Differentiate between circadian rhythms and photoperiodism. Give examples of each. What regulates ...

Answer to q. 1

Concepts to Consider: Photoperiodism is any response to changing lengths of day and night;
responses are tied to phytochrome, resulting in influences on timing of flowering, seed germination,
leaf abscission and shade avoidance; circadian rhythms are those based on a 24-hour cycle and may be
cued to phytochromes as well as cryptochormes, influencing sleep movements, stomatal opening and
closing, and opening and closing of flowers.

Answer to q. 2

Concepts to Consider: Auxins promote cell elongation, tropisms, apical dominance, and fruit
development; gibberellins promote stem elongation, flowering, and germination; cytokinins promote
mitosis and differentiation, delay senescence, and are involved in apical dominance; ethylene aids in
the ripening of fruits, promotes apical dominance, thigmomorphogenesis, and leaf abscission; abscisic
acid is an environmental stress hormone that causes stomatal closing and prevents seed germination in
undesirable conditions; brassinosteroids affect many developmental processes such as cell division,
cell elongation, light-induced differentiation, vascular development, and seed germination.

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