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Choose an approved animal or plant organ and a precise observational aim. The worked contexts include gas-exchange and transport structures; your centre may select a different suitable specimen. Define what you intend to observe, how orientation will be preserved and which features could support a structure–function explanation.
Video by Rachel Hamilton. This demonstration examines fish gills. It is one dissection context; the written lesson also discusses transport organs and recording anatomical evidence.
Viewing focus: Plan a suitable animal or plant dissection
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: Which visible features of gills could support efficient exchange?
Many filaments and lamellae provide a large exchange surface, and close blood–water contact can support a short diffusion route. State which features were actually visible and which require microscopic or physiological evidence.
After watching 2: Why should an observed drawing differ from an ideal textbook diagram?
It records the particular specimen and visible features, including orientation and limitations. A textbook model can guide interpretation but should not be copied as though it were the observation.
What you'll be able to do
Choose an approved animal or plant organ and a precise observational aim. The worked contexts include gas-exchange and transport structures; your centre may select a different suitable specimen. Define what you intend to observe, how orientation will be preserved and which features could support a structure–function explanation.
Before cutting, examine orientation and external features. In an animal organ, identify relevant openings and pathways; in plant material, choose a section exposing the tissue arrangement. Follow the approved handling, hygiene, sharps and disposal procedures, considering the source of animal material and any ethical issues.
Cut or separate tissue carefully so relationships remain interpretable. A heart section may reveal chamber walls and valve structures; a plant stem section may show arrangements of xylem and phloem. Use suitable magnification and illumination rather than assuming small features are visible unaided.
Make a clear biological drawing with single definite lines, representative proportions and labels that do not obscure structures. Add a scale bar or measured magnification when relevant. Avoid decorative shading and avoid adding textbook features that were not observed. Notes or photographs can support but should not replace a clear account of the actual specimen and method.
A thick ventricular wall can support an inference about pressure generation, and a hollow reinforced xylem pathway is consistent with bulk water transport under tension. Explain the mechanism linking the feature to function, while recognising that a dissection does not directly measure pressure, flow or living physiological responses.
Specimen preservation, cutting angle and damage can affect appearance. A transverse and longitudinal section can reveal different relationships. Compare with an appropriate reference and use uncertainty in identification where necessary; one distorted opening should not be treated as proof of a new anatomical feature.
Try each question before opening the worked response. Use precise biological terms, connect each cause to its effect, and check units and assumptions when interpreting data.
Common mistakes to avoid
Key takeaways
Question 1: A section shows one ventricle with a substantially thicker wall. Explain a functional inference and its limitation.
Separate structural evidence from physiological measurement.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.