The microscope in cell studies (3)
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1.
During a microscopy practical, a student needs to determine the magnification of their microscope. They use an eyepiece graticule and stage micrometre scale. The graticule shows that a field of view is 12 mm wide. The stage micrometre scale indicates that a length of 1 mm on the stage corresponds to 100 µm. Calculate the magnification of the objective lens.
Calculations:
- Stage Scale to Micrometre Conversion: 1 mm = 100 µm (given).
- Field of View to Micrometre Conversion: A field of view of 12 mm is equal to 12 x 103 µm.
- Relationship between Magnification, Field of View and Stage Scale: Magnification = (Field of View in µm) / (Stage Scale in µm).
Answer: The magnification of the objective lens is (12 x 103 µm) / (100 µm) = 1200x.
2.
A student is asked to draw a specimen viewed under a microscope. The specimen is a thin section of plant tissue. The student has observed cells with distinct cell walls, large vacuoles, and chloroplasts. Describe the steps the student should take to accurately draw these cells, including the key features to include in the drawing. Explain why accurate drawing is an important skill in biology.
To accurately draw cells from a microscope slide, the student should follow these steps:
- Initial Observation: Begin by making a general sketch of the overall field of view. Note the relative size and arrangement of the cells.
- Focus and Detail: Focus the microscope on a single cell. Adjust the magnification to clearly see the cellular structures.
- Outline the Cell: Carefully draw the outline of the cell, paying attention to its shape (e.g., rectangular, polygonal). Ensure the outline is accurate and proportional to the observed cell.
- Draw the Cell Wall: Clearly depict the cell wall as a distinct, rigid structure surrounding the cell membrane. Indicate its thickness if possible.
- Draw the Nucleus: The nucleus is typically a prominent feature. Draw it as a distinct, often spherical or oval structure. Consider the presence of a nucleolus within the nucleus.
- Draw the Vacuole: The large central vacuole is a key feature. Draw it as a large, clear space within the cell, occupying a significant portion of the cell volume.
- Draw Chloroplasts: If chloroplasts are present (as indicated in the question), draw them as small, green oval structures within the cytoplasm. Indicate their distribution within the cell.
- Labeling: Label the key structures: cell wall, nucleus, vacuole, and chloroplasts. Use clear, concise labels.
Importance of Accurate Drawing: Accurate drawing is crucial in biology for several reasons:
- Communication: Drawings provide a clear and unambiguous way to communicate observations to others.
- Analysis: Drawings allow for detailed analysis of cellular structures and their relationships.
- Comparison: Drawings facilitate comparison of different types of cells or specimens.
- Documentation: Drawings serve as a permanent record of observations.
3.
A student is using a compound microscope to observe a specimen. They have calibrated the eyepiece graticule and stage micrometre scale. The student measures the diameter of a bacterial cell as 450 micrometres using the stage micrometre scale. The eyepiece graticule shows that the diameter corresponds to 8.5 mm on the graticule. Calculate the actual diameter of the bacterial cell in micrometres and convert this to nanometres.
Calculations:
- Micrometre to Millimetre Conversion: 8.5 mm corresponds to 8.5 x 103 µm.
- Micrometre to Micrometre Conversion: The stage micrometre scale is calibrated in micrometres. Therefore, the diameter of the bacterial cell is directly given as 450 µm.
- Micrometre to Nanometre Conversion: 450 µm = 450 x 10-9 nm = 4.5 x 10-7 nm.
Answer: The actual diameter of the bacterial cell is 450 µm, which is equivalent to 4.5 x 10-7 nm.