Required Practical 5: Exchange or Transport Dissection

RP5 can use an animal or plant gas-exchange or mass-transport system, or an organ within one. The centre selects an appropriate specimen and procedure; the requirement is not to dissect every possible example. Define which structures you will identify and how the observations address a biological question.

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.