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Ch. 27 - Diversification of Eukaryotes
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook
All textbooksFreeman 8th EditionCh. 27 - Diversification of EukaryotesProblem 14
Chapter 27, Problem 14

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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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Step 1: Define the hypothesis for the experiment. The hypothesis could be that the presence of extracellular slime affects the speed at which Physarum polycephalum moves across the substrate.
Step 2: Design the experimental setup. You will need two groups of slime molds: one group with access to a substrate coated with extracellular slime and another group with a clean substrate without slime. Ensure that all other conditions, such as temperature, humidity, and light, are kept constant.
Step 3: Measure the initial speed of movement for both groups of slime molds. This can be done by timing how long it takes for the slime mold to move a set distance on the substrate.
Step 4: Introduce the extracellular slime to the substrate of the experimental group and allow the slime molds to move across the substrate again. Measure the speed of movement for both groups after the introduction of the slime.
Step 5: Analyze the data collected from both groups. Compare the speed of movement before and after the introduction of extracellular slime to determine if there is a significant difference. Use statistical methods to assess the impact of the slime on movement speed.

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Key Concepts

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

Physarum polycephalum Behavior

Physarum polycephalum is a plasmodial slime mold known for its ability to navigate mazes efficiently. It explores its environment by extending its network of protoplasmic tubes, retracting from dead ends, and optimizing its path to reach food sources. This behavior suggests a form of problem-solving and spatial awareness, which is crucial for understanding how it might use external cues to navigate.
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Behavior

Extracellular Slime as Memory

The theory that Physarum polycephalum uses extracellular slime deposits as a form of externalized memory is central to understanding its navigation strategy. These slime trails may serve as markers that prevent the mold from revisiting unproductive paths, effectively guiding it towards the shortest route to food. This concept is essential for hypothesizing how slime deposits influence movement speed and decision-making.
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Intracellular Receptors

Experimental Design in Biology

Designing an experiment to test the effect of extracellular slime on Physarum's movement involves controlling variables and measuring outcomes. Key elements include setting up a controlled environment, manipulating slime presence, and quantifying movement speed across substrates. Understanding experimental design principles is crucial for proposing a method to test the hypothesis about slime's impact on navigation efficiency.
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Experimental Design Example 1
Related Practice
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

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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.

642
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Textbook Question

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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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827
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Textbook Question

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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.

Develop simple experiments to test whether Physarum prefers (1) brightly lit or dark environments; (2) dry or moist conditions; (3) oats or sugar as a food source.

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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. Researchers have proposed that slime molds could be used to help to plan the paths of future roadways and railways. Justify this statement.

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