Summative Practice 10 – Question 7 & 8 (Form 4 Biology Textbook Exercise and Answer)

Question 7:
Coronary heart disease is the main cause of death in our country. The following factors can increase the risk of an individual contracting this disease:
• smoking
• unbalanced diet
• unhealthy lifestyle
Explain how these factors can contribute to coronary heart disease.

• Cigarette smoke contains nicotine.
• Nicotine causes addiction. 
• Nicotine shrinks blood vessels.
• Nicotine increases blood pressure.
• Causes accumulation of plaque.
• Causes thrombosis/arteriosclerosis.
• Cigarette smoke contains carbon monoxide.
• Carbon monoxide competes with oxygen to combine with haemoglobin to form carboxyhaemoglobin.
• Affects oxygen transport efficiency
• Causes difficulty in breathing and heart attack
• Cigarette smoke contains tar that forms a film on the alveoli wall which reduces gaseous exchange

Imbalanced diet
• High intake of fats/lipid/carbohydrates
• Cholesterol and fats accumulate and are deposited in the lumen of blood vessels.
• The lumen of the coronary artery becomes small and narrow.
• This can cause atherosclerosis, stroke or thrombosis.

Unhealthy lifestyle
• Lack of physical exercise and a sedentary lifestyle
• Can cause obesity, stress, high blood pressure and heart attack

Question 8:
(a) Explain how the rhythmic contraction of heart muscles occurs.
(b) Ali’s leg feels numb after sitting cross-legged for an hour. Suggest the action to be taken and give your reasons.
(c) Elly enjoys eating beef rendang and nasi lemak. Explain why this practice of eating in the long term can affect her health.

• The contraction of cardiac muscles is triggered and initiated by a group of specialised tissues known as sinoatrial node.

• Sinoatrial node generates electrical impulses similar to the ones generated by nerves.

• As the cardiac muscles are continuous and criss-cross each other, when a cell is stimulated, the stimulus is spread or conducted throughout the atrial wall of the heart.

• The waves of contraction are transmitted throughout the atria causing the atria to contract simultaneously and uniformly.

• The electrical impulse will spread to a second group of nodes known as the atrioventricular node.

• The electrical impulse will then spread through the bundle of His and Purkinje fibres till it reaches the apex of the heart.

• This induces a rhythmic electrical impulse wave throughout the ventricles and both ventricles contract simultaneously starting from the bottom to the base of the aorta and pulmonary artery.

• Ali needs to walk or move his feet so that the skeletal muscles on his feet can contract.

• The contraction of the foot skeletal muscles produce a force that pushes blood in the veins to return to the heart.

• The contraction of muscles also force blood to flow to foot tissues that suffer from a shortage of blood supply.

Beef rendang and nasi lemak cooked with coconut milk contain high lipid (triglycerides) and cholesterol.

Normally, the human body tends to store fats instead of using it to supply energy.

As a consequence, excess fats and cholesterol will be deposited on arterial walls (arteriosclerosis)
• The arterial lumen will become narrow, obstructing blood flow.

• This condition increases blood pressure (hypertension).

• The heart needs to work harder to pump blood. This adds more pressure to the heart.

• If the arterial lumen that becomes narrow is the coronary artery (the artery in the heart), a heart attack may occur, especially during an activity, or a person’s emotional condition which causes the heart to work harder. This condition is called angina and is caused by the lack of oxygen supply to cardiac muscles.

• The lack of blood and oxygen supply to the heart can cause some parts of the cardiac muscle to die. It can also turn fatal.

• If the deposits of cholesterol and fats, together with blood clots move to other parts, for example the brain, stroke may occur.

• Therefore, the individual should quit unhealthy eating habits in order to prevent stroke, hypertension and cardiovascular diseases.

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