Q.1. The process responsible for facilitating loss of water in liquid form from the tip of grass blades at night and in early morning is: (2020)
(d) Root Pressure
Root pressure (positive pressure) can be responsible for pushing up water to small heights in the stem.“It also observable at night and early morning when evaporation is low, and excess water collects in the form of droplets around special openings of veins near the tip of grass blades, and leaves of many herbaceous parts.
Such water loss in its liquid phase is known as guttation. Imbibition is the adsorption leading to absorption of water by hydrophillic substances. Plasmolysis is the shrinking of the cell membrane and cytoplasm when a cell is undergoing exosmosis. The loss of water in the form of water vapor from the aerial parts of the plant is called transpiration.
Q.2. Xylem translocates (2019)
(a) Water, mineral salts, some organic nitrogen and hormones
(b) Water only
(c) Water and mineral salts only
(d) Water, mineral salts and some organic nitrogen only
Xylem is a type of transport tissue which is present in vascular plants. The basic function of xylem is transportation. Xylem majorly transports water from roots to the parts of plants. Some times it also transports nutrients like mineral salts needed by the plant.
Q.3. What is the direction of movement of sugars in phloem? (2019)
(b) Non-multi directional
Food is transported by vascular tissue phloem from a source to sink. Source is a part that synthesises food and sink is a part that stores or needs the food. Since source and sink can be reversed depending on plant’s need, therefore direction of movement of sugar in phloem can be bidirectional, i.e., both upwards or downwards.
Q.4. Which of the following is not a feature of active transport of solutes in plants? (2019)
(a) Occurs against concentration gradient
(c) Occurs through membranes
(d) Requires ATP
Q.5. What will be the direction of flow of water when a plant cell is placed in a hypotonic solution? (2019)
(a) Water will flow in both directions
(b) Water will flow out of the cell
(c) Water will flow into the cell
(d) No flow of water in any direction
Q.6. Stomatal movement is not affected by (2018)
(c) O2 concentration
(d) CO2 concentration
High temperature, light and CO2 concentration affect opening and closing of stomata while O2 concentration has negligible effect on stomatal opening and closing.
Q.7. The water potential of pure water is (2017)
(a) Less than zero
(b) More than zero but less than one
(c) More than one
The water potential of pure water in an open container is zero because there is no solute and the pressure in the container is zero.
Q.8. Which of the following facilitates opening 0f stomatal aperture? (2017)
(a) Decrease in turgidity of guard cells
(b) Radial orientation of cellulose microfibrils in the cell wall of guard cells
(c) Longitudinal orientation of Cellulose microfibrils in the cell wall of guard cells
(d) Contraction of outer wall of guard cells
When turgidity increases within the two guard cells flanking each stomatal aperture or pore, the thin outer wall bulge out and force the inner walls into a crescent shape. This results in the opening of stomata. The opening of stomata is also aided by the radial orientation of cellulose microfibrils in the cell wall of guard cells rather than longitudinal orientation.
Q.9. A few drops of sap were collected by cutting across a plant stem by a suitable method. The sap was tested chemically. Which one of a following test results indicates that it is phloem sap? (2016)
(c) Low refractive index
(d) Absence of sugar
Phloem sap is generally alkaline with pH ranging from 7.3 - 8.5 and contains high levels of K+ and Mg2+. Hence, the chemical test for alkalinity will help to identify that the exudated sap is phloem sap. So, the correct answer is 'Alkaline'.
Q.10. Water vapour comes out from the plant leaf through the stomatal opening. Through the same stomatal opening carbon dioxide diffuses into the plant during photosynthesis. Reason out the above statements using one of following options. (2016)
(a) Both processes cannot happen simultaneously.
(b) Both processes can happen together because the diffusion coefficient of water and CO2 is different.
(c) The above processes happen only during night time.
(d) One process occurs during day time, and the other at night.
In actively growing plants, water is continuously evaporating from the surface of leaf cells through stomatal opening exposed to air. This is called transpiration. Through the same stomatal opening carbon dioxide diffuses into the plant during photosynthesis. Simultaneously as both are the process of simple diffusion occurs in order of diffusion pressure gradient or diffusion coefficient.
Q.11. Transpiration and root pressure cause water to rise in plants by: (2015)
(a) Pulling and pushing it, respectively
(b) Pushing it upward
(c) Pushing and pulling it, respectively
(d) Pushing it upward
Transpiration creates pulling (Negative pressure) force. Root pressure creates positive pressure developed in xylem. It is measured by manometer.
Q.12. A column of water within xylem vessels of tall trees does not break under its weight because of: (2015)
(a) Tensile strength of water
(b) Lignification of xylem vessels
(c) Positive root pressure
(d) Dissolved sugars in water
Due to tensile strength of water, a column of water within xylem vessels of tall trees does not break under its weight.
Q.13. Root pressure develops due to: (2015)
(a) Low osmotic potential in soil
(b) Passive absorption
(c) Increase in transpiration
(d) Active absorption
Active absorption creates root pressure. In this process, the expenditure of energy takes place for the movement of substances against concentration gradient.
Q.14. Roots play insignificant role in absorption of water in: (2015)
Pistia a hydrophyte plant where absorption of water by root is not important.