Nitrate and phosphate are useful as fertilizers in agriculture and gardening. Nitrate and phosphate aid agricultural production by producing more abundant crops. However, since the mass production of ammonia during the 1940's by way of the Haber process, it has been noted that a phenomenon known as “nitrate pollution” may occur. This pollution can be demonstrated by conducting this simple experiment. This experiment demonstrates two main ideas. The first is a test of what levels of nitrate and phosphate allow for optimum algal growth. The second demonstrates at which levels of nitrate and phosphate algal blooms may occur, causing harm to an aquatic ecosystem (Freeman, 2002).

Effect of Nitrate and Phosphate Levels on the Growth of Algae (PDF)


Intended Audience








Learning Objectives

  1. Given three Chlorella cultures with different concentrations of nitrate and phosphate, students will determine the effect of nitrate and phosphate levels on the growth of algae.
  2. Given three cultures with different concentrations of nitrate and phosphate, students will evaluate the nitrate and phosphate levels at which an increase in algal growth occurs in a closed system.


Student Background

It is recommended that students have prior knowledge of algae’s ability to carry out photosynthesis. Also, students should be familiar with laboratory safety.



  • Nitrate: NO3‾, a compound essential to fertilizing plants. It is, however, a common (dangerous) contaminant of groundwater. For more information, see The Nitrate Story.
  • Phosphate: PO43-, a compound necessary for the growth of plants. It is one of the main nutrients found in fertilizers. For more information, see Phosphate.
  • Algae: Photosynthetic organisms that live in many habitats, ranging from aquatic environments to the hot desert sands. They are an essential organism for the production of oxygen, as well as an important food source. However, too much algae (known as an algal bloom) can have an adverse effect on an ecosystem, causing many problems. For more information, see Smithsonian Algae Research.
  • Chlorella: a unicellular alga found in soil, water, and tree bark. Botanical names include Chlorella pyrenoidosa, Chlorella vulgaris.


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