Tag: significance of transpiration

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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

Water is ideal material for disposal of excess solar energy because

  1. Water is easily available and its specific heat is high

  2. Water evaporates from leaf surface and its latent heat is high

  3. Water is general solvent

  4. Upward movement of water creates a difference in water potential
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When plants use solar energy for the synthesis of their food, only a small part of solar energy used,  rest of the part of this energy evaporate from the surface of leaves by the process of transpiration and due to its high latent heat. It is the best material for disposing excess  solar energy.

So the correct answer is B. 

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

Who said that "transpiration is a necessary evil"?

  1. Bose

  2. Steward

  3. Anderson

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

Curtis proclaimed that transpiration is a necessary evil. Stomata allows gaseous exchange. Carbon dioxide is taken in for its fixation by Calvin cycle and oxygen produced during the photolysis is given out. This gaseous exchange takes place by the process of diffusion. When the stomata open for the gaseous exchange, the water vapor is lost by the process of transpiration.

So, the correct answer is option D.

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

Grafted flower is contained in saline water because

  1. Suitable nutrient available to flower

  2. Flower remains fresh in long duration due to less transpiration

  3. The flower is protected by microbes

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Water moves from high water potential to less water potential. Also it is assumed that transpiration loss of water equals water absorption. In saline water there will be less of transpiration loss as absorption will be less. Consequently there are less chances of wilting.