Cambridge IGCSE Marine Science Practical Skills 3: Marine organism observation and identification

Cambridge 0697 marks three practical activities in Topic 3: identifying and comparing specimens from cells to whole organisms, observing and drawing named groups, and constructing or using simple dichotomous keys. This note develops those Paper 2 skills without repeating the theory hub's classification explanations.

Select the observation method

Choose equipment from specimen size and required detail. A hand lens is suitable for external features of larger organisms. A light microscope reveals cells or small structures. A clear photograph can support identification when live or preserved material is unavailable.

Begin at low magnification to locate the specimen, centre it, then increase magnification if needed. Place a thin specimen on a clean slide, add a suitable mounting liquid, lower a coverslip at an angle and avoid trapping bubbles. Use the coarse focus only at low power, then fine focus. Illumination should reveal boundaries without washing out detail.

Treat slides and coverslips as breakable glass. Handle living material minimally, keep aquatic specimens moist in suitable water and return them only where collection and release are authorised. Do not collect protected organisms or damage habitat for a drawing.

Record observable evidence

Separate observation from inference. “Five jointed appendages are visible on one side” is an observation. “The animal is a crustacean” is an inference supported by several features. Record symmetry, segmentation, covering, appendages, antennae, shells, tube feet or tentacles where relevant.

Use a comparison table with the same feature categories for every specimen. Absence should be recorded only if the relevant region is visible. A damaged specimen or unclear photograph cannot prove that a feature is absent.

For vertebrates, compare skin covering, gas-exchange structures and visible reproductive evidence only when supplied. For fish, record operculum, scales, fin positions, lateral line and nares. For invertebrates, use the complete syllabus feature sets for crustaceans, cnidarians, echinoderms, molluscs and annelids.

Biological drawings

Use a sharp pencil and draw large enough to show relationships. Make clean single lines without sketching, shading or colour. Draw what is visible rather than an ideal textbook image. Preserve proportions and include a title.

Label with straight ruled lines that do not cross. Each line should touch the structure. Put labels outside the drawing and use syllabus terminology. If a scale is available, include a scale bar or calculate magnification. A drawing's value comes from accurate evidence, not decorative realism.

For a cell or tissue, show only boundaries visible at the chosen focal plane. For a whole organism, show diagnostic external features. Do not draw every repeated structure if the task requests a representative region, but state what the drawing represents.

Magnification and scale

Measure image size along the same dimension as the stated actual size: