Plant and Water (Short Questions and Answers)
One mark questions with answers
1. Which fraction of soil water is available to plants for absorption by roots?
Answer: capillary water
2. Expand DPD.
Answer: Diffusion pressure deficit
3. What will happen if a plant cell is kept in solution of higher water potential?
4. What will happen if a plant cell is kept in hypotonic solution for some time?
5. A plant cell kept in certain solution got plasmolysed. What was the nature of the solution?
6. Why is energy required to develop root pressure?
Answer: Every activity requires energy. Root pressure develops due to activity of living cells of the root.
7. Define guttation.
Answer: The loss or excretion of water in the form of liquid droplets from the leaves and other parts of an uninjured or intact plant is called guttation.
8. What are hydathodes?
Answer: Special structures found on margins and tips of the leaves made of epithem cells and water pores through which guttation takes place.
9. What is atmometer?
Answer: It is an apparatus for demonstrating and measuring pull caused by evaporation of water from a porous pot.
10. When separated by a semipermeable membrane water enters the sugar solution. What would you call the sugar solution -osmotically active or inactive?
Answer: Osmotically active
Two marks questions with answers
1. What is water potential? Why is it negative in value?
Answer: It is difference in chemical potential per molar volume of water in a system and that of pure state at the same temperature and pressure. Water potential of pure water at normal temperature and pressure is zero. In solution the value of water potential is always negative or less than zero.
2. A well watered herbaceous plant shows wilting in the afternoon of a dry sunny day. Why?
Answer: Wilting or loss of turgidity is quite common during noon due to transpiration being higher than the rate of water absorption.
3. How root/shoot ratio affects transpiration?
Answer: A low root/shoot ratio decreases the rate of transpiration while a high ratio increases the rate of transpiration because of greater availability of water due to more extensive root system.
4. A plant is transpiring rapidly. Will it show root pressure also?
Answer: The rapidly transpiring plants do not show any root pressure. Instead a negative pressure is observed in most of the plants.
5. Mention two differences between stomata and hydathodes.
Answer: Stomata are found in the aerial parts of all land plants whereas hydathodes occur on the leaves of only a few plants. The stomata can be opened or closed by the turgor changes in the guard cells whereas hydathodes possess permanent pores because the guard cells surrounding them are immobile.
6. Define the following terms:
(a) isotonic solution
(b) hypertonic solution
(c) hypotonic solution
Answer: (a) Isotonic solution is a solution of the same concentration
(b) Hypotonic solution is a solution of lower concentration than under consideration
(c) hypotonic solution is the solution of higher concentration than under consideration
7. What is osmotic pressure?
Answer: Osmotic pressure is pressure that is developed by a solution when separated from its pure solvent by a semi-permeable membrane.
8. Write two characteristics of diffusion?
Answer: (a) it is the movement of molecules from region of their high concentration to the region of their lower concentration
(b) this movement is independent of molecules of other gases moving in the same direction.
2. What conditions are necessary for imbibition?
Answer: The two conditions necessary for imbibition are as follows:
A diffusion pressure gradient must exist between the environment and the substance being imbibed. Secondly, a certain degree of affinity must exist between the environment and the substance being imbibed.
Three marks questions with answers
1. What is wilting? Mention the three types of wilting.
Answer: Wilting is the loss of turgidity of leaves and other soft aerial parts of a plant causing their drooping, folding and rolling.
Wilting is of three types- incipient wilting, temporary wilting and permanent wilting. In incipient wilting there are no external symptoms of wilting but the mesophyll cells have lost sufficient water due to transpiration being higher than the availability of water. It occurs during mid day for a brief period in almost all plants. Temporary wilting or transient wilting is the temporary drooping down of leaves and young shoots due to loss of turgidity during noon. At this time the rate of transpiration is maximum. The rate of water absorption is less due to shrinkage of roots and depletion of water around the root hairs. Permanent wilting is that state in the loss of turgidity of leaves when they do not regain the turgidity even on being placed in saturated atmosphere.
2. What do you understand by water potential?
Answer: The difference between the free energy of water molecule in pure water and the free energy in any other system (water in a solution or in a plant cell or tissues) is called, the water potential of that system.
Water potential is represented by Greek letter Psi (Ψ). Water potential is usually measured in bars. Water always moves from the area of high water potential to the area of low water potential. Thus, the movement of water molecule occurs down the energy gradient. The free energy of a solvent can be increased by increasing the temperature and pressure. The presence of solute particles reduces the free energy of water and thus, decreases the water potential. Water potential of pure water at atmospheric pressure is zero. Water potential of the solution is always less than zero or has negative values. Free energy of water in cell sap or solution is less than that of pure water, i.e., less than zero.
3. What is plasmolysis? What is the difference between plasmolysis and deplasmolysis?
Answer: Shrinkage of the protoplast of a cell from its cell wall under the influence of a hypertonic solution is called plasmolysis. In hypertonic solution water comes out of the cell due to exosmosis. As a result of continued exosmosis the protoplasm shrinks and pulls away from the cell wall.
Plasmolysis occurs when a tissue is placed in hypertonic solution whereas deplasmolysis occurs when freshly plasmolysed cells are kept in hypotonic solution or pure solvent. Plasmolysis is a result of exosmosis whereas deplasmolysis is a result of endosmosis.
4. What is the role of turgor pressure in plants?
Answer: 1. The opening and closing of stomata are caused by gain and loss of turgidity by their guard cell. Hence, they are often called “turgor-operated valves.”
- Turgor pressure (pressure potential or hydrostatic pressure) keeps a check on the excess entry of water into the cell.
- It keeps the cells and their organelles stretched which is essential for the proper functioning of the cells.
- It keeps the leaves fully expanded and properly oriented to light. Flower, young stems and other softer organs are able to maintain their form due to turgidity or turgor pressure.
- In case of loss of turgidity, the shoots droop down and the leaves show wilting.
Fill in the blanks:
- Molecules diffuse from a region of their ………. concentration to the region of their ………….. concentration.
- Pure water has ……….. diffusion pressure than a ………. solution.
- Osmotic pressure of a solution may also be referred to as the ………….
- The increase in the size of young cells due to ………….and ………….
- The difference in the diffusion pressure of a solution and a pure solvent at the same atmospheric pressure is known as ………..
- Addition of solute particles in pure water (or solvent) would ……….. its water potential.
- A piece of rubber when placed in water does not show imbibition. It is because there is no ………….. between rubber and water.
- Water potential is represented by a letter …………
- The water potential of pure water is…….
- Excessive transpiration produces…….
- higher / lower
- more / sugar
- osmotic potential
- osmotic pressure / turgor pressure
- diffusion pressure deficit
True and false statement
- The best way to demonstrate diffusion in the laboratory is to open a bottle of dilute nitric acid at one corner of the room.
- The movement of gas liquid or solid molecules is due to their kinetic energy.
- The direction of diffusion of one substance in any medium is dependent upon the movement of molecules of other substance present in the same medium.
- The concentration of a hypotonic solution is almost equal to that of cell sessile-appearing polyp.
- Turgor pressure is usually more than the osmotic pressure of the cell.
- Boiled potato tubers cannot be used as osmoscopes.
- Imbibition pressure is similar to turgor pressure.
- The diffusion pressure deficit of a flaccid cell is less than that of turgid cell.
- False (because dilute nitric acid is not volatile)
- False (molecules of different substances in a medium move independently.
- False (the concentration of hypertonic solution is less than that of cell sap).
- False (turgor pressure is always less than osmotic pressure)
- True (because the cell membrane loses its property of selective permeability, it becomes freely permeable to all types of ions)
- False (DPD of flaccid cell is maximum).