Comparative animal physiology – organ systems from Hydra to mammals

What it shows

Ten organisms, from Amoeba to the rat, are drawn as schematic side views with one organ system shown inside. Small or flat animals rely on diffusion; larger ones evolved tracheae, gills and lungs, open and closed circulations and hearts with two, three or four chambers, guts with one or two openings, flame cells, nephridia, Malpighian tubules and kidneys, and nervous systems from a nerve net to a brain. The temperature model treats ectotherms as kept in shade and uses a simple heat-loss rule for endotherms. Blood pressure along the loops is covered in the sim Single and double circulation.

How to use

Pick Animal A and Animal B, then choose a tab such as Circulation or Excretion. Labels point to the organs, the table compares all ten organisms and Run animates the flow. On Body temperature, press Run to measure from 0 to 40 °C, or set Surrounding temperature and press Record reading. On Nitrogenous waste, move Water available and tick Embryo develops in a shelled egg.

Parameters you can change

• Organ system Gas exchange, Circulation, Digestion, Excretion, Nervous system, Body temperature, Nitrogenous waste
• Animal A Amoeba (single cell), Hydra (cnidarian), Planarian (flatworm), Earthworm (annelid), Grasshopper (insect), Perch (bony fish), Frog (amphibian), Lizard (reptile), Pigeon (bird), Rat (mammal)
• Animal B Amoeba (single cell), Hydra (cnidarian), Planarian (flatworm), Earthworm (annelid), Grasshopper (insect), Perch (bony fish), Frog (amphibian), Lizard (reptile), Pigeon (bird), Rat (mammal)
• Surrounding temperature 0–40 °C
• Water available 0–100 %
• Embryo develops in a shelled egg
• Show endocrine glands

Questions to explore

1. Why can a flatworm manage without lungs or blood vessels while an earthworm cannot?
2. What advantage does a four-chambered heart give birds and mammals over frogs?
3. Why do birds and insects excrete uric acid instead of ammonia?