IMO Practice Test — Animal Kingdom
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
Adult starfish show radial symmetry, but their larvae are bilaterally symmetrical. This suggests echinoderms evolved from:
Bilaterally symmetrical ancestors
Asymmetrical sponges
Plants
Radially symmetrical adults only
Explanation: The bilateral larva indicates a bilaterally symmetrical ancestry, with radial symmetry secondarily acquired.
Question 2 of 6
A true coelom is an advantage because it:
Allows organs to develop, move and be cushioned independently of the body wall
Removes the need for a gut
Stops the animal moving
Replaces the nervous system
Explanation: A fluid-filled coelom gives space for organ development and movement, cushioning the organs.
Question 3 of 6
A worm is bilaterally symmetrical, triploblastic and has a fluid 'false' cavity not fully lined by mesoderm. It is a:
Pseudocoelomate (Aschelminthes)
Acoelomate flatworm
True coelomate annelid
Sponge
Explanation: A body cavity not fully lined by mesoderm is a pseudocoelom, characteristic of Aschelminthes.
Question 4 of 6
Why are amphibians tied to water for reproduction even though they live on land?
They lay eggs without shells that must stay moist, and gametes need water
They cannot breathe air
They have gills only
They are warm-blooded
Explanation: Amphibian eggs lack a protective shell and are laid in water; reproduction depends on a watery environment.
Question 5 of 6
Reptiles colonised dry land more successfully than amphibians largely because they have:
Dry scaly skin and shelled eggs that resist water loss
Moist skin
Gills throughout life
Feathers
Explanation: Dry scales reduce water loss and shelled (amniotic) eggs can develop on land, freeing reptiles from water.
Question 6 of 6
A bat flies and a whale swims, yet both are classed as mammals because they:
Have hair and feed their young on milk from mammary glands
Lay shelled eggs
Breathe with gills
Are cold-blooded
Explanation: Despite different lifestyles, hair and milk-producing mammary glands make both mammals.