NEET > Plant Physiology

Explore popular questions from Plant Physiology for NEET. This collection covers Plant Physiology previous year NEET questions hand picked by popular teachers.


Q 1.    

Correct4

Incorrect-1

The water potential of pure water is

A

less than zero

B

more than zero but less than one

C

more than one

Zero.

Explanation

Q 2.    

Correct4

Incorrect-1

Which of the following facilitates opening of stomatal aperture?

A

Decrease in turgidity of guard cells

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

Explanation

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 3.    

Correct4

Incorrect-1

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 the following test results indicates that it is phloem sap?

A

Acidic

Alkaline

C

Low refractive index

D

Absence of sugar

Explanation

Q 4.    

Correct4

Incorrect-1

Root pressure develops due to

A

passive absorption

active absorption

C

increase in transpiration

D

low osmotic potential in soil.

Explanation

Root pressure is positive pressure that develops in the xylem sap of the root of some plants. It is a manifestation of active water absorption.

Q 5.    

Correct4

Incorrect-1

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

tensile strength of water.

Explanation

Cohesion, adhesion and surface tension are the forces responsible for movement of water up the tracheary elements. Water molecules remain attached to one another by a strong mutual force of attraction called cohesion force. On account of cohesion force,the water column can bear a tension or pull of upto 100 atm. Therefore, the cohesion force is also called tensile strength. Its theoretical value is about 15,000 atm but the measured value inside the tracheary elements ranges between 45 atm to 207 atm. Water column does not further break its connection from the tracheary elements because of another force called adhesion force between their walls and water molecules. Another force called surface tension accounts for high capillarity through tracheids and vessels.

Q 6.    

Correct4

Incorrect-1

In a ring girdled plant

A

the shoot and root die together

B

neither root nor shoot will die

C

the shoot dies first

the root dies first.

Explanation

In girdling or ringing experiments, a ring of bark is cut from the stem. It also removes phloem. Nutrients collect above the ring, where the bark also swells up and may give rise to adventitious roots. Growth is also vigorous above the ring. The tissues below the ring not only show stoppage of growth but also begin to shrivel. Roots can be starved and killed, if the ring is not healed after some time. Killing of roots shall kill the whole plant, clearly showing that bark or phloem is involved in the movement of organic solutes towards root.

Q 7.    

Correct4

Incorrect-1

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

pulling and pushing it, respectively.

Explanation

The transpiration process, pulls water upwards with the help of cohesion and adhesion properties of water molecules. According to transpiration pull theory, due to transpiration, the water column inside the plant comes under tension.This is called 'transpiration pull'. On account of this tension, the water column is pulled up passively from below to top of the plant (almost like a rope). Root pressure is the pressure that forces water, absorbed from the soil, to move through the roots and up ({tex} i.e., {/tex} pushes it up) the stem of a plant. It may be due to both the osmosis of water from the soil into the root cells, and the active pumping of salts into xylem tissue which maintains a concentration gradient along which the water moves.

Q 8.    

Correct4

Incorrect-1

Which one gives the most valid and recent explanation for stomatal movement?

A

Starch hydrolysis

B

Guard cell photosynthesis

C

Transpiration

Potassium influx and efflux

Explanation

According to this theory, {tex} \mathrm { K } ^ { + } {/tex} ion enter and accumulate in guard cells during daytime, causing opening of stomata and during night, {tex} \mathrm { K } ^ { +} {/tex} ions move out of stomata and stomata closes.

Q 9.    

Correct4

Incorrect-1

Which of the following criteria does not pertain to facilitated transport?

A

Transport saturation

Uphill transport

C

Requirement of special membrane proteins

D

High selectivity

Explanation

Facilitated transport or facilitated division is the spontaneous passage of molecules or ions across a biological membrane passing through specific transmembrane integral proteins. Facilitated diffusion is mediated by protein channels and carrier proteins.Most transport proteins that mediate facilitated diffusion are very selective and only transport certain molecules. The major classes of proteins involved in facilitated diffusion are aquaporins, ion channels, and carrier proteins. Importantly, neither channels nor carrier proteins require energy to facilitate the transport of molecules; they enable molecules to move down their concentration gradients (downhill transport).

Q 10.    

Correct4

Incorrect-1

In land plants, the guard cells differ from other epidermal cells in having

A

cytoskeleton

B

mitochondria

C

endoplasmic reticulum

chloroplasts.

Explanation

The leaf and stem epidermis is covered with pores called stomata (sing., stoma), part of a stoma complex consisting of a pore surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts. The guard cells differ from the epidermal cells in the following aspects:
1. The guard cells are bean-shaped in surface view,while the epidermal cells are irregular in shape.
2. The guard cells contain chloroplasts, so they can manufacture food by photosynthesis (The epidermal cells do not contain chloroplasts). 3. Guard cells are the only epidermal cells that can synthesis sugar.

Q 11.    

Correct4

Incorrect-1

Guttation is the result of

A

diffusion

B

transpiration

C

osmosis

root pressure.

Explanation

Various ions from the soil are actively transported into the vascular tissues of roots, water follows its potential gradient and increase the pressure inside the xylem. This positive pressure is called root pressure.
Effect of root pressure is observable at night and early morning when evaporation is low and excess water collects in the form of droplets near the tip of leaves of many herbaceous plants. Such water loss in its liquid phase is known as guttation.

Q 12.    

Correct4

Incorrect-1

Given below is the diagram of a stomatal apparatus. In which of the following all the four parts labelled as {tex} \mathrm { A } , \mathrm { B } , \mathrm { C } {/tex} and {tex} \mathrm { D } {/tex} are correctly identified?

A

{tex}\mathrm A{/tex} - Subsidiary cell; {tex}\mathrm B{/tex} - Epidermal cell; {tex}\mathrm C {/tex} - Guard cell; {tex}\mathrm D{/tex} - Stomatal aperture

B

{tex}\mathrm A{/tex} - Guard cell; {tex}\mathrm B{/tex} - Stomatal aperture; {tex}\mathrm C {/tex} - Subsidiary cell; {tex}\mathrm D{/tex} - Epidermal cell

C

{tex}\mathrm A{/tex} - Epidermal cell; {tex}\mathrm B{/tex} - Guard cell; {tex}\mathrm C {/tex} - Stomatal aperture; {tex}\mathrm D{/tex} - Subsidiary cell

{tex}\mathrm A{/tex} - Epidermal cell; {tex}\mathrm B{/tex} - Subsidiary cell; {tex}\mathrm C {/tex} - Stomatal aperture; {tex}\mathrm D{/tex} - Guard cell

Explanation

{tex} \mathrm { A }{/tex} - Epidermal cell
{tex} \mathrm { B }{/tex} - Subsidiary cell
{tex} \mathrm { C }{/tex} -Stomatal aperture
{tex} \mathrm { D } {/tex}- Guard cell

Q 13.    

Correct4

Incorrect-1

Guard cells help in

transpiration

B

guttation

C

fighting against infection

D

protection against grazing.

Explanation

Stomata are the main organs for transpiration. The stem and leaf epidermis are provided with numerous stomata. Diffusion of water vapour through the stomatal pores is known as stomatal transpiration. Transpiration occurs while the stomata are open for the passage of carbon dioxide and oxygen during photosynthesis. Stomatal opening and closing is regulated by the movement of guard cells.

Q 14.    

Correct4

Incorrect-1

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

cohesion and adhesion.

Explanation

Cohesion, adhesion and surface tension are the forces responsible for movement of water up the tracheary elements. Water molecules remain attached to one another by a strong mutual force of attraction called cohesion force. On account of cohesion force,the water column can bear a tension or pull of upto 100 atm. Therefore, the cohesion force is also called tensile strength. Its theoretical value is about 15,000 atm but the measured value inside the tracheary elements ranges between 45 atm to 207 atm. Water column does not further break its connection from the tracheary elements because of another force called adhesion force between their walls and water molecules. Another force called surface tension accounts for high capillarity through tracheids and vessels.

Q 15.    

Correct4

Incorrect-1

Two cells A and B are contiguous. Cell A has osmotic pressure 10 atm, turgor pressure 7 atm and diffusion pressure deficit 3 atm. Cell B has osmotic pressure 8 atm, turgor pressure 3 atm and diffusion pressure deficit 5 atm.The result will be

A

no movement of water

B

equilibrium between the two

movement of water from cell A to B

D

movement of water from cell B to A.

Explanation

Diffusion pressure deficit is the reduction in the diffusion pressure of water in a system over its pure state. It is given by DPD = O.P - W.P (T.P). DPD determines the direction of net movement of water. It is always from an area or cell of lower DPD to the area or cell of higher DPD. So, cell A having lower DPD, water will move from cell A to B.

Q 16.    

Correct4

Incorrect-1

The translocation of organic solutes in sieve tube members is supported by

A

cytoplasmic streaming

B

root pressure and transpiration pull

P-proteins

D

mass flow involving a carrier and ATP.

Explanation

P-proteins (Phloem proteins) are components found in large amounts in phloem sieve tubes.
The main function of these bodies is to seal off the sieve tube element or sieve cell by bringing about the blockage of sieve plate. These bodies perform this function when the sieve element is injured. These bodies and callose together block the pores of sieve tube elements. P-protein bodies and callose form blocking plugs. These bodies remain along the walls of sieve tube elements. P-protein bodies are assigned some in the translocation of food material in the sieve tubes but is not universally accepted.

Q 17.    

Correct4

Incorrect-1

Potometer works on the principle of

A

osmotic pressure

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.

Explanation

Potometer is an instrument or apparatus with the help of which, rate of transpiration can be measured. Main types of potometers are as under:
Simple potometer, Farmer's potometer and Ganong's potometer.
The whole instrument is made of glass and is consisted of a long tube, having a side tube, bent at right angles.
A fresh plant shoot is cut under water and is inserted into the side tube through a cork, fitted into the mouth of this tube. The whole apparatus is filled with water and the joints are made air tight.
The apparatus is placed in the sunlight. Air bubble enters the tube and after this lower end of the tube is placed in the beaker, containing water. Water is absorbed by the shoot and is transpired through the leaves. Transpiration pull is created and the air bubble begins to move along with the transpiration pull.Readings are taken for the air bubble and thus amount of water absorbed and transpired is calculated.

Q 18.    

Correct4

Incorrect-1

Stomata of a plant open due to

influx of potassium ions

B

efflux of potassium ions

C

influx of hydrogen ions

D

influx of calcium ions.

Explanation

The mechanism of opening and closing of stomata is explained by active {tex}\mathrm {K^+}{/tex} ion transport theory. During day time :

During night or dark : {tex} \mathrm { CO } _ { 2 } {/tex} conc. increases in sub-stomatal cavities {tex} \square {/tex} ABA participation {tex} \square \ \mathrm { K } ^ { + } {/tex} ions exchange stopped {tex} \square \ \mathrm { K } ^ { + } {/tex} ions transported back into subsidiary cells {tex} \square {/tex} Decreased pH {tex} \square {/tex} Starch synthesized in guard cells {tex}\square{/tex} Decreased O.P. of guard cells {tex} \square {/tex} Exosmosis from guard cell {tex} \square {/tex} Stomata close.

Q 19.    

Correct4

Incorrect-1

Main function of lenticel is

A

transpiration

B

guttation

gaseous exchange

D

bleeding

Explanation

Lenticels generally appear under stomata.The lenticel of phellogen itself also has intercellular spaces. Because of this relatively open arangement of cells, the lenticels are regarded as structures permitting the entry of air through the periderm.
Lenticels are characterstics of woody stem but they are also found in roots of trees and other perennials for entry of oxygen through them.

Q 20.    

Correct4

Incorrect-1

Opening and closing of stomata is due to the

A

hormonal change in guard cells

change in turgor pressure of guard cells

C

gaseous exchange

D

respiration.

Explanation

The mechanism of opening and closing of stomata is explained by active {tex}\mathrm {K^+}{/tex} ion transport theory. During day time :

During night or dark : {tex} \mathrm { CO } _ { 2 } {/tex} conc. increases in sub-stomatal cavities {tex} \square {/tex} ABA participation {tex} \square \ \mathrm { K } ^ { + } {/tex} ions exchange stopped {tex} \square \ \mathrm { K } ^ { + } {/tex} ions transported back into subsidiary cells {tex} \square {/tex} Decreased pH {tex} \square {/tex} Starch synthesized in guard cells {tex}\square{/tex} Decreased O.P. of guard cells {tex} \square {/tex} Exosmosis from guard cell {tex} \square {/tex} Stomata close.

Q 21.    

Correct4

Incorrect-1

Passive absorption of minerals depends on

temperature

B

temperature and metabolic inhibitor

C

metabolic inhibitor

D

humidity.

Explanation

Rate of salt absorption increases when temperature increases but to a certain limit as salt absorption is inhibited at higher temperature because certain enzymes are not active at higher temperature and carriers are not synthesised. These carriers are required for active transport of salts from outer space in inner space.
Rate of diffusion of ions and molecules increases at enhanced temperature due to their increased kinetic activity. Thus passive salt absorption will increase.

Q 22.    

Correct4

Incorrect-1

Glycolate induces opening of stomata in

A

presence of oxygen

low CO{tex} _ { 2 } {/tex} concentration

C

high CO{tex} _{2 } {/tex}

D

CO{tex} _ { 2 } {/tex} absent.

Explanation

Zelitch ( 1963 ) suggested that glycolic acid is formed in the guard cells. This acid is formed under low concentration of CO{tex} _ { 2 }{/tex}. Glycolate formed gives rise to carbohydrates. Under this condition, osmotically active material is produced and ATP synthesis also takes place. ATP is produced during glyoxylate-glycolate shuttle. This ATP helps in the active pumping of water in the guard cells and stomata open. Stomata close when this process is reversed.

Q 23.    

Correct4

Incorrect-1

Loading of phloem is related to

increase of sugar in phloem

B

elongation of phloem cell

C

separation of phloem parenchyma

D

strengthening of phloem fiber.

Explanation

When the phloem cells, just near the source,for example green leaves attain higher concentration of sugars, it is called the process of phloem loading. Sucrose is photosynthesised in the chloroplasts of mesophyll cells of leaves. Mesophyll cells are connected with each other through plasmodesmata. Similarly plasmodesmata are also present between the mesophyll cells and companion cells and also between mesophyll cells and sieve tubes. There plasmodesmata are the "channels" meant for the passage of sucrose.

Q 24.    

Correct4

Incorrect-1

The movement of ions against the concentration gradient will be

active transport

B

osmosis

C

diffusion

D

all of the above.

Explanation

Active transport involves movement of materials across the membrane against the concentration gradient of the solute particles. It requires energy in the form of ATP and carrier molecules.

Q 25.    

Correct4

Incorrect-1

In soil, water available for plants is

A

gravitational water

B

chemically bound water

capillary water

D

hygroscopic water.

Explanation

Water occurs in the soil in the different forms as: free water, gravitational water, hygroscopic water, chemically combined water and capillary water. Free water is that water which runs away and is not held by the soil. Obviously it is not available to the plants. Gravitational water goes down into the deeper strata of earth and it is also, not available to the plants. Hygroscopic water is present in the form of thin films around the soil particles and it is also not available to the plants under normal condition but it may be available under adverse conditions. Chemically combined water is not available to the plants at all. The only water which is available to the plants capillary water. Capillary water makes up about 75{tex} \%{/tex} of the total water available to plants. The rest of soil water (hygroscopic, combined, free, gravitational and 25{tex} \%{/tex} capillary water) are not available to plants. These are called echard or unavailable water.