P.15 Biological Drawings

Purpose of Biological Drawings

• Goal: Accurately record observations from specimens or microscope slides, focusing on clarity and detail rather than artistic skill.
• Requirements: Drawings should accurately depict shape, proportions, and structure based on observed details, and may include calculated magnification and measurements.

Guidelines for Biological Drawings

1. Line Quality:

• Use clear, single lines without sketching or multiple attempts at the same line to avoid fuzziness.
• Draw with an HB pencil and use a quality eraser to correct mistakes cleanly.

1. Proportions and Scale:

• Ensure correct proportions of different parts. For accurate size and proportion, use an eyepiece graticule for measuring dimensions.
• Drawings should be large and make use of the available space but should not extend over any surrounding text.

1. No Shading or Coloring:

• Avoid any shading or coloring; the emphasis should be on outline and structure.

1. Draw What You See:

• Record actual observations, not assumed details based on prior knowledge.
• Carefully observe the specimen through the microscope without bias.

Types of Drawings

1. Low-Power Plan (Plan Diagram):

• Purpose: Shows the layout and organization of different tissues without individual cell detail.
• Characteristics:
  • Only outlines of tissues are drawn, not individual cells.
  • Helps in identifying boundaries between different tissues.
  • Often requires switching to a high-power lens temporarily to better locate boundaries before returning to low power for the overall view.

1. High-Power Detail (High-Power Drawing):

• Purpose: Depicts individual cells with visible internal details, such as organelles.
• Characteristics:
  • Use two lines to represent the thickness of cell walls in plant cells.
  • For cells in contact, show three lines to depict the adjoining cell walls and the boundary between them.
  • Include fine details visible under high power, such as nuclei, nucleoli, or vacuoles.

Labelling Drawings

• Label Lines:
  • Use a ruler for straight label lines, and place the line precisely on the structure it refers to without arrowheads.
  • Avoid crossing lines; organize labels to prevent overlapping or clutter.
• Text Orientation:
  • Labels should be horizontal regardless of the angle of the label line.
  • Write labels outside the drawing area, keeping the drawing space clear of text.

Additional Calculations and Measurements

1. Magnification Calculation:

• Refer to Chapter 1 for methods to calculate the magnification of your drawing if required.

1. Using an Eyepiece Graticule and Stage Micrometer:

• Measure objects under the microscope by calibrating the eyepiece graticule with a stage micrometer. This allows for precise size calculations.

Example Drawing Elements

• High-Power Plant Cell Drawing:
• Show cell walls, cytoplasm, nuclear envelope, nucleolus, vacuole, and chromosomes as observed.
• Apply the guideline for multiple lines for cell walls if cells are adjacent.

Summary of Key Points