Question

A physiological response of plants to the duration of light and darkness is
A. Daily phase cycle
B. Circadian rhythms
C. Biological clock
D. Photoperiodism

Answer 1

Hint: Plants have a number of sophisticated uses for light that go far beyond their ability to photosynthesize low-molecular-weight sugars using only carbon dioxide, light, and water.

Complete answer:
To their entire life cycle, all plants undergo the alteration that is changes of generations. This cycle of generations includes both diploid (2n) phase that is having 2 sets of chromosomes, the sporophyte, and the haploid (n) phase that is having only 1 set of chromosomes, gametophyte.
A circadian rhythm is defined as a natural, internal process that regulates the sleep-wake cycle and it repeats on each rotation of the Earth roughly every 24 hours. It can refer to any biological process that exhibits an endogenous, entrainable oscillation of about 24 hours.
Biological clock is explained as an inherent timing mechanism in a living system that is inferred to exist in order to explain the timing or periodicity of various behaviors and physiological states and processes
Photomorphogenesis is defined as the growth and development of plants in response to light. It allows plants to improve their use of light and space. Photoperiodism is the capacity to use light to track time. Plants can tell the time of day and time of year by sensing and using various wavelengths of sunlight. Phototropism is a directional response that allows plants to grow towards, or even away from, light.

The correct answer is option D.

Note:
Cryptochromes are another type of photoreceptor that is important in photoperiodism. Cryptochromes absorb blue light and UV-A. Cryptochromes entrain the circadian clock to light. It has been found that both the cryptochrome and the phytochrome abundance relies on light and the amount of cryptochrome can change depending on day-length. This shows how important both of the photoreceptors are in regards to determining day-length.