School › Reptiles and amphibians › Ages 10–11
Two ways of life: amphibians and reptiles
How amphibians live a 'double life' in water and on land, how reptiles became free of the water, why both are ectotherms, and a fair test on warming up in the sun.
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The word amphibian means 'double life'. Most amphibians start in the water and live on land as adults. There are about 6,770 kinds, in three groups: frogs and toads (the biggest group), salamanders, and caecilians, which have no legs.[1]
Amphibian skin is moist and lets water and gases through. Amphibians take in most of their water through their skin, and they breathe with their skin and mouth as well as lungs; most salamanders have no lungs at all.[1][3]
A tadpole has gills and a tail but no legs. During metamorphosis it loses its gills and tail, grows four legs and develops lungs. Frog eggs are protected by jelly but would dry out quickly, so they are laid in water or damp places.[1][3]
Reptiles have skin with tough scales made of keratin and a waxy layer that stops water loss. They lay eggs with a shell, often leathery, that can be laid on land, and the young hatch as small versions of the adults. Reptiles keep growing all their lives and shed their skin; a snake sheds its whole skin at once.[2][3]
Both groups are ectotherms: their body heat comes mainly from their surroundings. They bask in the sun to warm up and move into the shade or underground to cool down. This saves energy: a reptile can live on about a tenth of the food a mammal of the same size needs.[3][2]
The four groups of reptiles are lizards and snakes (the biggest group), turtles and tortoises, crocodiles and alligators, and the tuatara of New Zealand.[2]
Try it: Basking test
You need
- Two identical small plastic bottles (e.g. 330 ml)
- Water at room temperature
- Two thermometers
- A sunny windowsill or a sunny spot outside, and a shady spot
- Timer
Safety
Never look straight at the sun. If you work outside, wear a hat and stay with your group. Use plastic bottles, not glass. Wipe up spills.
What to do
- Fill both bottles with the same amount of water from the same jug. They are your 'lizards'.
- Measure and write down the starting temperature of each.
- Put one bottle in the sun and the other in the shade, at the same time.
- Measure the temperature of each bottle every 5 minutes for 30 minutes.
- Fair test: what did you change, what did you measure, and what did you keep the same?
- Draw a line graph with both bottles on it.
Play: Reptile, amphibian or both?
Is this true of reptiles, of amphibians, or of both?
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Quiz
Other ages: Ages 6–7 · Ages 15–16