This question shows a labelled diagram of an Entamoeba histolytica cyst and asks whether the labels a, b, c, d have been assigned correctly. Since the actual image is fixed, solve it by checking whether each expected structure has a sensible, single position inside a mature cyst.
- Cyst wall: This is the outermost, resistant covering that seals the parasite off from the harsh outside environment (like stomach acid or dry conditions) until it reaches a new host. It has to be the outermost labelled ring in any correct diagram.
- Chromatoid bodies (bars): These are rod-shaped or bar-shaped stores of ribonucleoprotein, sitting inside the cytoplasm, distinct in shape from the rounder glycogen mass, so they should occupy their own separate position, not overlap with the glycogen label.
- Glycogen mass (vacuole): This is a rounded, food-reserve region within the cytoplasm, providing energy once the cyst becomes active again (excystation), and it sits apart from the chromatoid bars.
- Nucleus (or nuclei): A mature Entamoeba histolytica cyst carries up to four small, similarly sized nuclei, each with a centrally placed karyosome, positioned inside the cytoplasm but distinct from both the glycogen mass and the chromatoid bars.
Since the outer wall, the chromatoid bars, the glycogen mass, and the nucleus (or nuclei) all occupy distinct, non-overlapping positions in a real Entamoeba cyst, a diagram that places a, b, c, d on these four structures in that non-overlapping way has labelled them correctly.
Let's summarize:
- Each structure in a mature cyst, the wall, chromatoid bars, glycogen mass and nucleus, occupies its own distinct spot, none should overlap with another in a correct diagram.
- Checking that the four labels do not clash with each other is enough to confirm a correct labelling without needing to redraw the whole cyst.
So the diagram represents the correct identification arrangement, option (3).