CBSE Class 11 Biology Transport In Plants Assignments

QUESTIONS

Very Short Answer Questions (1 mark each)

Question 1. Which part of the root is related with the absorption of water?
Answer: Root hairs.
In simple words: Root hairs absorb water and minerals from the soil.

Exam Tip: Mention root hairs specifically as they vastly increase the surface area for absorption.

Question 2. What makes the raisins to swell up when kept in water?
Answer: Endosmosis (the inward movement of water into the cells due to higher water potential outside).
In simple words: Water enters the raisins because the concentration of water is higher outside than inside.

Exam Tip: Always use the precise term - endosmosis - rather than general diffusion.

Question 3. Casparian strip is made of a substance which is impervious to water. Name this substance.
Answer: Suberin.
In simple words: Suberin is a wax-like waterproof substance found in the cell walls of the endodermis.

Exam Tip: Remember that suberin prevents the apoplastic movement of water, forcing it to enter the symplast.

Question 4. What will happen to water potential when a solute is added to water?
Answer: Water potential will decrease.
In simple words: Adding solutes makes water potential more negative because free water molecules decrease.

Exam Tip: Pure water has maximum water potential (\(\Psi_w = 0\)), and addition of solutes always lowers it.

Question 5. A plant cell when kept in a solution got plasmolysed. What was the nature of the solution?
Answer: Hypertonic.
In simple words: A hypertonic solution has more solute concentration, causing water to flow out of the cell.

Exam Tip: Differentiate clearly among hypertonic, isotonic, and hypotonic solutions.

Question 6. Mention two ways of absorption of water by root hairs in plants.
Answer: Apoplast pathway and symplast pathway.
In simple words: Water moves either through cell walls (apoplast) or through the cytoplasm connected by plasmodesmata (symplast).

Exam Tip: Briefly define both pathways if asked in a higher-mark question.

Question 7. Which form of sugar is transported through phloem?
Answer: Sucrose.
In simple words: Sucrose is a disaccharide sugar used for translocation in plants.

Exam Tip: Photosynthesis produces glucose, but it is converted to sucrose for transport.

Question 8. Give one example of imbibition.
Answer: Swelling of seeds when put in water or moist soil, or the swelling of wooden doors during the rainy season.
In simple words: Imbibition is the absorption of water by solid colloids without forming a solution.

Exam Tip: Mention dry seeds or wooden frames as classic examples.

Question 9. 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. Give its possible reason.
Answer: Due to exosmosis. Excess urea creates a hypertonic condition in the soil outside the roots, causing water to move out of the root cells, leading to plasmolysis and death of the plant.
In simple words: Too much fertilizer draws water out of the plant roots instead of supplying it.

Exam Tip: Use the scientific terms hypertonic solution and exosmosis.

Question 10. Why is energy required to develop root pressure?
Answer: Root pressure develops due to the active absorption of ions by root cells, which is an active transport process requiring metabolic energy (ATP).
In simple words: Ions are pumped into the roots against a concentration gradient, which uses energy.

Exam Tip: Link root pressure directly to active ion uptake.

Short Answer Questions-II (2 marks each)

Question 11. A well watered potted herbaceous plant shows wilting in the afternoon of a dry sunny day. Give reason.
Answer: During the afternoon, the rate of transpiration exceeds the rate of water absorption by the roots. This creates a water deficit, leading to a loss of turgidity in the plant cells, which results in wilting.
In simple words: Water is lost faster through leaves than roots can absorb it.

Exam Tip: Emphasize the imbalance between transpiration rate and water absorption rate.

Question 12. Do different species of plants growing in the same soil show the same rate of transpiration of a particular time? Justify your answer.
Answer: No, different species do not show the same rate of transpiration. The rate of transpiration is affected by plant factors such as the number and distribution of stomata, percentage of open stomata, water status of the plant, and canopy structure.
In simple words: Different plants have different structural adaptations that affect water loss.

Exam Tip: List at least two plant factors influencing transpiration.

Question 13. What is casparian strip? Write its significance in plants.
Answer: The Casparian strip is a band of suberized material present on the tangential and radial walls of the endodermal cells of roots.
Significance: It is water-impermeable, so it prevents water from flowing back out through the apoplast pathway and forces water and solutes to cross the plasma membrane of endodermal cells, allowing plants to regulate the types and amounts of solutes reaching the xylem.
In simple words: It acts as a waterproof check-point controlling what enters the vascular system.

Exam Tip: Highlight the role of endodermal selective transport.

Question 14. Xylem transport is unidirectional and phloem transport bi-directional. Why?
Answer: Xylem transport is unidirectional because water and minerals absorbed by roots must move upward to the stem, leaves, and aerial parts. Phloem transport is bi-directional because organic solutes (food) manufactured in source organs (leaves) can be transported upwards or downwards to storage organs, developing buds, or sinks depending on the plant's seasonal needs.
In simple words: Water only goes up from roots to leaves, but food moves wherever it is needed.

Exam Tip: Clearly define the source-to-sink relationship for phloem.

Question 15. How is transpiration different from guttation? Give two points.
Answer:
1. Transpiration involves the loss of water in the form of water vapour through stomata and general leaf surface, whereas guttation involves the loss of water in liquid droplets through hydathodes.
2. Transpiration occurs throughout the day under warm/dry conditions, whereas guttation typically occurs at night and early morning under high humidity and root pressure.
In simple words: Transpiration is water evaporating as gas, while guttation is water oozing out as liquid drops.

Exam Tip: Mention the structures involved: stomata for transpiration and hydathodes for guttation.

Short Answer Questions-I (3 marks each)

Question 16. When any dry plant material or seeds is/are kept in water, they swell up.
(a) Name the phenomenon involved in this change.
(b) Define this phenomenon.
(c) Give two conditions essential for the phenomenon to occur.
Answer:
(a) Imbibition.
(b) Imbibition is a special type of diffusion where water is adsorbed by solids or colloids (such as cellulose and proteins in seeds) causing an enormous increase in volume without forming a solution.
(c) Essential conditions: (i) Water potential gradient between the adsorbent and the liquid imbibed, and (ii) Affinity between the adsorbent and the liquid.
In simple words: Dry seeds soak up water due to capillary forces and chemical affinity, swelling up.

Exam Tip: Mention that no true solution is formed during imbibition.

Question 17. Differentiate between temporary and permanent wilting.
Answer:

In simple words: Temporary wilting fixes itself at night, but permanent wilting kills the plant because water is completely gone.

Exam Tip: Tabulate differences clearly with headings for full marks.

Question 18. What is mycorrhiza ? How is the mycorrhizal association helpful in absorption of water and minerals in plants?
Answer: Mycorrhiza is a symbiotic association between a fungus and the root system of higher plants. The fungal hyphae form a network around the root or penetrate root cells. They help in absorption by providing a large surface area that absorbs mineral ions and water from the soil much more efficiently and transfers them to the plant, while the plant supplies organic food and nitrogenous compounds to the fungus.
In simple words: Fungi expand root reach to absorb more water and minerals in exchange for food.

Exam Tip: Emphasize the mutual benefit (symbiosis) in the answer.

Question 19. Observe the given figure and give the answers of the following:
(a) Identify the process occuring in (I), (II) and (III).
(b) Differentiate between the process II and III.
(c) How many types of aquaporins form the water channels in the cell membrane.
Answer:
(a) (I) Uniport, (II) Antiport, (III) Symport.
(b) In Antiport, two molecules move across the membrane in opposite directions at the same time, whereas in Symport, two molecules cross the membrane in the same direction at the same time.
(c) 8 types of aquaporins.
In simple words: Carrier proteins transport molecules either alone (uniport), in opposite ways (antiport), or together in the same direction (symport).

Exam Tip: Memorize the three types of facilitated transport mechanisms clearly.

Question 20. Give the scientific term for the following statements/processes:
(a) Movement of water in roots exclusively through the cell wall.
(b) The positive hydrostatic pressure developed inside the cell or cell wall.
(c) A solution having relatively less concentration.
(d) Loss of water vapour from the aerial parts of the plants in the form of water vapours.
(e) Movement of a molecule across a membrane independent of other molecule.
(f) Water loss in its liquid phase through the special openings of veins near the tip of leaves of many herbaceous plants.
Answer:
(a) Apoplast pathway
(b) Turgor pressure
(c) Hypotonic solution
(d) Transpiration
(e) Uniport
(f) Guttation
In simple words: Match each biological description with its exact scientific term.

Exam Tip: One-word scientific terms must be spelled correctly.

Long Answer Questions (5 marks each)

Question 21. Minerals are present in the soil in sufficient amount. 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: Yes, plants must selectively adjust the types and quantities of solutes that reach the xylem because not all minerals absorbed from the soil are beneficial, and some may be toxic. Specific transport proteins located in the plasma membrane of root endodermal cells actively pump specific ions inward. Furthermore, the Casparian strip in the endodermis blocks passive flow through the apoplast, forcing all water and solutes to pass through the selectively permeable membranes of endodermal cells. Thus, the root endodermis acts as a metabolic control point that regulates the entry of solutes into the vascular cylinder.
In simple words: Root cell membranes and Casparian strips act as filters to let in only required minerals.

Exam Tip: Emphasize the role of the endodermis and transport proteins in selective mineral absorption.

Question 22. How do plants absorb water? Explain transpiration pull model in this regard.
Answer: Plants absorb water passively through root hairs by osmosis, driven by a water potential gradient. The uptake is largely maintained by the transpiration pull model (cohesion-tension-transpiration pull model):
1. Water evaporates from leaf mesophyll cells into the intercellular spaces and escapes through stomata into the atmosphere (transpiration).
2. This creates a negative water potential (tension) in the leaf xylem and mesophyll.
3. Water molecules exhibit strong mutual attraction (cohesion) and adhesion to xylem vessel walls, forming a continuous, unbroken water column from roots to leaves.
4. As water molecules are pulled up by transpiration, more water is drawn upward from the stem and roots, ultimately pulling water into roots from the soil.
In simple words: Evaporation from leaves creates a suction force that pulls water up from roots in an unbroken column.

Exam Tip: Clearly mention cohesion, adhesion, and tension forces in your answer.

Question 23. (a) Describe the pressure flow hypothesis of translocation of sugar in plants.
(b) Explain the mechanism of closing and opening of stomata.
Answer:
(a) Pressure Flow Hypothesis: Food (glucose) synthesized in leaves (source) is converted to sucrose. Sucrose is actively loaded into sieve tube cells of the phloem, creating a hypertonic condition inside the phloem. Water from adjacent xylem vessels moves into the phloem by osmosis. This builds up a high turgor pressure, forcing the phloem sap to flow towards areas of lower pressure (sink, where sugar is actively removed). At the sink, sucrose is unloaded, water leaves the phloem and returns to the xylem, reducing pressure.
(b) Opening and Closing of Stomata: Stomatal movement is controlled by the turgor pressure of guard cells. When guard cells take up potassium ions and water, they become turgid; their thicker inner walls pull apart, causing the stomatal pore to open. When water flows out of guard cells, they become flaccid, and the pore closes.
In simple words: Sugar flow is driven by pressure differences between source and sink, while stomata open and close due to water changes in guard cells.

Exam Tip: Draw flowcharts for mass flow and explain potassium ion influx for stomatal opening.