P.15 Biological Drawings

Purpose of Biological Drawings

Goal:
To accurately record observations from specimens or microscope slides. The focus is on clarity and detail rather than artistic ability.

Requirements:

• Drawings must accurately depict the shape, proportions, and structure of the specimen.
• Include calculated magnification and measurements when necessary.

Guidelines for Biological Drawings

1. Line Quality

• Clear, Single Lines:
  Use a clean HB pencil and avoid multiple attempts at the same line to prevent fuzziness.
• Correcting Mistakes:
  Use a quality eraser to correct any errors cleanly.

2. Proportions and Scale

• Accurate Proportions:
  Ensure that different parts of the specimen are drawn in correct relative sizes.
• Measurement Tools:
  Use an eyepiece graticule to measure dimensions accurately.
• Space Utilization:
  Drawings should be large enough to capture details but must not extend into surrounding text areas.

3. No Shading or Coloring

• Outline Only:
  Emphasize clear outlines and structure without adding any shading or color.

4. Draw What You See

• Observation-Based:
  Record only what is observed directly under the microscope. Avoid assumptions based on prior knowledge.
• Unbiased Recording:
  Focus on the actual details visible in the specimen.

Types of Biological Drawings

A. Low-Power Plan (Plan Diagram)

• Purpose:
  To show the layout and organization of different tissues without detailing individual cells.
• Characteristics:
  • Only the outlines of tissues are drawn.
  • Useful for identifying boundaries between different tissue types.
  • May require briefly switching to a high-power lens to accurately locate tissue boundaries.

B. High-Power Detail (High-Power Drawing)

• Purpose:
  To capture individual cells with visible internal details (e.g., organelles).
• Characteristics:
  • Use two lines to indicate the thickness of cell walls in plant cells.
  • When cells are in contact, depict three lines to show adjoining cell walls and their boundaries.
  • Include fine internal details such as nuclei, nucleoli, and vacuoles.

Labelling Drawings

Label Lines

• Straight Lines:
  Use a ruler to draw neat, straight label lines.
• No Arrowheads:
  Place the line precisely on the structure without adding arrowheads.
• Avoid Overlap:
  Organize labels to prevent clutter and overlapping lines.

Text Orientation

• Horizontal Labels:
  Ensure that all labels are written horizontally, regardless of the angle of the label line.
• Clear Drawing Area:
  Write labels outside the drawing area to keep the illustration itself clear.

Additional Calculations and Measurements

Magnification Calculation

• Reference Materials:
  Refer to your laboratory manual or Chapter 1 for methods on calculating the magnification of your drawing.

Using an Eyepiece Graticule and Stage Micrometer

• Accurate Measurements:
  Calibrate the eyepiece graticule with a stage micrometer to measure objects precisely under the microscope.

Example Drawing Elements

High-Power Plant Cell Drawing

• Include Key Structures:
  • Cell walls (using two lines, or three for cells in contact)
  • Cytoplasm
  • Nuclear envelope
  • Nucleolus
  • Vacuole
  • Chromosomes (if visible)

Follow the guidelines for line quality, proportion, and labeling to produce an accurate and detailed representation.

Summary of Key Points

Conclusion

Biological drawings serve as an essential tool for accurately documenting and communicating microscopic observations. By following these guidelines—focusing on clear line quality, accurate proportions, unbiased recording, and proper labeling—you can produce drawings that effectively capture the structure and details of your specimens. These accurate records are invaluable for subsequent analysis, discussion, and reporting in scientific studies.