Draw a neat, labelled diagram of a chloroplast.

Your diagram must show: • a double membrane (OUTER and INNER MEMBRANE) enclosing the organelle • STROMA — the colourless fluid matrix filling it • GRANA — stacks of disc-like membranes, drawn as piles of coins • THYLAKOID — one individual disc within a granum • STROMA LAMELLAE (intergranal lamellae) — the membranes connecting one granum to another

Labels required: outer membrane, inner membrane, stroma, granum, thylakoid, stroma lamella.

THE FEATURE THAT MUST BE RIGHT is the GRANA, drawn as stacks of discs like piles of coins, joined to one another by lamellae. A chloroplast drawn as a plain oval with dots is not a chloroplast diagram.

WHY THE STRUCTURE LOOKS LIKE THIS — worth a line beside the diagram, because it links structure to function: the GRANA hold the CHLOROPHYLL and are where the LIGHT REACTION happens. Stacking them into discs packs an enormous membrane surface into a small volume, which maximises light absorption. the STROMA is where the DARK REACTION happens — it contains the enzymes that fix carbon dioxide into glucose.

So the two stages of photosynthesis occur in two different parts of the same organelle, and a labelled diagram shows exactly where.

Draw large, in pencil, with labels outside on straight ruled lines.