Tag: regulation of stomatal opening

Questions Related to regulation of stomatal opening

The opening and closing of stomata in leaves of mesospheric plants is regulated by.

botany transport in plant homeostasis in plants regulation of stomatal opening stomata

  1. Changes in $CO _2$, K$+$ ions, and ABA concentration with simultaneous changes in the turgidity/flaccidity of guard cells

  2. Changes in the starch-sugar concentration in the guard cell

  3. Changes in the $H^+$ concentration in the guard cells

  4. Differential thickening of walls of the guard cells

Show answer
Correct Option: A

Choose the correct answers from the alternatives given.
Stomata open when guard cells

botany transport in plant homeostasis in plants regulation of stomatal opening stomata

  1. Sense an increase in CO2 in the air spaces of the leaf

  2. Flop open due to a decrease in turgor pressure

  3. Become more turgid due to an influx of $K^+$ followed by the osmotic flow of water

  4. Accumulate water by active transport

Show answer
Correct Option: C
Explanation:

When the concentration of the potassium ions and malate ions increase guard cells form potassium malate and stores it in vacuoles of the guard cells. This increases the osmotic concentration and hence water enters the guard cells by endosmosis. The turgor pressure of the guard cells increases due to endosmosis which finally leads to the opening of the stomata.

Hence,the correct answer is 'Become more turgid due to an influx of $K^+$ followed by the osmotic flow of water'.

Choose the correct answers from the alternatives given.
Which of the following changes in the cell sap of the guard cells is responsible for keeping stomata open during day time?

botany transport in plant homeostasis in plants regulation of stomatal opening stomata

  1. Decrease in osmotic pressure but increase in turgor pressure

  2. Increase in osmotic pressure but decrease in turgor pressure

  3. Increase in both osmotic and turgor pressures

  4. Decrease in both osmotic and turgor pressures

Show answer
Correct Option: C
Explanation:

The increased concentrations of potassium ions are balanced by malate ions that form potassium malate. This is stored in the vacuoles of the guard cells, increasing the osmotic concentration. Hence, the water enters the guard cells by endosmosis. The turgor pressure of the guard cells also increases due to this endosmosis causing the stomata to open.

Hence, the correct answer is 'Increase in both osmotic and turgor pressures'.

As the guard cells become turgid, outward stretching of their inner walls, open the stomata.

botany transport in plant homeostasis in plants regulation of stomatal opening stomata

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

When guard cells become turgid the inner wall cannot move in vertical direction or along the longitudinal axis. Neither it can move or stretch on inner side. This is because of extra cellulose deposition on inner wall and radial microfibrils emerging from the inner wall.
So as guard cells become turgid and pressure builds up, the outer wall is pushed outside, which pulls the inner wall towards outside, or radially outwards. This opens the stomatal pore.

Who explained the mechanism of opening and closing of scotoactive stomata?

botany transport in plant homeostasis in plants regulation of stomatal opening stomata

  1. Nishida

  2. Scarth

  3. Zelitch

  4. Levitt

Show answer
Correct Option: A
Explanation:

Scotoactive stomata are the stomata, which open in dark and close during the day time. Scotoactive stomata occur in succulents, e.g., cactus and bryophyllum. Succulents perform crassulacean acid metabolism or CAM in their photosynthesis. Nishida explained in succulents during night there is accumulation of organic acids, whereas during day time the organic acids breakdown releasing carbon dioxide, which keeps stomata closed. During night, because of formation of organic acids carbon dioxide is consumed and concentration of carbon dioxide is less.

The correct hypothesis to explain opening of stomata during night in succulent plants is

botany transport in plant homeostasis in plants regulation of stomatal opening stomata

  1. $CO _2$ used, pH increases and results in the accumulation of sugars.

  2. $CO _2$ accumulates, reduces pH and stimulates enzymes to bring about accumulation of sugars.

  3. Low $CO _2$ concentration, accumulation of organic acids resulting in the increased concentration of cell sap.

  4. Increases in $CO _2$ concentration brings conversion of organic acids into starch resulting in an increased uptake of $K^+$ and water.

Show answer
Correct Option: C
Explanation:

Scotoactive stomata are the stomata, which open in dark and close during the day time. Scotoactive stomata occur in succulents, e.g., cactus and bryophyllum. Succulents perform crassulacean acid metabolism or CAM in their photosynthesis. Nishida explained, that in succulents during night there is accumulation of organic acids, whereas, during day time the organic acids breakdown releasing carbon dioxide, which keeps stomata closed. During night, because of formation of organic acids carbon dioxide is consumed and concentration of carbon dioxide is less.

According to sugar concentration theory, during daytime, water is drawn from adjoining cells due to 

botany transport in plant homeostasis in plants regulation of stomatal opening stomata

  1. Endosmosis

  2. Exosmosis

  3. Diffusion

  4. None of the above

Show answer
Correct Option: A
Explanation:
During day time, glucose is produced in the guard cells, as it contains chloroplast, this increases the osmotic pressure in guard cells of the leaves and due to this, water is drawn from adjoining cells due to endosmosis. 
So, the correct answer is 'Endosmosis'

Choose the correct answers from the alternatives given.
Stomata are usually open

botany transport in plant homeostasis in plants regulation of stomatal opening stomata

  1. Whenever there is excess water in the soil

  2. At night, when the plant requires a supply of oxygen

  3. During the day, when the plant requires a supply of carbon dioxide

  4. All of the above

Show answer
Correct Option: C
Explanation:

Stomata are tiny openings present on the epidermis of the leaves and young stem. These structures help in transpiration as well as uptake of carbon dioxide. The carbon dioxide is utilised in the process of photosynthesis. Since carbon dioxide is not utilised during the night, its concentration increases which inhibit the uptake of the potassium ions and closing of stomata takes place.

Hence,the correct answer is 'During the day, when the plant requires a supply of carbon dioxide'.