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IB DemystifiedMYP Sciences

Human reproduction and puberty

Between about 8 and 14, everyone's body begins to change as it prepares for adulthood. Understanding puberty and human reproduction helps you know what to expect, look after your health, and understand how every person begins as a single fertilised cell.

Recommended for MYP 2 · About 3 lessons · Criteria A, B, C and D

151014202528daymenstruationlining breaks downlining thickenslining kept thick, ready for a fertilised eggovulation (about day 14):an egg is released from an ovaryA typical cycle. Cycles vary between people and from month to month; 21–35 days is common.
Figure 1. The menstrual cycle prepares the uterus each month for a possible pregnancy.
On this page
  1. Learning objectives
  2. Before you start
  3. Key vocabulary
  4. Understanding the ideas
  5. Key facts
  6. Reproduction and health in the real world
  7. Worked examples
  8. Assessment tips
  9. Check your understanding
  10. Practice questions
  11. Investigation
  12. Criterion-linked questions
  13. Challenge questions
  14. Topic check
  15. Review your mistakes
  16. Your progress

Learning objectives

By the end of this topic you should be able to:

  • describe the physical and emotional changes of puberty and their cause
  • describe the parts of the reproductive systems and what they do
  • describe the main events of the menstrual cycle
  • describe fertilisation, pregnancy and the role of the placenta
  • analyse growth data and plan fair surveys
  • discuss health in pregnancy and menstrual health in schools

Before you start

You will use these skills. If any feel shaky, review them first.

  • cells and specialised cells (see Cell organisation)
  • organ systems (see Nutrition and digestion)
  • reading tables and calculating differences

Key vocabulary

Puberty
The stage when the body changes from a child's to an adult's.
Hormone
A chemical messenger carried in the blood.
Gamete
A sex cell: a sperm cell or an egg cell.
Ovulation
The release of an egg from an ovary.
Fertilisation
The joining of the nuclei of a sperm cell and an egg cell.
Placenta
The organ that passes oxygen and nutrients to the baby and removes its waste.

Understanding the ideas

  1. Puberty

    During puberty, hormones cause a growth spurt and many other changes. In both girls and boys, body hair grows, sweat and oil glands become more active, and feelings can change. Girls develop breasts and begin to have periods; boys' voices deepen and their testes begin to produce sperm. The timing varies from person to person.

  2. The menstrual cycle

    Egg cells are made in the ovaries and sperm cells in the testes. Each month, an egg is released at ovulation and the lining of the uterus thickens. If the egg is not fertilised, the lining breaks down and leaves the body as a period (menstruation).

  3. Fertilisation and pregnancy

    If a sperm cell reaches the egg in the oviduct, their nuclei join at fertilisation. The fertilised egg divides and implants in the uterus lining. During about 40 weeks of pregnancy, the placenta supplies the baby with oxygen and nutrients and removes its waste.

  4. Why does it matter?

    Harmful substances such as alcohol and nicotine can cross the placenta, so health care in pregnancy matters. Good hygiene and access to menstrual products help young people stay healthy and in school.

  5. What does it connect to?

    This topic links to cells, inheritance and genetics, hormones and health in biology.

Key facts

  • Puberty usually starts between about 8 and 14 and is caused by hormones (oestrogen and testosterone).
  • Ovaries make eggs; testes make sperm.
  • Menstrual cycle: about 28 days (often 21–35); ovulation around the middle.
  • Fertilisation usually happens in the oviduct; the embryo develops in the uterus.
  • Placenta: oxygen and nutrients to the baby; carbon dioxide and waste back to the mother. The bloods do not mix.

Reproduction and health in the real world

Health workers in many countries visit pregnant women at home to give check-ups and advice. Some schools now provide free sanitary products and clean, private toilets so that girls do not miss lessons. Growth charts help doctors check that children are growing healthily.

Worked examples

Example 1: growth data

A boy is 149 cm at 12 and 163 cm at 14. What is his mean growth per year?

  1. Growth = 163 − 149 = 14 cm.
  2. Mean per year = 14 ÷ 2 = 7 cm per year.

Example 2: the placenta

Name two substances that pass from mother to baby through the placenta, and one that passes the other way.

  1. Mother to baby: oxygen and nutrients such as glucose.
  2. Baby to mother: carbon dioxide (and other waste).

Assessment tips

Questions on this topic often use diagrams of the menstrual cycle and growth data. Expect to:

  • Describe the changes of puberty and their cause.
  • Name reproductive organs and their functions.
  • Explain the menstrual cycle, fertilisation and the placenta.
  • Analyse growth data, spotting patterns and anomalies.

Common mistakes: saying fertilisation happens in the uterus; saying the mother's and baby's blood mix; thinking puberty starts at the same age for everyone; and confusing ovulation with menstruation.

Check your understanding

Quick questions on the ideas above. Try each one before using a hint.

Practice questions

Show

Investigation: modelling the placenta

Partially guided investigation · about 45 minutes · pairs

Research question
Which substances can pass through a thin membrane, like the membrane in the placenta: glucose, starch or both?
Scientific background
In the placenta, small molecules such as glucose and oxygen pass between the mother's and baby's blood, but large molecules and blood cells do not. Dialysis (Visking) tubing has tiny holes and can model this.
Hypothesis
Write your own prediction, with a scientific justification.
Variables
Identify your independent, dependent and control variables, and explain how you will control them.
Apparatus
Dialysis tubing, thread, beakers, glucose solution, starch solution, water, glucose test strips (or Benedict's solution and a water bath), iodine solution, dropping pipettes.
Method
  1. Tie one end of the tubing, fill it with a mixture of glucose and starch solutions, and tie the other end.
  2. Rinse the outside and place the tube in a beaker of water.
  3. After 20 minutes, test the water outside the tubing for glucose and for starch.
  4. Record which substance passed through the membrane.

Safety. Wear eye protection. Iodine stains skin and clothing. Take care with hot water if using Benedict's solution.

Then evaluate: in what ways is the tubing a good model of the placenta, and in what ways is it not?

Criterion-linked questions

Criterion B: inquiring and designing

Criterion C: processing and evaluating

Criterion D: reflecting on the impacts of science

Challenge questions

Harder problems in unfamiliar contexts. Plan before you calculate.

Topic check

Five questions picked at random from the whole topic. Take a new set whenever you like.

Review your mistakes

Questions you got wrong on this device appear here so you can try them again. Answer one correctly and it leaves the list.

Your progress

Tracked separately for each skill, on this device only.

SkillCorrectStatus

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