Adaptations of aquatic life: structure, behaviour and function
An adaptation is a trait of body or behaviour that helps an organism survive. Structural adaptations are body features: fish have a streamlined body, fins, scales covered with mucus and gills that take dissolved oxygen from the water; a gas-filled swim bladder keeps bony fish afloat; fish in dark deep water often have large eyes; the dolphin, a mammal, has a streamlined body, fins instead of legs and a breathing opening on top of its head. Behavioural adaptations are actions: whales use sound to communicate and hunt, and salmon hatch in fresh water, live in the sea and return to a river to breed. Physiological adaptations are changes in how the body works: some deep-sea fish slow their metabolism when oxygen is low, and the viper fish has a lot of haemoglobin. The types overlap, so we say “mainly”. Osmotic adaptations deal with water balance. In fresh water, water flows into a fish by osmosis, so freshwater fish pass a lot of dilute urine, and single-celled animals such as the amoeba collect water in a contractile vacuole. Most marine bony fish lose water to the sea, so they swallow sea water and remove the extra salt through the kidneys and special gill cells. Sharks keep a lot of urea in the blood so their osmotic pressure is close to the sea’s and they lose little water.
| Adaptation | Type (mainly) |
|---|---|
| gills | structural |
| whale calls | behavioural |
| slower metabolism at low oxygen | physiological |
| salmon returning to a river | behavioural |
Falling shapes, with a grown-up. Make three equal lumps of modelling clay into a ball, a flat disc and a pointed, streamlined drop shape. Drop them one at a time into a tall jar or bottle of water (or race them in pairs) and describe which falls fastest and which slowest. Say how the result explains the shapes of fish and dolphins. Then write one sentence about an adaptation of any sea animal you know and name its type.