ICSE – Grade 10 – Biology – Ch 04 – QA

1. What is osmosis? Explain with an example.
    Answer:
    Osmosis is the movement of water molecules from a region of higher water concentration (or dilute solution) to a region of lower water concentration (or concentrated solution) through a semi-permeable membrane.
    For example, when a raisin is placed in water, water enters the raisin through its semi-permeable skin, making it swell due to osmosis.

2. Define imbibition and state its significance in plants.
   Answer:
    Imbibition is the absorption of water by solid particles of a substance without forming a solution. It is a type of diffusion where water is absorbed by substances like seeds or wood, causing them to swell.
    It is significant because it helps in seed germination and in maintaining moisture in plant tissues.

3. What is diffusion? How is it useful to plants?
   Answer:
    Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration until equilibrium is achieved.
    In plants, diffusion helps in the exchange of gases like oxygen and carbon dioxide and in the movement of nutrients and water.

4. Differentiate between osmosis and diffusion.
   Answer:

• Osmosis is the movement of water molecules through a semi-permeable membrane, while diffusion is the movement of any molecules (solid, liquid, gas) without a membrane.
• Osmosis is specific to solvents like water, while diffusion can occur for solutes as well.
• Osmosis requires a semi-permeable membrane, diffusion does not.

5. What is active transport? How is it different from passive transport?
   Answer:
    Active transport is the movement of molecules against their concentration gradient (from lower to higher concentration) using energy in the form of ATP.
    In contrast, passive transport involves movement of substances along the concentration gradient without energy.
    Active transport requires carrier proteins and energy, while passive transport does not.

6. Explain the structure of a root hair and its role in water absorption.
   Answer:
    A root hair is a long, thin, unicellular outgrowth of an epidermal cell of the root. It increases the surface area for absorption.
    It has a cell wall, semi-permeable plasma membrane, cytoplasm, and a large central vacuole containing concentrated cell sap.
    Water enters the root hair by osmosis due to the difference in concentration between the cell sap and soil water.

7. What is plasmolysis? Describe the process with an example.
   Answer:
    Plasmolysis is the process in which the cytoplasm of a plant cell shrinks and detaches from the cell wall when placed in a hypertonic solution.
    This occurs due to exosmosis, where water moves out of the cell.
    For example, when a plant cell is placed in concentrated salt solution, it loses water and becomes plasmolysed.

8. What is turgor pressure? How does it help in plants?
   Answer:
    Turgor pressure is the pressure exerted by the cell contents against the cell wall due to water intake through osmosis.
    It helps in maintaining the shape and rigidity of plant cells and provides mechanical support to non-woody parts of the plant.
    Turgor pressure is essential for the opening of stomata and for various growth processes.

9. Describe the difference between turgid, flaccid, and plasmolysed cells.
   Answer:

• A turgid cell is full of water and exerts pressure against the cell wall.
• A flaccid cell has lost some water and becomes limp but not collapsed.
• A plasmolysed cell has lost most of its water, causing the cytoplasm to shrink and detach from the cell wall.

10. Explain the role of osmotic pressure in water absorption by roots.
    Answer:
     Osmotic pressure is the pressure required to stop the flow of water into a cell by osmosis. In root hairs, the cell sap has a higher osmotic pressure than the surrounding soil water, causing water to move into the cell.
     This helps in drawing water from the soil into the root cells through osmosis.

11. What is the significance of semi-permeable membrane in osmosis?
    Answer:
     A semi-permeable membrane allows only certain molecules, typically small ones like water, to pass through while preventing larger solute molecules.
     In osmosis, it enables the selective movement of water into or out of the cell, maintaining cellular balance and function.

12. State the conditions necessary for osmosis to occur.
    Answer:
     The conditions necessary for osmosis are:

• A semi-permeable membrane
• A difference in water concentration across the membrane
• Presence of water as the solvent
• The solute should not be able to pass through the membrane

13. How does water move from the soil to the xylem of the root?
    Answer:
     Water enters root hairs by osmosis due to a higher concentration of cell sap. It then moves from cell to cell through the cortex via osmosis and active transport. Finally, it enters the xylem vessels, which carry it upward.

14. What is the role of root pressure in water absorption?
    Answer:
     Root pressure is the force developed in roots due to continuous absorption of water. It helps in pushing water upward through the xylem, especially during the night or when transpiration is low.

15. Explain the process of endosmosis and exosmosis with examples.
    Answer:
     Endosmosis occurs when water moves into a cell placed in a hypotonic solution, e.g., raisins swelling in water.
     Exosmosis occurs when water moves out of a cell placed in a hypertonic solution, e.g., plant cells shrinking in salt solution.

16. Why are root hairs suited for absorption?
    Answer:
     Root hairs are long, narrow, and increase surface area. They have thin cell walls and concentrated cell sap, which helps in osmosis. Being close to soil particles also enables efficient water absorption.

17. Describe the three types of passive transport.
    Answer:
18. Imbibition – Absorption of water by hydrophilic substances.
19. Diffusion – Movement of molecules from high to low concentration.
20. Osmosis – Movement of water through a semi-permeable membrane from dilute to concentrated solution.

18. What is the difference between endosmosis and exosmosis?
    Answer:

• Endosmosis is the movement of water into the cell causing it to swell.
• Exosmosis is the movement of water out of the cell causing it to shrink.

19. What is the function of xylem and phloem?
    Answer:
     Xylem transports water and minerals from roots to the leaves. Phloem transports food prepared in the leaves to all parts of the plant.

20. Explain with an example how active transport works in roots.
    Answer:
     In roots, mineral ions like nitrates are absorbed from the soil even when their concentration is higher inside the cell. This requires energy (ATP), and the process is carried out by carrier proteins in the plasma membrane.

21. What is a hypertonic solution and how does it affect a plant cell?
    Answer:
     A hypertonic solution has a higher concentration of solutes than the cell sap. When a plant cell is placed in a hypertonic solution, water moves out of the cell, causing the cytoplasm to shrink and the cell to become plasmolysed due to exosmosis.

22. What is a hypotonic solution and how does it affect a plant cell?
    Answer:
     A hypotonic solution has a lower solute concentration than the cell sap. When a plant cell is placed in it, water enters the cell by endosmosis, making the cell turgid and increasing turgor pressure.

23. How does temperature affect the rate of osmosis?
    Answer:
     An increase in temperature increases the kinetic energy of water molecules, speeding up the movement across the membrane and thereby increasing the rate of osmosis.

24. Describe an experiment to demonstrate osmosis using a thistle funnel.
    Answer:
     Fill the thistle funnel with sugar solution and cover its mouth with a semi-permeable membrane. Immerse it in water taken in a beaker. Over time, water enters through the membrane into the funnel by osmosis, raising the liquid level in the funnel.

25. Why is water important to plants? Give any three reasons.
    Answer:
     Water is important for:
26. Photosynthesis (as a raw material),
27. Maintaining turgidity (for support),
28. Transporting nutrients and minerals through xylem.

26. What is the significance of turgor pressure in plants?
    Answer:
     Turgor pressure helps maintain the upright position of herbaceous plants, supports soft tissues, assists in cell enlargement and growth, and enables opening and closing of stomata.

27. Describe how mineral salts are absorbed by roots.
    Answer:
     Mineral salts are absorbed either passively along the concentration gradient or actively against the gradient using ATP energy through special carrier proteins in the root hair membrane.

28. What are the essential conditions for absorption of water by roots?
    Answer:
     Conditions include:

• Availability of water in soil
• Concentrated cell sap in root hairs
• Presence of semi-permeable membranes
• Temperature and metabolic activity for active transport

29. How does the concentration of cell sap affect water absorption?
    Answer:
     If the cell sap is more concentrated than soil water, osmosis occurs and water enters the root hair cells, enabling absorption.

30. Explain the process of absorption of water from soil to xylem in sequence.
    Answer:
     Water enters root hairs by osmosis → moves through cortex cells via osmosis and diffusion → reaches endodermis → passes into pericycle → finally enters xylem vessels for upward transport.

31. What is the difference between isotonic, hypertonic, and hypotonic solutions?
    Answer:

• Isotonic: Equal solute concentration inside and outside cell
• Hypertonic: Higher solute concentration outside, causes exosmosis
• Hypotonic: Lower solute concentration outside, causes endosmosis

32. What is the function of the root cap in absorption?
    Answer:
     The root cap does not absorb water; it protects the delicate tip of the root as it pushes through the soil.

33. How does transpiration help in water movement?
    Answer:
     Transpiration creates a suction force (transpirational pull) in the xylem, helping draw water upward from the roots to the leaves.

34. Name the three main physical forces that help in ascent of sap.
    Answer:

Root pressure (push from below)

Cohesion between water molecules

Adhesion between water molecules and xylem walls

35. What is water potential and why is it important?
    Answer:
     Water potential is the potential energy of water in a system. Water always moves from a region of higher to lower water potential. It determines the direction of water movement in plants.

36. What is the role of cohesion and adhesion in water movement?
    Answer:
     Cohesion keeps water molecules together, forming a continuous column. Adhesion helps water molecules stick to the xylem walls. Both aid in upward movement of water.

37. How does endosmosis help in maintaining turgidity?
    Answer:
     Endosmosis allows water to enter the plant cell, filling the vacuole and pressing the cytoplasm against the cell wall, which makes the cell turgid and structurally firm.

38. What happens to a plant cell when placed in a sugar solution?
    Answer:
     If the sugar solution is hypertonic, the plant cell loses water due to exosmosis and becomes flaccid or plasmolysed.

39. Why do seeds swell when soaked in water?
    Answer:
     Seeds swell due to imbibition, where dry seed coats absorb water and expand, initiating the germination process.

40. Why is transpiration important apart from water movement?
    Answer:
     Besides water transport, transpiration helps in cooling the plant, maintaining temperature, and creating suction force for absorption.

41. Explain why root hairs die quickly when removed from soil.
    Answer:
     Root hairs are delicate unicellular structures that depend on contact with moist soil for water. Once exposed to air, they dry out and lose function quickly.

42. What are carrier proteins and what is their role in roots?
    Answer:
     Carrier proteins are specialized membrane proteins that bind to mineral ions and help transport them into the cell using ATP in active transport.

43. What are hydrophilic substances? Name one example.
    Answer:
     Hydrophilic substances are materials that attract and absorb water. Example: cellulose in the cell wall.

44. How does root structure facilitate efficient absorption?
    Answer:
     Roots have root hairs with large surface area, thin walls, and concentrated sap. Their close contact with soil enhances efficient absorption.

45. How does temperature affect active transport in roots?
    Answer:
     Higher temperatures increase enzyme activity and respiration rate, thus producing more ATP, enhancing active transport efficiency.

46. Describe the role of the vacuole in a root hair cell.
    Answer:
     The vacuole stores concentrated cell sap, maintaining osmotic pressure and drawing water into the cell by osmosis.

47. What changes occur in a plant cell when it becomes flaccid?
    Answer:
     In a flaccid cell, water leaves by exosmosis, causing the cytoplasm to contract slightly and the cell to lose firmness.

48. How do water and minerals differ in their mode of absorption?
    Answer:
     Water is absorbed passively by osmosis, while minerals are absorbed by both passive diffusion and active transport using ATP.

49. Why does osmosis stop at equilibrium?
    Answer:
     At equilibrium, the concentration of water molecules becomes equal on both sides of the membrane, eliminating the driving force for movement.

50. What would happen if all plant cells became plasmolysed?
    Answer:
     If all plant cells became plasmolysed, the plant would wilt severely, metabolic activities would slow down, and the plant may eventually die due to lack of water and pressure.