Gases and light in water
Answers are for parents and teachers.
1
Oxygen in water falls from 11.3 mg per litre at 10 °C to 7.5 mg per litre at 30 °C. What is the fall?
11.3 − 7.5 = 3.8 mg per litre.
2
Write the chain from more CO₂ in sea water to harder shell building, in four steps.
More CO₂ dissolves; more carbonic acid, lower pH; CaCO₃ turns into soluble bicarbonate; shells harder to build.
3
Why do waves help water to hold oxygen?
They speed up the exchange of gas between the air and the water.
4
Why is the dark zone of the sea not empty of life, even without photosynthesis?
Animals there can live on food and energy that comes from the sunlit zone above or from other animals.
5
Reflection, absorption or scattering? (a) light bounces back from the surface; (b) light energy is taken in by the water.
(a) reflection; (b) absorption.