Reproduction: Flowering Plants, Humans and Reproductive Health
The Reproduction domain of UPMSP Intermediate Biology examines how organisms make copies of themselves - sexual reproduction in flowering plants, human reproduction and reproductive health - with emphasis on gamete formation, fertilisation and contraception.
Flowering plants
- A microspore mother cell (2n) undergoes meiosis to give four microspores; each pollen grain has a generative and a vegetative cell.
- In the ovule, one functional megaspore forms the 7-celled, 8-nucleate embryo sac: three antipodals, two synergids, one egg and two polar nuclei in the central cell.
- Double fertilisation: one male gamete fuses with the egg to form the 2n zygote, the other with the polar nuclei to form 3n endosperm. The ovule becomes the seed and the ovary the fruit.
Human reproduction
- One primary spermatocyte yields four spermatozoa; one primary oocyte yields only one ovum plus three polar bodies.
- In the 28-day menstrual cycle, the LH surge around day 14 triggers ovulation; the corpus luteum then secretes progesterone.
- The placenta secretes hCG, hPL, oestrogen, progesterone and relaxin.
Worked example
How many meiotic divisions are needed to produce 100 seeds? Each seed needs one fertilised ovule, so 100 megaspore mother cells undergo meiosis: 100 divisions. Fertilisation needs 100 pollen grains; one microspore mother cell gives four pollen grains, so 100 ÷ 4 = 25 divisions. Total = 125 meiotic divisions.
Traps that cost marks
- Endosperm is triploid; perisperm is persistent nucellus (pepper, beet), not endosperm.
- Apomixis (seed without fertilisation) is not parthenocarpy (fruit without fertilisation).
- hCG and hPL come from the placenta, not the pituitary.
- Ovulation is not the same event as menstruation.