Microbiology

Microbiology Study Guide

©2018 of 132 used tomove the organism. Green algae usually have cell walls containing cellulose, and undergo open mitosis without centrioles. Photosynthetic organisms are photoautotrophs, which mean that they are repositories of energy and are able to synthesize food directly from carbon dioxide, water, and energy from light. They accrue it as part of their potential energy. However, not all organisms that use light as a source of energy carry out photosynthesis. Photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon. In plants, algae, and cyanobacteria, photosynthesis releases oxygen. This is called oxygenic photosynthesis. Carbon dioxide is converted into sugars in a process called carbon fixation. Carbon fixation is a redox reaction, so photosynthesis needs to supply both a source of energy to drive this process and the electrons needed to convert carbon dioxide into a carbohydrate, which is a reduction reaction. In a general outline, photosynthesis is the opposite of cellular respiration, where glucose and other compounds are oxidized to produce carbon dioxide, water, and release chemical energy. Five divisions of unicellular algae are considered in microbiology because of their microscopic form and their unicellular characteristic. These organisms are classified in the kingdom Protista. Protozoa Protozoa are a diverse group of single-cell eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior (e.g., movement). Protozoa were regarded as the partner group of protists to protophyta, which have plant- like behavior (e.g., photosynthesis). Protozoans commonly range from 10-52 micrometers, but can grow as large as 1 mm, and are seen easily under a microscope. Protozoa are heterotrophic (they get food from the environment) microorganisms, and most species obtain large food particles by phagocytosis (cellular “eating”). The food particle is ingested into a food vacuole. Lysosomal enzymes then digest the nutrients in the particle, and the products of digestion are distributed throughout the cell. Some species have specialized structures called cytostomes through which particles pass in phagocytosis. Most protozoa have one nucleus, but some have both a macronucleus and one or more micronuclei. Contractile vacuoles may be present in protozoa to remove excess water, and food vacuoles are often observed. They move around with whip-like tails called flagella, hair-like structures called cilia, or foot-like structures called pseudopodia. Others do not move at all. Protozoa may absorb food via their cell membranes; some, like amoebas, surround food and engulf it, and yet others have openings or “mouth pores” into which they sweep food. All protozoa digest their food in stomach-like compartments called vacuoles. Protozoa play an important role as zooplankton, the free-floating aquatic organisms of the oceans. Here, they are found at the bases of many food chains, and they participate in many food webs. Many protozoa alternate between a free-living vegetative form known as a trophozoite and a resting form called a cyst. Achieve Page 19