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

For keeping stomata open, besides $K^+$ ions the guard cells require a constant supply of

  1. ABA

  2. ATP

  3. Organic acids

  4. Protons
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Guard cells help to regulate the rate of transpiration by opening and closing the stomata. When the guard cells are turgid/swollen, then this turgidity is caused by the accumulation of K ions in guard cells. As K ion level increases, the water potential of guard cells drops and water enters the guard cells and for diffusion of water and activity of guard cells, it requires energy which is utilized from ATP form of energy. Thus this requires a constant supply of ATP.
So the correct answer is 'ATP'.
Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Latest explanation for closure of stomata is 

  1. Starch glucose theory
  2. Active $K^+$ ions theory

  3. ABA theory

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
There are many theories regarding the closure of stomata. The latest explanation is ABA theory according to which ABA (abscisic acid) blocks the uptake of potassium ions by guard cells on dark. It also prevents efflux of hydrogen ions from the guard cells. ABA helps in lowering the pH in guard cells and making the acidic medium. This helps in the closing of the stomata.
So, the correct answer is 'ABA theory'.
Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

Identify the correct statements and find out the correct combination?
1. Accumulation of $K^+$ ions in guard cell does not require energy.
2. A high pH favors stomatal opening.
3. Movement of chloride ions into guard cells is in response to electrical differential created by $K^+$ ions.
4. With the entry of several $K^+$ ions and chloride ions, the water potential of guard cells increases.

  1. 1 and 3

  2. 1 and 2

  3. 2 and 3

  4. 3 and 4
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The opening and closing of stomata are controlled by many factors such as light, pH, amount of water and solute and the osmotic pressure.

So, the correct answer is '2 and 3'.

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

Stomata open during the day due to 

  1. Accumulation of $K^+$ ion and sugar

  2. High pH

  3. Osmotic effect of ions present in guard cells

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

Stomata are the structure present in the leaf which meant for exchange of gases and loss of water. Opening and closing of stomata are regulated by guard cells. Lloyd found that in daytime starch gets converted into sugar which accumulates in guard cells.

Fujino found that in the presence of light there is the influx of potassium ion in guard cells which causes the opening of stomata.
High pH favours the closing of stomata.
So, the correct answer is 'Accumulation of K+ ion and sugar'.

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

Role of Na$^+$ in stomatal opening is now universally accepted.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The opening and closing of stomata are governed by the increase and decrease of solute concentration in guard cell, causing the using or losing the water. Generally, the stomatal opening is affected by the light.
So, the answer is 'False'.
Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

According to Steward's starch hydrolysis theory which one of the following is the principal reason for the opening of stomata during daytime

  1. Influx of K$^+$ ions into guard cells under influence of ABA hormone.

  2. Conversion of sugar into starch in guard cells.
  3. Efflux of K$^+$ ions from guard cells under influence of ABA hormone.
  4. Photosynthetic utilisation of CO$ _2$ in guard cells.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Steward's theory posits that the photosynthetic utilization of CO2 in guard cells during the day increases the pH, which activates phosphorylase to convert starch into sugar, thereby increasing osmotic pressure.

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

What causes opening of stomata?

  1. Thin wall of guard cell facing stomatal pore is stretched more, curves in and the pore opens.

  2. Thin wall of guard cell facing stomatal pore is stretched more, moves in and the pore opens.

  3. As thin wall of guard cell is stretched less, the guard cell wall facing the stomatal pore moves in and pore opens.

  4. Thick wall of guard cell facing the stomatal pore is stretched less, moves in and the pore opens.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Stomata are the structure present in the leaf which meant for exchange of gases and loss of water. Opening and closing of stomata are regulated by guard cells. Lloyd found that in daytime starch gets converted into sugar which accumulates in guard cells.

Fujino found that in the presence of light there is the influx of potassium ion in guard cells which causes the opening of stomata.
High pH favors the closing of stomata.
So, the correct answer is 'Thick wall of guard cell facing the stomatal pore is stretched less, moves in and the pores opens.'

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

Find the correct pair of statements :
(i)  The influx of Cl into guard cells during stomatal opening is active.
(ii) Entry of sucrose from companion cells into sieve tubes at source involves the expenditure of energy.
(iii) At the sinks, sucrose moves out of phloem by passive transport.
(iv) Efflux of K$^+$ from guard cells during stomatal closure does not involve energy expenditure.

  1. ii, iv

  2. ii, iii

  3. i, iii

  4. iii, iv
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The influx of $K^+$ into guard cells during stomatal opening is active.

Movement of Sucrose from companion cells to sieve tubes is against its concentration gradient so protons are transported along with it in the opposite direction which involves the use of energy.
At the sink, the sugar moves out of the phloem tube into the cells by active transport.
Efflux of $K^+$ from guard cells does not involve the expense of energy as it is along the concentration gradient.
So the correct answer is 'ii, iv'.

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

Accumulation of which one of the following acids results in closure of stomata 

  1. Malic acid

  2. Aspertic acid

  3. PEP

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

Accumulation of maleic acid in stomata causes its closure. 

This causes an efflux of potassium ions too. Then exosmosis occurs and the cells become flaccid.
So the correct answer is 'Malic acid'.

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

Accumulation of which one of the following acids results in closure of stomata?

  1. Malic acid

  2. Aspartic acid

  3. PEP

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

When there is the rise in pH it causes hydrolysis of starch into sugar which accumulates in guard cells which results in the opening of cells. For this mechanism, cytokinins, malic acid, and cAMP are required.

Abscisic acid is the stress hormone which results in the closing of stomata.
So, the correct answer is 'Malic Acid'.

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

When turgidity is lost in guard cells, the stomatal pore

  1. Remains unchanged

  2. Gets plasmolysed

  3. Closes

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

Guard cells get swollen up or turgid due to absorption of water so the stomatal pore is opened up.

When the turgidity is lost they lose their shape and cause the closing of the stomatal pore.
Plasmolysis occurs when cells are placed in hypertonic solutions.
So the correct answer is 'Closes'.

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

Stomata of a plant open due to 

  1. Influx of potassium ions

  2. Efflux of potassium ions

  3. Influx of hydrogen ions

  4. Influx of calcium ions
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Stomata of a plant open due to influx of potassium ions. This turgidity is caused by the accumulation of K+ (potassium ions) in the guard cells. As K+ levels increase in the guard cells, the water potential of the guard cells drops, and water enters the guard cells.
So, the correct answer is 'Influx of potassium ions'
Multiple choice blackman's principle of limiting factors photosynthesis in higher plants biology

According to Steward's starch hydrolysis theory, which one of the following is the principal reason for the opening of stomata during day time?

  1. Efflux of $K^+$ ions from guard cells under the influence of ABA hormone.
  2. Photosynthetic utilization of $CO _2$ in guard cell.
  3. Influx of $K^+$ ions into guard cells under the influence of ABA hormone.

  4. Conversion of sugar into starch in guard cell.
Reveal answer Fill a bubble to check yourself
B 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 latter absorb water from epidermal cells, swell up and open the stomatal pore.

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

Stomata open at day because in day the guard cells have

  1. To help gas exchange

  2. A low pH
  3. A high level of sugar, organic acid ATP and $K^+$ ion

  4. Unequally thickened walls
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

During day, light photosynthesis occurs in guard cells as they contain chloroplast. The soluble sugars formed in this process may contribute in increasing the osmotic potential of guard cells and hence resulting in stomatal opening. However, very small amounts of soluble sugars (osmotically active) have been extracted from the guard cells which are insufficient to affect water potential. As a result of photosynthesis CO$ _2$ concentration in guard cells decreases which leads to increased pH up of organic acids, chiefly malic acid during this period in guard cells. The formation of malic acid would produce proton that could operate in an ATP-driven proton K+ exchange pump moving protons into the adjacent epidermal cells and K ions into guard cells and thus may contribute in increasing the osmotic pressure of the guard cells and leading to stomatal opening. Reverse process would occur in darkness.

Therefore, the correct answer is option C.

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

Coversion 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

When the leaf is exposed to light, the process of photosynthesis begins. As the photosynthetic reactions proceed in the guard cells, the residual carbon dioxide is converted to carbohydrates. The disappearance of carbon dioxide from the cytosol of the guard cell results in an increase in the cellular pH. 
As the pH rises, the activity of the enzymes, that convert starch and sugars to organic acids increases. The higher concentration of organic acids results in a higher concentration of hydrogen ions. The hydrogen ions of the guard cells are then exchanged for potassium ions in the subsidiary cells.
This increased concentration of potassium, combined with the higher levels of organic acids, lowers the osmotic potential of the guard cells, and, since water moves from regions of high osmotic potential to regions of lower osmotic potential, water will move from the subsidiary cells into the guard cells. This movement of water increases the turgor pressure (inner pressure) of the guard cells and causes them to swell. Thus, the stomata open.