Tag: blackman's principle of limiting factors

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Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Active $K^{+}$ ion exchange mechanism of opening and closing of stomata was given by

  1. Khorana

  2. Scarth

  3. Levitt

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

Potassium is an important macronutrient for plants. Potassium ions cause turgor movement of guard cells. 

Gain of potassium ions by guard cells causes a decrease in water potential of guard cells which leads to inflow of water into the guard cells. This makes guard cells turgid and they swell. Increase in turgidity of guard cells opens the stomatal pore. 
Movement of potassium ions out from guard cells results in an increase in water potential, they lose water due to exosmosis, become flaccid and stomatal pore closes. 
This mechanism of stomatal opening and closing was first stated by Levitt.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Active $K^+- H^+$ exchange theory explains

  1. Ascent of sap

  2. Phloem conduction

  3. Ion absorption

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

Transpiration occurs through stomata. The opening and closing of stomatal pore depends on the turgidity of guard cells. When guard cells become turgid the stomata open and when guard cells become flaccid the stomata close. 

According to the most widely accepted theory of 'Active $K^+$−$H^+$ exchange' the guard cells become turgid or flaccid in response to entry and exit of potassium ions. The entry and exit of potassium ions is balanced by the entry and exit of protons to maintain electrical neutrality.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

The conversion of starch to organic acid is essential for stomatal

  1. Closure

  2. Growth

  3. Intitiation

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

During stomatal opening starch gets converted to organic acids, like malic acid. The dissociation of organic acid increases proton concentration. The protons move out of guard cells and to maintain electrical neutrality potassium ions move into the guard cells. The inflow of potassium ions results in a drop in water potential in guard cells, due to which water moves into guard cells making them turgid and stomata open.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Which of the following one function as primary osmotic substance in opening and dosing of stomata _______________.

  1. Water

  2. Starch

  3. Sugar

  4. K - malate
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

According to the modern K+ malate theory, the accumulation of potassium malate in the guard cells lowers the water potential, causing water to enter and the stomata to open.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Which ion is accumulated in the guard cells before opening of stomata?

  1. $PO _4$
  2. $K^+$
  3. $Mg^{++}$
  4. $Na^+$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to the most widely accepted theory of stomatal opening and closing, potassium ions are involved in turgor movement of guard cells. Inflow of potassium ions decreases water potential in guard cells, which leads to inflow of water. Consequently guard cells swell and stomatal pore opens. When potassium ions move out, these events are reversed and stomatal pore closes.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Guard cells control

  1. Intensity of light entering

  2. Photosynthesis

  3. Closing and opening of stomata

  4. Change in green colour
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Transpiration is the process of loss of water, in vapour form, through stomata. The process depends on the turgidity of guard cell. An increase in turgidity of guard cells opens stomatal pore, whereas a decrease in turgidity of guard cells closes stomatal pore. The change in turgidity of guard cells is brought about by reversible influx and efflux of potassium ions.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Conversion of starch to organic acid is essential for

  1. Stomatal closure

  2. Stomatal opening

  3. Stomatal initiation

  4. Stomatal growth
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Starch is osmotically inactive and does not contribute to decrease in water potential. Conversion of starch to organic acids like malic acid promotes uptake of ions like potassium. This decreases water potential and helps in uptake of water. Thus making guard cells turgid and opening of stomata.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Stomata in angiosperms open and close due to

  1. Their genetic constitution

  2. Effect of hormones

  3. Change of turgor pressure in guards cells

  4. Pressure of gases inside the leaves
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Changes in turgidity of guard cells, regulate the opening and closing of stomata. When guard cells are turgid, stomatal pore opens and when guard cells are flaccid stomatal pore closes.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

The metal ion involved in the stomatal regulation is or Stomata will open, if there is accumulation of the following elements in the guards cells

  1. Iron

  2. Magnesium

  3. Zinc

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

Potassium ions movement into and out of guard cells is related to the turgidity and consequent opening and closing of stomatal pore.

Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Stomata open because of

  1. Oxygen in the air

  2. Increased turgidity of the guard cells brought about by exposure to light

  3. Vacuoles in guard cells

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

Guard cells have chloroplast, on exposure to light, there is synthesis of sugar in guard cells. The increase in sugar concentration causes water to move in from surrounding cells, thus making guard cells turgid. Increase in turgidity of guard cells leads to stomatal opening.