Example 1
A cell has ribosomes and circular DNA but no nucleus. Classify it.
These features support a prokaryotic cell. Ribosomes occur in both major cell types, so the absence of a nucleus is decisive here.
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Year 12 · SACE Stage 2
Cell types and organelles
Classify cells and match organelles to their functions.
Method and worked examples
Cells are the basic structural and functional units of living organisms, and new cells arise from existing cells. Prokaryotes lack a membrane-bound nucleus; eukaryotes have a nucleus and membrane-bound organelles. Both have DNA, cytoplasm, ribosomes and a cell membrane. Plants and fungi have cell walls, but their wall composition differs; animal cells lack a cell wall.
The nucleus contains nuclear DNA; the nucleolus helps assemble ribosomal components. Ribosomes synthesise proteins. Rough endoplasmic reticulum and Golgi process and route many secreted proteins, while smooth ER has lipid-related roles. Lysosomes digest materials, vacuoles store substances, and the cytoskeleton supports organisation and movement. Mitochondria support aerobic respiration; chloroplasts carry out photosynthesis.
Example 1
Example 2
Trace a typical exported protein after translation begins.
It enters the rough ER pathway, is carried in vesicles to the Golgi, then reaches the cell membrane in a secretory vesicle.
Watch out: They have structures including ribosomes and a chromosome, but lack a membrane-bound nucleus.