Photosynthesis in Unicellular Algae

Algae are the world’s solar panels. Although they harness less than half as much energy from the sun as solar panels, life would be hard pressed to continue without them. Algae, the base foundation for waterborne food chains, use photosynthesis to convert the sun’s energy into sugars and release oxygen as a byproduct. As a whole, these slimy and mostly autotrophic microorganisms surpass plants in producing oxygen for our environment.

The common green algae you see on lakeside rocks are colored by the same green pigment found in most common plant leaves, chlorophyll. Eukaryotic algae have chloroplasts, organelles that contain the energy-capturing and coloring pigments such as chlorophyll. Prokaryotic algae have no chloroplasts and instead have only thylakoids which hold their pigments. These pigments are responsible for absorbing photons from certain wavelengths of light, usually in the range of 400 – 600 nanometers. There are many different types of primary pigments, such as phycocyanin (blue-green), phycoerythrin (red-purple), and fucoxanthin (golden-brown). Secondary pigments may also be present that may mask the primary pigment’s color and change the light spectrum absorbed.

Scientist often disagree when it comes to classifying various algae, but the photosynthetic process in unicellular algae, such as Euglena, is essentially the same as the process in their close relatives, the plants. The process begins with photons of light being absorbed by the primary pigment located in the chloroplast.

In the first stage of photosynthesis, referred to as the Light Reaction, the absorbed photons create a higher energy state which is used to break apart water molecules. This produces oxygen, free electrons, and positive hydrogen ions. In this step, electrons move through an electron transport chain located in the thylakoid membrane and are used to produce Adenosine Triphosphate (ATP). This process of adding a phosphate group to adenosine diphosphate is called photophosphorylation. NADPH, an electron carrier, is also formed from NADP+.

In the second step, called a Dark Reaction, the end products of the Light Reaction, ATP and NADPH, are utilized to synthesize sugars from carbon dioxide.

The Calvin-Benson cycle, a complex and cyclic pathway, uses the energy available from ATP and NADPH to add ribulose biphosphate or other carbon compounds to carbon dioxide in order to form glucose or similar sugars.

Factors that affect photosynthesis are: the wavelengths of the light, concentration of carbon dioxide, and temperature. Since algae are found in a variety of locations, from the arctic to undersea thermal vents, it is apparent that this diverse group of Protists have learned to adapt. For instance, cyanobacteria, some of which exist at depths where light cannot penetrate heavily enough to cause significant excitation in the electrons, have evolved specialized pigments to facilitate the process. Sometimes, these factors can affect one another. Such is the case when temperature fluctuations cause carbon dioxide to be processed at differing rates.

We refer to photosynthetic algae as photoautotrophs. This is because they are able to create complex organic compounds, such as glucose, from nothing more than water, light, and carbon dioxide.
These algae produce tons of oxygen, recycle carbon dioxide, and form many symbiotic relationships in our environment, such as coral reefs that host algae in exchange for the utilizable energy they produce.