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Ch. 27 - Diversification of Eukaryotes
All textbooksFreeman 8th EditionCh. 27 - Diversification of EukaryotesProblem 11
Chapter 26, Problem 11

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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Step 1: Understand the question. The question is asking about the movement mechanism of the plasmodial slime mold Physarum polycephalum. It gives a brief description of how the slime mold navigates a maze and asks you to identify the best description of its movement.
Step 2: Recall what you know about the different types of cell movement. Cilia and flagella are hair-like structures that some cells use to move. Amoeboid motion is a crawling-like movement where the cell forms temporary projections called pseudopodia. Gliding motility is a type of movement where the cell slides along a surface.
Step 3: Consider the information given in the question. The slime mold is described as exploring the maze, retracting branches from dead-end corridors, and growing along the shortest path to the food. This suggests a type of movement that is flexible and adaptable, rather than rigid and directional like the movement provided by cilia or flagella.
Step 4: Based on the information given and your knowledge of cell movement, the best answer is likely that the slime mold moves by amoeboid motion. This type of movement allows the cell to change shape and direction in response to its environment, which fits with the behavior described in the question.
Step 5: Therefore, the correct answer is (c) The slime mold moves by amoeboid motion.

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Key Concepts

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

Amoeboid Motion

Amoeboid motion is a type of movement used by certain cells and organisms, including slime molds, characterized by the extension and retraction of pseudopodia. This process involves the flow of cytoplasm, allowing the organism to change shape and move in a fluid manner. In Physarum polycephalum, this motion enables it to explore its environment and navigate through complex structures like mazes.
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Gliding Motility

Gliding motility refers to a form of movement observed in some microorganisms, including slime molds, where they move smoothly over surfaces without the use of flagella or cilia. This movement is often facilitated by the secretion of a slimy film that reduces friction, allowing the organism to travel efficiently. In the context of Physarum, gliding motility may play a role in its ability to explore and navigate toward food sources.
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Externalized Memory

Externalized memory in slime molds, such as Physarum polycephalum, refers to the ability of the organism to leave behind slime trails that serve as a form of memory. These trails help the slime mold avoid previously explored dead ends, effectively guiding its movement toward optimal paths. This concept highlights the unique cognitive-like behavior of slime molds, which can adapt their exploration strategies based on past experiences.
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Related Practice
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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. 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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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. Does an organism without a brain have the ability to use an externalized 'memory'—a spatial 'slime map' that the organism uses to avoid moving to regions where it has been before? Researchers addressed this question by placing a U-shaped trap between Physarum and its food (see diagram that follows). Twenty-three out of 24 slime molds reached the food when plain agar was used as the growth substrate. However, when the agar was coated with extracellular slime, only 8 of 24 found the food. The mean time in hours that it took the successful slime molds to reach the food when placed on plain agar or agar pre-coated with extracellular slime was compared (P=0.012). Use the P value provided to determine if the difference is significant or not. What conclusion can be drawn from the graph shown here?

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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. Propose an experiment that would test whether the coating of extracellular slime changed the speed at which the slime mold moved across the substrate.

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