Biology Homework Chapter 16: Protists
Textbook assignment: Chapter 16: The Origin and Evolution of Microbial Life, sections 12-19.
- 16.12 Protist diversity is causing biologists to revise classification of this group, again using energy and carbon sources as classification criteria. Some protists are photosynthetic (algae) while others are heterotrophs (protozoans). Some gain food by external digestion of organic materials, similar to fungi nutritional processes, while others are parasites, and some are capable of both photosynthesis and chemical heterotrophy (euglena). However, tradition protist classifications are giving way to other schemes that emphasize phylogentic relationships.
- 16.13 Eukaryotic cell types are more complex than prokaryotic cells, including an endomembrane system (folded membranes) and embedded bactaria-like structures. In a process called endosymbiosis, prokaryotic cells (mitochondria and chloroplasts) "infected" eukaryotic host cells, establishing a symbiotic relationship. Many protists live in symbiosis with other life forms.
- 16.14 Classification of protista is complicated by the diversity of forms. Former classification systems of protists included a group called "protozoa"; this group has been redefined and new subdivisions created that emphasizes the DNA patterns as indicating close relationships. The SAR group is divided into
- Stramenopiles, including diatoms and brown algae, both autotrophic, and water molds, which are hetrotrophic. Dinoflagellates have complex shells of silicate, while brown algae form colonies.
- Alveolates, including dinoflagellates — a group which gets its energy through photosynthesis, chemosynthesis, or both — and ciliates. A number of parasites that cause human disease such as malaria also belong to this group.
- Rhizaria, which includes amoebas and foraminiferans, single-celled organisms with calcium carbonate shells.
- 16.15 Algae are efficient at converting light energy from the sun into chemical energy, and could provide a replacement for fossil fuels.
- 16.16 Another criteria for classification could be used: the molecular or morphological similarities of structures within the cells. The excavates are identified by their modified mitochondria, which do not use electron transport chains but rather anaerobic processes to produce energy.
- 16.17 Cellular and plasmodial slime molds have both single and multicellular stages or form supercells with multiple nuclei to survive changes in their environments. They are closely related to amoebas, which can extend lobe-shaped pseudopodia to capture food. These organisms have been grouped together as amoebozoans.
- 16.18 Another "supergroup" contains the archaeplastids, which include all algae. Algae are photosynthetic protists containing chloroplasts; they include dinoflagellates, diatoms, green algae, brown algae (kelp), and red algae. Algae can be multicellular colonies forming seaweed. Like plants, they have both gametophyte and sporophyte "generations".
- 16.19 While only a few years ago, most biologists believe that multicellular life evolved from colonial algae, which may have developed structures that enabled it to live on land, many now believe that at least two other processes led to the development of non-plant forms of multicellular life: choanoflagellates gave rise to animals, while nuclerieds gave rise to fungi.
Read the following weblecture before chat: Protist Forms
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
- Watch the animation on Corals. What are symbiotes? What symbiotes live in the coral polyps? What is coral bleaching? Why is it bad for the coral colony?
- Use the exercise on classifying microscopic protists and fungi to explore the differences between these two groups. Read throug the instructions, then view at least three different slides and use the information on habitat, nurition, and locomotion to identify the cell as a protist or fungus.
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.
- Required: Complete the Mastery Exercise with a score of 85% or better.
- Optional: Test yourself with the textbook multiple choice questions and note any that you miss that still don't make sense. Bring questions to chat!
- Go to the Moodle and take the quiz for this 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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