Chapter 2 — Hormonal Co-ordination in Living Organisms · Biology. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 34 questions on this lesson, each with an explanation.
The bending of a plant's stem toward light is called...
Correct answer: (A) Phototropism
Explanation: Phototropism is the plant's response to light; the stem bends toward the light (positive phototropism).
Which of these glands is considered an exocrine (duct) gland with external secretion?
Correct answer: (C) The sweat gland
Explanation: The sweat gland is an exocrine gland with a duct that pours sweat onto the skin surface; the other glands mentioned are endocrine and secrete into the blood.
The chemical substance secreted by an endocrine gland in small amounts that affects a particular organ (the target organ) is called...
Correct answer: (C) A hormone
Explanation: A hormone is a chemical substance secreted by endocrine glands in small amounts; it travels through the blood to the target organ to affect it.
When light comes from one side onto the stem, auxin moves to the shaded side, which makes the stem...
Correct answer: (A) Bend toward the light
Explanation: Auxin accumulates on the shaded side, elongating its cells more, so the shaded side grows longer and the stem bends toward the light.
Plant roots grow toward the source of water in the soil; this is which tropism?
Correct answer: (D) Positive hydrotropism
Explanation: The root grows toward water, so its hydrotropism is positive.
Gibberellin was first discovered from a fungus that infects the rice plant and makes it grow abnormally tall; this disease is called...
Correct answer: (D) Foolish seedling disease
Explanation: Gibberellin was isolated from a fungus that causes foolish seedling disease in rice (excessive stem elongation).
In Went's experiment on the coleoptile, when he placed an agar block containing auxin on one side of the cut coleoptile tip, what happened?
Correct answer: (C) The coleoptile bent away from the auxin side
Explanation: Auxin increases cell elongation on the side where it is present, so that side grows longer and the coleoptile bends toward the other side (away from the auxin).
Dwarf mutant X of a pea plant grows to normal height when sprayed with gibberellin, while dwarf mutant Y stays short even after the same spraying. Which explanation fits both results?
Correct answer: (B) X cannot make gibberellin, while the cells of Y cannot respond to gibberellin
Explanation: Supplying the hormone corrects the dwarfism of X, so X was short because it lacked gibberellin. Y stays short even when the hormone is supplied, so the problem is in its cells' response to gibberellin, not in the amount of hormone.
In plant tissue culture, if we increase the ratio of auxin to cytokinin in the medium, what is most likely to form?
Correct answer: (A) Roots
Explanation: A high auxin-to-cytokinin ratio encourages root formation, while the opposite (higher cytokinin) encourages the formation of stems and shoots.
Two coleoptiles are lit from the right side only. In coleoptile A a thin impermeable mica sheet is inserted just below the tip on the right (lit) side; in coleoptile B the same sheet is inserted on the left (shaded) side. What is expected?
Correct answer: (C) A bends towards the light, while B shows little or no bending
Explanation: Light makes auxin move to the shaded side, and it must then pass down that side to make its cells elongate. In A the sheet blocks the lit side only, so auxin still passes down the shaded side and A bends towards the light; in B the shaded side is blocked, so there is little or no bending.
The first 10 questions in every subject are free, each with an explanation.