CBSE Class 11 Biology – Transport in Plants | Long Answer Type Questions with Answers (NCERT Based)

Course & Examination Details

Course: CBSE Class 11 Biology
Unit: Unit IV – Plant Physiology
Chapter: Chapter 11 – Transport in Plants
Prescribed Textbook: NCERT
Board: CBSE

CBSE Board Examination Significance

• Long answer questions assess conceptual depth, clarity, and logical presentation
• Frequently asked as 5-mark questions
• Answers must be well-structured, NCERT-specific, and diagram-supported (where applicable)

Section A: Diffusion (Q1–Q6)

Q1. Explain diffusion in plants. Discuss its characteristics and significance.

Ans:
Diffusion is the passive movement of molecules from a region of higher concentration to lower concentration until equilibrium is reached. It occurs due to random molecular motion and does not require energy. In plants, diffusion is significant for gaseous exchange during respiration and photosynthesis. Oxygen diffuses into cells while carbon dioxide diffuses out. Diffusion also enables movement of water vapour during transpiration. Its rate depends on factors such as concentration gradient, temperature, molecular size, and nature of the medium. Although diffusion is effective over short distances, it is insufficient for long-distance transport in plants. Hence, plants possess specialized conducting tissues. Diffusion maintains cellular homeostasis and supports essential physiological processes.

Q2. Describe the factors affecting diffusion in plants.

Ans:
The rate of diffusion in plants is influenced by several factors. The concentration gradient is the primary driving force; a steeper gradient increases diffusion rate. Temperature affects kinetic energy of molecules—higher temperature accelerates diffusion. Molecular size also matters; smaller molecules diffuse faster than larger ones. The nature of the medium influences diffusion, as it occurs fastest in gases, slower in liquids, and slowest in solids. Surface area available for diffusion and diffusion distance also affect the rate. These factors together determine how efficiently gases and small molecules move within plant tissues.

Q3. Why is diffusion insufficient for long-distance transport in plants?

Ans:
Diffusion is insufficient for long-distance transport because it is slow and non-directional. It depends solely on random molecular movement and concentration gradients, making it effective only over microscopic distances. Plants are large multicellular organisms that require rapid and directional transport of water, minerals, and food. Diffusion alone cannot meet these demands. Therefore, plants have evolved specialized vascular tissues—xylem for water and minerals and phloem for food transport—which enable mass flow over long distances efficiently.

Q4. Differentiate between diffusion and mass flow in plants.

Ans:
Diffusion involves passive movement of molecules from higher to lower concentration without energy expenditure and is non-directional. It is effective over short distances only. Mass flow, on the other hand, is the bulk movement of substances from source to sink, driven by pressure differences. It is directional and much faster than diffusion. Mass flow is responsible for long-distance transport in plants, such as water movement in xylem and food translocation in phloem.

Q5. Explain the role of diffusion in gaseous exchange.

Ans:
Gaseous exchange in plants occurs mainly through diffusion. Carbon dioxide enters leaves through stomata during photosynthesis, while oxygen diffuses out. During respiration, oxygen diffuses into cells and carbon dioxide diffuses out. Intercellular spaces within leaves facilitate diffusion by reducing diffusion distance. Diffusion ensures continuous supply of gases required for metabolic activities, maintaining physiological balance within plant tissues.

Q6. How does temperature influence diffusion in plants?

Ans:
Temperature directly affects the rate of diffusion. An increase in temperature raises the kinetic energy of molecules, causing them to move faster and diffuse more rapidly. Conversely, low temperatures reduce molecular motion, slowing diffusion. Thus, diffusion-dependent processes such as gaseous exchange and transpiration are influenced by environmental temperature.

Section B: Osmosis (Q7–Q13)

Q7. Define osmosis and explain its importance in plant life.

Ans:
Osmosis is the movement of water molecules across a semi-permeable membrane from a region of higher water potential to lower water potential. It is vital for plants as it enables absorption of water by root hairs, maintains cell turgidity, and supports growth. Osmosis regulates opening and closing of stomata and maintains rigidity in herbaceous plants. It also facilitates movement of water between cells, ensuring proper hydration and physiological balance essential for plant survival.

Q8. Explain plasmolysis and its significance.

Ans:
Plasmolysis is the shrinkage of the protoplast away from the cell wall when a plant cell is placed in a hypertonic solution. Water moves out of the cell by osmosis, causing loss of turgidity. Plasmolysis demonstrates the semi-permeable nature of the plasma membrane and the importance of osmotic balance. It helps in understanding cell membrane properties and water relations in plant cells.

Q9. What is water potential? Discuss its components.

Ans:
Water potential is a measure of the free energy of water that determines the direction of its movement. It is represented by Ψw and has two main components: solute potential (Ψs), which lowers water potential due to dissolved solutes, and pressure potential (Ψp), which increases water potential due to turgor pressure. Water always moves from higher to lower water potential, guiding water movement within plant tissues.

Q10. Describe the role of osmosis in root hair absorption.

Ans:
Root hairs absorb water from soil primarily through osmosis. Soil water has higher water potential compared to root hair cell sap. Due to this gradient, water enters root hairs through the semi-permeable plasma membrane. The absorbed water then moves through cortex cells to xylem. Osmosis thus initiates the process of water transport in plants.

Q11. How does osmosis regulate stomatal movement?

Ans:
Osmosis controls stomatal opening and closing by regulating turgidity of guard cells. When guard cells absorb water by osmosis, they become turgid and stomata open. Loss of water causes guard cells to become flaccid, closing stomata. This mechanism regulates transpiration and gaseous exchange.

Q12. Differentiate between hypotonic, hypertonic, and isotonic solutions.

Ans:
In a hypotonic solution, water potential outside the cell is higher, causing water entry and turgidity. In a hypertonic solution, water potential outside is lower, leading to water loss and plasmolysis. In an isotonic solution, water potential is equal inside and outside, resulting in no net water movement.

Q13. Why do plant cells not burst in hypotonic solutions?

Ans:
Plant cells possess a rigid cell wall that resists excessive expansion. When water enters by osmosis, turgor pressure develops, but the cell wall exerts equal wall pressure. This balance prevents bursting, unlike animal cells.

Section C: Transpiration (Q14–Q19)

Q14. Define transpiration and explain its significance.

Ans:
Transpiration is the loss of water vapour from aerial parts of plants, mainly through stomata. It plays a vital role in generating transpiration pull, which aids in ascent of sap. Transpiration helps cool the plant body, maintains cell turgidity, and facilitates mineral transport. Despite causing water loss, it is essential for plant survival.

Q15. Describe the mechanism of transpiration.

Ans:
Transpiration begins with evaporation of water from mesophyll cells into intercellular spaces. Water vapour then diffuses out through stomata along a concentration gradient. Continuous evaporation creates negative pressure, generating transpiration pull that draws water upward through xylem.

Q16. Explain factors affecting transpiration.

Ans:
External factors include light, temperature, humidity, and wind. Internal factors include leaf area, number of stomata, and cuticle thickness. These factors collectively regulate the rate of transpiration.

Q17. Why is transpiration called a necessary evil?

Ans:
Although transpiration causes water loss, it is essential for mineral transport, cooling, and ascent of sap. Hence, it is considered a necessary evil.

Q18. Explain transpiration pull.

Ans:
Transpiration pull is the suction force created due to continuous water loss from leaves. It generates negative pressure in xylem, pulling water upward from roots.

Q19. Describe the role of transpiration in cooling plants.

Ans:
Evaporation of water during transpiration absorbs heat energy, cooling the plant body and preventing overheating.

Section D: Water and Mineral Transport (Q20–Q25)

Q20. Describe absorption of water by roots.

Ans:
Water is absorbed by root hairs through osmosis. It moves through apoplast and symplast pathways to reach xylem for upward transport.

Q21. Explain apoplast and symplast pathways.

Ans:
Apoplast pathway involves movement through cell walls, while symplast pathway involves cytoplasmic movement through plasmodesmata.

Q22. Explain the ascent of sap.

Ans:
Ascent of sap is upward movement of water and minerals through xylem, mainly driven by transpiration pull.

Q23. Describe the cohesion–tension theory.

Ans:
The theory states that cohesion between water molecules and tension created by transpiration pull move water upward in xylem.

Q24. What is root pressure? State its role.

Ans:
Root pressure is positive pressure generated by osmotic ion uptake in roots. It aids water movement in small plants.

Q25. Explain mineral absorption and transport in plants.

Ans:
Minerals are absorbed as ions through diffusion or active transport and transported upward through xylem with water.

Best Suited For

• CBSE Class 11 Annual Examinations
• NCERT-based evaluations
• 5-mark answer writing practice