A factor that helps isn't always required
- The idea
- Predict
- See it
- Why
- Check
The idea
“If adding something makes the result much bigger, the result must need it.”
A huge jump makes it easy to decide the result depends on that factor. The rows where it was missing often tell a different story.
The short version
The mistake: If adding something makes the result much bigger, the result must need it.
What's actually true: A factor is required only if the result fails without it. If the result still happens without it, the factor just helps.
- To test whether a factor is required, look where it was missing. If the result still happened there, it isn't required.
- E. coli can build all 20 amino acids from glucose and the salts in the flask. When amino acids are supplied, the cells skip that work and divide faster.
- Words like required, must and only are strong claims. One row with the result but without the factor rules them out.
On the exam: Before you call a factor required, find the row without it. If the result still happens there, it only helps.