KS3 · Biology
A healthy pregnancy
A foetus gets its oxygen and nutrients through one lifeline from its mother. So if that lifeline carries the good stuff in, what else can travel along it?
Follow one substance to the foetus
A pregnant mother takes in a substance — alcohol from a drink, say, or nicotine from a cigarette. Both are drugs: substances that have an effect on the body once they are taken in. Alcohol is a depressant — it slows down the messages travelling between the brain and the body.
Drag along the route. Every stop is one oxygen and nutrients use too.
Oxygen and growth
Reason it through
Why can smoking or taking drugs during pregnancy lead to a baby being born early or small?
First link · your turn
A pregnant mother smokes or takes drugs. What vital supply to the foetus can this cut down?
Sort the consequences
Short-term or long-term?
Pick a consequence, then choose which group it belongs in.
Still to sort
Short-term consequence (0)
The pregnancy ends too soon, or the baby is born early or small.
Long-term consequence for the baby (0)
A condition or risk that stays with the baby after it is born.
When a pregnant mother takes drugs, smokes or drinks alcohol, the consequences can show up at different times.
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
The lifeline that brings a foetus oxygen and nutrients can carry harmful substances in too.
What you need to know
- A drug is a substance that has an effect on the body when it is taken in. Drugs can be taken as medicines or recreationally — and alcohol and the nicotine in cigarettes are legal drugs.
- From around eight weeks until birth, the developing baby is called a foetus.
- The placenta is an organ attached to the uterus wall. In it, the mother's blood and the foetus's blood flow next to each other and substances are exchanged; the foetus's blood then travels along the umbilical cord to the foetus.
- Some drugs, alcohol and chemicals in cigarette smoke (such as nicotine) can pass through the placenta, in the same way as oxygen and nutrients.
- A substance that is harmful to an adult is even more harmful to a foetus, because the foetus is smaller and still developing.
The big picture
A foetus gets oxygen and nutrients from its mother's blood through the placenta, where the two blood supplies flow next to each other and substances are exchanged. Some drugs, alcohol and chemicals in cigarette smoke, such as nicotine, pass across by that same route. Because a foetus is smaller and still developing, they can harm it even more than they would harm an adult — with short-term consequences such as miscarriage, premature birth and low birth weight, and long-term ones such as addiction, SIDS and FASD.
Key points
Worked example
Problem
A pregnant mother takes a drug regularly. Explain how this could lead to her baby being born with an addiction.
⚠ Watch out
Thinking the mother's blood flows into the foetus, or that the placenta keeps harmful substances out. Neither is right: the two blood supplies flow next to each other, and some substances still pass across.
Memory hook
One lifeline, two cargoes: the road that carries oxygen and nutrients to the foetus carries some harmful substances too.
Check yourself
Cover the page and try this: trace the four stops nicotine takes from a cigarette to the foetus, then name one short-term and one long-term consequence linked to smoking.
Flashcards
(13)What is a drug?
What kind of drug is alcohol, and what does it do?
What is a foetus?
What is the placenta?
Do the mother's blood and the foetus's blood mix in the placenta?
What travels along the umbilical cord?
Name three kinds of substance that can pass through the placenta.
Why is a harmful substance even more harmful to a foetus than to an adult?
How can drugs and smoking slow a foetus's growth?
What is a miscarriage?
List the three short-term consequences.
Match each long-term consequence to its substance: addiction, SIDS, FASD.
What problems will a child with FASD have?
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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How this lesson was checked. This KS3 Biologylesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 30 September 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.