Paper II — 2023 July (Supplementary) (2010 Scheme) — Q13
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Paper II
2023 July (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Draw and label fertilized egg of ascaris
Q132 marksShort Notes
Answer
A labelled diagram cannot be rendered in this text-based answer; the description below covers the key structural/labelling features.
Fertilized egg of Ascaris lumbricoides:
Shape: broadly oval/rounded.
Shell: thick, comprising three layers — an outer mammillated (bumpy/coarsely granular) albuminous coat, a middle thick, transparent, glycoprotein (chitinous) shell, and an inner lipid (vitelline) membrane — the mammillated outer coat is the single most distinctive labelling feature.
Colour: typically bile-stained golden-brown, though the mammillated coat is occasionally absent (a “decorticated” egg), appearing as a smooth, colourless egg in a minority of cases.
Contents: a single, large, unsegmented, granular ovum (fertilized cell mass) filling most of the egg interior, with a clear space visible at each pole between the ovum and the shell.
Size: approximately 60–75 μm × 40–50 μm.
Contrast (labelling note): the unfertilized egg is more elongated, has a thinner shell, a more irregular/patchy mammillated coat, and contains a mass of coarse, disorganized refractile granules rather than a single well-defined ovum — an important distinguishing feature from the fertilized egg specifically asked for here.
