The correct answer is: B. Ultraplankton
Ultraplankton are the smallest phytoplankton, with a size range of 0.2-20 micrometers. They are mostly bacteria and small algae, and they are often difficult to see with a light microscope. Ultraplankton are an important part of the marine food web, and they play a role in the cycling of nutrients.
Nanoplankton are slightly larger than ultraplankton, with a size range of 2-200 micrometers. They include many different types of algae, as well as some bacteria. Nanoplankton are an important food source for zooplankton, and they play a role in the production of oxygen in the ocean.
Net plankton are the largest phytoplankton, with a size range of 200-2000 micrometers. They include many different types of algae, as well as some bacteria. Net plankton are an important food source for fish, and they play a role in the production of oxygen in the ocean.
Picoplankton are the smallest photosynthetic organisms in the ocean, with a size range of 0.2-2 micrometers. They are mostly bacteria, but they also include some algae. Picoplankton are an important part of the marine food web, and they play a role in the cycling of nutrients.