1. What Is Reproduction?
Reproduction is the process by which living things produce offspring (new individuals) of the same species. It is one of the seven characteristics of living things, alongside movement, feeding, and growth.
Two Types of Reproduction
Humans reproduce sexually, which is why we have two different reproductive systems (one in males and one in females) each producing a different type of sex cell (gamete).
2. The Human Reproductive System
A. The Male Reproductive System
The male reproductive system's job is to produce sperm cells and deliver them into the female body during reproduction.
B. The Female Reproductive System
The female reproductive system's job is to produce egg cells, provide the site where fertilisation can happen, and support the development of a baby if the egg is fertilised.
C. Comparing the Two Systems
3. The Menstrual Cycle
The menstrual cycle is a monthly sequence of changes in the female reproductive system that prepares the body for a possible pregnancy. It typically lasts around 28 days, though this varies from person to person, and is controlled by hormones, mainly oestrogen and progesterone.
The Four Main Stages
Stage 1: Menstruation (Days 1–5) If the egg released in the previous cycle was not fertilised, the thickened lining of the uterus breaks down and is released from the body through the vagina. This is called a period, and typically lasts 3–7 days.
Stage 2: The Uterus Lining Rebuilds (Days 6–13) The lining of the uterus (the endometrium) starts to thicken again, building up a rich, blood-supplied layer in preparation for a possible pregnancy. At the same time, an egg matures inside one of the ovaries.
Stage 3: Ovulation (Around Day 14) A mature egg is released from the ovary and travels down the oviduct. This is called ovulation, and it's the point in the cycle when pregnancy is most likely if sperm are present.
Stage 4: The Luteal Phase (Days 15–28) The uterus lining continues to thicken, ready to receive a fertilised egg. If the egg is not fertilised, hormone levels drop, and the cycle starts again with menstruation (back to Stage 1).
Why Does the Menstrual Cycle Happen?
The menstrual cycle exists to prepare the female body for a possible pregnancy every month. If fertilisation happens during the cycle, the fertilised egg implants into the thickened uterus lining and pregnancy begins — and the menstrual cycle pauses until after the baby is born. If fertilisation does not happen, the lining is no longer needed, so the body sheds it and starts building a fresh one in the next cycle.
4. Key Terms Glossary (Quick Revision)
- Reproduction: The production of offspring by living things
- Sexual reproduction: Reproduction involving two parents and the fusion of sex cells
- Asexual reproduction: Reproduction involving only one parent
- Gamete: A sex cell (sperm or egg)
- Fertilisation: The joining of a sperm cell and an egg cell
- Zygote: The new cell formed immediately after fertilisation
- Testes: Male organs that produce sperm
- Ovaries: Female organs that produce eggs
- Uterus: The organ where a baby develops during pregnancy
- Menstrual cycle: The monthly cycle of changes in the female reproductive system
- Ovulation: The release of an egg from an ovary
- Menstruation:The shedding of the uterus lining (a period)
Frequently Asked Questions
Q: What is the main difference between sexual and asexual reproduction?
A: Sexual reproduction needs two parents and the fusion of a sperm and an egg; asexual reproduction needs only one parent and produces genetically identical offspring.
Q: Where does fertilisation usually happen in the human body?
A: Fertilisation usually takes place in the oviduct (Fallopian tube), when a sperm cell fuses with an egg cell.
Q: How long does the average menstrual cycle last?
A: About 28 days on average, though it's completely normal for it to range from around 21 to 35 days.
Q: What happens if the egg released during ovulation is not fertilised?
A: The thickened uterus lining is not needed, so it breaks down and leaves the body as a period (menstruation), and the cycle begins again