Drawings

Biological drawings are a fundamental skill in biology, used to record observations, understand structures, and communicate scientific findings. They differ significantly from artistic drawings, emphasizing clarity, accuracy, and adherence to specific conventions

Purpose and Importance

• Recording Observations: Drawings are made to capture what is seen under a microscope (from slides or photomicrographs). This helps in understanding and remembering structures.

• Clarity and Detail: They provide a clear, simple representation, showing specific features and essential details that might be difficult to convey otherwise.

• Understanding Structure-Function Relationships: Drawings help link the form of biological structures to their roles, such as the biconcave shape of red blood cells for oxygen diffusion.

• Analysis and Interpretation: They are used to interpret and predict results, as seen in genetic diagrams used to predict offspring genotypes and phenotypes.

Types of Drawings

There are generally two main types of biological drawings:

• Low-Power Plan Diagrams (LPP): These diagrams show only the outlines of tissues and their distribution within an organ. Individual cells are not drawn in a low-power plan. They are typically made from specimens viewed under lower magnifications.

  • Examples include plan diagrams of transverse sections (TS) of plant stems, roots, and leaves, or blood vessels like arteries and veins.

• High-Power Detail Drawings: These drawings show details of individual cells or a small group of representative cells within a tissue. They include organelles if visible. They are made when visualizing cells at higher magnification.

  • Examples include drawing specific cell types like red blood cells, monocytes, neutrophils, and lymphocytes, or detailed views of muscle fibers or sarcomeres.

Conventions and Quality Guidelines

To produce a good biological drawing, several rules should be followed:

• Pencil and Lines: Use a sharp HB pencil (or H) and a good eraser. Lines should be clear, clean, continuous, and single (not fuzzy, sketchy, or overlapping).

• Shading and Color: Avoid shading or coloring.

• Size and Proportions: Drawings should be large enough to use most of the available space on the page, but not extend beyond it. Overall shape and proportions of components must be accurate. An eyepiece graticule can be used to ensure correct proportions.

• Drawing What You See: It is crucial to draw what you actually observe, not what you think you should see from a textbook.

• Labels:

  • Labels should be written horizontally.

  • Use a ruler for label lines.

  • Label lines must stop precisely at the structure being labelled.

  • Do not use arrowheads on label lines.

  • Label lines should not cross each other.

  • Labels should be placed outside the drawing itself.

  • All relevant structures should be labelled, and a clear title indicating the specimen and viewing conditions should be included.

• Annotations: Short notes can be added next to labels to describe or explain features of biological interest.

Magnification and Measurement

• Calculating Magnification: Magnification (M) is calculated as Image Size (I) divided by Actual Size (A) (M = I/A). This can be done for drawings, photomicrographs, and electron micrographs.

• Scale Bars: Images and drawings typically include a scale bar to indicate the actual size of the specimen. You may need to add a scale bar to your drawing.

• Units: Appropriate units (millimetre (mm), micrometre (μm), nanometre (nm)) should be used, remembering conversions (1mm = 1000µm).

• Eyepiece Graticule and Stage Micrometer: These tools are used for making measurements of cells, tissues, and organs under a microscope and for calibrating the graticule to determine real size.

Specific Drawing Contexts

• Cells: Drawings of animal and plant cells show organelles and overall structure. Prokaryotic cells also have specific features to draw, like cell walls, circular DNA, and ribosomes.

• Tissues/Organs: Plan diagrams are common for organs like plant stems, roots, and leaves, as well as blood vessels and airways.

• Molecular Structures: Diagrams can also represent complex molecular structures like proteins (e.g., peptide bonds, tertiary structures, antibodies), or the fluid mosaic model of cell membranes.

• Microscopy: Drawings are made from observations under light (optical) microscopes and electron microscopes (TEM, SEM). Electron micrographs offer greater resolution and detail compared to light micrographs.

Exam Tips

• Show All Working: When calculating magnification or actual size, it is essential to show every step of your working clearly and fully.

• Time Management: Drawing questions are often designed to take a specific amount of time (e.g., approximately equal to other questions).

• Practice: Regular practice in drawing from microscope specimens and photographs is encouraged to become confident and skilled.