Phytoplankton perform all the following except?

Question

provide a source of carbon for the atmosphere

provide a source of oxygen for the atmosphere

balance levels of carbon dioxide in the atmosphere

provide source of food for many organisms

Answer 1

They do now provide carbon for the atmosphere.  They would actually undergo photosynthesis to use up the carbon dioxide in the atmosphere and make oxygen availible to other organisms.  If you need to know more,, look up the photosynthesis question.