Compare and contrast the different types of protists in freshwater systems. Which could be used to track a lake's environmental conditions?

Question

What will be an ideal response?

Answer 1

Amebas (or amoebas) are free-living predators that engulf prey by phagocytosis. Free-living amebas can harbor bacterial pathogens such as Legionella pneumophila, which contaminates water supplies and air ducts. Amebas move by extension of lobe-shaped pseudopods. Foraminiferans are a type of ameba that make needle-like pseudopods that radiate in all directions. Their shells are made of calcium carbonate (CaCO3), which are found in reefs, beach sand, and sedimentary rock. Because these shells capture the isotopic signature of oxygen, they can be used as units for geological analysis. The oxygen captured in CaCO3 has an isotopic signature of the water where the ameba lives. If the water is warm, the lighter oxygen isotopes (16O) will evaporate slightly more than the heavier oxygen isotopes (18O). Thus, the water will have a heavier isotopic signature of oxygen (higher 18O/16O) as water temperatures rise. If a foram lives during a time when the Earth's temperature is warm, it will have a heavier oxygen isotope ratio in its shell than a foram living during a time when the Earth's temperature is cool.

Alveolates are known for their complex outer covering, or cortex. The cortex contains networks of vesicles called cortical alveoli that store calcium ion and in some species grow protective plates. In contrast to Amebas, alveolates move by cilia and flagella. Alveolates equipped with paired flagella or cilia are known as flagellates and ciliates, respectively. Flagella (singular, flagellum) and cilia (singular, cilium) are essentially equivalent organelles composed of microtubules and enveloped by the cell membrane. They are covered by an extension of the plasma membrane. Ciliates contain short microtubule projections, driven by ATP. Cilia are shorter than flagella and more numerous, and usually cover a broad surface. Cilia beat in coordinated waves that maximize motility (cell propulsion) and food acquisition.