Gas Exchange in Humans: Answers

Describe the journey taken by a molecule of oxygen from the air until it is delivered to our tissues for respiration.

We breathe in air containing oxygen through our nose and mouth, which travels through the trachea, bronchi and bronchioles until it reaches the alveoli. Oxygen molecules pass through the walls of the alveolus and the capillary wall to get into the bloodstream. The oxygen travels in the bloodstream to various tissues of the body, which will use the oxygen for aerobic respiration.

What is meant by the term gas exchange?

Gas exchange is the movement of oxygen from our lungs into our bloodstream and the movement of carbon dioxide from our bloodstream into our lungs.

Suggest ways in which the alveoli are adapted for efficient gas exchange.

Alveoli have an extremely large surface area for gas exchange and have a rich blood supply for diffusion to take place. They also have moist walls which facilitate diffusion by allowing gases to dissolve and the walls are only one cell thick, which means that gases only have to diffuse a short distance.

What term is used to describe how the process of gas exchange takes place: active transport, diffusion, transpiration or osmosis?

Gas exchange takes place by active transport because oxygen and carbon dioxide move down their concentration gradients from a region of high to low concentration.

Explain how the movement of the diaphragm and rib cage helps us to breathe in and out.

When we breathe in, our diaphragm contracts and flattens while the rib cage moves up and outwards. This increases the volume of the chest cavity, resulting in a lower pressure in the thorax. The lower pressure causes air to be sucked into the lungs. When we breathe out, the diaphragm relaxes and forms a domed shape. The rib cage moves down and in, reducing volume and increasing pressure in the thorax. The increased pressure forces air out of the lungs.

If you’re struggling to understand how changes in pressure can suck air in or push air out, I think it helps to think of a turkey baster. When the balloon at the end is fully inflated, the pressure drops and it can suck up oil and meat juices. If you squeeze the balloon, the reduced volume causes an increase in pressure which squirts the juices onto your roast turkey. It’s exactly the same concept with volume and pressure inside our lungs.

Smoking can cause a condition called emphysema where the alveoli are broken down and have a reduced surface area. How will this affect gas exchange?

A reduced surface area means less gas exchange will take place. Oxygen will pass from the alveoli to the bloodstream at a slower rate and less oxygen will reach the rest of the body. The lack of oxygen is why people suffering with emphysema feel tired and lethargic.