NCERT Solutions for Class 11 Science Biology Chapter 11 Transport In Plants are provided here with simple step-by-step explanations. These solutions for Transport In Plants are extremely popular among Class 11 Science students for Biology Transport In Plants Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 11 Science Biology Chapter 11 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 11 Science Biology are prepared by experts and are 100% accurate.
Page No 54:
Question 1:
Which of the following statements does not apply to reverse osmosis?
a. It is used for water purification.
b. In this technique, pressure greater than the osmotic pressure is applied to the system
c. It is a passive process
d. It is an active process
Answer:
Reverse osmosis is an active process because it requires energy for transporting water molecules against the concentration gradient. In this process, pressure greater than osmotic pressure is applied to the system to reverse the process. This technique is used for water purification.
Hence, the correct answer is option c.
Page No 54:
Question 2:
Which one of the following will not directly affect transpiration?
a. temperature
b. light
c. wind speed
d. chlorophyll content of leaves
Answer:
Transpiration is affected by several external factors like temperature, light, humidity, wind speed. Internal factors like number and distribution of stomata, percent of open stomata, water status of the plant and canopy structure also affect plant transpiration rate.
Hence, the correct answer is option d.
Page No 54:
Question 3:
The lower surface of leaf will have more number of stomata in a
a. dorsiventral leaf
b. isobilateral leaf
c. both a and b
d. none of the above
Answer:
In dorsiventral leaf, no stomata is present in the upper epidermis. The lower epidermis contains numerous stomata.
Hence, the correct answer is option a.
Page No 54:
Question 4:
The form of sugar transported through phloem is
a. glucose
b. fructose
c. sucrose
d. ribose
Answer:
Transport of food in phloem is bidirectional. Phloem sap mainly consists of water, sucrose, some other sugars, hormones, and amino acids.
Hence, the correct answer is option c.
Page No 54:
Question 5:
The process of guttation takes place
a. when the root pressure is high and the rate of transpiration is low.
b. when the root pressure is low and the rate of transpiration is high
c. when the root pressure equals the rate of transpiration
d. when the root pressure as well as rate of transpiration are high.
Answer:
In many herbaceous plants, root pressure is high at night or early in the morning as transpiration is low at this time. So, the excess water collects as droplets around the special openings of veins near the tip of grass blades and leaves. This is known as guttation.
Hence, the correct answer is option a.
Page No 55:
Question 6:
Which of the following is an example of imbibition
a. uptake of water by root hair
b. exchange of gases in stomata
c. swelling of seed when put in soil
d. opening of stomata
Answer:
Imbibition is a special type of diffusion when water is absorbed by solids-colloids-causing to increase in volume. The classical example of imbibition is the absorption of water by seeds and dry woods.
Hence, the correct answer is option c.
Page No 55:
Question 7:
When a plant undergoes senescence, the nutrients may be
a. accumulated
b. withdrawn
c. translocated
d. None of the above
Answer:
When a plant undergo senescence, nutrients are translocated from the part undergoing to senescence to non-senescened parts.
Hence, the correct answer is option c.
Page No 55:
Question 8:
Water potential of pure water at standard temperature is equal to
a. 10
b. 20
c. Zero
d. None of the above
Answer:
Water potential of pure water at standard temperature is equal to zero. Dissolving solutes in water reduces water potential.
Hence, the correct answer is option c.
Page No 55:
Question 9:
Mycorrhiza is a symbiotic association of fungus with root system which helps in
A. Absorption of water
B. Mineral nutrition
C. Translocation
D. Gaseous exchange
Options:
a. Only A
b. Only B
c. both A and B
d. both B and C
Answer:
The symbiotic association between plant roots and fungus is known as mycorrhiza. It helps in the absorption of water and mineral nutrients dissolved in it.
Hence, the correct answer is option c.
Page No 55:
Question 10:
Based on the figure given below which of the following statements is not correct?
a. Movement of solvent molecules will take place from chamber A to B.
b. Movement of solute will take place from A to B.
c. Presence of a semipermeable is a pre-requisite for this process to occur.
d. The direction and rate of osmosis depends on both the pressure gradient and concentration gradient.
Answer:
Osmosis is the diffusion of water across a selectively permeable membrane. Water moves from high concentration region to low concentration region until equilibrium is attained. No movement of solutes take place. The net direction and rate of osmosis depends on both the pressure gradient and concentration gradient.
Hence, the correct answer is option b.
Page No 56:
Question 11:
Match the followings and choose the correct option
| Column I | Column II | ||
| A. | Leaves | i. | Anti-transpirant |
| B. | Seed | ii. | Transpiration |
| C. | Roots | iii. | Negative osmotic potential |
| D. | Aspirin | iv. | Imbibition |
| E. | Plasmolyzed cell | v. | Absorbtion |
Options:
| a. | A-ii, | B-iv, | C-v, | D-i, | E-iii |
| b. | A-iii, | B-ii, | C-iv, | D-i, | E-v |
| c. | A-i, | B-ii, | C-iii, | D-iv, | E-v |
| d. | A-v, | B-iv, | C-iii, | D-ii, | E-i |
Answer:
| Column I | Column II | ||
| A. | Leaves | ii. | Transpiration |
| B. | Seed | iv. | Imbibition |
| C. | Roots | v. | Absorbtion |
| D. | Aspirin | i. | Anti-transpirant |
| E. | Plasmolyzed cell | iii. | Negative osmotic potential |
Hence, the correct answer is option a.
Page No 56:
Question 12:
Mark the mismatched pair.
| a. | Amyloplast : | store protein granule |
| b. | Elaioplast : | store oils or fats |
| c. | Chloroplasts : | contain chlorophyll pigments |
| d. | Chromoplasts : | contain coloured pigments other than chlorophyll |
| e. | Leucoplast : | contains colourless pigments |
Answer:
Leucoplast is of three types-amyloplasts, aleuroplasts, and elaioplast. Amyloplasts store carbohydrates. For example- potato whereas the aleuroplasts store proteins.
Hence, the correct answer is option a.
Page No 56:
Question 1:
Smaller, lipid soluble molecules diffuse faster through cell membrane, but the movement of hydrophilic substances are facilitated by certain transporters which are chemically ____________.
Answer:
Page No 56:
Question 2:
In a passive transport across a membrane, when two different molecules move in opposite direction and independent of each other, it is called as ___________.
Answer:
In a passive transport across a membrane, when two different molecules move in opposite direction and independent of each other, it is called as antiport.
Page No 56:
Question 3:
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:
Osmosis is a special kind of diffusion, in which water diffuses across the cell membrane. The rate and direction of osmosis depends upon both pressure gradient and concentration gradient.
Page No 57:
Question 4:
A flowering plant is planted in an earthen 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:
A flowering plant is planted in an earthen pot and irrigated. Urea is added to make the plant grow faster, but after some time the plant dies. This may be due to exosmosis in plants.
Page No 57:
Question 5:
Absorption of water from soil by dry seeds increases the _____________, thus helping seedlings to come out of soil
Answer:
Absorption of water from the soil by dry seeds increases the imbibition pressure, thus helping seedlings to come out of the soil.
Page No 57:
Question 6:
Water moves up against gravity and even for a tree of 20m height, the tip receives water within two hours. The most important physiological phenomenon which is responsible for the upward movement of water is _______________________.
Answer:
Water moves up against gravity and even for a tree of 20m height, the tip receives water within two hours. The most important physiological phenomenon which is responsible for the upward movement of water is transpiration pull.
Page No 57:
Question 7:
The plant cell cytoplasm is surrounded by both cell wall and cell membrane. The specificity of transport of substances are mostly across the cell membrane, because _________________.
Answer:
The plant cell cytoplasm is surrounded by both cell walls and cell membranes. The specificity of transport of substances is mostly across the cell membrane because the cell membrane is selectively permeable.
Page No 57:
Question 8:
The C4 plants are twice as efficient as C3 plants in terms of fixing CO2 but lose only _________ as much water as C3 plants for the same amount of CO2 fixed.
Answer:
The C4 plants are twice as efficient as C3 plants in terms of fixing CO2 but lose only half as much water as C3 plants for the same amount of CO2 fixed.
Page No 57:
Question 9:
In a plant, translocation in the xylem is unidirectional while in phloem it is bidirectional. Explain.
Answer:
Page No 57:
Question 10:
Identify the process occurring in I, II and III
Answer:
Page No 57:
Question 11:
Given below is a table. Fill in the gaps
| Property | Simple diffusion | Facilitated transport | Active Transport | |
| i | Highly selective | ________________ | Yes | ________________ |
| ii | Uphill transport | ________________ | ________________ | Yes |
| iii | Requires ATP | ________________ | ________________ | ________________ |
Answer:
| Property | Simple diffusion | Facilitated transport | Active Transport | |
| i | Highly selective | No | Yes | Yes |
| ii | Uphill transport | No | No | Yes |
| iii | Requires ATP | No | No | Yes |
Page No 58:
Question 12:
Define water potential and solute potential.
Answer:
Water potential (Ψw) is the kinetic energy of water. When a solute is dissolved the water potential reduces. The magnitude of this lowering due to dissolution of solute is called solute potential (Ψs). Solute potential is always negative.
Page No 58:
Question 13:
Why is solute potential always negative? Explain yw = ys + yp
Answer:
When a solute is dissolved in water, it lowers the kinetic energy of water or concentration of water decreases. Thus, water potential is reduced. As, water potential of pure water is considered zero, so solute potential is always negative.
Water potential (Ψw) of a cell is affected by two components: solute potential (Ψs) and pressure potential (Ψp). So, the relation is as follows:
Ψw = Ψs + Ψp
Page No 58:
Question 14:
Tradescantia leaf epidermal peel was taken and
a. Placed in salt solution for five minutes.
b. After that it was placed in distilled water.
When seen under the microscope what would be observed in a and b?
Answer:
a. If Tradescantia leaf epidermal peel is placed in a salt solution for five minutes the leaf cells will lose water and shrink as they are placed in hypertonic solution. Under the microscope, we will see that the cells are plasmolyzed.
b. After that when it is placed in distilled water (hypotonic solution) the cells will gain water and again become turgid.
Page No 58:
Question 15:
Differentiate between Apoplast and Symplast pathways of water movement. Which of these would need active transport?
Answer:
| Apoplast | Symplast |
| 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 root). | 1. The symplast is the system of inter connected protoplasts. |
| 2. Water movement is comparatively faster. | 2. Water movement is comparatively slower. |
None of these pathways need active transport.
Page No 58:
Question 16:
How does water moves within the root?
Answer:
Water enters into the roots from the soil through osmosis. As soil has comparatively high water potential than cytoplasm, water enters into the plant. Once water is absorbed by the root hairs, it can move deeper into root layers either by symplastic or apoplastic pathway.
Page No 58:
Question 17:
Give the location of casparian strip and explain its role in the water movement.
Answer:
Page No 58:
Question 18:
Differentiate between guttation and transpiration.
Answer:
| Guttation | Transpiration |
| 1. In this case, water is lost from leaf margin in the form of water droplets. | 1. In this case, water is lost as vapour from the aerial parts of the plant. |
| 2. It occurs through special structures called hydrathodes. | 2. It mostly occurs through stomata. |
Page No 58:
Question 19:
Transpiration is a necessary evil in plants. Explain.
Answer:
Transpiration is the process where water is lost as vapour from the aerial parts of the plant. This cools the plant and creates a transpiration pull that helps to absorb more water and minerals from the soil. So, it is necessary for the plant. However, if excessive water is lost through transpiration it will cause witting of the plant and the plant may die. Thus, transpiration is considered as a necessary evil for plants.
Page No 58:
Question 20:
Describe briefly the three physical properties of water which helps in ascent of water in xylem.
Answer:
The three physical properties of water that helps in ascent of water in xylem are –
1. Cohesion - It is the mutual attraction between water molecules.
2. Adhesion - It is the attraction of water molecules to polar surfaces.
3. Surface tension - Here the water molecules are attracted to each other in the liquid phase more than to water in the gas phase.
Page No 58:
Question 21:
A gardener forgot to water a potted plant for a day during summer, what will happen to the plant? Do you think it is reversible? If yes, how?
Answer:
During summer days rate of transpiration is high due to higher temperature. If the gardener forgets to water the plant for a day, it will increase its transpiration rate and the plant will wilt.
As, the condition was for shorter duration of time (one day) it is reversible. If the gardener adds water to the plant. The plant cells will gain water and again becomes turgid.
Page No 58:
Question 22:
Identify a type of molecular movement which is highly selective and requires special membrane proteins, but does not require energy.
Answer:
In facilitated diffusion movement of molecules is highly selective and requires special membrane proteins. As the movement of molecules occur across the concentration gradient, this process does not require energy.
Page No 58:
Question 23:
Correct the statements:
a. Cells shrink in hypotonic solutions and swell in hypertonic solutions.
b. Imbibition is a special type of diffusion when water is absorbed by living cells.
c. Most of the water flow in the roots occurs via the symplast.
Answer:
a. Cells swell in hypotonic solutions and shrink in hypertonic solutions.
b. Imbibition is a special type of diffusion when water is absorbed by dead or living cells.
c. Most of the water flow in roots occurs via the apoplast.
Page No 58:
Question 1:
Minerals absorbed by the roots travel up the xylem. How do they reach the parts where they are needed most? Do all the parts of the plant get the same amount of the minerals?
Answer:
Minerals are required in the growing regions of plants such as apical and lateral meristems, young leaves, flowers, fruits, seeds, and storage organs. These parts of the plant are supplied with more amount of minerals.
Based on their requirement, minerals are also mobilized from older parts of the plant to younger parts.
Thus, plants ensure optimum utilization of minerals.
Page No 58:
Question 2:
If one wants to find minerals and in the form they are mobilised in the plant, how will an analysis of the exudate help?
Answer:
Page No 59:
Question 3:
From your knowledge of physiology can you think of some method of increasing the life of cut plants in a vase?
Answer:
If a plant is cut and place in a vase, its life can be increased by immediately placing them in water. this will ensure that the air does not move faster into the conducting tissue and plug the cell.
- Mineral nutrients can be added to the water that can increase their life span.
- Plant hormone, cytokinin can be sprayed on the plant, that will delay the senescence/ death of the plant.
Page No 59:
Question 4:
Do different species of plants growing in the same area show the same rate of transpiration at a particular time? Justify your answer.
Answer:
Rate of transpiration depends on the following plant factors:
- Number and distribution of stomata
- Percentage of open stomata
- Water status of the plant
- Canopy structure
However, if the morphology of the two species is similar then the external factors such as velocity, humidity, temperature, light intensity etc will determine the rate of transpiration.
Page No 59:
Question 5:
Water is indispensable for life. What properties of water make it useful for all biological processes on the earth?
Answer:
Properties of water that make it useful for all biological processes are stated as follows:-
- Water is a major solvent as it is a polar molecule. This ensures that the important substances or solutes are dissolved in water and transported from one place to another.
- It is the major constituent of protoplasm that constitutes approximately 90% of the protoplasm.
- Water acts as a medium to transport various substances upwards to the shoot system in plants due to its solvent properties, strong cohesive and adhesive forces.
- Water is involved in photosynthesis, pollination in flowering plants, external fertilization, and many other biological processes.
- Water acts as an agent to control temperature. The specific heat of the water helps in attaining the cooling effect and maintains a stable internal temperature of an organism.
Page No 59:
Question 6:
How is the intracellular levels of ions maintained higher than extracellular levels in animal cells?
Answer:
Movement of ions across the membrane is regulated by ion channels. These ion channels are "gated" mans they may be open or closed. When the cell mimbrane is in resting potential, the sodium-potassium (Na+/K+) pump creates a charge gradient across the plasma membrane by carring 3Na+ out of the cell for every 2K+ ion going inside the cell. Hence, the membrane is polarised as the outer surface of the membrabne possess a positive charge and its inner surface becomes negatively charged.
This makes intracellular levels of K+ higher than the extracellular levels.
Page No 59:
Question 7:
Cut pieces of beetroot do not leave colour in cold water but do so in hot water. Explain.
Answer:
The cut pieces of beetroot do not leave the colour in cold water but do so in hot water because high temperature ruptures the cell membrane that releases the beetroot pigment in water, giving it a reddish colour.
Page No 59:
Question 8:
In a girdled plant, when water is supplied to the leaves above the girdle, leaves may remain green for sometime then wilt and ultimately die. What does it indicate?
Answer:
Girdling is an experiment in which ring of a bark on a tree is removed upto the depth of the phloem layer. During girdling, system of xylem vessels from root to the leaf can supply water. But, a possible loss of xylem vessels can occur during girdling that cuts off water supply. Thus, in a girdled plant when water is supplied to the leaves above the girdle, leaves may remain green for sometime as leaves can synthesize the food through photo synthesis, then after sometimes it will due to non-availability of water, resulting in a death of the plant.
Page No 59:
Question 9:
Various types of transport mechanisms are needed to fulfil the mineral requirements of a plant. Why are they not fulfilled by diffusion alone?
Answer:
Page No 59:
Question 10:
How can plants be grown under limited water supply without compromising on metabolic activities?
Answer:
During limited water supply, plants have the ability to reduce the rate of transpiration by closing their stomata.
They use anti-transpirants such as abscisic acid as well that checks the rate of transpiration. Therefore, plants can manage to carry out their important physiological processes in limited water supply.
Page No 59:
Question 11:
Will the ascent of sap be possible without the cohesion and adhesion of the water molecules? Explain.
Answer:
Cohesive and adhesive properties of water are responsible for the ascent of sap or the transport of water. Without cohesion and adhesion, ascent of sap is not possible. Cohesion forces hold together the water molecules, so that the vaccum is not created in xylem vessels. Adhesion between the water molecule and the cell wall make a thin film of water along the xylem vessels so that it can be pulled by transpiration pull.
Page No 59:
Question 12:
Keep some freshly cut flowers in a solution of food colour. Wait for sometime for the dye to rise in the flower, when the stem of the flower is
held up in light, coloured strands can be seen inside. Can this experiment demonstrate which tissue is conducting water up the stem?
Answer:
Coloured strands show that there is a continuous channel of water throughout the stem. This is the xylem vessel that conducts water upwards.
Page No 59:
Question 13:
When a freshly collected Spirogyra filament is kept in a 10% potassium nitrate solution, it is observed that the protoplasm shrinks in size:
a. What is this phenomenon called?
b. What will happen if the filament is replaced in distilled water?
Answer:
(b) When spirogyra is replaced in distilled water, it reabsorbs water. The protoplast will gain its original shape. This process is called deplasmolysis.
Page No 59:
Question 14:
Sugar crystals do not dissolve easily in ice cold water. Explain.
Answer:
At normal room temperature, pure water has tremendous free energy. This free energy is reduced at low temperature making the dissolution of sugar crystals difficult in cold water.
Page No 59:
Question 15:
Salt is applied to tennis lawns to kill weeds. How does salting tennis lawns help in killing of weeds without affecting the grass?
Answer:
1 cup salt in 2 cup of water makes a salt solution that is hypertonic solution. When salt solution is sprayed on weeds, it starts killing them. Care has to be taken while spraying salt solution as it will harm useful grass also. It should be sprayed specifically on weeds.
Page No 59:
Question 16:
What is the chemical composition of xylem and phloem sap?
Answer:
Xylem sap consists of water, mineral nutrients and some solution.
Phloem sap consists of the sucrose (disaccharide suger) harmones, amino acids etc.
Page No 59:
Question 17:
Observe the figure and answer the question provided below the figure.
Why does tube B show higher water rise than A?
Answer:
Tube B will show higher water rise than tube A because of capillary action. Due to less surface area of tube B, there will be more surface tension thus tube B shows higher rise in water level. Capillary action occurs when the adhesion to the surface material is stronger than the cohesive forces between the water molecules.
Page No 60:
Question 18:
What are ‘aquaporins’? How does presence of aquaporins affect osmosis?
Answer:
Page No 60:
Question 19:
ABA (Abscisic acid) is called a stress hormone.
a. How does this hormone overcome stress conditions?
b. From where does this hormone get released in leaves?
Answer:
a. Stress hormone abscisic acid works under stress conditions in plants. When water is scarce in the environment, it signals the stomata to get closed. This prevents transpiration thereby reducing water loss. It also increases the tolerance of plants to various types of stress.
b. This hormone is released from the chloroplast of the leaves.
Page No 60:
Question 20:
We know that plants are harmed by excess water. But plants survive under flooded condition. How are they able to manage excess water?
Answer:
During excess water conditions, plants reduce their rate of transpiration by closing stomata. But this condition is temporary, prolonged flooding can cause anaerobic conditions in roots as air is trapped in the soil which will eventually lead to death of the plant.
Page No 60:
Question 21:
Differentiate between diffusion and translocation in plants.
Answer:
| Diffusion | Translocation |
| 1) Diffusion is the movement of solute from region of higher concentration to the region of lower concentration. | 1) Translocation is the movement of organic compounds from one part of the plant to another. |
| 2) No energy is required. | 2) It requires energy |
| 3) It is a passive process. | 3) It is an active process. |
Page No 60:
Question 22:
How is facilitated diffusion different from diffusion?
Answer:
| Diffusion | Facilitated Diffusion |
| 1) Diffusion is movement of molecules from region of higher concentration to region of low concentration. | 1) Diffusion of molecules occur against a concentration gradient by the help of proteins without using energy from ATP. |
| 2) Its a slow process and no enerty is required. | 2) Its a fast process and no energy is required. It takes place with the help of porin proteins. |
Page No 60:
Question 23:
Explain the mass flow hypothesis of transport in phloem.
Answer:
Ernst Munch was the first scientist who gave the pressure flow hypothesis also known as mass flow hypothesis in 1930. It explains the transport of solute or sugars i.e. sucrose in the phloem tissue.
It involves 3 steps:
1) Pholen Loading
2) Translocation of solutes
3) Phloem unloading
Page No 60:
Question 24:
Observe the diagram and answer the following;
a. Are these types of guard cells found in monocots or dicots?
b. Which of these shows a higher water content (i) or (ii)?
c. Which element plays an important role in the opening and closing of stomata?
Answer:
(a) These guard cells are found in dicot plants which are bean shaped structures.
(b) The guard cells in figure (i) have more water content as they are turgid. Guard cells in figure (ii) are flaccid, when they lose water and close stomatal pare.
(c) Potassium (K+) ions play an important role in opening and closing of stomata. K+ ions move inside the guard cells and thus lower their water potential. This result in movement of water inside the guard cell which make them turgid and opens stomata.
Page No 61:
Question 25:
Define Uniport, Symport and Antiport. Do they require energy?
Answer:
The biologival membranes have mechainms for the movement of substances actoss the membranes.
They have special type of membrane transport system such as
1) Uniport - It is a membrane transport system that requires an integral membrane protein and is involved in facilitated diffusion. In responc to stimulus, the channer gets open for flow of specific molecules in a one way or specific direction. They do not require any kind of energy.
2) Symport - It involves the movement of two or more different molecules or ions, across the membrane in the same direction. It does not require energy for transportation.
3) Antiport - It is involved in secondary active transport of two or more molecules across the membrane. The movement is facilitated in opposite direction and does not affect the transport of other molecules.
Page No 61:
Question 1:
Minerals are present in the soil in sufficient amounts. Do plants need to adjust the types of solutes that reach the xylem? Which molecules help to adjust this? How do plants regulate the type and quantity of solutes that reach xylem?
Answer:
Plants require to adjust the type and quantity of solutes which reach the xylem. The transport proteins of endodermal cell help in maintaining & adjusting solute movement. As minerals are present in very low concentration, they are remobilised from older parts of the plant to the youngs developing parts. Before leaves starts to fall, minerals are moved to other parts. Minerals that are readily mobilised are phosphorus, sulphur, nitrogen, potasium. Calcium is present in stem cell wall which provide structural integrity do not mobilise in plants.
Page No 61:
Question 2:
Plants show temporary and permanent wilting. Differentiate between the two. Do any of them indicate the water status of the soil?
Answer:
| Temporary wilting | Permanent wilting |
| 1) It is temporary dropping of young leaves and shoots as the turgidity of cells is lost. | 1) It is the permanent loss of turgidity in the cells of the leaves and other parts of plant. |
| 2) It occurs due to increased rate of transpiration in decreased rate of water supply. | 2) It occurs in increased rate of transpiration and rate of absorption is below critical level. |
| 3) Plants regain their normal activity when water supply is resumed. | 3) Plants eventually dies even if water supply is resumed. |
Page No 61:
Question 3:
Why are natural membranes selectively permeable. Give examples.
Answer:
Natural membranes or cell membranes are selectively permeable because they allow entry or exit of certain specific molecules only. Other wise, many essential molecules could leave the cell or many harmful molecules can enter the cell. Thus, damaging the cell.
For example, only small non-polar molecules can pass through the cell membrane. Polar molecules need the help of carrier proteins to transport along the membrane some molecules also transport through the membrane again against the concentration gradient. In that care, energy (ATP) is applied (active transport).
Page No 61:
Question 4:
Halophytes may show cell pressure very much higher than atmospheric pressure. Explain how this can happen?
Answer:
Plants that can grow and survive in saline water are called halophytes. Saline water contains higher concentration of salt and all solutions have a lower water potential than pure water. So, the water potential is less in the soil as compared to that in the plant cells. In such a siluation the plant faces water stress due to low water availability. However, halophytes show certain adaptations to over come this stress. They store excess salts in their vacuoles. This grater a much high internal osmotic cell pressure than atmospheric pressure.
Page No 61:
Question 5:
The radio labelled carbon in carbon dioxide supplied to potato plants in an experiment was seen in the tuber eventually. Trace the movement of the labelled carbon dioxide.
Answer:
Plants absorb carbon dioxide during photosynthesis to make the food. If radio labelled carbon in carbon dioxide is supplied to the plant, we can track the movement of carbon moleculs through different plant parts. Photosynthesis takes place in the leaves. So, first it is traced in the leaf parenchyma. After the completion of photosynthesis, the radio active carbon can be detected in the carbohydrate formed. Sooner, the carbohydrate is converted into starch where we can detect the presence of the radio active carbon. After conversion into starch, it moves to the sink where it is get stored. In case of potato the tubers act as sink. But before reaching to the tuber it is transported through the phloem. So, radioactive carbon can also be detected in the phloem also. So, the overall movement of the radioactive carbon is as follows:
leaves → phloem → tuber.
Page No 61:
Question 6:
Water molecule is very polar. Polar end of molecule attracts opposite charges on another water molecule (acts like magnet). How will you explain this property of water with reference to upward movement of water? Comment on the upward movement of water given the intermolecular hydrogen bonding in water.
Answer:
Water molecules are polar in nature. When two water molecules come close to each other the slightly negatively charged oxygen atom of one water molecules forms a hydrogen bond with the slightly positive hydrogen atom of another water molecule. This attractive force along with the inter molecular forces are mainly responsible for creating surface tension in liquid water. This helps the plants to draw water from the root through the xylem to the leaf. Cohesive force between water molecules helps to create a continuous water column in the xylem. Transpiration pull helps to pull up the water through xylem. Adhesion and surface tension of water molecules also help in that process.
Thus, multiple forces act cumulatively during ascent of sap in plants.
Page No 62:
Question 7:
Comment on the experimental setup
a. What does the setup demonstrate?
b. What will happen to the level of water if a blower is placed close to setup.
c. Will the mercury level fluctuate (go up/down) if phenyl mercuric acetate is sprayed on leaves?
Answer:
a. This setup demonstrate transpirational pull.
b. If a blower's placed close to setup it will increase the transpiration rate. As high wind velocity increases the rate of transpiration. As a result, the water level will go down.
e. Phenyl mercuric acetate acts as a metabolic inhibitor and reduces the stomatal opening. This reduces the rate of transpiration. So, loss of water through the plant leaves will close or stop and the mercury level remains stable.
View NCERT Solutions for all chapters of Class 11