# Explain why DNA replication is described as semi-conservative.

> IB DP Biology Standard Level (2023 syllabus) — D1.1 DNA replication · Explain · 4 marks

> During DNA replication, each strand of the double helix serves as a template for the synthesis of a new complementary strand. The term 'semi-conservative' was confirmed experimentally by Meselson and Stahl in 1958 using nitrogen isotope labelling.

## Mark scheme (4 marks)

1. The two strands of the parental double helix are separated / unwound prior to replication.
2. Each original (parental) strand acts as a template for the synthesis of a new complementary strand.
3. Each resulting daughter DNA molecule contains one original (parental) strand and one newly synthesised strand.
4. The process is 'semi-conservative' because half of each new DNA molecule is conserved from the original / parental molecule.

## Key terms

- [semi-conservative](https://www.gradenine.co.uk/glossary/semi-conservative)
- [DNA replication](https://www.gradenine.co.uk/glossary/dna-replication)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-dna-replication-is-described-50f44a85) · Published by Druglandscape Ltd.