Biology Homework Chapter 16: Prokaryotes
Textbook assignment: Chapter 16: The Origins and Evolution of Microbial Life, sections 1-11.
We have three distinct topics in this chapter; keeping in mind which "subsection" you are in will help you organize the material.
- 16.1 Prokaryotes are single-celled, very small, found in habitats not habitable by eukaryotic life forms, and appear from fossil evidence to be the oldest or earliest life forms. They include two domains, Bacteria and Archaea.
- 16.2 Two criteria are used to classify prokaryotes: shapes and cell wall composition. Shapes fall into three groups: spherical cells are cocci, rod-shaped cells are bacilli, and spiral-shaped cells are spirochetes. Cell wall composition depends on peptidoglycan sugar polymers, which respond differently to Gram stain, allowing us to to group bacteria into "gram-positive" and "gram-negative" groups. Extensions called flagella (long, naked protein structure) and fimbriae (short and hairlike) can also be used to identify bacteria.
Prokaryotes use their projecting structures to sense their environment, transfer materials, and move in their aquatic environments.
- 16.3 Because of their rapid rate of reproduction through binary fission, and the simplicity of their DNA circlet, prokaryotes with favorable mutations can expand into their environment and out-compete their predecessors, or "convert" them by passing the new DNA sequences as plasmids through pili transfers. Endospore coats enable prokaryotes to survive periods of drought, and in some species, filaments seek out water and nutrients between soil particles.
- 16.4 Prokaryotes can also be classified by how they get energy and carbon. Some prokaryotes are autotrophes that can produce their own food from light and get carbon from CO2 (photoautotrophes) or from organic sources (photoheterotrophes). Some are able to break down nonorganic molecules for energy (chemoautotrophes) and CO2 as their carbon source, but most prokaryotes are chemoheterotrophes that absorb energy and carbon from other organic sources.
- 16.5 Multiple species of prokaryotes can form cooperative colonies called biofilms which stick to surfaces, spreading disease.
- 16.6 Many prokaryotes are natural decomposers that break down organic compounds. These can be used industrially to clean up human waste or environmental problems such as oil spills in a process called bioremediation.
- 16.7 Prokaryotes are divided into Bacteria (one RNA polymerase, no entrons, inhibited antibiotic sensitivity, peptidoglycan in cell wall, unbranched carbon chains in membrane lipids) and Archaea (multiple RNA polymerase forms, some introns, antibiotic sensitivity not inhibited, peptidoglycan absent from cell wall, some branched carbon chains in membrane lipids).
- 16.8 Archaea can be found in habitats hostile to most other life forms, including places too salty (halophiles), too hot (thermophiles), or lacking oxygen (methanogens). They are also found in more conventional environments, including all depths of ocean water.
- 16.9 Bacteria are classified by gram stain response, shape, energy source, and carbon source.
- Proteobacteria are gram-negative, and identified by a specific rRna sequence. This group includes E. coli, and the bacteria that cause cholera, as well as those that fix nitrogen in the soil.
- Gram-positive bacteria include actinomycetes, once confused with fungi. This group includes staph and strep bacteria.
- Cyanobacteria are photosynthetic bacteria found in lakes; under certain conditions, they will multiply rapidly and use up the oxygen in the lake, killing off other organisms.
- Chlamydias live in eukaryotic host cells, and cause a number of diseases.
- Spirochetes are helical bacteria that are also the source of disease, such as Lyme disease and syphilis.
- 16.10 Bacteria can cause disease by excreting poisons (exotoxins such as botulism and staph) or producing cell-wall complexes that act as poisons (endotoxins such as salmonella) to the host.
- 16.11 Koch's postulates are a set of principles that determine whether a particular bacterium causes a specific disease. Using Koch's postulates allowed Barry Marshal to determine that the cause of stomach ulcers was not lifestyle, but a specific bacterium, H. pylori.
- The bacterium must be found in every case of a given disease.
- A researcher must be able to isolate the bacterium from an infected victim.
- When the isolated bacterium transfered to a healthy organism, the organism must contract the disease.
- A researcher must be able to isolate the bacterium from the newly infected organism.
Read the following weblecture before chat: Prokaryotic Forms
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Work through the Click and Learn activity Winogradsky Column: Microbial Ecology in A Bottle. Read the background tab, then use the slide to examine each layer in the Winodradsky column. How do the bacterial organisms found in the bottle differ in the different microenvironments? What factors affect isolation of different types of bacteria into the different layers? How does the bottle simulate an actual pond environment?
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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