Almost every cell identification question in this chapter is settled by one recalled contrast, not by reasoning. A prokaryote (a bacterium) has a cell wall and a cell membrane with its DNA free in the cytoplasm, but NO nucleus and NO membrane-bound organelles at all, so no mitochondria and no chloroplasts. A eukaryote (animal, plant, fungus, alga) always has a nucleus and mitochondria.
Trigger: a checklist of features, or a question of the form 'which cell type', or 'which cells have or lack this organelle'.
Instances:
(i) bacterium: cell wall yes, nucleus no, mitochondria no, chloroplasts no;
(ii) animal cell: nucleus and mitochondria yes, cell wall no, chloroplasts no;
(iii) plant or algal cell: cell wall, nucleus, mitochondria, chloroplasts and a large vacuole all yes;
(iv) fungal cell: cell wall and nucleus yes, chloroplasts no.
One tell fixes the cell: 'a wall plus no mitochondria', or 'no nucleus', pins a prokaryote, and the rest then follows without checking each organelle.
