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.

Verified step by step guidance

1. Understand the problem: The question is asking about the mechanism of movement in Physarum polycephalum, a plasmodial slime mold, and provides four options to choose from. The slime mold's behavior in the maze is described as exploring, retracting from dead ends, and growing along the shortest path to food.
2. Recall the characteristics of Physarum polycephalum: This organism is a single-celled, multinucleate slime mold that moves by extending and retracting its cytoplasm. It does not have cilia or flagella, which are structures used for propulsion in other organisms like certain protists or sperm cells.
3. Define amoeboid motion: Amoeboid motion is a type of movement where the organism changes its shape by extending pseudopodia (temporary projections of cytoplasm) and flowing its cytoplasm into these extensions. This is a characteristic movement of amoebas and similar organisms, including Physarum.
4. Eliminate incorrect options: a) Cilia and b) Flagella are not involved in Physarum's movement, as it lacks these structures. d) Gliding motility is a different mechanism seen in some bacteria and protists, where the organism moves smoothly along a surface without pseudopodia.
5. Conclude the correct answer: Based on the description of Physarum's movement and its use of pseudopodia, the best description of its movement is c) The slime mold moves by amoeboid motion.

Key Concepts

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. It is essential for locomotion and feeding, enabling the organism to navigate through its environment effectively.

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 along surfaces efficiently. Understanding this concept is crucial for explaining how Physarum polycephalum navigates its environment.

Externalized Memory

Externalized memory in the context of Physarum polycephalum refers to the organism's ability 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 food sources. This concept highlights the unique cognitive-like behavior of slime molds, which can adapt their exploration strategies based on past experiences.