We cover the structure and function of monerans in more detail in the section on microorganisms in the Organismal Biology chapter.

 

    Phylum Bacteria

    Bacteria are heterotrophic and can act as symbionts, parasites, or decomposers.

 

    Phylum Cyanobacteria (blue-green algae)

    Cyanobacteria are autotrophs that can perform photosynthesis.

 

    Kingdom Protista

    Protists are eukaryotic. In general, protists are less complex than the other eukaryotes and originated earlier in evolutionary history. Most are unicellular, though some are organized in colonies and some others are multicellular. The kingdom Protista can be separated into three primary divisions: animal-like, plantlike, and funguslike.

 

    The animal-like protists are heterotrophic and motile. The most important protozoa for the SAT II Biology are the amoebas, sporozoa, and ciliates:

 

    Phylum Rhizopoda

    The members of phylum Rhizopoda are amoebas, known for their constantly changing body structure. Amoebas use membrane extensions called pseudopods (“false feet”) to move and to surround food particles, which they then engulf into their cytoplasm via phagocytosis. Amoebas generally live in fresh water, but some are found in soil or salt water. If an amoeba finds its way inside a human through contaminated drinking water, it can cause severe dysentery.

 

    Phylum Apicomplexa

    The phylum Apicomplexa consists of spore-forming parasitic organisms, also known as sporozoa. The adult form lives inside the cells of animals. The spores are transmitted to other host animals, usually by a carrier animal. For example, a mosquito bite transmits plasmodium, an apicomplexan that lives in red blood cells and causes malaria.

 

    Phylum Ciliophora

    All members of the phylum Ciliophora propel themselves by waving many short, hairlike structures called cilia in a coordinated fashion; cilia also help draw food particles into the oral groove. Unlike other protozoa, ciliates have two nuclei: the smaller micronucleus is involved in reproduction, while the macronucleus controls the organism’s metabolic processes. A paramecium is the classic example of a ciliate protozoan.

 

    The plantlike protists include euglenoids and various kinds of algae. They are all photo-synthetic autotrophs, transforming light energy into food. Some are unicellular, but many are multicellular, forming fibrous seaweed structures.

 

    Phylum Euglenophyta

    Euglenoids are classified with the plantlike protists because many of them photosynthesize. But these unicellular organisms have flagella that allow them to move.

 

    Phylum Phaeophyta

    Brown algae of phylum Phaeophyta are all multicellular seaweeds, ranging in size from an inch to almost the length of a football field (the large varieties are called kelp). Brown algae provide both food and shelter to many animals in the coastal marine ecosystem.