How does a stained preparation compare with a hanging drop for studying the morphology and motility of bacteria?
The correct answer and explanation is:
Correct Answer:
A stained preparation is better for studying morphology, while a hanging drop is better for studying motility.
Explanation (300 words):
When studying bacteria under a microscope, scientists use different techniques to observe their structure and behavior. Two common methods are stained preparations and hanging drop preparations, and each has its strengths and limitations depending on the goal of the observation.
A stained preparation involves applying a dye (such as crystal violet, methylene blue, or safranin) to bacterial cells so they become more visible under the microscope. This method is especially useful for studying the morphology (shape, size, and arrangement) of bacterial cells. It allows clearer visualization of structures such as cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped), as well as arrangements like chains or clusters. However, staining usually involves heat-fixing the bacteria, which kills the cells. Because of this, motility (movement) cannot be observed in stained preparations.
In contrast, a hanging drop preparation involves suspending a drop of living bacterial culture on a coverslip and observing it under a microscope. This method keeps the bacteria alive, so it is ideal for studying motility. Bacteria that are motile will show purposeful, directional movement, often powered by flagella. This technique can also help distinguish true motility from Brownian motion (random vibration caused by water molecules). However, because the bacteria are not stained, their internal structures and precise shapes may be harder to see clearly, especially in low-contrast settings.
In summary:
- Stained preparation: excellent for morphology, not for motility.
- Hanging drop: excellent for motility, limited clarity for morphology.
Therefore, both techniques are complementary—each is suited for a different purpose in bacterial study.