Q 01/05

Which gas building up in the blood, rather than a lack of oxygen, triggers the human urge to breathe?

A) Nitrous oxide

B) Carbon dioxide

C) Sulfur dioxide

D) Carbon monoxide

Answer · why

B) Carbon dioxide

Carbon dioxide is what the brainstem's sensors track, so free divers who over-breathe before a dive can black out underwater without ever feeling a ne...

Q 02/05

Which Russian physiologist won a 1904 Nobel Prize for work on digestion, not for his famous salivating dogs?

A) Ivan Pavlov

B) Ivan Sechenov

C) Dmitri Mendeleev

D) Élie Metchnikoff

Answer · why

A) Ivan Pavlov

Ivan Pavlov was the first Russian Nobel laureate. He was measuring the digestive juices of dogs when he noticed them drooling before any food arrived,...

Q 03/05

Which sea animal has three hearts and blue blood, coloured by a copper-rich protein instead of an iron-rich one?

A) Starfish

B) Jellyfish

C) Octopus

D) Seahorse

Answer · why

C) Octopus

Octopus blood is pumped by one main heart for the body and two smaller ones that push it through the gills. The main heart goes quiet whenever the ani...

Q 04/05

Which gas from ordinary compressed air dissolves in a diver's tissues and forms the bubbles that cause 'the bends'?

A) Helium

B) Hydrogen

C) Neon

D) Nitrogen

Answer · why

D) Nitrogen

Nitrogen makes up most of the air in a scuba tank and is not used up by the body. If a diver surfaces too fast, it comes out of solution like the fizz...

Q 05/05

Which lubricant inside a human joint holds the gas bubbles behind the pop of a cracked knuckle?

A) Amniotic fluid

B) Synovial fluid

C) Interstitial fluid

D) Cerebrospinal fluid

Answer · why

B) Synovial fluid

Synovial fluid takes about 20 minutes to reabsorb the gas, which is why the same knuckle will not crack twice in a row. Studies have found no link bet...