Reproduction and Developmental Biology
Reproduction and Developmental Biology
This domain tests gametogenesis, human reproductive cycles, fertilisation, early development, and flowering-plant reproduction. Expect questions on hormone control, chromosome number and the fate of embryonic layers.
Core rules
- Spermatogenesis produces four haploid sperm from one primary spermatocyte. Oogenesis produces one haploid ovum and polar bodies. Fertilisation restores the diploid number.
- FSH stimulates follicle development; a surge of LH triggers ovulation. The corpus luteum secretes progesterone, which maintains the endometrium. If fertilisation does not occur, the corpus luteum degenerates and menstruation follows.
- Cleavage forms a blastocyst; implantation occurs in the uterus. Gastrulation forms ectoderm, mesoderm and endoderm. The placenta allows exchange but maternal and fetal blood do not normally mix.
- In angiosperms, double fertilisation produces a diploid zygote and a triploid endosperm.
Worked example
A pollen tube releases two sperm into the embryo sac. One fuses with the egg to form the 2n zygote. The other fuses with two polar nuclei to form the 3n endosperm. Reasoning: the embryo needs food storage tissue, and the second fusion explains the triploid endosperm.
Traps
Ovulation is not the same as menstruation. Progesterone is not the hormone that triggers ovulation; LH is. The placenta is not a barrier to all substances. Meiosis produces haploid gametes, not diploid ones. Polar bodies are not functional eggs.