Biology

Plant Transport and Physiology

1,834 Questions

Access a comprehensive set of questions on plant transport mechanisms and physiological adaptations. Topics include water movement, translocation of food, and plant responses to external stimuli. These biology questions are essential for medical entrance exams and other science competitive tests.

Xylem and phloem transportTranspiration and evaporationPlant adaptationsGeotropic and phototropic responsesWater absorption by rootsRespiration in roots

Plant Transport and Physiology Questions

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.

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

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

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.

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

Conversion of starch to organic acids is required for 

  1. Stomatal opening

  2. Stomatal closing

  3. Stomatal formation

  4. Stomatal activity
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Lloyd the stomatal movement is regulated by interconversion of starch and organic acids. When starch is converted into organic acid in the presence of enzymes and light, guard cells get turgidity and eventually causes the opening of stomata.