Practise analysing absorption and action spectra at HL depth, linking pigment wavelengths to photosynthetic rate and using algal light data to justify ecological conclusions.
In water, shorter wavelengths of light such as blue and green penetrate deepest, and longer wavelengths of light penetrate less far. Red light does not reach depths of more than 50 m . Marine algae live at various water depths. Certain species of algae contain the pigments that enable them to adapt to life at different depths.
The graphs show the absorption and action spectra for two species of algae: Ulva taeniata, which is green, and Porphyra nereocystis, which is red.
Absorption / \%
In each species, identify the colour of light that is used mainly for photosynthesis.
Ulva taeniata:
Porphyra nereocystis:
Deduce, with a reason, which algae lives at a greater depth.
Describe how the rate of photosynthesis could be measured in a marine alga, to produce an action spectrum.