MadSci Network: General Biology |
Hi, Ray. There are actually many different types of organisms that make up what we generally refer to as plankton. The type of organism usually brought to mind when we use the term plankton is a group of microscopic plants more appropriately called phytoplankton. The diet of phytoplankton depends on size and metabolism. They all need to get some form of carbon and some form of nitrogen from their environment to survive. Some phytoplankton are producers. This means that they use CO2 to produce the sugars and starches they need to survive (a process I'm sure you have heard of - photosynthesis). So, you might say that these plants "eat" CO2. They also need to have some trace minerals, phosphate, and sulfates (collectively called nutrients) to survive. These nutrients and their nitrogen sources (such as ammonia or nitrate) are absorbed from the water around the phytoplankton. When very high levels of nutrients suddenly flow into the water, you may get what is called a bloom of the phytoplankton. The producers also need some form of energy to drive their photosynthesis. Most phytoplankton get this energy from sunlight, although some in the sediment can use chemical energy to drive their metabolism. There are also phytoplankton that cannot use CO2. These are called consumers. They absorb their nutrients, nitrogenous compounds and the sugars/starches from their environment. They therefore typically grow in dense populations where there is more food, such as near particles containing lots of producers that excrete sugars or near bacteria that the phytoplankton can break open with enzymes that they excrete. There are also animals that are considered plankton, called zooplankton. Very small zooplankton feed on bacteria (technically called bacteriplankton). As we move to larger sizes, we see zooplankton feeding on progressively larger phytoplankton. Have fun!
Try the links in the MadSci Library for more information on General Biology.