NEET Biology: Transport in Plants questions with solutions

Q1. Chemical analysis of phloem shows the presence of

1. More amount of carbohydrates
2. organic nitrogenous compounds
3. Minerals
4. Both A and B

Answer: Both A and B

Phloem carries photosynthates, so it contains a high amount of carbohydrates. It also transports organic nitrogenous compounds such as amino acids, which is why both A and B are present.

Q2. The force responsible for raising water in \( 100 \mathrm{ft} \) tall plant is

1. Transpiration pull
2. Root pressure
3. Air pressure
4. Capillary action

Answer: Transpiration pull

Transpiration from the leaves creates negative pressure (tension) in the xylem, pulling water upward over great heights. Root pressure and capillary action are too weak to raise water to about 100 ft.

Q3. Xylem translocates:

1. Water only
2. Water and mineral salts only
3. Water, mineral salts and some organic nitrogen only
4. Water, mineral salts, some organic nitrogen and hormones

Answer: Water, mineral salts, some organic nitrogen and hormones

Xylem mainly transports water and mineral ions, but it can also carry small amounts of organic nitrogen compounds and hormones. So the most complete option is the one including all of these substances.

Q4. In a ring girdled plant:

1. The root dies first
2. The shoot and root die together
3. Neither root nor shoot will die
4. The shoot dies first

Answer: The root dies first

In a ring-girdled plant, the phloem is removed or damaged, stopping the downward movement of food from the leaves to the roots. The roots are cut off from their energy supply first, so they die before the shoot.

Q5. Loading of phloem is related to

1. increase of sugar in phloem
2. elongation of phloem cell
3. separation of phloem parenchyma
4. strengthening of phloem fibre

Answer: increase of sugar in phloem

Phloem loading is the process of adding sugars, mainly sucrose, into the phloem sieve elements. This increases sugar concentration and helps create the pressure gradient needed for translocation.

Q6. Sieve tubes are suited for translocation of food because they possess

1. bordered pits
2. no end walls
3. broader lumen and perforated cross walls
4. no protoplasm

Answer: broader lumen and perforated cross walls

Sieve tubes transport sugars efficiently because their cells form long conducting channels with a broad lumen, and the sieve plates (perforated cross walls) allow sap to pass from one element to the next. This structure minimizes obstruction and supports mass flow of food.

Q7. Which of the following facilitates opening of stomatal aperture?

1. Decrease in turgidity of guard cells
2. Radial orientation of cellulose microfibrils in the cell wall of guard cells
3. Longitudinal orientation of cellulose microfibrils in the cell wall of guard cells
4. Contraction of outer wall of guard cells

Answer: Radial orientation of cellulose microfibrils in the cell wall of guard cells

Radially arranged cellulose microfibrils make the guard-cell wall expand unevenly, so turgor pressure bends the cells apart and opens the pore. The other options either reduce turgor or describe wall behavior that would not promote opening.

Q8. The process responsible for facilitating loss of water in liquid form from the tip of grass blades at night and in early morning is?

1. Root pressure
2. Imbibition
3. Plasmolysis
4. Transpiration

Answer: Root pressure

Root pressure is the positive pressure generated in roots that can force water out through leaf tips or margins as droplets, especially at night or early morning. This is the process behind guttation, not transpiration.

Q9. Which of the following is not a feature of active transport of solutes in plants?

1. Requires ATP
2. Occurs against concentration gradient
3. Non-selective
4. Occurs through membranes

Answer: Non-selective

Active transport in plants is selective because membrane transport proteins recognize specific ions or molecules. It also uses ATP, moves substances against their concentration gradient, and occurs across membranes.

Q10. The water potential of pure water is:

1. Less than zero
2. More than zero but less than one
3. More than one
4. Zero

Answer: Zero

Water potential is defined relative to pure water at standard pressure, and pure water is assigned a value of zero. Any solute or pressure change makes the value deviate from zero.

Q11. What will be the direction of flow of water when a plant cell is placed in a hypotonic solution?

1. No flow of water in any direction.
2. Water will flow in both directions.
3. Water will flow out of the cell.
4. Water will flow into the cell.

Answer: Water will flow into the cell.

A hypotonic solution has a lower solute concentration than the plant cell, so water enters the cell by osmosis. This makes the cell become turgid as water moves inward.

Q12. 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:

1. no movement of water
2. equilibrium between the two
3. movement of water from cell A to B
4. movement of water from cell B to A

Answer: movement of water from cell B to A

Water moves from a region of lower diffusion pressure deficit to higher diffusion pressure deficit. Since cell B has DPD 5 atm and cell A has DPD 3 atm, water will move from B to A. This also matches the idea that the cell with lower turgor and higher net suction draws water in.

Q13. Which one gives the most valid and recent explanation for stomatal movements?

1. Potassium influx and efflux
2. Starch hydrolysis
3. Guard cell photosynthesis
4. Transpiration

Answer: Potassium influx and efflux

The most accepted modern explanation is the potassium ion theory: K+ influx into guard cells lowers water potential, water enters, and stomata open; K+ efflux reverses this and closes them. This is more valid and recent than older ideas like starch hydrolysis.

Q14. When water moves through a semi permeable membrane then which of the following pressure develops?

1. O. P.
2. S. P.
3. T. P.
4. W. P.

Answer: O. P.

The pressure developed due to osmosis across a semipermeable membrane is osmotic pressure. It is the pressure needed to prevent the net movement of water through the membrane.

Q15. Water potential of actively absorbing cells is:

1. always +ve
2. always –ve
3. always 0
4. always > 1

Answer: always –ve

Actively absorbing cells contain dissolved solutes, which lower their water potential below that of pure water. A lower water potential means it is negative relative to zero for pure water.

Q16. The water potential and osmotic potential of pure water are:

1. zero and zero
2. 100 and 100
3. zero and 100
4. 100 and zero

Answer: zero and zero

Pure water is the standard reference, so its water potential is defined as zero. With no dissolved solutes, there is no osmotic effect, so osmotic potential is also zero.

Q17. Water potential in the leaf tissue is positive (+) during

1. excessive transpiration
2. low transpiration
3. excessive absorption
4. guttation

Answer: guttation

During guttation, root pressure forces xylem sap out through hydathodes as liquid droplets, so the leaf tissue can have positive pressure potential. In transpiration, water potential is generally negative because water is being pulled out as vapor.

Q18. Water potential is equal to

1. ψs + ψp
2. ψs = T.P.
3. ψp + ψw
4. ψs + ψp

Answer: ψs + ψp

Water potential (ψw) is determined by the combined effects of solute potential (ψs) and pressure potential (ψp). In plant physiology, ψw = ψs + ψp, so the correct choice is the one showing that sum.

Q19. With increase in the turgidity of a cell surrounded by water the wall pressure will:

1. increase
2. decrease
3. fluctuate
4. remain unchanged

Answer: increase

When a cell becomes more turgid, water enters and the protoplast presses harder against the cell wall. This increases wall pressure because the wall must resist a greater outward force.

Q20. Root pressure develops due to:

1. Low osmotic potential in soil
2. Passive absorption
3. Increase in transpiration
4. Active absorption

Answer: Active absorption

Root pressure is generated when root cells actively transport mineral ions into the xylem, lowering water potential and causing water to enter by osmosis. This buildup of positive pressure is therefore linked to active absorption, not transpiration or passive uptake.