Transport In Plants
Q1.What is meant by Apoplast pathway? Why does it occur in cortex and not in endodermis?
Ans 1. Passive absorption of water: A force develops during water absorption in the shoot system where transpiration is occurring. The transpiration than create a tension in xylem due to loss of water from its aerial parts. Tension spreads in all the xylem channels of the root. This may be due to:
1. Rate of water absorption.
2. Amount of water absorbed.
3. The shoot may continue to absorb water even in the absence of root.
Apoplast pathway: water moves from soil to cell wall of root hair cell, endodermis, pericycle, xylem parenchyma and xylem channels. Water in the xylem channel is under more negative pressure so it draws water from soil through intervening apoplast along the gradient. It takes place trough the cell wall. It does not occur in endodermis because; endodermis cells contain casparian strips which are water resistant.
Q2. How does the absorption and loss of potassium ions in the guard cells bring about the opening and closing of stomata?
Ans. 2 Role of potassium ions in transpiration: Levitt explained the mechanism of stomata action. In light starch produced during photosynthesis is converted into organic acids which cause a low concentration of potassium ions. When the concentration of organic acid is increased in guard cells, this increases the concentration of cell sap followed by subsequent absorption of water. In dark photosynthesis stops, accompanied by an increased concentration of CO2, the organic acids are converted into starch. The water comes out of guard cells it reduces the truer pressure and stomata get s closed.
Q3. What are the two types of interaction of water molecules that allow water to travel upwards in the plants? What other physical process aids in water transport to the top of the trees? Explain.
Ans. 3The water molecules attract each other by mutual force .this force is called cohesive force. The attraction between the walls of xylem elements and other water molecules is known as adhesion. Root hair absorb water from the soil, movement of water from soil to root hair results from the pressure exerted by cortical cells of the root into the xylem vessels, resulting to raise the water column in ascending parts of the plant and is called root pressure. As a result of transpiration water is drawn in the intercellular spaces from mesophyll cells which consequently draw water osmotically from the nearby cells and thus a diffusion pressure deficit is developed. Due to this the adjacent cells take water from xylem of vein of leaf. This xylem is connected with the xylem of root through stem xylem. A tension is setup in the water column of the xylem and the whole column is physically pulled up.
Ques. The principal pathway of water translocation in angiosperms is
(a) sieve cells (b) sieve tube elements
(c) xylem vessel system (d) xylem and phloem.
Ques. Stomatal movement is not affected by
(c) O2 concentration
(d) CO2 concentration.
Ques. Which of the following facilitates opening of stomatal aperture?
(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
Ques. 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.
(a) The above processes happen only during night time.
(b) One process occurs during day time and the other at night.
(c) Both processes cannot happen simultaneously.
(d) Both processes can happen together because the diffusion coefficient of water and CO2 is different.
Ques. A column of water within xylem vessels of tall trees does not break under its weight because of
(a) lignification of xylem vessels
(b) positive root pressure
(c) dissolved sugars in water
(d) tensile strength of water.
Ques. Transpiration and root pressure cause water to rise in plants by
(a) pushing it upward
(b) pushing and pulling it, respectively
(c) pulling it upward
(d) pulling and pushing it, respectively.
Ques. Which one gives the most valid and recent explanation for stomatal movement?
(a) Starch hydrolysis
(b) Guard cell photosynthesis
(d) Potassium influx and efflux
Ques. In land plants, the guard cells differ from other epidermal cells in having
(c) endoplasmic reticulum
Ques. Guttation is the result of
(a) diffusion (b) transpiration
(c) osmosis (d) root pressure.
Ques. Guard cells help in
(c) fighting against infection
(d) protection against grazing.
Ques. The rupture and fractionation do not usually occur in the water column in vessel/tracheids during the ascent of sap because of
(a) weak gravitational pull
(b) transpiration pull
(c) lignified thick walls
(d) cohesion and adhesion.
Ques. Potometer works on the principle of
(a) osmotic pressure
(b) amount of water absorbed equals the amount transpired
(c) root pressure
(d) potential difference between the tip of the tube and that of the plant.
Ques. Stomata of a plant open due to
(a) influx of potassium ions
(b) efflux of potassium ions
(c) influx of hydrogen ions
(d) influx of calcium ions.
Ques. Main function of lenticel is
(a) transpiration (b) guttation
(c) gaseous exchange (d) bleeding.
Ques. Opening and closing of stomata is due to the
(a) hormonal change in guard cells
(b) change in turgor pressure of guard cells
(c) gaseous exchange
Ques. Glycolate induces opening of stomata in
(a) presence of oxygen
(b) low CO2 concentration
(c) high CO2
(d) CO2 absent.
Ques. In guard cells when sugar is converted into starch, the stomatal pore
(a) closes completely (b) opens partially
(c) opens fully (d) remains unchanged.
Ques. At constant temperature, the rate of transpiration will be higher at
(a) sea level
(b) 1 km below sea level
(c) 1 km above sea level
(d) 1.5 km above sea level.
Ques. Conversion of starch to organic acids is required for
(a) stomatal opening
(b) stomatal closing
(c) stomatal formation
(d) stomatal activity.
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