Chapter 16: HORMONES

  Human Hormones

    Pituitary gland is an endocrine [ductless] gland. The hormones of pituitary gland stimulate testes and ovaries to produce their hormones. It also stimulates thyroid and adrenals to secrete their hormones. Pituitary gland produces growth hormone necessary for normal growth of a person.

Other endocrine glands are thyroid [secretes thyroxin controls metabolism of carbohydrates, proteins and fats lack of which causes goiter]; pancreas [produce insulin lack of which causes diabetes] and adrenals [produce adrenalin which helps adjust to stress].

                     Glands of the Human body

                                                                   Fig 1: Glands of the body

Plant Hormones

Auxins: These are indole compounds. Helps the cells grow longer, rooting of stems, promote flowering, prevent early dropping of fruits and leaves but enhance dropping of old leaves. It is also used as weed killer of dicots.

Gibberellins: helps in the growth of stems, elongation of fruits. All are acidic.

Cytokinins: Promote cell division.

Ethylene: Hastens ripening of fruits by increasing their respiration rate.

Abscisic acid: inhibits growth, leads to wilting of leaves.


Thyroxin causes morphosis of tadpoles into frogs. Thyroxin needs iodine, so if the water in which tadpoles swims don’t have iodine. The tadpoles can’t become frogs.

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