▶️ Answer/Explanation
(a) (i)
The structure that releases egg cells: K
The structure where fertilisation usually occurs: P
The structure where an embryo implants: L
(a) (ii)
L: Uterus
M: Vagina
N: Cervix
(b)
Adaptive features of egg cells include:
- Energy stores: The cytoplasm contains a large amount of nutrients (yolk) to support the zygote after fertilisation until it can implant .
- Jelly coat: A protective outer layer (zona pellucida) that hardens after the entry of a sperm cell to prevent polyspermy (fertilisation by more than one sperm) .
Part (a)(i) – Function Identification:
- K (Ovary): The ovaries are the site of oogenesis (egg production). During ovulation, a mature egg is released from the ovary into the abdominal cavity to be picked up by the oviduct.
- P (Oviduct / Fallopian Tube): This tube connects the ovary to the uterus. Fertilisation (the fusion of sperm and egg) typically happens here as the egg travels toward the uterus.
- L (Uterus Lining / Endometrium): If fertilisation is successful, the zygote divides to form an embryo which embeds (implants) itself into the soft, blood-rich lining of the uterus to develop.
Part (a)(ii) – Anatomy Identification:
- L (Uterus): Often called the womb, this is the muscular organ where the fetus develops.
- N (Cervix): This is the ring of muscle at the lower neck of the uterus that separates it from the vagina. It helps hold the fetus in place during pregnancy and dilates during birth.
- M (Vagina): This is the muscular tube leading from the external genitals to the cervix. It acts as the birth canal and receives the penis during intercourse.
Part (b) – Adaptations:
Egg cells (ova) are highly specialized for their function. Unlike sperm, which are built for motility (movement), eggs are built for survival and development. They are large cells packed with cytoplasm containing energy stores to sustain early division. They also possess a chemical mechanism in their jelly coat that changes immediately upon fertilisation, creating a barrier that ensures only one set of male chromosomes enters the egg.