(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.
| S/N | Endocrine glands | Hormone produced | functions |
| 1 | Thyroid | ||
| 2 | Insulin | ||
| 3 | Development of secondary sexual characters of females |
Explanation
(i) Effect of gravity on plant growth: The (main) root grows down in response to gravity/positively geotropic; the (main) stem/shoot/grows upwards away from gravity/negatively geotropic.
(ii) Experiment to demonstrate the effect of gravity on the roots of a plant: -
- Select three germinating bean seedlings/seeds on a moist/damp sawdust/wet blotting paper
- Pin/keep one seedling in a horizontal position
- Place another seedling in a vertical position with the radicle pointing upwards
- Place the third upwards vertical with the radicle pointing downwards, to serve as control
- After few/2-3 days, it will be observed that the radicle of the seedling placed horizontally bends/ grows downwards
- the radicle of seedling placed vertically bends/grows downwards
- Indicating positive geotropism/ positive response to gravity.
- The seedling placed vertically with radicle point downwards did not bend. (N.B. observation must correspond with the experimental procedure to score).
ALTERNATIVE to 1 (a)
- (ii) Take a clinostat and two bean seedlings
- Pin one seedling horizontally on damp/moist/wet/cotton wool/blotting paper attached to the cork of the clinostat
- Pin the other seedling onto some damp/moist/wet cotton wool/blotting paper attached to the cotton tile
- Start the motor of the clinostat; Observe the seedlings after 8 —10 hrs.
- It will be observed that the radical of the seedling placed horizontally bends/grows down wards
- Indicating/showing positive geotropism.
(b) Detection of bitter taste in humans
- Taste buds are unevenly distributed on the surface of the tongue
- Taste buds for detecting bitterness are at the back/end of the tongue
- For a substance to be tasted it must be dissolved in a solution/saliva
- When bitter substance is dissolved in saliva, sensory cells at end/back of the tongue are stimulated
- Which pass impulses to the brain; Which interprets the taste as bitter.
(c) Hormones of endocrine glands and their functions
| S/N | Endocrine glands | Hormone produced | Function |
| 1 | Thyroid | Thyroxin | influences growth/development; Regulates/controls rates of metabolism |
|
2 3 |
Pancreas Ovary/ovaries |
Insulin Oestrogen |
Control blood sugar level/causes liver to convert to convert glucose to glycogen Development of secondary sexual characters of females |