Human Physiology: common misconceptions

If your child says… “Every animal has lungs.”

Ask together

Where can oxygen enter an earthworm that has no lungs?

What’s true

Insects use air tubes, while frogs use both lungs and skin.

If your child says… “The fluid around the lungs passes oxygen into blood.”

Ask together

Does inhaled air reach the sacs or the fluid outside the lungs?

What’s true

Pleural fluid reduces rubbing between the lung coverings.

If your child says… “Higher pressure inside the lungs pulls air in.”

Ask together

Which way does air move between higher and lower pressure?

What’s true

Air enters when outside pressure exceeds lung pressure.

If your child says… “Vital capacity includes every bit of air in my lungs.”

Ask together

How could measured breathed-out air include air that stays inside?

What’s true

Vital capacity excludes residual air; total lung capacity includes it.

If your child says… “Both gases move from the air sacs into blood.”

Ask together

If carbon dioxide pressure is higher in arriving blood, which way should it cross?

What’s true

Each gas follows its own pressure difference; solubility and barrier thickness also affect exchange.

If your child says… “Once oxygen sticks to haemoglobin, it stays there.”

Ask together

How could oxygen reach cells if it never left haemoglobin?

What’s true

Oxygen attaches reversibly, and increased carbon dioxide, acidity and warmth favour release.

If your child says… “Once carbon dioxide becomes bicarbonate, it cannot change back.”

Ask together

What do the reverse arrows allow bicarbonate to become?

What’s true

Carbonic anhydrase, abundant in red cells, speeds this reversible conversion.

If your child says… “Oxygen is the main signal controlling ordinary breathing.”

Ask together

If carbon dioxide rises without oxygen falling, should those sensors still respond?

What’s true

During ordinary regulation, rising carbon dioxide and acidity strongly stimulate breathing sensors.