Phytoplankton are a group of microscopic organisms that are found in the oceans and seas around the world. Taxonomically they are split into seven divisions. They range in size from 1 micrometer to over 100 micrometers in diameter. If you were to stack 1000 one micrometer phytoplankton end to end, the length of that stack would equal the width of a penny!

Phytoplankton typically grow in the upper regions of the water column. This allows them easy access to sunlight, as they require this radiant energy to carry out photosynthesis. Phytoplankton contain a variety of different pigments which are useful to ecologists for the following reasons:

1.  All phytoplankton contain chlorophyll a. Its presence in water indicates the presence of (a) photosynthetic organism(s). It can be extracted from the water sample and can be used to indicate the quantity of phytoplankton in a sample.

2.  In addition to chlorophyll a, all phytoplankton contain accessory pigments e.g. chlorophylls a, b, c, carotenoids and phycobilins. The accessory pigments are specific to different taxonomic groups of organisms e.g. green algae contain chlorophylls a and b, but no c.  Diatoms contain a and c but not b. Thus, the presence of accessory pigments in a water sample can be used to indicate the presence or absence of different groups of algae.
 

ABSORPTION SPECTRA

Any pigment that is extracted from an algal cell and then purified absorbs light at a characteristic wavelength. For example, a pure acetone solution of chlorophyll a absorbs strongly in the blue and red. Each pigment absorbs varying wavelengths of light. However, collectively they absorb enough radiant energy to carry out their needs.

Click here to see the absorption spectra for chlorophyll a and b.

They use this energy to incorporate inorganic carbon compounds (CO₂ and HCO₃^-) into organic compounds. They also produce oxygen as a byproduct. Phytoplankton were among the first organisms to do this and as a result an oxygen holocaust occurred. In order to survive, organisms evolved the ability to use this oxygen and aerobic respiration evolved. This set the stage for life as we know it today.  Phytoplankton also serve as a major source of oxygen and sink for carbon dioxide. As such, they are extremely important in the environment.
 

UV-A AND UV-B RADIATION

UV-A radiation consists of short wavelengths (between 320-400 nm). U-VB, on the other hand, has shorter wavelengths (280-320 nm). Both, however, are shorter in wavelength when compared to the visible spectrum.  The ozone layer is responsible for filtering out most ultraviolet radiation.  However, ozone depletion has compromised the atmosphere's ability to protect life from this radiation.

OZONE DEPLETION

Ozone is a molecule that consists of three oxygen atoms (O₃). In the stratosphere, the oxygen that we breathe, 0₂ is broken down by light energy into two oxygen atoms. These atoms are very reactive and combine to from ozone. For every ten million molecules of air, two million are breathable oxygen, and only three are ozone.

This small amount, however, is enough to prevent most UV-B radiation from reaching the earth's surface. Humans have damaged the ozone layer by adding molecules that contain chlorine and bromine.  These have typically been found in refrigeration and air conditioning coolants. They react chemically with the ozone and cause it to break apart. If you would like more information on the chemistry and physics behind these reactions, click here.  The point is that ozone depletion is bad news for life on earth. It protects us from excessive UV-B radiation. UV-B radiation is high enegy and can penetrate deeply into water, leaves, and skin! It can adversely affect the ability of cells to metaboloize and can damage genetic material. It can also lead to decreased productivity in the world's ocean and agricultural areas!