Tag: photosynthesis in higher plants

Questions Related to photosynthesis in higher plants

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

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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. $Fe^{2+}$

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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

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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

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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

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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

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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.

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

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

  1. Khorana

  2. Scarth

  3. Levitt

  4. Kohli

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Correct Option: C
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.

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

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

  1. Ascent of sap

  2. Phloem conduction

  3. Ion absorption

  4. Stomatal movement

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Correct Option: D
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.

The conversion of starch to organic acid is essential for stomatal

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

  1. Closure

  2. Growth

  3. Intitiation

  4. Opening

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Correct Option: D
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.

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

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

  1. Water

  2. Starch

  3. Sugar

  4. K - malate

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Correct Option: D