Reproduction — Edexcel Modular - OL Revision Notes & Topical Questions

Reproduction Edexcel O Level Modular Biology: what to do next

These Reproduction Edexcel O Level Modular Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Reproduction Edexcel O Level Modular Biology understanding with the practice questions below, then reread any Reproduction Edexcel O Level Modular Biology point you were unsure about before moving on.

Sexual reproduction requires gametes to join. Asexual is quick and efficient in a stable environment, whereas the variation from sexual reproduction helps populations survive environmental change and disease.

The role of flowers is to enable plant gametes to come together in fertilisation.

Germination experiment

• place cress seeds on damp cotton wool in dishes with different conditions (warm and cold, with and without water).
• O - the cress seeds are taken from the same parent plant, S - same number of seeds, same light.
• Measure the percentage germination after a week.
• Seeds need water, oxygen and warmth.

Genes are short lengths of DNA that code for a protein and are found on chromosomes.

Seed dispersal methods and their features can be compared in a table.

Why disperse seeds?

The pollen grain contains the male gamete (nucleus); the ovule contains the female gamete (egg cell nucleus). After fertilisation the zygote divides by mitosis to form an embryo plant within the seed. Both gametes are haploid and the zygote is diploid, which keeps the chromosome number constant between generations.

In addition to oestrogen and progesterone, the menstrual cycle is controlled by FSH and LH, both released from the pituitary gland in the brain. The four hormones interact:

After fertilisation in the oviduct, the zygote divides to form an embryo, which travels to the uterus and implants. A structure called the placenta forms at the implantation site and provides the developing embryo with nutrients and oxygen from the mother's blood, essential for growth and development.

The placenta allows diffusion across a thin barrier with a large surface area, and also secretes hormones such as progesterone. The foetal and maternal blood do not mix, so the mother's blood pressure does not damage fragile foetal vessels.

In the uterus the embryo is surrounded by amniotic fluid contained within the amniotic membrane (sac). The fluid cushions the foetus from bumps when the mother moves, and protects it during development; it also maintains a constant temperature.

Secondary sexual characteristics are the changes that occur during puberty, driven by sex hormones.

The contraceptive pill contains oestrogen and progesterone, which inhibit FSH release so that no follicle matures and ovulation does not occur.

Menstrual cycle summary by day

• days 1 to 5 menstruation;
  • days 5 to 14 lining repairs under oestrogen;
  • day 14 ovulation after the LH surge;
  • days 15 to 28 progesterone maintains the lining;
  • if no fertilisation, progesterone falls and the cycle restarts.

When reading a hormone graph, name the hormone for each line, quote values at a given day, and link each peak to its effect: the LH peak just before day 14 causes ovulation, and the progesterone peak a week later maintains the thick lining.