Tag: photosynthesis in higher plants

Questions Related to photosynthesis in higher plants

Which of the following scientists is credited with the mechanism of opening and closing of stomata related to $K^+$ exchange?

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

  1. Levitt

  2. Sayre

  3. Scarth

  4. Lloyd

Show answer
Correct Option: A
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. 
  • Levitt 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 'Levitt'.

The effect of accumulation of $K^+$ ions in guard cells

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

  1. Solute potential increases

  2. Water potential decreases

  3. Water potential increases

  4. Both A and B

Show answer
Correct Option: D
Explanation:

The opening and closing of stomata are controlled by the accumulation of potassium ion. Potassium ion is found in the guard cell of the plant. The increase in the solute potential and a decrease in water potential is affected by potassium ion in the plant.

So, the correct answer is 'Both A and B'.

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.

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

  1. ii, iv

  2. ii, iii

  3. i, iii

  4. iii, iv

Show answer
Correct Option: A
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'.

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

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

  1. Malic acid

  2. Aspertic acid

  3. PEP

  4. OAA

Show answer
Correct Option: A
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'.

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

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

  1. Malic acid

  2. Aspartic acid

  3. PEP

  4. OAA

Show answer
Correct Option: A
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'.

When turgidity is lost in guard cells, the stomatal pore

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

  1. Remains unchanged

  2. Gets plasmolysed

  3. Closes

  4. Opens fully

Show answer
Correct Option: C
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'.

Stomata of a plant open due to 

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

  1. Influx of potassium ions

  2. Efflux of potassium ions

  3. Influx of hydrogen ions

  4. Influx of calcium ions

Show answer
Correct Option: A
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'

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

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

  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.

Show answer
Correct Option: B
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.

Stomata open at day because in day the guard cells have

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

  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

Show answer
Correct Option: C
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.

Which photoreceptor controls the opening & closing of stomata?

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

  1. Chlorophylls a

  2. Chlorophylls b

  3. Phytochrome

  4. Carotene

Show answer
Correct Option: C
Explanation:

Plants have photoreceptors, which are proteins that are specially designed to perceive light and signal certain biological effects in the plant. There are two types of photoreceptor proteins in plants - Phytochromes and Blue light receptors. Phytochromes absorb red light and far red light and help the plants to sense seasonal changes in night length, or photoperiod, thereby controlling the opening and closing of stomata.