11.5 Human Reproduction

A free GCSE Biology lesson for AQA (8461) from OBA School: reproductive systems, sex hormones and puberty. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Name the parts of the male and female reproductive systems and give their functions
• Describe the roles of testosterone and oestrogen
• Describe the changes that happen at puberty and explain that they are caused by hormones
• Explain what ovulation is and how often it happens

Key words

• Puberty: The stage of development when reproductive hormones cause the body to become sexually mature.
• Secondary sex character- istics: Body changes at puberty, e.g. breasts developing or the voice deepening.
• Testosterone: The main male reproductive hormone, made in the testes. It stimulates sperm production.
• Oestrogen: The main female reproductive hormone, made in the ovaries.
• Ovulation: The release of a mature egg from an ovary, roughly every 28 days.
• Fertilisation: The joining of the nucleus of a sperm with the nucleus of an egg.

The male reproductive system

• Testes (testicles); Function Make sperm and the hormone testosterone
• Scrotum; Function Bag of skin that holds the testes outside the body, where it is slightly cooler – better for sperm production
• Sperm ducts; Function Carry sperm from the testes towards the urethra
• Glands (prostate gland and seminal vesicles); Function Add fluid containing nutrients to the sperm, making semen
• Urethra; Function Tube through the penis that carries semen (and, at other times, urine) out of the body
• Penis; Function Places semen into the vagina during sexual intercourse

The female reproductive system

• Ovaries; Function Contain eggs; from puberty one egg matures and is released about every 28 days; make oestrogen and progesterone
• Oviducts; Function Carry the egg from the ovary to the uterus; fertilisation happens here
• Uterus; Function Muscular organ where an embryo implants in the thick lining and develops into a baby
• Cervix; Function Ring of muscle at the entrance to the uterus
• Vagina; Function Where sperm are deposited during intercourse; the birth canal

Puberty and the sex hormones

At puberty (usually between about 10 and 15 years old) the pituitary gland starts to release more FSH and LH. These stimulate the testes or ovaries to make the sex hormones, which cause the secondary sex characteristics.

• Sperm production starts; Girls: oestrogen (from the ovaries) Eggs begin to mature; ovulation and periods start
• Voice deepens (breaks); Girls: oestrogen (from the ovaries) Breasts develop
• Facial and body hair grows; Girls: oestrogen (from the ovaries) Hips widen
• Muscles develop; testes and penis grow; Girls: oestrogen (from the ovaries) Pubic and underarm hair grows

Some changes, such as pubic and underarm hair and a growth spurt, happen in both boys and girls.

Worked example: exam tip

“Give the role of testosterone.” (2 marks)
It is the main male reproductive hormone, made in the testes (1). It stimulates sperm production / causes male secondary sex characteristics (1).

Answer: name the gland and an effect

Ovulation and the maths of reproduction

Once a girl reaches puberty, eggs begin to mature in her ovaries. About every 28 days one egg is released: this is ovulation. The egg travels along the oviduct. If it meets a sperm, fertilisation may happen.

Worked example: estimating numbers

A woman has regular 28-day cycles from age 13 to age 51. Estimate how many eggs she releases.
Cycles per year ≈ 365 ÷ 28 = 13.0… Years = 51 − 13 = 38
Eggs ≈ 13 × 38 = 494

Answer: about 500 eggs (ignoring any pregnancies)

Key fact: A woman is born with all her eggs. A man makes new sperm continuously from puberty – roughly 1500 every second.

Common mistakes

• Saying fertilisation happens in the uterus. It usually happens in the oviduct.
• Saying the testes make semen. They make sperm; glands add the fluid that makes semen.
• Mixing up oestrogen (female, from the ovaries) and testosterone (male, from the testes).
• Saying the pituitary makes oestrogen. The pituitary makes FSH and LH; the ovaries make oestrogen.

Revision questions

Try these, then check your answers below each one.

Question 1. What is the main female reproductive hormone made in the ovaries? (Choose from: Testosterone, Oestrogen, Adrenaline, Insulin.)

Answer: Oestrogen

Working: Oestrogen is the main female reproductive hormone, produced in the ovaries.

Question 2. What is the main role of testosterone? (Choose from: It stimulates sperm production, It causes ovulation, It lowers blood glucose, It controls the metabolic rate.)

Answer: It stimulates sperm production

Working: Testosterone, made in the testes, stimulates sperm production (and male secondary sex characteristics).

Question 3. True or false? After puberty, a woman usually releases an egg about every 28 days.

Answer: True

Working: True. One egg is released roughly every 28 days.

Related lessons

• Previous lesson: 11.4 The Role of Negative Feedback
• Next lesson: 11.6 Hormones and the Menstrual Cycle
• In this chapter: 11.1 Principles of Hormonal Control
• In this chapter: 11.2 The Control of Blood Glucose Levels
• In this chapter: 11.3 Treating Diabetes

Continue in the full course

This lesson is section 11.5 (AGCBH1105) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.