net transport of molecules from a low to high concentration and this would not require input of energy.

Answer

(a) The cell swell in hypotonic solution and shrink in hypertonic solution.

(b) Imbibition is a special type of diffusion when water is adsorbed by living cells.

(c) Most of the water flow in roots occurs via the apoplast way.

Answer

The minerals absorbed are transported up the stem, to all parts of plant through the transpiration stream. The chief sinks for the mineral elements are the growing region of the plant, such as the apical and lateral meristems, young leaves, developing flowers, fruits, seeds and the storage organs.

Unloading of the mineral ions occurs via fine vein endings through diffusion and active uptake by the cells. In plants, xylem are involved in transport of inorganic nutrients where phloem transport only organic materials.

Mineral ions are frequently remobilised from older parts of plant like leaves to the younger regions. Elements most readily mobiliser are phosphorus, sulphur, nitrogen, potassium, and some elements that forms the structural component are not remobilised e.g., calcium.

Answer

The plant exudate (plant sap) is a mixture of the organic/inorganic compounds and ions, minerals, sugars and amino acids. If we chemically analyse these we can get to know which mineral nutrient is transported in which form in the plants. e.g., nitrogen is absorbed and transported $\mathrm{a}$ is $NO_{2}$ and $NO_{3}$ and sulphur in sulphate ion forms etc.

Answer

The life of cut plant in a vase can be increased by placing them in water immediately as air will rapidly move into the water conducting tissue and plug the cell. Also, provide nutrients and elements in a varied concentration can increase the life span of plants.

One phytohormone called cytokine can also be sprayed or plants can be dipped in the solution, as it delays the senescence of plant.

Answer

The rate of transpiration depends on number of factors. If the two species are related and have similar morphology then only external factors will determine the rate of transpiration like wind velocity, humidity temperature, light intensity etc.

Thinking Process

Water is indispensable for life. No life on earth is possible without water. It is required by all organisms in performing vital functions, in plants water is required for the manifestation of its various vital activities.

Answer

Properties of water that make it useful for all biological processes on the earth are

(i) Water is the major solvent through which mineral nutrients enter a plant from the soil solution.

(ii) It is an ideal solvent with neutral $\mathrm{pH}$.

(iii) Water is the major constituent of protoplasm. It constitute approximately $90 %$ of the protoplasm.

(iv) Water act as a medium for translocation of nutritive substances. Mineral nutrients are absorbed by the roots. Carbohydrates that are formed during photosynthesis are transported by water from cell to cell, tissue to tissue and organ to organ.

(v) In plants, water is involved in photosynthesis by incorporating hydrogen atom into carbohydrate and oxygen atoms are further released as $\mathrm{O}_{2}$.

(vi) Water act as agent for temperature control. The specific heat of water helps plant in maintaining a relative stable internal temperature.

(vii) In some plants water is necessary for pollination. Like in bryophytes and pteridophytes, they essentially require water for the fertilisation process.

Thinking Process

The excitability of sensory cells, neurons and muscles depends on ion channels, signal transducers that provide a regulated path for the movement of inorganic ions such as $\mathrm{Na}^{+}, \mathrm{K}^{+}, \mathrm{Ca}^{2+}$, and $\mathrm{Cl}^{-}$across the plasma membrane in response to various stimuli.

Answer

Ion channels are ‘gated’, i.e., they may be open or closed. The $\mathrm{Na}^{+}, \mathrm{K}^{+}$, ATPase create a charge imbalance across the plasma membrane by carrying $3 \mathrm{Na}^{+}$out of the cell for every $2 \mathrm{~K}^{+}$ion carried inside making the inside negative relative to outside.

The membrane is said to be polarised. That is the reason the intracellular levels of $\mathrm{K}^{+}$are higher than extracellular levels in animals cells.

Answer

Cut pieces of beetroot do not leave colour in cold water but do so in hot water because pigment of beetroot dissolve and diffuse readily in hot water as hot temperature help in leaking of the plasma membrane and release of beetroot pigment.

Answer

In a girdled plant, when water is supplied to the leaves above the girdle, leaves may remain green for sometime because leaves can synthesise their own carbohydrate food through photosynthesis, then wilt due to non-availability of water.

The system of xylem vessels from root to the leaf vein can supply the needed water, during girdling there is a possible loss of xylem vessels and the water supply cuts off, resulting in death of plant.

Answer

Various types of ions, minerals and organic compound are transported in plants in various modes, e.g.

(i) Food substances synthesised in leaves are translocated downward towards root and stem.

(ii) Similarly food is translocated upwards to the developing leaves, buds and fruits.

(iii) Radial transport of food occurs across the stem from the cells of pith, from cortex etc, towards epidermis.

(iv) Ions and minerals are transported upwards through xylem.

Since, diffusion is a slow process and allows movement of molecules for short distances only, it cannot filled and alone carry out the above mentioned movements of organic and inorganic substances. Therefore, a need arises for special long distance transport systems that permits and move substances at a much faster rate, i.e., mass or bulk flow system through conducting tissues (translocation).

Answer

Under conditions of limited water supply, plants reduce the loss of water through transpiration by shutting down stomata. But they carry out the important life processes like photosynthesis, respiration and transport of food, etc.

Answer

No, the ascent of sap is not possible without the cohesive and adhesive properties of water as they play an important role in transport of water because of the following reasons

(i) Cohesion forces hold together the water molecule in the conducting channels, so vacuum is not created.

(ii) Adhesive forces between the water molecule and cellulose of cell wall make a thin film of water along the channels so, this film can be pulled up by transpiration pull drawing more and more water upwards in the conducting channels from the root.

Answer

Yes, it shows that xylem tissue conducts water.

Answer

(a) Plasmolysis is the name of the phenomenon, occurring is Spirogyra filament when placed in $10 %$ potassium nitrate solution (hypertonic solution). It occurs as water from the cell is drown out to extracellular fluid causing the protoplast to shrink away from cell wall.

(b) When the Spirogyra again reabsorb water, protoplast will again and will come back in its original shape. This phenomenon is known as deplasmolysis.

Answer

Pure water has tremendous free energy at normal room temperature. That is called water potential. When the water temperature drops down, the free energy is reduced so, sugar does not get dissolved easily in, i.e., cold water.

Answer

Salt solution being hypertonic, causes exo-osmosis in plants. 1 cup salt in 2 cup of water, fairly well dissolved when sprayed on weed plants, start killing them. This salt concentration is then increased in subsequent sprays, if the weeds are still thriving in the field.

Answer

Xylem sap consists of mainly water and some solutes or mineral nutrients.

Phloem sap mainly consists of the sucrose, a kind of transport sugar which is a diasaccharide, hormones and amino acids are also found in phloem sap of the plants.

Answer

The tube $B$ will show higher level than tube $A$ because of the capillary action.

Thinking Process

Peter Agre was awarded Nobel Prize in chemistry (2003) for discovering Aquaporins.

Answer

Aquaporins are integral membrane proteins. These form pores or channels in the membrane. The water can flow more rapidly through these pores to inside of the cell, as compared to the process of diffusion.

These are plumbing systems of the cells. These selectively conduct water in and out of the cells, while preventing the passage of ions and other solutes.

Answer

A. Stress hormone ABA (Abscisic Acid) gives signals to stomata to get closed, whenever there is scarcity of availability of water to the plant. This prevents the loss of water through transpiration by leaves. It also increases the tolerance of plants to various kinds of stresses.

B. It (ABA) is released or transported from stem apices to leaves.

Answer

Plants can get rid of excess water by increasing the transpiration rate but upto a certain limit. Prolong water logged conditions for roots may lead to the death of the plant (as they can not respire).

Answer

Difference between diffusion and translocation in plants is as follows

Answer

Difference between diffusion and facilitated diffusion is as follows

Answer

Mass flow hypothesis was first proposed by Ernst Munch (1930). It explains the transport of solute or sugars, i.e., sucrose in the phloem tissue.

It involves the following three steps

(a) Phloem loading

(b) Translocation of solutes

(c) Phloem unloading

Loading of sieve tubes takes place in leaves. Photosynthetic cells make sugars, particularly sucrose, and other organic solutes.

Companion cells use energy to collect solutes by active transport. As solute concentration increases in the companion cells, water enters by osmosis.

A pressure is created, which pushes the solutes through plasmodesmata into the sieve tubes. It is an active process.

Translocation of sucrose takes place through phloem column. Increase in hydrostatic pressure inside sieve tubes is greatest at the source and lowest at the sink It pushes sucrose etc., from source to sink.

Unloading of the sieve tubes takes place at the sink sites.

It results in active transport of sugars out of the pholem converting them into complex sugars. Loss of solutes from the phloem create a high water potential, and water moves out of phloem, returning back to xylem.

Sinks are the regions where solutes i.e., sugars or food are being used, e.g., roots, fruits, storage organs and regions of growth.

Answer

(a) The guard cells are bean-shaped which are found in dicot plants.

(b) The guards cells in figure (i) are turgid as, they pull the inner wall of the cell outside thus, they have more water. (ii) cells are flacid, this condition results when cells lose water and close stomatal pore.

(c) The $\mathrm{K}^{+}$ions when move from neighbouring cells to guards cells, lowering their water potential as a result the water moves inside making them turgid and thus opening stomata.

Answer

The biological membranes have many mechanism for movement of substances to and for. Some are active and some are passive. Specific membrane proteins are also involved for special types of transport mechanisms.

Uniport This is a membrane transport system by a integral membrane protein that is involved in facilitated diffusion. These channels get open in response to a stimulus for free flow of specific molecules in a specific direction. These transport molecule with solute gradient without energy expenditure.

Symport This involves the movement of two or more different molecules or ions, across the membrane in the same direction, with no energy expenditure.

Antiport also called exchanger. This integral membrane protein is involved in secondary active transport of two or more different molecules or ions across the membrane in opposite directions, without affecting the tansport of other molecules.

Answer

Yes, plants need to adjust the type and quantity of solutes that reach the xylem. The transport proteins of endodermal cell help in maintaining and adjusting solute movement. As the minerals are present in soil as charged particles with a very low concentration as compared of roots, they, all cannot be complately passively transported across cell membranes of root hairs.

Thus, minerals are transported both by active and passive processes, to the xylem. Upon reaching xylem, they are further transported, i.e., upwards to sinks through transpiration stream. At the sink regions mineral ions are unloaded through diffusion and active uptake by receptor cells.

Some of the mineral ions moving frequently through xylem are

(i) Nitrogen travels in plants as inorganic ions $NO_{2}$ and $NO_{3}$ but much of the nitrogen moves in the form of amino acids and related organic compounds.

(ii) Sulphur and Phosphorus small amount of these two nutrients are carried in organic forms.

(iii) Mineral ions are frequently remobilised particularly from older senescing parts. Older dying leaves export much of their mineral content to younger leaves. Similarly, before leaf fall in decidous plants, minerals are removed to other parts.

Elements most readily mobilised are phosphorus, sulphur, nitrogen and potassium. Some elements that are structural components like calcium are not remobilised.

Answer

Wilting refers to the loss of turgidity of leaves and other soft aerial parts of a plant causing droping, folding and rolling of non-woody plants. It occurs when rate of loss of water is higher than the rate of absorption.

Answer

(a) Animal bladder: Selectively Permeable (SL)

(b) Plasmalemma (plasma membrane of cells): Selectively Permeable (SL)

(c) Tonoplast : Selectively Permeable (SL)

(d) Parchment membrane : Semipermeable (SP)

(e) Egg membrane : Semipermeable (SP)

Thinking Process

Halophytes have been defined as salt tolerant plants having cellular, biochemical, physiological and anatomical mechanisms allowing them to survive in high salinity conditions.

Answer

The halophytes have salt secreting glands in their epidermal tissue. The help in removal of excess salts from their internal tissue to maintain their osmolarity and the atmospheric pressure on them.

Answer

If a radio labelled carbon $\mathrm{C}^{14}$ in is supplied to patato plants while it’s carrying out photosynthesis in the presence of light, the $\mathrm{C}^{14} O_{2}$ will be fixed and form radioactive products of photosynthesis, i.e., glucose $C_{6}^{14} H_{12} O_{6}$.

This radioacative glucose is converted to sucrose which would again be radioactive due to transfer of $\mathrm{C}^{14}$ from previous sugar molecule. These sucrose molecules then move into pholem and transported to other parts of plant.

Autoradiography technique detects the radioactive carbon (present in sugars) and traces the components and movement in the plant, i.e., through sieve tube channels of phloem from leaves (sources) to different parts (sink).

Answer

Attraction of water molecules to polar surfaces describes the adhesive properties of water. Besides, the cohesive properties include the attraction between water molecules. These two cohesive and adhesive properties contributes and help in the upward movement of water by providing.

The intermolecular hydrogen bonding in water ensures that more water molecules are attraction to each other in liquid state than in the gaseous state. This contributes to surface tension which in turn accounts for high capillarity in the xylem column.

Thinking Process

There is continuous loss of water from its body surface in the form of water. Maximum amount of water plants absorb gets lost to environment in this form. It is said transpiration. This is a necessary evil in the plants.

Answer

(a) Transpirational pull is demonstrated by this set up.

(b) Constant air blowing will increase the rate of transpiration so, level of water will go down.

(c) The mercury level will go down, if phenyl mercuric acetate is sprayed on leaves.