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Microbio Lab 4
| Question | Answer |
|---|---|
| Total magnification formula | the power of the objective lens multiplied by the power of the ocular lens (eyepiece). For example, if you have a 40x objective lens and a 10x eyepiece, the total magnification is 400x (40 x 10 = 400x). |
| What's the total magnification for a 10x lens? | 10 x 10 = 100 |
| What's the total magnification for a 40x lens? | 40 x 10 = 400 |
| What's the total magnification for a 100x (oil immersion) lens? | 10 * 100 = 1000 (oil immersion) |
| What is the purpose of aseptic technique? | To prevent contamination of cultures, media, and the lab environment by maintaining sterility during microbial handling. |
| What is the streak plate method used for? | To isolate individual colonies from a mixed microbial population on an agar plate. |
| How does the pour plate technique work? | A diluted microbial sample is mixed with agar and poured into a Petri dish to allow colony formation within and on the surface of the agar. |
| What is the purpose of the spread plate method? | To evenly distribute a microbial sample across the surface of an agar plate for colony counting or isolation. |
| Why perform serial dilutions? | To reduce a microbial population to a countable number of cells, often used before plating to determine concentration (CFU/mL). |
| What is the main difference revealed by Gram staining? | Distinguishes bacteria as Gram-positive (purple) or Gram-negative (pink) based on cell wall structure. |
| What does simple staining show? | The shape, size, and arrangement of bacterial cells using a single dye. |
| Acid-Fast Stain | Detects Mycobacterium species that have waxy mycolic acid cell walls. |
| Name and describe three main types of media. | Selective: Supports growth of certain microbes only. Differential: Shows visible differences (e.g., color changes). Enriched: Contains nutrients for fastidious organisms. |
| Bright-field Microscopy | Uses visible light to illuminate stained or naturally pigmented specimens, producing a colored image on a bright background. |
| Dark-field Microscopy | Illuminates specimens with oblique light so they appear bright against a dark background, ideal for observing live, unstained microorganisms. |
| Phase-contrast Microscopy | Converts phase shifts in light into brightness differences, revealing internal cell details without staining. |
| Differential Interference Contrast (DIC) Microscopy | Uses polarized light and interference to create a pseudo-3D image with high contrast of live, unstained samples. |
| Electron Microscopy (TEM & SEM) | Uses electron beams instead of light to visualize cellular ultrastructure (TEM) or detailed surface topography (SEM) |
| Eyepiece (Ocular Lens) | The lens you look through; typically magnifies the image 10×. |
| What are the objective lenses used for? | Provide different levels of magnification (commonly 4×, 10×, 40×, and 100× oil immersion). |
| What is the function of the revolving nosepiece? | Holds and rotates the objective lenses, allowing easy magnification changes. |
| What is the stage on a microscope? | The flat platform where slides are placed for viewing. |
| What do the stage clips or mechanical stage do? | Hold the slide securely and allow smooth movement for precise positioning. |
| What is the coarse adjustment knob used for? | Moves the stage up and down rapidly to bring the specimen into general focus (used with low power only). |
| What is the fine adjustment knob used for? | Provides small, precise focusing after the coarse adjustment (used with high power objectives). |
| What is the function of the arm? | Connects the base and upper parts; used for carrying the microscope safely. |
| What does the base of the microscope do? | Supports the microscope and contains the light source or mirror. |
| What is the purpose of the light source? | Provides the light needed to view the specimen; can be a built-in lamp or external mirror. |
| Diaphragm (Iris Diaphragm) | Controls the amount of light that passes through the specimen. |
| What does the condenser do? | Focuses the light from the illuminator onto the specimen for a clearer image. |
| What is the body tube? | Maintains the correct distance between the ocular and objective lenses. |
| What does the head of the microscope contain? | Houses the optical components (ocular and objective lenses). |
| What is the function of the microscope slide? | A rectangular glass plate that holds the specimen for viewing under the microscope. |
| Oil Immersion Lens | The 100× objective; used with immersion oil to increase resolution by reducing light refraction. |
| What’s the first step before focusing a brightfield microscope? | Place the slide securely into the slide clip on the stage. |
| Which objective lens should you start with when focusing? | Begin with the 10× objective lens, ensuring the specimen is centered under the lens. |
| How do you initially bring the specimen into view? | While looking at the microscope, use the coarse focus to raise the stage until it stops. |
| How should you adjust the condenser before focusing? | Raise the condenser to its highest position, set the condenser dial to “0”, and close the condenser diaphragm. |
| How do you locate the specimen under the microscope? | While looking through the microscope, lower the stage slowly using the coarse focus until the image appears. |
| What should you do once the specimen is nearly in focus? | Use the fine focus knob to sharpen the image. |
| How do you begin adjusting for maximum resolution? | Close the field diaphragm until the edges come into view. |
| What should you do when you see the diaphragm edges? | Adjust the condenser height to make the edges sharp and centered. |
| Once the diaphragm edges are sharp, what’s next? | Open the field diaphragm until its edges align with the edge of the field of view. |
| What must you do to increase magnification? | Rotate the nosepiece to the 40× objective and adjust the fine focus slightly. |
| What if the image looks cloudy or disappears at 40×? | Clean oil off the 40× objective and refocus. |
| What’s the correct procedure to use the 100× objective? | After focusing at 40×, rotate the nosepiece so no lens is over the slide. Place a drop of immersion oil on the specimen. Rotate the 100× objective into place. |
| How do you sharpen the image under oil immersion? | Use the fine focus knob carefully for the clearest image. |
| Steps Condensed | slide, 10x, coarse raise stage, condensor high close diagraph, lower stage til image, fine focus, close diaphragm for edges, open, fine, 40x, `100x |
Created by:
smurtab