Teacher sheet · Ages 10–11 · about 45–50 minutes
How fish live in water
Lesson page: echoesof.science/school/fish/ages-10-11/ · Pupil worksheet: echoesof.science/school/fish/ages-10-11/print/
Learning aims
- Name the three groups of fish and their features.
- Explain how gills take dissolved oxygen from water.
- Explain how a swim bladder affects floating and sinking.
- Carry out a fair test with repeats.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: can a fish drown? Take ideas. |
| 10 min | Read the text; sort pictures into the three groups. |
| 20 min | Swim bladder diver investigation. |
| 5 min | Which group? game. |
| 5 min | Quiz and discussion of results. |
Materials for the experiment
- A clear 1.5 or 2 litre plastic bottle with cap, full of water
- Three plastic pipettes (droppers)
- Three small metal nuts or blobs of modelling clay
- A cup of water
- Towels
Safety: Wipe up spilled water straight away. Do not squeeze the bottle near anyone's face, and keep the cap screwed on.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| Fish breathe in the oxygen atoms of the water molecule (H₂O). | Fish use oxygen gas dissolved in the water, not the oxygen inside water molecules. |
| Fish float because they are light. | Fish change their buoyancy with the gas in the swim bladder. |
| All fish have bones. | Sharks and rays have skeletons of cartilage. |
Worksheet answers
- Jawless fish (lamprey or hagfish); cartilaginous fish (shark, ray or skate); bony fish (any bony fish, e.g. a goldfish).
- Water passes over the gills; oxygen dissolved in the water passes through the thin walls of the gill folds into the blood.
- Changed: the size of the air bubble. Observed: which diver sank first / how hard we squeezed. Same: bottle, water, nuts, the way we squeezed.
- Warm water holds less dissolved oxygen than cold water, so there is less oxygen for the fish.
Quiz answers
- What is the skeleton of a shark made of? Cartilage. Sharks and rays are cartilaginous fish.[1]
- Why must a fish pass a lot of water over its gills? Water holds much less oxygen than air. Gills take dissolved oxygen out of the water.[4]
- Which water can hold more dissolved oxygen? Cold water. Cold water holds more dissolved oxygen.[6]
- What does the swim bladder help a fish do? Control whether it floats or sinks. It controls buoyancy.[1]
- What does the lateral line sense? Vibrations and movement in the water. It runs along each side of the fish.[2]
- What does 'ectotherm' mean for a fish? Its body temperature depends on the water around it. Fish cannot control their own body temperature.[3][8]
Going further
Look at a fish scale under a hand lens or microscope (from the fishmonger, washed) and try to count the growth rings. Pairs of rings are used by scientists to estimate a fish's age.
Sources used in this lesson
- [1] Biology 2e, 29.2 Fishes (OpenStax (Rice University)): reliability High
- [2] Fish anatomy (South Carolina Department of Natural Resources): reliability High
- [3] Wild Kids: Fish (student guide) (Arizona Game and Fish Department): reliability High
- [4] Life in water: vertebrates, breathing (American Museum of Natural History): reliability High
- [6] Dissolved oxygen and water (U.S. Geological Survey, Water Science School): reliability High
- [8] Ectotherm (Encyclopaedia Britannica): reliability Medium-high
- [9] Buoyancy: Archimedes' principle (NASA Glenn Research Center): reliability High
- [10] Boyle's law (NASA Glenn Research Center (Beginner's Guide to Aeronautics)): reliability High
Full list with links and a note on each source's reliability: echoesof.science/school/fish/sources/
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