Subjective and Short questions for photoperiodism

Subjective questions for photoperiodism:

  1. What is photoperiodism? Give its historical background.
  1. Give classification of plants on the basis of photoperiodic responses.
  2. What is critical period? Explain.
  3. What are phytochromes? Give their mechanism of action.
  4. Discuss role of hormones in photoperiodism.


  1. What is photoperiodism?

Ans:     The response of plant to the relative length of light and dark period is called photoperiodism.

  1. Give three photoperiodic responses of plants.

Ans:     Flowering in short day and long day plants. Formation of tubers in potato and bulbs in onion is also promoted by short days. Short days promote enlargement of tap root and storage of food in radish and carrot.

  1. What are (a) Short Day Plants (SDP)? Give example.

Ans: The plants that flower when day length is less than a certain critical length are called short day plants. Examples of short day plants are Biloxi soybean. Cocklebur, Xanthium, Tobacco and Strawberry.

  1. What are day neutral plants? Give example.

Ans:  There arr also known as day length indifferent plants. Such plants  flower under any photoperiod. Its examples are tomato. cucumber, and cotton. maize and garden pea.

  1. What are long day plants? Give example.

Ans: The plants that flower when day length is more than a certain critical length are called long day plants. Its examples of long day plants are cabbage. spring wheat and spring barely.

  1. What is critical period for photaperintlie responses?

Ans:  The limit of the photoperiod up to which the short day plants flower is called critical photoperiod of short day plants. The limit above which long day plant flowers is called critical photoperiod of long day plants.

  1. Differentiate between inductive and non-inductive photoperiods.

Ans: If a photoperiod causes flowering in a plant. it is called inductive photoperiod. If it does not cause flowering, then it is non-inductive.



  1. What are phytochromes?

Ans:    The proteins present in the leaves which absorb light of different wave lengths are called phytochromes.

  1. What is Photoconversion?

Ans:    The Pr phytochrome absorbs red light. It is converted into Pfr. Similarly when Pfr absorbs far red it is converted to Pr form. This is known as photoconversion.

  1. What is Thermal conversion?

Ans:    Pfr spontaneously converted into Pr in the.dark. This method of conversion is very slow. It takes a few hours. It depends on temperature. Therefore. it is called thermal conversion. Pr form does not show thermal conversion.

  1. What was the observation of Chailakhyan about florigen?

Ans:   Chailakhyan suggested that two factors are involved in the floss ering stimulus. First factor is gibberellins and the second factor is anthesins. Both gibberellin and anthesins collectively acts a florigen. But it cannot be proved experimentally.

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