Mechanisms of Breathing

1. 1. The respiratory structure of fish is the
   (1 mark)

• lamellae

• gills

• filaments

• gill arches

Answer explanation

The respiratory structure of fish is the gills, which are made up of rows of filaments supported by the gill arch.
The filaments consist of many thin and flat lamellae supplied with blood capillaries.

Lamella < filament < gill

2. 2. Select the correct match between the organisms and their respiratory structures. (2 marks)

• Insect - tracheole

  Fish - gill

  Frog - lungs & skin

  Human - lungs

• Insect - tracheole

  Fish - lungs

  Frog - gill

  Human - alveolus

• Insect - tracheole

  Fish - gill

  Frog - lungs & skin

  Human - alveolus

• Insect - gill

  Fish - alveolus

  Frog - lungs & skin

  Human - tracheole

Answer explanation

The respiratory structures is the structure where GASEOUS EXCHANGE occurs.

In humans, the lungs are sacs which contain alveoli for gas exchange. In contrast, in fish, the gills itself are made of filaments and lamellae hence gaseous exchange occurs throughout the gills.

3. 3. Which of the following is NOT a common adaptation of respiratory structures for gaseous exchange in humans and animals? (1 mark)

• Large total surface area to volume ratio

• Thin for rapid gas diffusion

• Have a network of blood capillaries/tracheoles for gas transport

• Moist for gases to dissolve

Answer explanation

The gills are not adapted to be moist as fish live in aquatic environments with dissolved gases.

4. 4. During inhalation in fish, the mouth opens and the floor of the buccal cavity is lowered. The opercular cavity is enlarged and the operculum is ______. This _______ the pressure in the buccal cavity to draw water into the mouth. (2 marks)

5. 5. The diagram shows the structures involved in the human breathing mechanism.

6. Name the structures labelled 1, 2 and 3. Explain the process of exhalation in humans. (8 marks)

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6. 6. Why are the lungs of amphibians not as efficient as human lungs? (2 marks)

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Answer explanation

• - When a frog exhales, some air is expelled through the nostrils but some air remains in the buccopharyngeal cavity.

• - This air which contains carbon dioxide mixes with inhaled air.