Biology

Plant Transport and Physiology

2,012 Questions

Access a comprehensive set of questions on plant transport mechanisms and physiological adaptations. Topics include water movement, translocation of food, and plant responses to external stimuli. These biology questions are essential for medical entrance exams and other science competitive tests.

Xylem and phloem transportTranspiration and evaporationPlant adaptationsGeotropic and phototropic responsesWater absorption by rootsRespiration in roots

Plant Transport and Physiology Questions

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Significance of transpiration lies in

  1. Circulation of water

  2. Absorption and distribution of water

  3. Regulating the temperature of the plant body

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Transpiration generates tension in plants. This tension is the main pulling force which pulls water to great heights in vascular plants. Thus, transpiration leads to the ascent of sap. Without transpiration water and minerals will not rise from roots to aerial parts of plants and trees. Transpiration also causes surface cooling of leaves and hence regulates the temperature of the plant body. At the same time, it is essentially a wasteful process. As much as 99 percent of water absorbed by a plant goes waste into the atmosphere. Thus, transpiration has been called as a necessary evil.

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Exchange of gases occur through 

  1. Stomata

  2. Lenticels

  3. Root surface

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In plants, gas exchange occurs through small pores in the leaf surface called stomata. Stomata can open to allow the exchange of gasses and close to reduce water loss from the plant. In the covering of the secondary structure of the stem of woody plants gas exchange is made through the lenticels of the periderm (small breaches of the cork). The cork of mature roots is also perforated by non-suberized pores called lenticels. These enable oxygen to reach the intercellular spaces of the interior tissues and carbon dioxide to be released into the atmosphere.

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Which of the following processes lower the temperature of leaves cooling effect?

  1. Respiration

  2. Photosynthesis

  3. Transpiration

  4. Hydrolysis
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Transpiration is essentially similar to evaporation of water. It is the loss of water in vapour form through stomata. Water molecules tend to remain in the liquid state rather than moving to vapour state; so during evaporation water molecules absorb a lot of heat energy, this generates a cooling effect.

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

If transpiration stops than

  1. Upward movement of water by roots will stop.

  2. Turgidity of the cells will be not be affected at all.

  3. All metabolic processes will stop.

  4. Upward movement of water by roots will continue and all the metabolic processes will occur as usual.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Most acceptable theory for the ascent of sap is the 'Physical force theory', called as 'Cohesion-Tension' or 'Cohesion-Transpiration pull theory'. This theory was put forward by Dixon and Joly. According to this theory ascent of sap in plants is a physical process, the lifting force for which is provided by the pulling force generated by transpiration. 

The cohesion forces between the water molecules help in maintaining a continuous water column and the adhesion forces between water molecules and the tracheary elements help in sticking to water to the xylary elements. Both of these forces help in maintaining a continuous water column in the xylary elements, which is lifted up by transpiration pull. Hence, if transpiration stops upward movement of water from roots will stop.

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Which of the following can regulate the rate of transpiration?

  1. Endodermal cells

  2. Mesothermal cells

  3. Stomata

  4. Roots
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Stomata can regulate the rate of transpiration by simply controlling how open or closed they are (via the guard cells). Stomata that are open wider will facilitate a greater rate of transpiration, while stomata that are more narrowly opened will reduce the rate of transpiration.

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Choose the correct answers from the alternatives given.
Which of the following is not a part of the transpiration cohesion-adhesion theory of the ascent of xylem sap?

  1. The evaporation of water from the mesophyll cells, which initiates a pull of water molecules from neighbouring cells and eventually from the tracheids

  2. The transfer of this pull from one water molecule to the next due to the cohesion caused by hydrogen bonds

  3. The hydrophilic walls of the narrow tracheids and vessels that help to maintain the column of water against the force of gravity

  4. The use of proton pumps to create membrane potentials that facilitate the accumulation of mineral ions.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The forces of cohesion (attraction among water molecules) and adhesion (attraction between water molecules and the walls of the xylem vessels), together help to form a thin, unbroken column of water which leads to the mass flow of water in apoplastic pathways. These forces act due to the cohesive and adhesive properties of water. In plants, the capillarity is aided by the small diameter of the tracheary elements like the tracheids and the vessel elements. The proton pump has no role in the facilitation of water and minerals.

Hence,the correct answer is 'The use of proton pumps to create membrane potentials that facilitate the accumulation of mineral ions'.

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Generally stomata found on the lower surface of leaf. Thus, approximate percentage of transpiration through abaxial surface is

  1. 47 %

  2. 57 %

  3. 67 %

  4. 97 %
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Stomata are usually confined in more number on the lower sides of the leaves. The lower surface is called as abaxial surface and the upper surface is called as the adaxial surface. Hence, maximum percentage i.e., 80- 95% of transpiration occurs from the lower surface.

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Which one is the driving force for the process of passive absorption of water in roots?

  1. Root pressure

  2. Transpiration in leaves

  3. Activity of aquaporins

  4. Increase in imbibition pressure in root cells
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Passive absorption is absorption by the pull from transpiration without the active involvement of root cells, The shoots and leaves of the plant experience transpiration due to evaporation of water from their surface.

So, the answer is, "Transpiration in leaves".

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Transpiration ratio is the ratio of moles of H$ _{2}$O transpired / moles of CO$ _{2}$ fixed. This ratio is measure of

  1. The efficiency of guard cells on stomatal movement.

  2. Effectiveness of stomata is maximizing photosynthesis, while minimizing water loss.

  3. Distinguishing a xerophyte from a glycophyte.

  4. Stomatal pore size of the leaves.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Water is required to generate the reducing power, which is used to reduce carbon dioxide during photosynthesis. The water molecules are split up and oxygen released as a by-product. The protons are used to synthesize reducing power. Now all the water that is absorbed is never used up. In fact, the water that is actually used is a small fraction of water that is absorbed. Hence, transpiration ratio is calculated to find out the effectiveness of stomata in maximizing photosynthesis and minimizing loss of water.

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Water moves up against gravity and even for a tree of $20$m height, the tip receives water within two hours. The most important physiological phenomenon which is responsible for the upward movement of water is ____________.

  1. Cohesive forces

  2. Adhesive forces

  3. Transpiration pull

  4. Root pressure
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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). A tension of one atmosphere is sufficient to pull water to a height of about $20$ meters.

So, the correct answer is 'Transpiration pull'

Multiple choice botany the leaf mechanism of absorption mineral absorption significance of transpiration

Choose the correct answers from the alternatives given.
Which of the following forces is responsible for moving water up to the tops of the tallest trees?

  1. Atmospheric pressure

  2. Root pressure

  3. Guttation

  4. Transpiration
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Loss of water from the leaves causes water stress to develop from the top of the trees which forces more and more water to rise from the roots to the leaves. The column of the water is maintained due to cohesion and adhesion forces and the water moves up due to transpiration pull.

Hence,the correct answer is 'Transpiration'.

Multiple choice biology tissues, organs, organ system, organism tissues of animals animal tissues and its type tissues: animal tissues fluid connective tissue

State whether true or false. 

The epidermal layer in plants does not have intercellular spaces. 

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The epidermis is the outermost cellular layer which covers the whole plant structure, i.e., it covers roots, stem, leaves, flowers and fruit. It is composed of a single layer of living cells, although there are exceptions. The epidermis is usually closely packed, without intercellular spaces or chloroplasts.