Laboratorio de Biología: Observando células procariotas
Introduction to Prokaryotic Cells
Overview of Cell Types
- The cell is the fundamental unit of life, and all living matter must be organized into a cellular structure. Activities necessary for life occur within cells.
- Cells are classified into two main types: prokaryotic and eukaryotic, with the key distinction being the presence or absence of a nucleus. Prokaryotes lack a nuclear structure, while eukaryotes have their genetic material stored in a central nucleus.
Historical Context
- The terms "prokaryote" and "eukaryote" were introduced in the 20th century, despite the discovery of cells dating back to the 1st century. Early distinctions between cell types were made by scientists like Ernst Haeckel and Edward Chatton.
- Chatton coined the terms to differentiate between nucleated (eukaryotic) and non-nucleated (prokaryotic) cells, which gained popularity among scientists over time due to their clarity in classification.
Characteristics of Prokaryotic Cells
Structural Features
- Prokaryotic cells are identified by their lack of a defined nucleus; instead, their genetic material is typically organized in a single circular chromosome located in the cytoplasm. They also lack membrane-bound organelles, making them structurally simpler than eukaryotes.
- All prokaryotes are unicellular organisms with cell walls composed mainly of peptidoglycan, generally resulting in smaller sizes compared to eukaryotic cells. Some prokaryotes exhibit various shapes such as elongated, round, spiral or helical forms.
Observing Prokaryotic Cells through Microscopy
Sample Preparation
- Yogurt serves as an excellent sample for observing prokaryotes under a microscope since it contains millions of bacteria that ferment milk regardless of its source (homemade or industrial). A staining procedure is necessary due to the small size of these cells for better visibility under light microscopy.
- The preparation involves taking yogurt on a wooden stick, spreading it on a slide, gently heating it to avoid damage while maintaining its natural color before adding methylene blue stain for contrast during observation. This process helps distinguish bacterial structures more clearly under microscopic examination.
Microscopic Observation Techniques
- When using microscopes to observe prokaryotes like those found in yogurt, starting with lower magnification objectives facilitates focusing before switching to higher magnifications (40x) for detailed observation where mostly round-shaped bacteria (cocci) can be identified as part of Lactobacillus and Streptococcus genera used in yogurt production.
- For enhanced clarity at high magnification levels (immersion oil technique), applying immersion oil helps concentrate light effectively through smaller apertures required for viewing these tiny organisms without losing focus during adjustments made on the microscope's revolving nosepiece.
Conclusion & Next Steps
Future Observations
- In upcoming sessions, there will be observations focused on eukaryotic cells following this introduction to prokaryotics.