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Ch. 27 - Diversification of Eukaryotes
Chapter 26, Problem 9

Consider the following: Plasmodium has an unusual organelle called an apicoplast. Recent research has shown that apicoplasts are derived from chloroplasts via secondary endosymbiosis and have a large number of genes related to chloroplast DNA. Glyphosate is one of the most widely used herbicides. It works by poisoning an enzyme located in chloroplasts. Biologists are testing the hypothesis that glyphosate could be used as an antimalarial drug in humans. How are these observations connected?

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Step 1: Understand the background information. Plasmodium is a genus of parasitic protozoa that causes malaria in humans. It has an unusual organelle called an apicoplast, which is derived from chloroplasts via secondary endosymbiosis and contains genes related to chloroplast DNA.
Step 2: Understand the role of glyphosate. Glyphosate is a widely used herbicide that works by poisoning an enzyme located in chloroplasts. This enzyme is essential for the growth and survival of plants.
Step 3: Connect the information. Since apicoplasts in Plasmodium are derived from chloroplasts and contain similar genes, it's possible that the enzyme glyphosate targets in chloroplasts is also present in apicoplasts.
Step 4: Understand the hypothesis. Biologists are testing the hypothesis that glyphosate could be used as an antimalarial drug. This is based on the assumption that glyphosate could poison the enzyme in apicoplasts, thereby killing Plasmodium.
Step 5: Summarize the connection. The observations are connected in that the presence of chloroplast-like organelles in Plasmodium (apicoplasts) could potentially make the parasite susceptible to glyphosate, a herbicide that targets an enzyme in chloroplasts. This forms the basis of the hypothesis that glyphosate could be used as an antimalarial drug.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Apicoplasts

Apicoplasts are specialized organelles found in certain parasitic protists, such as Plasmodium, the causative agent of malaria. They are derived from chloroplasts through a process known as secondary endosymbiosis, which involves the engulfing of a photosynthetic organism by a non-photosynthetic one. Apicoplasts retain some genetic material similar to that of chloroplasts, suggesting they may perform functions related to metabolism and biosynthesis, crucial for the survival of the parasite.

Secondary Endosymbiosis

Secondary endosymbiosis is a process where a eukaryotic cell engulfs another eukaryotic cell that has already undergone primary endosymbiosis, leading to the formation of new organelles. This phenomenon is significant in the evolution of various protists, allowing them to acquire chloroplasts from photosynthetic ancestors. In the case of Plasmodium, the apicoplast is a remnant of this process, highlighting the evolutionary adaptations of the organism to its parasitic lifestyle.
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Glyphosate and Its Mechanism

Glyphosate is a broad-spectrum systemic herbicide that inhibits a specific enzyme pathway known as the shikimic acid pathway, which is essential for the synthesis of certain amino acids in plants and some microorganisms. This pathway is absent in animals, making glyphosate a selective herbicide. The hypothesis that glyphosate could serve as an antimalarial drug stems from its potential to target similar metabolic pathways in the apicoplast of Plasmodium, potentially disrupting the parasite's survival and growth.
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Related Practice
Textbook Question

Evaluate the following statements regarding motility in protists. Select True or False for each statement. T/F Amoeboid motion is common in species with cell walls. T/F Some protists use flagella to swim. T/F Some protists use cilia to swim, which are shorter and more numerous than flagella. T/F Amoeboid motion requires ATP and interactions between the proteins actin and myosin.

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Textbook Question

How can dinoflagellates be harmful to humans? a. They are transmitted by mosquitoes and cause malaria. b. They produce toxins that can be absorbed by clams and other shellfish which, when eaten by people, can lead to paralytic shellfish poisoning. c. They cause amoebic dysentery which leads to severe diarrhea and dehydration. d. They are transmitted by tsetse flies and cause 'sleeping sickness.'

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Textbook Question

The text claims that the evolutionary history of protists can be understood as a series of morphological innovations that established seven distinct lineages, each of which subsequently diversified based on innovative ways of feeding, moving, and reproducing. Explain how the Alveolata support this claim.

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Textbook Question

Suppose a friend says that we don't need to worry about the rising temperatures associated with global climate change. She claims that increased temperatures will make planktonic algae grow faster and that carbon dioxide (CO2) will be removed from the atmosphere faster. According to her, this carbon will be buried at the bottom of the ocean in calcium carbonate shells. As a result, the amount of carbon dioxide in the atmosphere will decrease and global warming will decline. Comment.

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Textbook Question

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized 'memory' that 'reminds' it not to retry dead ends. Which of the following best describes movement in Physarum? a. Cilia propel the slime mold. b. Flagella propel the slime mold. c. The slime mold moves by amoeboid motion. d. The slime mold moves by gliding motility.

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Textbook Question

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized 'memory' that 'reminds' it not to retry dead ends. Physarum is a plasmodial slime mold, whereas Dictyostelum is a cellular slime mold. Compare and contrast movement by the migrating slug stage of Dictyostelium to the plasmodial stage of Physarum.

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