Exact copies at Higher Level: The same statement as SL. At HL it is the start of a longer story: how the copy is made, strand by strand, and how mistakes are caught.
Practise this as you read
- Outline why replication is needed for growth, tissue replacement and reproduction.
- Explain why the copies must have identical base sequences.
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
The big idea: DNA replication copies one DNA molecule to make two. Both have exactly the same base sequence as the original.
The points to remember
- Replication turns one DNA molecule into two molecules.
- Both new molecules have the same base sequence as the original: they are exact copies.
- The base sequence carries the genetic information, so both copies carry the same genes.
- Replication happens before a cell divides, so each new cell can get a complete copy.
Remember it as: One molecule in, two out, the same sequence in both.
Real example: red blood cells. Your bone marrow makes about 2 million red blood cells every second. Every cell that divides to make them first copies all of its DNA, so the new cells carry the same genes.
Study smarter, not longer
Most students waste 40% of study time on topics they already know. Our AI tracks your progress and optimizes every minute.
Why copy at all?: Every time a cell divides, each new cell needs a complete, exact copy of the DNA. Cells divide for three reasons.
Reproduction
- A bacterium copies its DNA, then splits into two new organisms.
- Cells that make sex cells copy their DNA first too.
Growth
- A fertilized egg divides again and again.
- A human body has trillions of cells, all from one.
Tissue replacement
- Worn-out or damaged cells are replaced.
- Skin, gut lining and blood are renewed all the time.
Real example: the lining of the gut. The cells lining the small intestine wear away and are replaced every few days. Stem cells at the base of the lining divide constantly, copying their DNA each time, so every new lining cell has the same genes.
Do not mix them up: Replication copies the DNA. Cell division comes after it and shares the two copies between the two new cells.
How it is asked: A short 'outline why DNA is replicated' or 'state what is the same about the copies', often as the first part of a longer replication question.
Explain why the DNA in the two cells made when a gut lining cell divides must be identical to the DNA of the parent cell.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.