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

Which of the following theory of stomatal opening and closing is given by Levitt?

  1. Theory of starch - glucose transformation
  2. Theory of active $K^+$ transport

  3. Theory of starch - sugar interconversion

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

There are three main theories about the mechanism of stomatal movement.

  1. 'Guard Cell Photosynthesis' (proposed by Schwendener, 1881).
  2. 'Starch Hydrolysis' and Starch sugar interconversion theory (proposed by Sayre, 1923 and 1926 and other contributions were made by Lloyd and Steward)
  3. Malate or potassium ion pump hypothesis (proposed by Levitt, 1974). 
According to the potassium ion pump theory, rise in pH of guard cells (due to photosynthesis and consequent decrease of carbon dioxide) causes hydrolysis of starch to form phospho enol pyruvate (PEP). PEP combines with carbon dioxide to form organic acids, like oxalic acid. The organic acids get ionised and the proton passes out of guard cells and potassium ion is actively absorbed and accumulated. This results in absorption of water from adjacent cells,  guard cells become turgid and stomata open.

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

Who proposed the theory of starch sugar inter conversion for opening and closing of the stomata?

  1. Steward

  2. Yin and Tung

  3. Sayre

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

Starch hydrolysis theory is the classical theory for stomatal opening and closing. It was originally proposed by Sayre, 1923. According to this theory, guard cells contain starch, which is hydrolysed to form glucose under high pH caused due to reduced carbon dioxide concentration. The carbon dioxide concentration is reduced due to the process of photosynthesis Glucose increases the osmotic concentration and hence, DPD of guard cells. The later absorb water from epidermal cells, swell up and open the stomatal pore. Major contributors to this theory were Lloyd, 1908, who proposed starch sugar interconversions; Sayre, proposed that starch hydrolysis occurs with rise of pH and Steward, suggested that closing movement requires ATP.

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

Which of the following conditions help in opening of stomata?

  1. Darkness, pH 5, high $CO _2$ concentration
  2. pH 7, low $CO _2$ concentration and light
  3. pH 5, low $CO _2$ concentration and light
  4. High $CO _2$ concentration, low $K^+$ ion concentration in guard cells
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Malate or potassium ion pump hypothesis was first proposed by Levitt, 1974. According to this theory, there is a decrease of carbon dioxide in guard cells. During light exposure there is hydrolysis of starch to form phospho enol pyruvate (PEP). PEP combines with carbon dioxide to form organic acids, like oxalic acid. The organic acids get ionised and the proton passes out of guard cells and potassium ion is actively absorbed and accumulated. 

Potassium ions combine with malate and passes into small vacuoles. Chloride ions are also absorbed from outside to maintain electroneutrality. As a result of accumulation of ions there is a reduction in water potential of guard cells. The reduction in water potential causes absorption of water from adjacent cells, guard cells become turgid and stomata open.

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

Leaves that appear wilted in day time recover at night because

  1. Light is essential for photosynthesis.

  2. The stomata close down, temperature decreases and transpiration is reduced and plant is able to absorb more water from the soil.

  3. Respiration and translocation of organic substances increases.

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

Wilting of leaves occur in response to plasmolysis, when plant cells lose lot of water due to exosmosis. During day time, when temperature is high, there is high transpiration if plants are not able to absorb enough water the leaves will wilt. After sunset the temperature and consequently rate of transpiration drop. Hence, there is less water loss from plants and plants generally overcome the wilt.

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

The opening and closing of the stomata is regulated by

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

Most widely accepted theory for opening and closing of guard cells is the malate or potassium ion pump theory, first proposed by Levitt, 1974. 

According to this theory, rise in pH of guard cells (due to photosynthesis and consequent decrease of carbon dioxide) causes hydrolysis of starch to form phospho enol pyruvate (PEP). 
PEP combines with carbon dioxide to form organic acids, like oxalic acid. The organic acids get ionised and the proton passes out of guard cells and potassium ion is actively absorbed and accumulated. Potassium ions combine with malate and passes into small vacuoles. Chloride ions are also absorbed from outside to maintain electroneutrality. As a result of accumulation of ions there is a reduction in water potential of guard cells. The reduction in water potential causes absorption of water from adjacent cells, guard cells become turgid and stomata opens.

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

When stomata opens, the pH of guard cells

  1. Increases

  2. Decreases

  3. Remain the same

  4. Both A and B
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When stomata open, K+ ions are actively pumped into guard cells, and organic acids (like malic acid) are produced, which dissociate into H+ and malate ions. The removal of H+ ions from the guard cells causes the pH to increase.

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

Stomata of CAM plants ______________________.

  1. Are always open

  2. Open during the day and close at night

  3. Open during night and close during the day

  4. Never open
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

CAM (Crassulacean Acid Metabolism) plants open their stomata at night to take in CO2 to minimize water loss due to transpiration in hot, dry environments.

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

Which of the following theory gives the latest explanation for closure of stomata?

  1. ABA theory

  2. Munch theory

  3. Starch - glucose theory
  4. Active $K^+$ transport theory
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

According to the most widely accepted view, stomata open or close due to turgor movement in guard cells. When guard cells gain water they swell and become turgid and stomata open. When guard cells lose water they become flaccid and stomata close. 

The turgor movements in guard cells depend on the inflow and outflow of potassium ions. When potassium ions move inside guard cells, the water potential of guard cells decrease and they gain water and swell. When potassium ions move out the process is reversed.

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.