Development of Secondary Sexual Characteristics

As children grow into adults they go through puberty — a stage when the body changes ready for reproduction. The changes that happen (other than the reproductive organs themselves) are called secondary sexual characteristics.

These changes are triggered by sex hormones:

• In females, the hormone is oestrogen, made in the ovaries.
• In males, the hormone is testosterone, made in the testes.

A hormone is a chemical messenger released into the blood by a gland. It travels around the body and brings about a change in its target organs. At puberty the ovaries start releasing oestrogen and the testes start releasing testosterone, and these hormones cause the body changes below.

Exam tip. Be ready to name the hormone AND name the gland that makes it: oestrogen → ovaries (female); testosterone → testes (male). Examiners often ask for both.

Oestrogen is the main female sex hormone. It is made in the ovaries and its level rises at puberty. Oestrogen causes the secondary sexual characteristics seen in females:

• Breasts develop (the mammary glands grow).
• The hips widen (the pelvis broadens, helping later childbirth).
• Menstruation begins — the start of the menstrual cycle, when the uterus lining is built up and shed each month.
• Body hair grows, for example underarm and pubic hair.

So when an exam question says "explain the role of oestrogen", the answer is that oestrogen controls the development of female secondary sexual characteristics — then list the changes above.

Exam tip. Learn the spelling oestrogen (the British spelling with the "oe"). The marking point is usually the hormone name plus at least one correct change it causes.

Testosterone is the main male sex hormone. It is made in the testes and its level rises at puberty. Testosterone causes the secondary sexual characteristics seen in males:

• The voice deepens (the voice "breaks" as the voice box grows).
• Facial hair and more body hair grow.
• The muscles develop (the body becomes more muscular).
• Sperm production begins in the testes.

So when an exam question asks for the "role of testosterone", the answer is that testosterone controls the development of male secondary sexual characteristics — then list the changes above.

Here is a simple summary of which hormone causes which changes:

Exam tip. Do not mix the hormones up. Testosterone is male (testes → testosterone — both start with "test"), oestrogen is female (ovaries → oestrogen — both start with "o").

Once fertilisation has happened and the embryo implants in the uterus, it develops surrounded by protective structures. One of these is the amnion — a thin membrane that forms a bag around the embryo.

The amnion encloses amniotic fluid — a watery liquid that surrounds the developing embryo (and later the fetus). This fluid has an important protective job:

• Amniotic fluid cushions the embryo, absorbing physical shocks, bumps and knocks from the outside (for example if the mother bumps her abdomen).
• It supports the embryo on all sides and helps keep it at a steady temperature.

So if a question asks "how is the developing embryo protected?", the marking point is that the amniotic fluid cushions/protects it against physical shocks (bumps and knocks).

Exam tip. Keep the words clear: the amnion is the membrane (bag); the amniotic fluid is the liquid inside that does the cushioning. The mark is for fluid protecting against physical shocks/bumps — not "providing food" (that is the placenta's job).

Two separate ideas come together in this subtopic — they are easy to mix up, so keep them clearly apart:

Topic	Key structure / hormone	What it does
Female puberty (3.13)	Oestrogen (made in the ovaries)	Breasts develop, hips widen, menstruation begins, body hair grows
Male puberty (3.13)	Testosterone (made in the testes)	Voice deepens, facial/body hair, muscles develop, sperm production
Protecting the embryo (3.12)	Amniotic fluid (held in the amnion)	Cushions the embryo against physical shocks/bumps

A quick way to lock it in:

1. Oestrogen = female changes (think "ovaries → oestrogen").
2. Testosterone = male changes (think "testes → testosterone").
3. Amniotic fluid = cushion for the embryo (think of it as a built-in water cushion).

Exam tip. A common multi-mark question gives a table of body changes and asks you to put each under the correct hormone, then a separate part asks how the embryo is protected. Score full marks by never swapping the hormones and by saying amniotic fluid protects against physical shocks.