On the right are the four cycle hormones drawn as curves over 28 days. FSH starts a follicle growing; the follicle pours out rising oestrogen, which thickens the uterine lining (the band beneath the graph). Watch how oestrogen climbs through the first two weeks. ▶ Play to run the cycle day by day and watch each curve rise and fall.
Keep watching the same graph and stop at day 14. When oestrogen peaks it triggers a sharp surge of LH — that tall spike. The LH surge makes the mature follicle burst and release the egg: this is ovulation, the fertile point of the cycle. ⏭ Step day by day up to the surge and watch the marker reach day 14.
After ovulation the empty follicle becomes the corpus luteum, which secretes progesterone — the curve that now rises and maintains the thick lining. If no embryo implants, the corpus luteum dies, progesterone falls, the lining is shed as menstruation, and FSH rises to begin a new cycle. ↻ Reset and ▶ Play to see the whole loop.
Switch to the Gametogenesis tab. A diploid (2n) germ cell divides by meiosis. On the left, spermatogenesis splits it equally into four haploid sperm. On the right, oogenesis divides unequally, keeping the cytoplasm in one large ovum and discarding the rest as tiny polar bodies. ▶ Play to watch both divisions run.
Stay on the same diagram. Both processes use meiosis to halve the chromosome number to haploid (n), so fertilisation can restore 2n. But the outcomes differ: four small, motile sperm versus one large ovum stocked with cytoplasm for the embryo — the polar bodies simply carry away the extra chromosomes. ⏭ Step to compare the two columns side by side.
Open the Flower & fertilisation tab. A pollen grain lands on the stigma and grows a pollen tube down through the style to the ovule, carrying two male gametes. There, double fertilisation happens: one gamete + the egg → zygote (2n); the other + the polar nuclei → endosperm (3n). ▶ Play to grow the tube and fertilise the ovule.