Summative Practice Chapter 8 – Question 8 & 9 (Form 4 Biology Textbook Exercise and Answer)

Question 8:
The human respiratory systems of humans and grasshoppers have different adaptations to maximise the rate of gaseous exchange. State the similarities and differences between the human respiratory system and the grasshopper breathing system.

• The respiratory surface is moist to dissolve oxygen for diffusion.
• The respiratory surface is thin for fast gas diffusion.
• The respiratory surface has a large ratio of total surface area to volume that allows more gases to diffuse through it.

System/organ: lungsSystem/organ: tracheal system
Air enters the trachea through the nostrilsAir enters the trachea through the spiracles
The nasal cavity does not have any valvesSpiracles have valves
The trachea branches into bronchus/bronchiThe trachea branches into tracheoles
Bronchus/bronchi end in alveoliTracheoles have dead-ends
Gaseous exchange occurs in the alveoliGaseous exchange occurs in the tracheoles
The trachea is supported by cartilage rings to prevent collapseThe trachea is supported by chitin rings
Alveoli is covered in a network of blood capillariesThe tracheoles are not covered with blood capillaries but come into direct contact with body cells
Oxygen is transported to body cells through bloodOxygen diffuses directly from the tracheole to body cells
Gaseous exchange is facilitated by intercostal muscles and diaphragmGaseous exchange is facilitated by abdominal muscles

Question 9:
(a) Explain how air is inhaled into the lungs.
(b) Explain how a carbon dioxide molecule is carried from the body cell to the alveolus to be expelled.

• Air is inhaled when the external intercostal muscles contract and the internal intercostal muscles relax.

• This action causes the rib cage to rise upwards and outwards.

• At the same time, the diaphragm muscles contract, lowering and flattening the diaphragm.

• The volume of the thoracic cavity increases while the pressure decreases, and air is drawn into the lungs due to the higher atmospheric pressure on the outside.

• The higher CO2 partial pressure in body cells compared to that of the tissue capillaries causes CO2 to diffuse from body cells into blood plasma.

• A small portion of carbon dioxide blood plasma is dissolved and another portion is transported by the haemoglobin.

• Most of the carbon dioxide diffuses into the red blood cells (erythrocytes).

• In the erythrocytes, carbon dioxide combines with water to form carbonic acid (H2CO3).

• Carbonic acid dissociates to bicarbonate ions (HCO3) and hydrogen ions.

• HCO3 diffuses into the blood plasma and is carried to the lungs. HCO3 ions then combine with H+ to form carbonic acid (H2CO3).

• Carbonic acid then dissociates to produce carbon dioxide and water.

• The high in the lung capillaries as opposed to the low CO2 partial pressure in the alveoli causes CO2 to diffuse from the lung capillaries into the alveoli and subsequently, expelled through exhalation.

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