Explain the two main physical/ chemical processes by which carbon dioxide molecules in the air move to the cells of phytoplankton in the ocean

The two physical/ chemical processes by which carbon dioxide molecules in the air move to the cells of phytoplankton in the ocean are the photosynthesis and the biological carbon pump.

Explanation:

The biological carbon pump is the action of organisms to move carbon during chemical and biological interactions from the surface into the deeper ocean and then to rocks.  

The biological carbon pump its composed of three processes, which are the photosynthesis, the gravity and the food web interactions. They are all part of the carbon cycle.

During the photosynthesis, the phytoplankton take up carbon dioxide from the atmosphere that is dissolved in the surface water, and receives the energy from the sun to turn it into glucose and oxygen.  

In the cells of the phytoplankton, glucose is transformed into other organic compounds. This material has organic carbon that can end in two ways: it is incorporated to marine organisms during the food web interactions or it can be remineralised forming calcium carbonate in the ocean surface.  

The remineralization can be done by many organisms to build its shells or skeletons, or by chemical processes that happen in the ocean. This process allows more carbon dioxide to enter the water and to continue the cycle.

So when marine organisms die, all its organic components sink into the bottom of the ocean and carbon-rich sediments are form. And after millions of years, these sediments turn into rocks after going through chemical and physical phenomenon.