3.7.1 The Role of Human Nervous System (Structured Question 1 & 2)

Question 1:
Diagram below shows a cross-section of part of the nervous system.

Name structure P.

State the function of P.

Why is Q swollen at the dorsal root?

Complete the Diagram with the neurones involved in a reflex action. Mark the direction of the impulse movement on the neurones.

Compare two structures of a sensory neurone and a motor neurone.

If the spinal nerve is cut off at R, what is the effect on the organ which is connected to it?
Explain your answer.

Azmin’s finger accidentally touches a flame.
Explain briefly how his reflex action functions to avoid the injury.

P : Spinal cord

Function of P : Controls reflex actions.

To place the cell bodies of the afferent neurones.



The organ is unable to respond. Impulses cannot flow to the effector.

- The receptor detects heat and triggers an impulse.
- The impulse is sent to the spinal cord through the afferent neurone.
- The impulse flows through the afferent neurone which synapses with the interneurone and then synapses with the efferent neurone.
- The efferent neurone sends an impulse to the effector.
- The hand is pulled away from flame.


1.   Ethylene is a small hydrocarbon gas.
2.   It is a plant hormone which is synthesized during the ripening of fruits.
3.   Ethylene is responsible for the changes in texture, softening, color, and other processes involved in ripening. 
4.   Ethylene
(a) Speeds up the ripening of fruits by stimulating the production of cellulose. Cellulase hydrolyses the cellulose in plant cell walls, making the fruit soft.
(b) Promotes the breakdown of complex carbohydrate into simple sugar. This make ripe fruit tastes sweeter than an unripe fruit.
5. Ethylene gas is used commercially to ripen tomatoes, bananas and pears.

3.6 Plant Hormones

3.6 Plant Hormones
1.      Growth of shoots towards sunlight is called positive phototropism.
2.      Growth of shoots away from sunlight is called negative phototropism.
3.      In plants, hormones play an important role in growth processes such as seed germination, growth of roots and development of fruits.
4.      There are many types of plant hormones, such as auxins and ethylene
Effects of Auxins on Growth Responses
1.      Auxins are produced in the apical meristems of the shoot tip and the root tip in the cell division zone.
2.      In the shoot tip, high concentrations of auxins stimulate cell elongation.
3.      The effect of high concentrations of auxins in the root tip is different from that in the shoot tip. In the root tip, a high concentration of auxins inhibits cell elongation.

3.4.1 The human kidney

The Excretory System
1.   The excretory system plays an important role in homeostasis.
2.   The primary organs of the excretory system are kidneys.
The human kidney
1.   The kidneys filter blood and form urinewhich exits the body through the ureters, urinary bladder and urethra.
2.Urine is fluid which consists of water, urea and other dissolved wastes.
3.The human kidney shows three distinct regions
(a) Cortex(outer light-red region)
(b) Medulla(inner dark-red region)
(c) Pelvis(central cavity in which the ureter directly connects to)

The Nephron
1.   Each kidney consists of millions of microscopic tubules called nephron.
2.   A nephron consists of three major parts:
 (a) the glomerulus
 (b) the Bowman’s capsule, and
 (c) renal tubule
3.   The renal tubule is made up of the
 (a) proximal convoluted tubule
 (b) loop of Henle
 (c) distal convoluted tubule

3.4 Homeostasis in Humans

3.4 Homeostasis in Humans
1.      The internal environment consists of interstitial fluid and blood plasma that constantly bathe the cells.
2.      Homeostasis is the process of regulating the physical and chemical factors in the internal environment, so that these factors can be maintained in a dynamic equilibrium and optimum condition.
     (a) The physical factors include body temperature, blood pressure and osmotic pressure.
     (b) The chemical factors in the blood include partial pressure of oxygen and carbon dioxide, and the salt and sugar levels.