The big idea: Every organism carries its own instructions, its genetic material. In every living organism, that molecule is DNA.
The points to remember
- Genetic material: the molecule that stores the instructions for building and running an organism.
- It is copied when cells divide and passed on to the next generation.
- In all living organisms the genetic material is DNA (deoxyribonucleic acid).
- Bacteria, plants, fungi and animals all use this same molecule.
Remember it as: Every living thing, one molecule: DNA.
Real example: one breakfast, four kinds of organism: Yoghurt is made by bacteria, bread rises because of yeast (a fungus), the flour comes from wheat (a plant), and you are an animal. All four store their instructions in DNA.
In a school lab you can even see DNA: crushed strawberries, washing-up liquid, salt and ice-cold alcohol give white, stringy strands of it.
When a question asks you to name the genetic material, one word earns the mark:
Name the molecule exactly: Write DNA (or deoxyribonucleic acid). 'Nucleic acid' on its own is too vague, and 'RNA' is wrong for a living organism.
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The big idea: Every virus carries genetic material, and in some viruses it is RNA, not DNA.
That does not break the rule, because viruses are not considered living.
The points to remember
- Every virus carries genetic material: DNA in some viruses, RNA in others.
- RNA viruses include the influenza virus and SARS-CoV-2, the virus that causes COVID-19.
- Viruses are not considered living: they are not made of cells and have no metabolism of their own.
- A virus is copied only inside a living host cell, using that cell's machinery.
- So the rule stands: every living organism uses DNA.
Remember it as: RNA in a virus is no exception: a virus is not alive.
Here is a real RNA virus at work inside a cell it has infected:
Real example: the COVID-19 virus: SARS-CoV-2 carries its genetic material as one long strand of RNA, about 30 000 bases long. On its own it does nothing. Inside a human cell it uses the cell's machinery to make thousands of copies of itself.
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How it is asked: Two shapes so far: a Paper 1A item that tests the rule and the virus exception together, and a one-mark Paper 2 State. Here is each, worked through.
Which features are common to every virus? I. not living. II. carries genetic material. III. carries DNA. A. I and II only. B. I and III only. C. II and III only. D. I, II and III.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
The Paper 2 version is one mark for one exact word:
Wheat plants grown from the seeds of one parent plant look very similar to each other. State the molecule that wheat plants use as their genetic material.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
If the question is about a virus: Read whether it asks about a living organism or a virus. A student is told that the Zika virus carries RNA. The student concludes that not all living organisms use DNA as their genetic material. The reply is always the same: viruses are not living, so they are not exceptions to the rule.