Transport in Plants (PYQs)

Correct Answer: (c)
Substances that have a hydrophilic moiety, find it difficult to pass through the membrane, their movement has to be facilitated by the membrane protein without expenditure of ATP energy. Facilitated diffusion cannot cause net transport of molecules from a low to a high concentration or uphill transport.

Correct Answer: (a)
Guard cells help in transpiration. Transpiration is the evaporation of water from the aerial parts of plants, especially leaves but also stems, flowers and roots. Stomatal opening allows the diffusion of carbon dioxide and oxygen during photosynthesis.

Correct Answer: (d)
Stomata present on lower surface of plant leaves effectively exchange gases without allowing much loss of water from the leaves.

Correct Answer: (c)
Passive absorption is the movement of solvent particles from a region of low solute concentration to a region of high solute concentration through a selectively permeable membrane. Active absorption involves use of ATP.

Correct Answer: (b)
Imbibition pressures developed during germination of seeds and spores are of higher magnitude. Imbibition is the first step in germination of seeds. When the seeds are soaked in water, they imbibe water and swell. The water is imbibed by the seed coat and then by other tissues of embryo and endosperm. Thus, the process of imbibition initiates the seed germination.

Correct Answer: (d)
A fresh water protozoan when placed in marine water medium, loss of water takes place i.e., exosmosis. Hence the contractile vacuole will decrease in size.

Correct Answer: (b)
During scarcity of water in the soil, stress hormone abscisic acid is produced which brings about stomatal closure. ABA inhibits the uptake of K+ by the guard cells and promotes leakage of malic acid from guard cell due to results in loss of water from guard cell due to its lower osmotic potential. Guard cell becomes flaccid leading to closure of stomatal aperture. ABA also causes stomatal closure under high concentration of CO2 in the guard cells.

Correct Answer: (b)
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.

Correct Answer: (d)
Light, temperature and concentration of CO2 affect opening and closing of stomata. They are not affected by O2 concentration.

Correct Answer: (a)
Guttation is mainly due to root pressure.

Correct Answer: (d)
Transpiration is a process of loss of water in the form of vapours from the aerial parts of the plants. Transpiration is inversely proportional to the air humidity. Thus higher the rate of transpiration would be higher when humidity is low.

Correct Answer: (b)
Potometer : It is an apparatus for measuring the rate of transpiration.

Correct Answer: (a)
Wall pressure is equal and opposite to the turgor pressure. Wall pressure (WP) may be defined as ‘the pressure exerted by the cell wall over the protoplast to counter the turgor pressure. Normally wall pressure is equal and opposite of turgor pressure (WP = TP) except when the cell become flaccid.

Correct Answer: (b)
Phenyl Mercuric Acetate (PMA) is an antitranspirant. Antitranspirants are compounds applied to the leaves of plants to reduce transpiration without affecting gaseous exchange. They are used on christmas trees, cut flowers, newly transplanted shrubs, and in other applications to preserve and protect plants from drying out too quickly. They have also been reportedly used to protect leaves from salt burn and fungal diseases. Anti Transpirants are of two types: 1. Metabolic inhibitors 2. Film forming antitranspirants

Correct Answer: (b)
The rupture and fractionation do not usually occur in the water column in vessel/tracheids during the ascent of sap because of cohesion and tension. The water molecules have a great mutual attraction to each other or tremendous cohesive power which is sometimes as much as 350 atmospheres. Thus, the transpiration pull develops a negative pressure in the uppermost xylem cells. It is transmitted from there into the xylem of stems, and then to the roots.

Correct Answer: (a)
Starch is converted to malic acid (organic acid) through the action of an enzyme phosphoenol pyruvate carboxylase (PEPC) under condition of high pH when most of the CO2 is utilized due to high photosynthetic rate during daytime.

Correct Answer: (d)
When a plant cell is placed in hypotonic solution water will flow into the cell as water moves from high water potential to low water potential.

Correct Answer: (b)
P-protein is the supporting factor for the translocation of organic solutes in sieve tubes. (Note: Key says (b) mess flow involving a carrier and ATP. But standard text suggests Mass Flow Hypothesis (Munch) is driven by turgor pressure gradient, not direct ATP in the sieve tube flow itself, but ATP is used in loading/unloading. 'Carrier' might refer to loading mechanism. However, P-proteins are phloem proteins involved in sealing damaged sieve tubes. The most accepted mechanism is Mass flow (bulk flow). Option (b) is likely referring to Mass flow (spelled mess flow?) and active loading. Answer Key in PDF is (b). So I will stick to (b) Mass flow involving carrier and ATP).

Correct Answer: (d)
The main cause of guttation in plants is root pressure. During night when root pressure is high, water drops ooze out with the assistance of special structures called hydathodes which help in guttation.

Correct Answer: (b)
Movement of ions against concentration gradient involves the expenditure of energy. Diffusion involves the movement of solute particles from region of higher concentration to a region of lower concentration. Pinocytosis is cell drinking. Brownian movement is the random to and fro movement of atoms and molecules.

Correct Answer: (d)
The direction of movement of sugar in phloem is bi-directional. The Pressure Flow Hypothesis, also known as the Mass Flow Hypothesis, is the best-supported theory to explain the movement of sap through the phloem. It was proposed by Ernst Munch, a German plant physiologist in 1930. A high concentration of organic substances, particularly sugar, inside cells of the phloem at a source, such as a leaf, creates a diffusion gradient (osmotic gradient) that draws water into the cells from the adjacent xylem. This creates turgor pressure, also known as hydrostatic pressure, in the phloem. Movement of phloem sap occurs by bulk flow (mass flow) from sugar sources to sugar sinks. The movement in phloem is bidirectional, whereas, in xylem it is unidirectional (upward). Because of this multi-directional flow, coupled with the fact that sap cannot move with ease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to be flowing in opposite directions.

Correct Answer: (a)
Osmotic potential is the potential of a solution to cause movement of water into it across a semi- permeable membrane. Water potential is the tendency of water to leave a system. For pure water, both are zero.

Correct Answer: (c)
Closure of lid of pitcher in a pitcher plant is a paratonic movement (nastic movement) induced by touch of insect (Thigmonasty). (Note: Key says (c) Paratonic movement. Explanation mentions Turgor movement is involved in leaf movements like Mimosa, but pitcher closure is often cited as thigmonastic/paratonic due to external stimulus).

Correct Answer: (c)
Carbohydrates are commonly found as starch in plant storage organs. It is chemically non-reactive and osmotically inactive polysaccharide with a molecular weight. Carbohydrates perform a vital role in living organisms. Starch and other polysaccharides serve as energy storage in plants, particularly in seeds, tubers, etc. which provide a major energy source for animals, including humans.

Correct Answer: (d)
Translocation of organic solutes occur through sieve tubes in the form of sucrose. Transportable form of sugar is sucrose.

Correct Answer: (b)
During day time, due to photosynthesis, malic acid forms, which breaks into H+ and malate. H+ ions move out of guard cells and K+ ions enter forming potassium malate which makes guard cells turgid and stomata opens.

Correct Answer: (c)
The hydrostatic pressure developed inside the cell wall due to endosmosis is called turgor pressure. Due to turgor pressure, the rigid cell wall offers resistance. This resistance which works in a direction opposite to turgor pressure is the wall pressure.

Correct Answer: (d)
The rate of transpiration is inversely proportional to the atmospheric pressure. Increased height above the sea level lowers the atmospheric pressure and increases the rate of evaporation.

Correct Answer: (a)
Due to tensile strength of water, a column of water within xylem vessels of tall trees does not break under its weight.

Correct Answer: (c)
The principal pathway of water translocation in angiosperms is xylem vessel system.

Correct Answer: (b)
Water potential is regarded as the tendency of water to leave a system. Pure water has the highest possible water potential which is zero. All solutions have a water potential lower than that of pure water.

Correct Answer: (b)
Minerals can move upward and downward (bidirectional movement) as well as laterally in phloem. Phloem plays an important role in translocation of minerals.

Correct Answer: (b)
Active transport always involves the expenditure of energy for the movement of substances against concentration gradient.

Correct Answer: (c)
D.P.D. or suction pressure (S.P.) = O.P. – T. P. Hence D.P.D. for A = 4 bars, B = 0 bars, C = 5 bars, D = 4 bars. We know that direction of movement of water is from lower D.P.D. (S.P.) to higher D.P.D. (S.P.). Thus flow will be from B to A, C, and D.

Correct Answer: (c)
Water movement between cells is due to D.P.D (Diffusion Pressure Deficit). Water moves from lower DPD to higher DPD.

Correct Answer: (d)
By convention, the water potential of pure water at standard temperature, which is not under any pressure, is taken to be zero.

Correct Answer: (a)
Grass being a monocot, has dumb-bell shaped stomata in their leaves.

Correct Answer: (a)
Root pressure is positive hydrostatic pressure. It develops in tracheary element at night and in early morning.

Correct Answer: (d)
Bending of tentacles in Venus fly trap or Drosera after coming in contact with an insect is thigmonastic or chemonastic movement of variation or turgor movement. The mechanism by which the trap snaps shut involves a complex interaction between elasticity, turgor and growth. In the open, untripped state, the lobes are convex , but in the closed state, the lobes are concave. It is the rapid flipping of this bistable state that closes the trap, but the mechanism by which this occurs is still poorly understood. When the trigger hairs are stimulated, an action potential involving calcium ions is generated, which propagates across the lobes and stimulates cells in the lobes and in the midrib between them. These cells become flaccid due to water loss. Loss of turgor pressure in these cells causes leaves to “roll up” during water stress.

Correct Answer: (a)
The opening and closing of stomata are caused by influx and efflux of potassium ions (K+). The increase of K+ results in opening of stoma and decrease of K+ causes closing of stoma. The turgidity of guard cells induces the opening of the pores of stomata found on the surface of leaves.

Correct Answer: (c)
Active transport is highly selective.

Correct Answer: (c)
In active transport, materials are transported across a membrane with the help of mobile carrier protein and ATP. In passive transport, substances move along the concentration gradient, i.e., from its higher concentration to its lower concentration.

Correct Answer: (d)
Transpiration pull and cohesion theory of Dixon and Jolly is the most widely accepted theory for ascent of sap.

Correct Answer: (a)
Minerals absorbed by roots move to the leaf through xylem. This movement is upward.

Correct Answer: (d)
Turgor pressure is the pressure that develops in a cell due to osmotic diffusion of water inside it and is responsible for pushing the membrane against cell wall. Stomata open under conditions of increased turgor pressure in guard cells and close under conditions of decreased turgor pressure in guard cells. When turgid, they swell and bend outward. As a result, the stomatal aperture opens. When they are flaccid, the tension from the wall is released and stomatal aperture closes.

Correct Answer: (b)
Under water logged conditions, roots die due to lack of air for respiration.

Correct Answer: (b)
Potometer is an apparatus used for measuring the rate of transpiration. The potometer does not measure the rate of transpiration accurately because not all of the water that is taken by the plant is used for transpiration (water taken might be used for photosynthesis or by the cells to maintain turgidity). The potometer measures the rate of uptake of water. To measure transpiration rate directly, rather than the rate of water uptake, utilize a scientific instrument which quantifies water transfer at the leaves.

Correct Answer: (d)
Pure water has maximum water potential. Water potential in the leaf tissue becomes greater than pure water under conditions of excessive humidity when the leaves cannot lose water by transpiration. Hence, water is lost as droplets via hydathodes by the process of guttation.

Correct Answer: (b)
Transpiration is responsible for saturation of the atmosphere.

Correct Answer: (a)
Transpiration creates pulling (Negative pressure) force. Root pressure creates positive pressure pushed in xylem. It is measured by manometer.

Correct Answer: (b)
Capillary water is the water held in the pores of the soil that is available to plant roots.

Correct Answer: (b)
Bulliform cells are large, bubble-shaped epidermal cells that occur in groups on the upper surface of the leaves of many grasses. These cells become flaccid due to water loss. Loss of turgor pressure in these cells causes leaves to “roll up” during water stress.

Correct Answer: (d)
Active absorption creates root pressure. Root pressure, the expenditure of hydrostatic pressure place for the movement of substances against concentration gradient.

Correct Answer: (c)
Movement of water will be from low DPD to high DPD i.e from A to B. DPD of A = 3 atm. DPD of B = 5 atm. Water moves from A (lower DPD) to B (higher DPD).

Correct Answer: (d)
Water potential is defined as the difference between the chemical potential of water at any point in a system and that of pure water under standard conditions. The unit of measurement of water potential is pascal, Pa (1 mega pascal, Mpa = 10 bars). It is represented by greek letter PSi (ψ). Water potential has two components- solute potential which is always negative and pressure potential which is usually positive. Therefore water potential ψw is expressed as: ψw = ψs + ψp

Correct Answer: (a)
When sugar is converted into starch, the osmotic concentration of guard cells fall and they lose water to adjacent cells and stomata closes.

Correct Answer: (a)
Nerium is a xerophytic plant and has sunken stomata, confined to lower epidermis to reduce the rate of transpiration. Nerium oleander L. (Apocynaceae), the only species currently classified in the genus Nerium, is an evergreen shrub or small with all parts of the plant being toxic . It is cultivated worldwide and is one of the most poisonous of commonly grown garden plants.

Correct Answer: (a)
Pistia is a hydrophyte plant where absorption of water by root is not important.