4.2.2 - Mammalian gas exchange

Question 1

What do effective gas exchange surfaces have?

Answer 1

Large surface area
Rich blood supply to maintain concentration gradients
Moist walls to allow gases to dissolve and then diffuse in and out faster
Thin layers to minimise diffusion pathways
Permeable surfaces that allow gases to diffuse through

Question 2

What is significant about the linings of passages in the human exchange system?

Answer 2

They secrete mucus and they are lined with cilia.
Dust and pathogens get trapped in mucus and this is sweeped to stomach by cilia so no dust or pathogens enter the lungs.

Question 3

Features of the alveoli in humans.

Answer 3

Epithelial wall is one cell thick.
Capillaries surrounding the alveoli also have one cell thick walls.
The capillaries provide a rich blood supply which maintains concentration gradient.

Question 4

Describe what happens during inhalation in humans.

Answer 4

Diaphragm contracts and flattens.
intercostal muscles contract which moves the ribs up and out
This increases the volume of lungs but decreases the pressure so air is able to move in.

Question 5

Describe what happens during exhalation in humans.

Answer 5

Diaphragm relaxes and moves up.
Intercostal muscles relax which moves the ribs down and in.
This reduces the volume of the lungs but increases the pressure so air moves out.