Explanation:

Phytoplanktons

Phytoplankton, also known as microalgae, are microscopic plant organisms that live in aquatic environment both fresh and salty. Some phytoplankton are bacteria,  some are protists, and most are single- celled plants. Among the common  kinds are cyanobacteria, silica-encased diatoms, dinoflagellates, green algae, and chalk-coated occolithophores.

Phytoplankton growth depends on the availability of carbon dioxide, sunlight, and nutrients.

Statement 1 is correct: They are limited to the uppermost layers of the ocean where light intensity is sufficient for photosynthesis to take place. This photosynthetic rate decreases as the depth in the aquatic system increases  owing to reduction in light intensity.

The photosynthetic rate increases with an increase in temperature, but diminishes sharply after a point is reached as the protoplasmic activity cannot be maintained at temperatures above 40 degree centigrade. Thus, temperature together with illumination influences  the seasonal variation of phytoplankton production more specifically on temperate latitudes. Phytoplanktons produce more than 60% of oxygen produced from all the plants.

Statement 2 is incorrect: Phytoplankton, like land plants, require nutrients such as nitrate, phosphate, silicate, iron and calcium at various levels depending on the species. Some phytoplankton can fix nitrogen and can grow in areas where nitrate concentrations are low. They also require trace amounts of iron which limits phytoplankton growth in large areas of the ocean because iron concentrations are very low.

Other factors influencing phytoplankton growth rates include water temperature and salinity, water depth, wind, and what kinds of predators are grazing on them.