4.2—Recognising plant organelles in EM images

Identify a plant organelle in an electron micrograph by combining its shape, membranes and position with the surrounding cell context—not by relying on one dark spot.

A chloroplast has a double boundary and internal thylakoid stacks; a vacuole is a large space bounded by the tonoplast; a nucleus has an envelope and chromatin; an amyloplast contains starch granules. Use a TEM-style 2D internal view when the micrograph shows sections through organelles.

A plant cell containing a large vacuole, a cellulose wall and several chloroplasts is more likely to be a photosynthetic leaf cell than an animal cell. The combination is stronger evidence than any single feature.

Electron microscopy gives a dead specimen snapshot and the section plane can hide or distort structures. State what the image supports; do not infer an organelle that is not resolved.