In plant physiology, the 'Photoperiodism' refers to the response of plants to: MCQ with Answer and Explanation

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In plant physiology, the 'Photoperiodism' refers to the response of plants to:

A. The intensity of light

B. The direction of light

C. The wavelength of light

D. The relative lengths of day and night (light and dark periods)

Answer: Option D

Solution (By JKSSB Mock Tests)

Photoperiodism is the physiological reaction of organisms, particularly plants, to the length of the day or a dark period. It is the mechanism by which plants measure the relative lengths of light and dark periods to regulate developmental processes, most notably the timing of flowering. Plants are classified as short-day plants, long-day plants, or day-neutral plants based on their flowering response to photoperiod. The photoreceptor pigment phytochrome is crucial in perceiving these light/dark signals.

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Question #1

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In plant physiology, the 'Osmotic pressure' is the pressure that must be applied to a solution to prevent the inward flow of water across a semipermeable membrane. It is directly proportional to the:

A. Temperature only

B. Concentration of solute particles

C. Size of the solute molecules

D. Volume of the solution

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Correct Answer: Option B

Explanation:
Osmotic pressure (OP) is a colligative property of a solution, meaning it depends on the number of solute particles dissolved in a given volume of solvent, not on the nature or size of the particles. It is defined as the hydrostatic pressure that must be applied to a solution to prevent the net flow of water (osmosis) into the solution across a semipermeable membrane. According to the van't Hoff equation, osmotic pressure is directly proportional to the molar concentration of solute particles and the absolute temperature. The more concentrated the solution, the higher its osmotic pressure.

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Question #2

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Consider the following statements about the human excretory system:
1. ADH increases water reabsorption.
2. Aldosterone increases sodium reabsorption.
3. Renin converts angiotensinogen to angiotensin I.
Which of the above is/are correct?

A. 1 and 2 only

B. 2 and 3 only

C. 1, 2, and 3

D. 1 and 3 only

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Correct Answer: Option C

Explanation:
All are correct: ADH (water), aldosterone (Na⁺), renin (angiotensinogen cleavage).

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Question #3

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The scientist who discovered the 'transforming principle' in bacteria was:

A. Avery, MacLeod, McCarty

B. Hershey and Chase

C. Watson and Crick

D. Frederick Griffith

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Correct Answer: Option D

Explanation:
Frederick Griffith in 1928 demonstrated the transformation of non-virulent pneumococci to virulent by heat-killed virulent strain, suggesting a transforming principle. Avery et al. later identified it as DNA. Hershey-Chase confirmed DNA is genetic material.

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