How do humans and flowering plants reproduce sexually?
Gametogenesis and the menstrual cycle in humans, fertilisation, and sexual reproduction and the life cycle in flowering plants.
A focused answer to WJEC A-Level Biology Unit 4, covering gametogenesis and the structure of gametes, the hormonal control of the menstrual cycle, fertilisation, and sexual reproduction in flowering plants.
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What this dot point is asking
WJEC wants you to describe gametogenesis and the structure of gametes, explain the hormonal control of the menstrual cycle, describe fertilisation, and outline sexual reproduction in flowering plants.
Gametogenesis and gametes
A sperm is adapted to reach and penetrate the egg: the flagellum gives movement, the midpiece mitochondria supply ATP, and the acrosome releases enzymes to digest the egg's outer layers. The egg is adapted to nourish the embryo and to block extra sperm after one has entered.
The menstrual cycle
The cycle is coordinated by four hormones in a feedback loop. FSH from the pituitary stimulates a follicle to develop, and the follicle secretes oestrogen; oestrogen repairs and thickens the uterus lining and, at a high level, triggers a surge of LH that causes ovulation around day . The empty follicle becomes the corpus luteum, which secretes progesterone to maintain the lining ready for implantation. High oestrogen and progesterone inhibit FSH and LH by negative feedback; if no embryo implants, the corpus luteum breaks down, progesterone falls, and the lining is shed as menstruation.
Fertilisation and plant reproduction
In flowering plants, pollination transfers pollen from anther to stigma, a pollen tube grows down the style to the ovule, and double fertilisation forms both the diploid zygote and the triploid endosperm (a food store). The ovule then becomes a seed and the ovary becomes the fruit.
Examples in context
Example 1. The contraceptive pill. The combined pill contains oestrogen and progesterone, which by negative feedback suppress FSH and LH so no follicle matures and no LH surge occurs, preventing ovulation. This is a direct medical application of the cycle's feedback control, often examined by WJEC.
Example 2. Wind versus insect pollination. Grasses produce huge amounts of light, smooth pollen and have feathery exposed stigmas for wind pollination, whereas insect-pollinated flowers have bright petals, nectar and sticky, sculptured pollen. Comparing these adaptations shows how plant reproduction is tuned to its pollination method.
Try this
Q1. Name the hormone whose surge triggers ovulation. [1 mark]
- Cue. Luteinising hormone (LH).
Q2. Explain why sperm cells contain many mitochondria. [2 marks]
- Cue. They release ATP to power the flagellum so the sperm can swim to the egg.
Q3. Explain why fertilisation must follow meiosis to keep a constant chromosome number across generations. [2 marks]
- Cue. Meiosis halves the chromosome number to make haploid gametes; fertilisation fuses two haploid gametes, restoring the diploid number.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC 20184 marksExplain the roles of oestrogen and progesterone in the menstrual cycle.Show worked answer →
Oestrogen, secreted by the developing follicle, repairs and thickens the uterus lining and, at high levels, triggers a surge in LH that causes ovulation.
After ovulation the corpus luteum secretes progesterone, which maintains the thickened uterus lining ready for implantation.
Both hormones inhibit FSH and LH by negative feedback; if no implantation occurs, the corpus luteum breaks down, progesterone falls, and the lining is shed (menstruation).
Markers reward oestrogen thickening the lining and triggering the LH surge, and progesterone maintaining the lining.
WJEC 20215 marksCompare the structure of a sperm cell and an egg cell, and explain how each is adapted to its function in fertilisation.Show worked answer →
A sperm cell is small and motile with a flagellum (tail) to swim to the egg, and many mitochondria in its midpiece to release the ATP needed for swimming.
It has an acrosome at the tip containing digestive enzymes that break down the layers around the egg so the sperm can penetrate.
An egg cell is much larger and non-motile, with stored food (in the cytoplasm and yolk) to nourish the early embryo, and a zona pellucida that hardens after one sperm enters to prevent polyspermy (fertilisation by more than one sperm).
Both are haploid, made by meiosis, so fertilisation restores the diploid number.
Markers reward the sperm adaptations (flagellum, mitochondria, acrosome), the egg adaptations (food store, block to polyspermy), and both being haploid.
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Sources & how we know this
- WJEC A-level Biology specification — WJEC (2015)