Correct Option
The correct option isBoth are single cells.
Explanation
In sexually reproducing organisms, the female gamete is known as an ovum or egg. Despite significant variations in size, structure, and development methods across different species (such as birds and mammals), the fundamental biological classification of the gamete remains consistent.
Option Analysis
- Both are covered by a hard calcareous shell. is Incorrect. A hen's egg is covered by a hard, calcareous shell to protect the embryo during external development. In contrast, a human ovum is not covered by a hard shell; it is protected by cellular and membranous layers such as the zona pellucida and corona radiata.
- Both are single cells. is Correct. Both the hen's egg and the human ovum are single cells. The hen's egg (specifically the yolk surrounded by the membrane) is a classic example of a macroscopic single cell, often cited to demonstrate that cells can be large enough to be seen with the naked eye. The human ovum is a microscopic single cell. Both are haploid gametes.
- Both are fertilised externally. is Incorrect. Fertilization is internal in both hens and humans. In hens, fertilization occurs inside the reproductive tract before the hard shell is secreted around the egg.
- Both develop into embryos outside the mother's body. is Incorrect. Hens are oviparous, meaning the embryo develops outside the mother's body within the laid egg. Humans are viviparous, meaning the embryo develops inside the mother's uterus.
Key Takeaway
Regardless of the organism's size or the reproductive strategy (oviparous vs. viviparous), the unfertilized egg (ovum) is structurally a single cell.