RBSE Class 12 Biology Chapter 6- Water Absorption and Ascent of Sap in Plants provides complete information related to the plant system involved in water absorption, passive and active water absorption, mechanisms and factors affecting water absorption. It also includes a detailed explanation of root pressure theory, physical force theory, vital force theory, the pathways of water in the plant, ascent sap and its mechanism.
These important questions help students to ace their exams. By practising these important questions, students can analyze their preparation, get a thorough knowledge about all the important terminologies and perform best in their examinations.
The Rajasthan Board Class 12 Solutions are the best study material for both class assignments and other board examinations. By practising these important questions, students can gain deep knowledge about the topics explained in this chapter and also help students to be well prepared for their upcoming examinations.
RBSE Class 12 Biology Chapter 6 Important Questions
RBSE Biology Chapter 6: MCQs Type Questions
Q.1. Which tissue is responsible for the upward movement of water during the ascent of sap in plants?
(a)Cortex.
(b)Vessels.
(c)Tracheids.
(d)Vessels and Tracheids.
Sol: (d)Vessels and Tracheids.
Q.2. Water is absorbed through roots by ______.
(a)Osmosis.
(b)Diffusion.
(c)Apoplast.
(d)Symplast.
Sol: (b)Diffusion.
Q.3.Which of the following parts of roots absorbs water?
(a)Root apex.
(b)Root hair region.
(c)Maturation region.
(d)Region of elongation.
Sol: (b)Root hair region.
Q.4. Who presented the Cohesion tension of water and transpiration pull?
(a)Godlewski.
(b)J.C.Bose.
(c)Strasburger.
(d)Dixon and Jolly.
Sol: (d)Dixon and Jolly.
Q.5. Accessible water to the plants from the soil is______.
(a)Flowing water.
(b)Capillary water.
(c)Hygroscopic water.
(d)Gravitational water.
Sol: (b)Capillary water.
Q.6.The flow of water from the root hairs to the xylem of the root is called ______.
(a)Symplast.
(b)Apoplast.
(c)Vacuolar.
(d)Lateral flow.
Sol: (d)Lateral flow.
Q.7. In which of the following processes the metabolic energy is not consumed?
(a) Active water absorption.
(b) Passive water absorption.
(c) Water absorption.
(d) Root absorption.
Sol: (a) Active water absorption.
Q.8.Which is the most resistant way for water absorbed in plants to reach the xylem?
(a)Apoplast.
(b)Symplast.
(c)Vacuolar pathway.
(d)Membrane pathway.
Sol: (b)Symplast.
Q.9.Which of the following are not the factors that affect the rate of water absorption?
(a) Soil aeration.
(b) Soil temperature.
(c) Capillary force.
(d) The concentration of soil solution.
Sol: (c) Capillary force.
Q.10. Which of the following processes is independent of transpiration?
(a)Passive water absorption.
(b)Apoplastic pathway.
(c)Root absorption.
(d)Active water absorption.
Sol: (d)Active water absorption.
Q.11. Who presented the theory of active absorption of water in plants?
(a)Godlewski.
(b)Kramer
(c)Strasburger.
(d)Dixon and Jolly.
Sol: (b)Kramer
Q.12. The rate of absorption of water is almost equal to the rate of __________.
(a) Transpiration.
(b) Osmosis.
(c) Ionic exchange.
(d) Diffusion.
Sol: (a) Transpiration.
Q.13. Which of the following plant factors affect the rate of water absorption?
(a)Root System.
(b)Transpiration.
(c)Metabolic Activities of Root Cells
(d)All of the above.
Sol: (d)All of the above.
Q.14.Ascent of sap occurs due to __________.
(a)Cortex.
(b)Vessels.
(c)Tracheids.
(d)Vessels and Tracheids.
Sol: (d)Vessels and Tracheids.
Q.15. Passive absorption of mineral salts is not dependent on __________.
(a)Osmosis.
(b)Diffusion.
(c)Ionic exchange.
(d)None of the above.
Sol: (d)None of the above.
Q.16. The optimum temperature at which maximum absorption can take place ranges between __________.
(a) 20° to 30°C.
(b) 10° to 20°C.
(c) 30° to 40°C.
(d) 15° to 20°C.
Sol: (a) 20° to 30°C
Q.17.Which of the following is a rapid type of absorption of water?
(a) Active absorption.
(b) Passive absorption.
(c) Salt absorption.
(d) Root absorption.
Sol: (b)Passive absorption.
Q.18. Which of the following processes occurs in the absence of roots?
(a)Passive water absorption.
(b)Apoplastic pathway.
(c)Root absorption.
(d)Active water absorption.
Sol: (a)Passive water absorption.
Q.19. The rate of the pathway of water in plants
(a) Apoplastic pathway is faster than the symplastic pathway.
(b) Symplastic pathway is faster than the apoplastic pathway
(c) Both the apoplastic and symplastic pathways are equal.
(d) None of the above.
Sol: (a) Apoplastic pathway is faster than the symplastic pathway
Q.20. Which of the following statements is true?
(a) The higher rate of transpiration the rate of water absorption decreases.
(b)The higher rate of transpiration the rate of water absorption becomes zero.
(c)The higher rate of transpiration the rate of water absorption increases.
(d)The rate of transpiration and the rate of water absorption will also be the same.
Sol: (c)The higher rate of transpiration the rate of water absorption increases.
RBSE Biology Chapter 6:Short Answer Type Questions.
Q.1. Define the process of water absorption.
Sol. Water absorption in plants can be defined as the total amount of required force for the passive absorption generated by the transpiration from the aerial parts of the plants. This is completely a physical process, in which the plant’s metabolic energy is not consumed.
Q.2.What is the Ascent of sap?
Sol: The upward movement of water along with dissolved minerals from a region of positive pressure- root to a region of negative pressure-shoot regions, against the gravitational force is called the ascent of sap. This mechanism of movement of water is caused by multiple forces like transpiration pull and root pressure.
Q.3. Define the pathway of water in plants.
Sol: In general, there are no special organs for water absorption in lower plants. All cells of the plant’s body absorb water and other required minerals. According to Kramer’s observation, there are two types of water absorption in plants: Active absorption of water and Passive absorption of water.
Q.4. What is the Symplast Pathway?
Sol: The pathways of ion and water created by symplast are known as the symplastic pathway. In this pathway, the water is transmitted from one cell to another cell through plasmodesmata. This pathway offers resistance to the flow of water since the selective plasma membrane of the root cells handles the intake of ion and water.
Q.5. Which part of the root performs the process of absorption of water.
Sol: The young parts of the root are involved in the process of absorption of water. These parts include:
- Root cap.
- Root apex.
- Regions of elongation
- Regions of maturation.
Q.6.Define lateral flow.
Sol: The flow of water from the root hairs to the xylem of the root is called the lateral flow. The three different pathways of the lateral flow of water are
- Symplast Pathway.
- Apoplast Pathway.
- VacuolarPathway.
Q.7.What are the factors that affect water absorption?
Sol: There are many factors, which affects the rate of water absorption. Among the active and passive absorption of water, passive absorption of water is mainly affected by the following factors:
- Soil aeration.
- Soil temperature.
- Available soil water.
- The concentration of soil solution.
Q.8.Define Root hair?
Sol: Root hairs are the large number of elongated, microscopic cells developed from the outermost layer of the cells in roots. They are the central part from which small and lateral roots develop.
Q.9. What are the different pathways of the lateral flow of water?
Sol: The three different pathways of the lateral flow of water are
- Symplast Pathway.
- Apoplast Pathway.
- VacuolarPathway.
Q.10. What is capillary water?
Sol: The water that remains within the soil as a continuous film around the soil particles and its interspaces, which are held by the capillary force is called capillary water.
Q.11.Who first proposed transpiration pull and cohesion of water theory?
Sol: The transpiration pull and cohesion of water theory were first proposed by Dixon and Joly in the year 1894. These were also supported by Clark and Curtis
Q.12.What is active absorption of water?
Sol: The absorption of water against the concentration gradient by the utilization of metabolic energy is called the active absorption of water. During the active absorption of water, the minerals, ions from the outer space of the cell move into the inner space and it generally occurs against the concentration gradient.
Q.13.What is Apoplast Pathway?
Sol: In the apoplast pathway, water is transported from root hair to xylem through the nonliving cell wall of intercellular spaces present in the cells. In this pathway, the flow of water is uncontrolled and is caused through the diffusion.
Q.14.How is water transported in plants?
Sol: Water is transported in the plants with the help of conductive tissues and individual cells of the vascular system. Water moves along the water potential gradient and enters the root hairs and xylem through either apoplast or symplast pathways. This is how the water is carried from the roots to the stem and other parts of the plant.
Q.15.What is soil temperature?
Sol: Soil temperature is simply defined as the measurement of the warmth in the soil. An ideal temperature of a soil required for planting plants should be in between 18° to 24° C. The measurement of the soil temperature where maximum water is absorbed lies in between 20° to 30° C.
Q.16. What is a root cap?
Sol: The apical part of the root is covered by a structure called the root cap which protects the apex of the root. It is a type of tissue present at the tip of a plant root. This terminal part of the root provides a protective layer to the root growing tip.
Q.17.What is transpiration pull?
Sol: The suction force used to draw the water in an upward direction from the roots to the leaves. The amount of water received by the leaves is used for photosynthesis and the excess amount of water is released into the atmosphere in the form of vapours through the openings in the leaves known as stomata. This pulling force is called a transpiration pull.
Q.18.What is passive absorption of water?
Sol: The absorption of water without the utilization of metabolic energy is called passive absorption of water. Passive absorption of water occurs due to osmosis.
Q.19.What is an apoplast?
Sol: Apoplast is the system of adjacent, continuous cell walls. It refers to the space outside the plasma membrane within which the molecules can freely diffuse. It is mainly involved in the transportation of ion and water through the apoplastic pathway in the cortex.
Q.20. List out the functions of Root cap?
Sol: Root cap is the terminal part of the root, which are involved in the following functions:
- It protects the apex of the root.
- It provides a protective layer to the root growing tip.
- It also helps in the uptake of water and other nutrients.
- It secretes mucilage, which acts as a lubricant for the root to make its way through the soil.
RBSE Biology Class 12: Long Answer Type Questions
Q.1.Write the differences between active and passive water absorption?
Sol: Difference between Active water absorption and Passive water absorption are:
| Active Water Absorption | Passive Water Absorption |
| Utilizes metabolic energy. | Utilizes solar energy. |
| Occurs in the presence of roots. | Occurs in the absence of roots. |
| Water is absorbed by roots. | Water is absorbed through roots. |
| Involves symplast movement of water. | Involves apoplast movement of water. |
| Active absorption is independent of transpiration. | Passive absorption is dependent on transpiration. |
| Takes place during the high water level in the soil. | Takes place during the low water level in the soil. |
| The rate of absorption of water is comparatively slow. | The rate of absorption of water is comparatively fast. |
| Water is absorbed by osmosis and non-Osmosis methods. | Water is absorbed as a result of tension created by the transpiration pull. |
Q.2. What is transpiration pull theory for the ascent of sap.
Sol: Cohesion and Transpiration Pull Theory was first proposed by Dixon and Joly in the year 1894. This theory was proposed based on the following features:
(i) Cohesion and Adhesion:
Cohesion is the mutual attraction between water molecules. The walls of tracheids and vessels of xylem are made-up of lignin and cellulose and have a strong affinity for water (adhesion).
(ii) Tension: Transpiration pull develops a negative pressure or tension in xylem sap which is transmitted down to the root.
Q.3. Explain how the soil aeration and soil temperature affects the rate of water absorption.
Sol: There are many other factors, which are involved in the rate of water absorption.
Soil Aeration
In soil aeration, the absorption of water takes place rapidly in well aerated soil such as loamy soil. In waterlogged soil, the rate of absorption of water becomes slow and in some cases zero.
Soil temperature
The rate of absorption of water will be high when the temperature of the soil reaches the range of 20° to 30°C. Low soil temperature decreases the rate of absorption of water and at the freezing temperature the rate of absorption of water will decrease to zero.
Q.4. Describe an experiment to demonstrate root pressure theory in plants.
Sol:
Root pressure theory was put forward by Joseph Priestley in 1916. According to this theory, root pressure is a positive pressure that develops in the xylem sap of the root of some plants.
Root pressure can be demonstrated and measured with the help of a manometer.
The value of root pressure in plants is upto 2.0atm and the water rises upto 20.0meter height by 2.00atm. The theory was put forward by Priestley (1916).
Here is a simple experiment root pressure.
Set up the apparatus as shown in the above diagram.
- Take a potted plant of balsam or tomato that has been well watered.
- Cut off its stem measuring 5-8 cm above the soil level.
- Fix a narrow glass tubing containing some coloured water to the cut end of the stump with the help of rubber tubing.
- Support the glass tubing by means of a stand covering the open end of glass tubing with a small petri dish in order to prevent evaporation of water.
- A drop of non-drying oil can be poured over the surface of coloured water.
- Mark the level of coloured water as A.
- Instead of glass tubing, a pressure measuring instrument called a manometer can also be fixed to the cut end of the stump by means of rubber tubing .
- Place the apparatus in a moist, cool and shady place for a couple of hours.
- The level of coloured water in the glass tube will rise to the new mark, say B.
- In case the manometer is attached, the mercury level is found to be pushed upwards. The pressure is read on the graduated scale.
The rise in the level of coloured water in the glass tubing is due to pumping of sap by root The phenomenon is called root pressure. The same is read directly by the manometer.
Q.5. Write an account of the mechanism of absorption of water by plants.
Sol: The mechanism of water absorption was first proposed by Kramer in the year 1959. In this theory, he explained how water enters the root hair. The absorption of water in plants occurs in two independent processes.
Active absorption
Absorption of water is caused by the forces present in the root called active absorption of water. In this method, around 2 to 4 percent of the total amount of water is absorbed by plants. This type of absorption takes place mainly during the humid nights when the rate of transpiration is very low.
Passive absorption
This is the main method of absorption of water in plants. In this method, around 96-98 percent of water is absorbed by plants. During passive absorption , the factors of absorption operate in the transpiring surface of the plant. The loss of water from the leaves results in the shortage of water, which results in a tension in the water column present in the xylem vessels of the leaf. This pull is transmitted to the water column of the stem and finally to the roots. This tension is negative and is called the suction force of transpiration pull.
Q.6. Describe the active absorption of water.
Sol: Active absorption of water takes place where the availability of the soil water is high and the rate of transpiration is very low.
In this process:
- The metabolic energy of the cells are used.
- Roots are active in this method of absorption.
- 2-4 percent of the total water is absorbed by this method of absorption.
- Active absorption of water plays an important role during the night times, where the rate of transpiration becomes very low.
Q.7. Explain in brief the three different pathways of water conduction plants.
Sol: The three major pathways of water movement are:
Apoplast Pathway.
In this pathway, water moves from root hair to xylem through the intervening cell walls without crossing any cell membranes. The Apoplast pathway provides the least resistance to movement of water and is interrupted by the presence of impermeable ligno suberin casparian strips in the walls of endodermal cells.
Symplast Pathway.
In this pathway, water moves from cell to cell through their protoplasm and does not enter cell vacuoles. The cytoplasm of the adjacent cells are connected through the bridges called plasmodesmata. For entering into the symplast, water has to pass through the cell membrane at least at one place. It is also called the trans-membrane pathway.
Vacuolar Pathway.
In this pathway, individual root cells function as tiny osmotic systems and absorb water from soil through the process of osmosis. The movement of water molecules in the vacuolar pathway begins from the cell wall and finally reaches the central vacuole passing via the plasma-lemma, cytoplasm, and tonoplast. From the root hair- eel, water passes into vacuoles through osmosis. The process is continued till the total amount of water enters the xylem parenchyma cells.
Q.8. Give the differences between Apoplast and Symplast.
Sol: Differences between Apoplast and Symplast are:
| Apoplast | Symplast |
| Consist of intercellular spaces and cell walls. | Consist of protoplasm. |
| Consist of non-living parts. | Consist of living parts. |
| There is no effect on water movement. | Metabolic states interfere with the flow of water in this pathway. |
| More ion and water are transported through the apoplastic pathway in the cortex. | Water and ions are mainly delivered through the symplastic pathway beyond the cortex. |
| Apoplastic pathway is fast. | Symplastic pathway is slower than the apoplastic pathway. |
Q.9. What is the pathway of water in plants? Draw a neat labelled diagram of lateral movement in plants.
Sol: After the entry of water into the plants from the root hairs, it move to the xylem vessels within the roots, mainly by three pathways:
- Apoplast pathway
- Symplast pathway
- Vacuolar Pathway.
The flow of water from the root hairs to the xylem vessels is called the lateral flow.
Q.10. Explain in detail about the water absorbing organs in plants?
Sol: There are no special organs in plants for water absorption. In lower plants, like mosses, liverworts and other nonvascular plants, the osmosis process is involved in the absorption of water from roots to other parts of the plant.
The higher plants have a well developed root system, which functions in the absorption of water.
Young region: The absorption of water occurs in this young region of the roots. It is divided into four regions based on their functions.
- Root cap: This is the terminal part of the root, which provides a protective layer to the root’s growing tip.
- Zone of the cell division: This is the subterminal part of the root, which includes meristematic cells. These parts or regions of the root are responsible for the growth of the root and are also called the root apex.
- Zone of elongation: It is also called the zone of elongation, which is present just behind the root apex. This is the part of the root apex that has thousands of root hairs, which play an important role in absorption of water.
- Zone of maturation: It is the mature part of the root, which carries out less absorption of water due to the lignification and suberization of cells.
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