CBSE Class 11 Biology – Transport in Plants | Short 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 Relevance

• Short answer questions test conceptual clarity and explanation skills
• Commonly asked in annual examinations
• Answers must be concise, structured, and NCERT-specific
• Diagrams may be added in exams, but explanations remain textual

Section A: Diffusion (Q1–Q12)

Q1. Explain diffusion and its significance in plants.

Ans: Diffusion is the passive movement of molecules from a region of higher concentration to lower concentration until equilibrium is achieved. In plants, diffusion is essential for gaseous exchange during respiration and photosynthesis. Oxygen and carbon dioxide move through intercellular spaces and stomata by diffusion. It also helps in the movement of water vapour during transpiration and maintains cellular equilibrium without energy expenditure.

Q2. Why is diffusion considered a slow process in plants?

Ans: Diffusion is considered slow because it depends solely on random molecular movement and concentration gradients. It is effective only over short distances, such as across cell membranes or intercellular spaces. In large multicellular plants, diffusion alone cannot meet transport requirements, which is why specialized vascular tissues like xylem and phloem are necessary for long-distance transport.

Q3. Describe factors affecting the rate of diffusion in plant cells.

Ans: The rate of diffusion in plant cells depends on concentration gradient, temperature, molecular size, and the nature of the medium. A steeper concentration gradient and higher temperature increase diffusion rate. Smaller molecules diffuse faster than larger ones. Diffusion occurs more rapidly in gases than in liquids and solids due to lower resistance.

Q4. Differentiate between diffusion and facilitated diffusion.

Ans: Diffusion is the passive movement of molecules along a concentration gradient without assistance. Facilitated diffusion is also passive but requires specific carrier proteins or channels for movement across membranes. Facilitated diffusion is selective and faster for certain molecules, while simple diffusion occurs directly through the lipid bilayer and is non-specific.

Q5. How does diffusion help in transpiration?

Ans: Diffusion plays a key role in transpiration by enabling the movement of water vapour from leaf intercellular spaces to the atmosphere. Water evaporates from mesophyll cells and diffuses through stomata along a concentration gradient. This diffusion of water vapour maintains transpiration pull, which indirectly helps in the upward transport of water through xylem.

Q6. Why is diffusion important at the cellular level?

Ans: At the cellular level, diffusion helps in exchange of gases, nutrients, and waste products between cells and their surroundings. Oxygen diffuses into cells for respiration, while carbon dioxide diffuses out. Diffusion also maintains ionic balance and supports metabolic activities, making it vital for normal cellular functioning.

Q7. Explain the role of diffusion in gaseous exchange in plants.

Ans: Gaseous exchange in plants occurs mainly through diffusion. During photosynthesis, carbon dioxide diffuses into leaves through stomata, while oxygen diffuses out. During respiration, oxygen enters cells and carbon dioxide exits. The intercellular spaces facilitate diffusion by reducing the distance for gas movement.

Q8. How does concentration gradient influence diffusion?

Ans: Concentration gradient is the main driving force for diffusion. A higher concentration difference between two regions increases the rate of diffusion. As diffusion proceeds, the gradient gradually decreases until equilibrium is reached. Without a concentration gradient, diffusion does not occur.

Q9. Can diffusion alone meet transport needs of tall plants? Explain.

Ans: No, diffusion alone cannot meet transport needs of tall plants because it is effective only over short distances. Tall plants require rapid and directional movement of water, minerals, and food. This is achieved through specialized conducting tissues like xylem and phloem, which allow mass flow transport.

Q10. Explain the relationship between diffusion and temperature.

Ans: Temperature directly affects diffusion rate. An increase in temperature raises the kinetic energy of molecules, causing them to move faster and diffuse more rapidly. At lower temperatures, molecular movement slows down, reducing the rate of diffusion. Thus, diffusion is temperature dependent.

Q11. Why is diffusion described as a passive process?

Ans: Diffusion is called a passive process because it does not require metabolic energy. Molecules move spontaneously along a concentration gradient due to their inherent kinetic energy. The cell does not expend ATP for diffusion, making it an energy-independent transport mechanism.

Q12. State two limitations of diffusion in plants.

Ans: Diffusion is slow and non-directional, making it unsuitable for long-distance transport. It is effective only for small molecules and short distances. These limitations necessitate the presence of specialized transport systems in higher plants.

Section B: Osmosis (Q13–Q25)

Q13. Define osmosis and explain its importance in plants.

Ans: Osmosis is the movement of water across a semi-permeable membrane from higher water potential to lower water potential. It is crucial for water absorption by root hairs, maintenance of cell turgidity, stomatal movement, and growth. Osmosis helps plants maintain rigidity and ensures continuous water supply to cells.

Q14. Explain the role of semi-permeable membrane in osmosis.

Ans: A semi-permeable membrane allows passage of water molecules but restricts solute particles. This selective permeability is essential for osmosis. In plant cells, the plasma membrane acts as a semi-permeable membrane, enabling controlled movement of water based on water potential differences.

Q15. What happens when a plant cell is placed in a hypotonic solution?

Ans: When placed in a hypotonic solution, water enters the plant cell by osmosis. The cell swells and becomes turgid as pressure builds up against the cell wall. The rigid cell wall prevents bursting and provides mechanical support to the plant.

Q16. Describe plasmolysis in plant cells.

Ans: Plasmolysis occurs when a plant cell is placed in a hypertonic solution, causing water to leave the cell by osmosis. The protoplast shrinks and detaches from the cell wall. Plasmolysis demonstrates the importance of osmotic balance and semi-permeable membranes.

Q17. Explain water potential and its components.

Ans: Water potential is the measure of free energy of water and determines the direction of water movement. It has two main components: solute potential, which decreases water potential, and pressure potential, which increases it. Water always moves from higher to lower water potential.

Q18. Differentiate between isotonic and hypertonic solutions.

Ans: In an isotonic solution, the water potential inside and outside the cell is equal, resulting in no net water movement. In a hypertonic solution, external water potential is lower, causing water to move out of the cell, leading to plasmolysis.

Q19. How does osmosis help in opening and closing of stomata?

Ans: Osmosis regulates stomatal movement by controlling turgidity of guard cells. When guard cells gain water by osmosis, they become turgid and stomata open. Loss of water makes guard cells flaccid, causing stomatal closure. This regulates transpiration and gaseous exchange.

Q20. Why are plant cells resistant to bursting during osmosis?

Ans: Plant cells possess a rigid cell wall that exerts wall pressure against expanding protoplast. This counteracts osmotic pressure, preventing bursting even in hypotonic solutions. The balance between turgor pressure and wall pressure maintains cell stability.

Q21. Explain the significance of turgidity in herbaceous plants.

Ans: Turgidity provides mechanical support to herbaceous plants lacking woody tissues. Turgid cells maintain upright posture of stems and leaves. Loss of turgidity results in wilting. Thus, osmosis-driven turgidity is essential for plant form and function.

Q22. What is active transport of ions and how is it related to osmosis?

Ans: Active transport involves movement of ions against concentration gradient using energy. Accumulation of ions lowers water potential inside root cells, facilitating osmotic entry of water. Thus, active transport indirectly supports osmosis during water absorption.

Q23. Why is osmosis considered a special type of diffusion?

Ans: Osmosis is considered a special type of diffusion because it involves movement of only water molecules across a semi-permeable membrane. Like diffusion, it is passive and driven by potential gradient, but it specifically requires a membrane.

Q24. Explain exosmosis with an example.

Ans: Exosmosis is the movement of water out of a cell when placed in a hypertonic solution. For example, when a plant cell is placed in concentrated sugar solution, water moves out, causing plasmolysis.

Q25. State two differences between diffusion and osmosis.

Ans: Diffusion involves movement of any molecules and does not require a membrane, whereas osmosis involves only water and requires a semi-permeable membrane. Diffusion occurs in all media, while osmosis occurs only in liquid systems.

Section C: Transpiration (Q26–Q38)

Q26. Define transpiration and explain its importance.

Ans: Transpiration is the loss of water vapour from aerial parts of plants, mainly through stomata. It helps in generating transpiration pull, which aids in ascent of sap. Transpiration also cools the plant, maintains cell turgidity, and facilitates mineral transport.

Q27. Describe the three types of transpiration.

Ans: Transpiration occurs in three forms: stomatal transpiration through stomata, cuticular transpiration through the cuticle, and lenticular transpiration through lenticels. Stomatal transpiration is the most significant, contributing the majority of water loss in plants.

Q28. Explain 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. This continuous loss creates negative pressure, resulting in transpiration pull.

Q29. Why is transpiration called a necessary evil?

Ans: Transpiration causes excessive water loss, which can be harmful, yet it is essential for mineral transport, cooling, and ascent of sap. Because of this dual nature—harmful yet necessary—it is called a necessary evil.

Q30. How does light intensity affect transpiration?

Ans: Light stimulates stomatal opening, increasing transpiration rate. In darkness, stomata usually close, reducing transpiration. Thus, transpiration is higher during daytime due to increased light intensity.

Q31. Explain the effect of humidity on transpiration.

Ans: High humidity reduces transpiration because it lowers the diffusion gradient of water vapour between leaf and atmosphere. Low humidity increases transpiration by maintaining a steep concentration gradient.

Q32. How does transpiration contribute to ascent of sap?

Ans: Transpiration creates negative pressure in leaf xylem, producing transpiration pull. This pull draws water upward through xylem from roots to leaves, enabling ascent of sap in tall plants.

Q33. Explain the role of wind in transpiration.

Ans: Wind removes the humid air surrounding leaf surfaces, maintaining a steep diffusion gradient. This increases the rate of transpiration. Extremely strong winds, however, may cause stomatal closure, reducing transpiration.

Q34. State two internal factors affecting transpiration.

Ans: Internal factors include leaf area and number of stomata. Larger leaf area and more stomata increase transpiration, while thick cuticle and sunken stomata reduce water loss.

Q35. What is stomatal transpiration and why is it maximum?

Ans: Stomatal transpiration is water loss through stomata. It is maximum because stomata are numerous and actively regulated, allowing significant water vapour diffusion during gaseous exchange.

Q36. Explain the cooling effect of transpiration.

Ans: Transpiration causes evaporation of water from leaf surfaces, absorbing heat energy. This cools the plant body, preventing overheating during high environmental temperatures.

Q37. Does transpiration occur at night? Explain.

Ans: Transpiration greatly decreases at night because stomata generally close in absence of light. However, a small amount of cuticular transpiration may still occur.

Q38. What is transpiration pull?

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

Section D: Water and Mineral Transport (Q39–Q50)

Q39. Describe absorption of water by roots.

Ans: Water is absorbed mainly by root hairs through osmosis. Soil water has higher water potential than root hair cell sap. Water moves through apoplast and symplast pathways before entering xylem for upward transport.

Q40. Explain apoplast and symplast pathways.

Ans: In apoplast pathway, water moves through cell walls and intercellular spaces. In symplast pathway, water moves through cytoplasm via plasmodesmata. Both pathways operate during water absorption in roots.

Q41. What is ascent of sap?

Ans: Ascent of sap refers to upward movement of water and dissolved minerals from roots to aerial parts through xylem. It is essential for photosynthesis, transpiration, and growth.

Q42. Explain the cohesion–tension theory.

Ans: The cohesion–tension theory states that water molecules stick together due to cohesion and adhere to xylem walls. Transpiration creates tension that pulls the continuous water column upward against gravity.

Q43. Why is cohesion important in water transport?

Ans: Cohesion between water molecules maintains an unbroken water column in xylem vessels. This continuity is essential for effective transmission of transpiration pull from leaves to roots.

Q44. Define adhesion and state its role.

Ans: Adhesion is the attraction between water molecules and xylem walls. It helps prevent downward pull of water due to gravity and stabilizes the water column.

Q45. What is root pressure and when is it effective?

Ans: Root pressure is positive pressure generated by osmotic ion uptake in roots. It is effective during low transpiration conditions and in small plants, but insufficient in tall trees.

Q46. Why is transpiration pull more important than root pressure?

Ans: Transpiration pull is strong and continuous, capable of lifting water to great heights. Root pressure is weak and intermittent, making transpiration pull the dominant force in tall plants.

Q47. How are minerals absorbed by roots?

Ans: Minerals are absorbed as ions through diffusion or active transport. Active absorption requires energy and carrier proteins, especially when mineral concentration in soil is low.

Q48. What is active transport of minerals?

Ans: Active transport is energy-dependent movement of mineral ions against concentration gradient using membrane proteins. It enables selective mineral uptake by roots.

Q49. How are minerals transported to aerial parts?

Ans: Minerals dissolved in water move upward through xylem along with transpiration stream. Their transport depends largely on transpiration pull.

Q50. Why is water transport essential for plants?

Ans: Water transport supplies minerals, maintains turgidity, supports photosynthesis, regulates temperature, and ensures overall physiological functioning and survival of plants.

Best Suited For

• CBSE Class 11 Annual Examinations
• NCERT-based school tests
• Structured answer writing practice