Theory question 101
Plant Responses and Hormones(a)(i) What is the effect of gravity on plant growth?
(ii) Describe an experiment to demonstrate the effect of gravity on the roots of plants.
(b) Explain how bitter taste is detected in humans.
(c) Copy and complete the table below on endocrine glands and their functions.
SN | Endocrine Glands | Hormone Produced | Function
1. | Thyroid | ________ | ________
2. | ________ | Insulin | ________
3. | ________ | ________ | Development of secondary sexual characters of females
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(a)(i) Roots grow towards gravity (positively geotropic); shoots grow away from it (negatively geotropic).
(ii) Pin three germinating bean seedlings on moist cotton wool/blotting paper: one with the radicle horizontal, one pointing up, one pointing down (control); keep moist and dark; after 2–3 days the horizontal and upward radicles have curved downwards; this shows positive geotropism. (Or: use a clinostat — on a rotating clinostat a horizontal radicle grows straight, on a stationary one it bends down.)
(b) A bitter substance dissolves in saliva; it stimulates taste buds for bitterness, found mainly at the back of the tongue; sensory cells send impulses along the sensory nerve to the brain; the brain interprets the taste as bitter.
(c) 1. Thyroid — thyroxine — controls metabolic rate, growth and development.
2. Pancreas (islets of Langerhans) — insulin — lowers blood sugar by converting glucose to glycogen.
3. Ovary — oestrogen — development of female secondary sexual characters. (Spellings must be correct.)
In (a)(ii) always include a control seedling.