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Biology
Transport in Plants
48 questions from 28 papers, each with its answer.
- 48 questions
- 28 papers
- 1.36% of Biology
Transpiration – Transpiration Pull
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Given below are two statements: Statement I: The forces generated by transpiration can lift a xylem-sized column of water over 130 meters height. Statement II: Transpiration cools leaf surfaces sometimes 10 to 15 degrees, by evaporative cooling. In the light of the above statements, choose the correct answer from the options given below:
Transpiration pull can lift water over 130 m and evaporative cooling lowers leaf temperature.
A system of xylem vessels from the root to the leaf vein can supply the needed water. A pull force is created as water evaporates through stomata. These forces generated by transpiration can create pressure sufficient to lift a xylem-sized column of water over 130 metres high. Apart from creating transpiration pull for absorption and transport of plants it also helps in cooling leaf surfaces, sometimes 10 to 15 degrees by evaporative cooling.
Water Movement up a Plant – Properties of Water
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Match List-1 with List-2.
Pick the matching item from Column II for each row.
Column I
- A. Cohesion
- B. Adhesion
- C. Surface tension
- D. Guttation
Column II
- I. More attraction in liquid phase
- II. Mutual attraction among water molecules
- III. Water loss in liquid phase
- IV. Attraction towards polar surfaces
Correct answer: A → II, B → IV, C → I, D → III
Water Absorption by Roots – Apoplast Pathway
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Which of the following is not observed during apoplastic pathway?
Transport in Xylem
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Xylem translocates:
Phloem transport - pressure flow hypothesis
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Which of the following helps in maintenance of the pressure gradient in sieve tubes?Companion cells are closely associated with sieve tube elements and help maintain the pressure gradient required for translocation of food (loading and unloading of sugars) through the sieve tubes.
Phloem transport and mineral nutrient mobility
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Select the incorrect statement.Unloading of sucrose at the sink (during phloem transport, the pressure flow/mass flow mechanism) does actively involve the utilization of ATP (active transport), so the statement that it does not involve ATP utilization is incorrect.
Mass flow hypothesis of phloem transport
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Identify the correct statements regarding Mass flow hypothesis. (A) Mass flow is faster than diffusion. (B) Mass flow is the result of pressure difference between the end points. (C) Different substances involved in mass flow move at different paces. (D) Mass flow can result through either a positive or a negative hydrostatic pressure gradient. Choose the correct answer from the options given below:Mass flow (bulk flow) is faster than diffusion (A is correct) and results from a pressure gradient (positive or negative) between the source and sink ends (B and D are correct). However, in mass flow, all substances move together at the same rate/pace (they are simply carried along in the bulk flow), not at different paces — so C is incorrect. Correct: A, B, D only.
Direction of translocation in phloem vs xylem
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Given below are two statements: Statement I: The process of translocation through phloem is unidirectional but through xylem, it is bidirectional. Statement II: The most readily mobilized elements are phosphorus, sulphur, nitrogen and potassium. In the light of the above statements, choose the most appropriate answer from the options given below:Translocation through the phloem is actually bidirectional (can move up or down depending on source-sink relationships), while movement through the xylem is generally unidirectional (upward) — so Statement I, which states the opposite, is incorrect. The most readily mobilized mineral elements are indeed phosphorus, sulphur, nitrogen and potassium, so Statement II is correct.
Transpiration – mechanism of stomatal opening
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Which of the following facilitates opening of stomatal aperture?
Radial microfibrils let turgid guard cells bow outwards.
Cellulose microfibrils in the guard cell walls are oriented radially rather than longitudinally, which makes it easy for the stoma to open when guard cells become turgid.
Transpiration and gas exchange through stomata
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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 the following options.
$H_2O$ and $CO_2$ diffuse independently along their own gradients.
Stomata are the only openings through which exchange of oxygen, carbon dioxide and water occurs. Diffusion of $CO_2$ and water vapour can occur together, as each depends on the partial pressure gradient of the respective gas between the cells and the surrounding air (and they have different diffusion coefficients).
Phloem transport – nature of phloem sap
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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?
Phloem transport
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Function of companion cells isSieve tube elements lack a nucleus at maturity, and their functions are controlled by the nucleus of the adjacent companion cells, to which they are connected by pit fields.
According to the pressure flow (mass flow) hypothesis, sucrose made in the mesophyll cells is moved into the companion cells and then into the living sieve tube cells by active transport. This is called phloem loading.
Because loading is active (it uses ATP), it is not a passive process.
Loading makes the phloem hypertonic, so water enters it from the xylem by osmosis; the companion cells do not supply water.
Hence the function of companion cells is loading of sucrose into sieve elements. -
The translocation of organic solutes in sieve tube members is supported by -The accepted mechanism for the translocation of sugars from source to sink is the pressure flow or mass flow hypothesis.
At the source (for example a leaf), sucrose is moved into the companion cells and then into the sieve tube cells by active transport, using carrier proteins and the energy of ATP. This is phloem loading.
Loading makes the phloem sap hypertonic, so water enters the sieve tubes from the adjacent xylem by osmosis and builds up a high turgor pressure.
This pressure pushes the sap in bulk through the sieve tubes towards the sink, where the pressure is lower.
At the sink, the sugar is again removed actively (phloem unloading), and water moves out.
Root pressure and transpiration pull are concerned with the ascent of water in xylem.
So translocation in sieve tube members is supported by mass flow involving a carrier and ATP.
Plant-Water Relations
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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 beDiffusion pressure deficit (DPD) = osmotic pressure (OP) - turgor pressure (TP).
For cell A: DPD = 10 - 7 = 3 atm.
For cell B: DPD = 8 - 3 = 5 atm.
DPD is the suction pressure of a cell; it measures the ability of the cell to absorb water.
Water always moves from a cell with lower DPD to a cell with higher DPD (i.e. from higher water potential to lower water potential), whatever the osmotic pressures may be.
Cell B has the higher DPD (5 atm) and cell A has the lower DPD (3 atm).
So water will move from cell A to cell B, even though cell A has the higher osmotic pressure.
Plant Movements
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The ability of the Venus Flytrap to capture insects is due to -The Venus flytrap (Dionaea muscipula) is an insectivorous plant. Each leaf has two lobes bearing sensitive trigger hairs.
When an insect touches the trigger hairs (usually twice), an electrical signal is generated.
This causes a rapid change in the turgor pressure of the cells at the midrib and in the lobes, as water moves rapidly out of some cells and into others.
As a result the lobes snap shut in a fraction of a second and the marginal bristles interlock, trapping the insect.
Plants do not have muscle cells, and the closure is an active response of the plant, not a passive one; chemical stimulation by the prey only keeps the trap closed for digestion.
So the ability of the Venus flytrap to capture insects is due to rapid turgor pressure changes.
Absorption of Mineral Ions
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Passive absorption of minerals depends onPassive absorption of minerals takes place by diffusion, ion exchange and mass flow, along a concentration gradient, without using metabolic energy (ATP).
So it is not affected by metabolic inhibitors (which affect only active absorption).
However, the rate of diffusion depends on temperature, since molecules move faster at higher temperature.
So passive absorption of minerals depends on temperature.
That is every question in Transport in Plants for this filter.
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