WAEC Biology Past Question 20

biology question

WAEC Biology Past Question 20

(a) Explain the following terms:

(i) voluntary action.

(ii) involuntary action.

(b) State three functions each of:

(i) insulin;

(ii) auxin.

(c) Describe an experiment to show that plant roots respond positively to gravity.

 

Question extracted from June 1992 SSCE Biology 2 Section B Essay Question number 4

 

Solution

(1) Voluntary action – A voluntary action is basically an action which you yourself start by your own conscious effort.

 

Your cerebral cortex –the brain sends impulses from it to the effectors (muscles or glands) through the spinal cord with relay neurons and lastly a motor neurons.

 

In this action, an impulse is carried from the sensory neuron through the spinal cord to the brain which interprets and sends the message back through the motor neuron to effector organ.

 

Voluntary actions are under the control of the will and are not automatic. Examples are running, writing, jumping, laughing, reading, and smiling.

 

(ii) Involuntary action or reflex action- An involuntary action is a rapid or automatic response to a stimulus. It does not involve the brain for initiation.

 

Therefore, the action is not under the control of the will. It is one which takes place without the conscious choice of an organism.

 

If it takes place particularly in response to a stimulus, it will be referred to as flex. Involuntary actions are opposite of voluntary actions that takes place due to choice.

 

Involuntary actions may or may not happen with the awareness of the individual that is doing it. Example of reflex actions are sneezing, coughing, knee jerk, salivation, secretion of grand, heartbeat, hiccups, digestion and blinking of eyes.

 

Breathing can as well be considered as an involuntary and voluntary, since the breath can be held through apnea.

 

(b)(i) Functions of insulin are:

(1) To help in oxidation of glucose to produce energy.

Insulin is a hormone which plays a key role in the regulation of blood glucose levels. A lack of insulin, or an inability to effectively respond to insulin, can each result to the development of the symptoms of diabetes.

 

(2) to help in the regulation of the level of glucose in the blood.

Insulin helps control blood glucose levels by signaling the liver and muscle and fat cells to absorb glucose from the blood. Insulin as a result helps cells to absorb glucose to be used for energy.

 

If the body has enough energy, insulin signals the liver to absorb glucose and store it in the form of glycogen.

 

The liver can store about 5% of its mass as glycogen. A few of the cells in the body can take glucose from the blood without insulin, but the majority of cells do need insulin to be present.

 

3) Added to its function in the control of blood sugar levels, insulin is as well involved in the storage of fat and it helps in protein synthesis in a few cells.

 

(ii) 3 Functions of auxin

(1) Promotes lateral bud development

The main function of auxin is to help plants grow. Auxin stimulates plant cells to elongate, and the apical meristem of a plant is one of the major places that auxin is produced.

 

This is because the apical meristem is also the location that all the other parts of a plant grow from – the stem, leaves, and flowers. Auxin not only elongates cells, but it specifically elongates them in response to the environment.

 

(2) It promotes reproduction, flowering and fruit formation in plants

Seeds as well produce auxin as they develop, and this assists the fruit surrounding the seed to grow. Food grown in greenhouses is normally not as developed as food grown in direct sunlight, due to the fact that sunlight stimulates the production of auxin.

 

(3) It enhances the production of adventitious roots.

Auxin as well elongates root cells down into the ground, while at the same time elongating cells in the stem upward.

 

This occurrence, is referred to as gravitropism and assists the plant to develop a strong underground support system and get nutrients from the ground, in addition to assisting it to grow tall towards the sunlight.

c) Experiment to show that plant roots respond positively to gravity:

 

Aim- To demonstrate that plant roots respond positively to the force of gravity

 

Apparatus: A bean seedling, Wet blotting paper, damp saw dust, cupboard.

 

Procedure:

Put a few dust on a wet blotting paper and place the bean seedling on the saw dust horizontally. Lift the set up and put it inside a dark cupboard to take away light for some days.

 

Observation: After some days, you will discover that the root has curved and growing downwards whereas the shoot grows upward.

 

Conclusion: Since the root has grown downwards and the shoot upwards, we can say that roots respond to gravity, exhibiting positive geotropism whereas the shoot exhibits negative geotropism.

seed germination

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