Tag: blackman's principle of limiting factors

Questions Related to blackman's principle of limiting factors

Which is the latest explanation for the closure of stomata?

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

  1. Starch glucose theory

  2. Active $K^+$ ion theory

  3. ABA theory

  4. None of the above

Show answer
Correct Option: B
Explanation:
  • K+ ion theory was proposed by Levitt in 1974. K ions are balanced by malate ions present in guard cells and also by taking in some Cl ions. 
  • This ion exchange occurs through the expenditure of ATP energy.
  • Plant hormone ABA acts on guard cells, which interfere with the exchange of K+ H+ ions in guard cells, results in a reverse of the reaction of the opening of stomata, hence stomata closed.
  •  Hence, Active K+ ion theory is the latest explanation for the closure of stomata.
  • So, the correct answer is  'Active K+ ion theory'.

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

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

  1. Theory of starch - glucose transformation

  2. Theory of active $K^+$ transport

  3. Theory of starch - sugar interconversion

  4. None of the above

Show answer
Correct Option: B
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.

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

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

  1. Steward

  2. Yin and Tung

  3. Sayre

  4. Imamura

Show answer
Correct Option: C
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.

Which of the following conditions help in opening of stomata?

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

  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

Show answer
Correct Option: B
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.

Leaves that appear wilted in day time recover at night because

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

  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

Show answer
Correct Option: B
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.

The opening and closing of the stomata is regulated by

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

  1. $Na^+$

  2. $K^+$

  3. $Mg^{2+}$

  4. $Fe^{2+}$

Show answer
Correct Option: B
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.

When stomata opens, the pH of guard cells

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

  1. Increases

  2. Decreases

  3. Remain the same

  4. Both A and B

Show answer
Correct Option: A

Stomata of CAM plants ______________________.

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

  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

Show answer
Correct Option: C

Opening of stomata is not affected by ___________.

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

  1. $N _2$

  2. $K^+$ ions

  3. Starch

  4. None of these

Show answer
Correct Option: A

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

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

  1. ABA theory

  2. Munch theory

  3. Starch - glucose theory

  4. Active $K^+$ transport theory

Show answer
Correct Option: D
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.