• Quick retrieval from earlier learning (Evolution and fossil evidence; DNA, genes and chromosomes). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Who is famous for the theory of evolution by natural selection? (Isaac Newton / Albert Einstein / Charles Darwin / Marie Curie) → Charles DarwinPrompt: He studied finches and tortoises on the Galápagos Islands.
2. Where is DNA found in an animal cell? (outside the cell / in the cell wall / mainly in the nucleus / in the chloroplasts) → mainly in the nucleusPrompt: It is the control centre of the cell.
3. Evolution: which statement is true? (Individual animals evolve during their own lifetime. / Dinosaurs and early humans lived at the same time. / Humans evolved from modern chimpanzees. / Species can become extinct.) → Species can become extinct.Prompt: Evolution is about populations over many generations.

• Show a microscope image of cells and ask what students think they are looking at.
• Share the objective: Natural selection and resistance. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Before the Industrial Revolution most peppered moths were pale. Soot darkened tree bark, and dark moths became common. Why?
• Step 1: Dark moths survived to breed more, so the dark allele became more common.
• Step 2: So the answer is: Dark moths were better camouflaged, so fewer were eaten by birds
• Answer: Dark moths were better camouflaged, so fewer were eaten by birds
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. Why should patients finish a course of antibiotics? (To kill all the bacteria, so resistant ones are less likely to survive and spread / To make the antibiotic taste better / Because antibiotics kill viruses / To make their immune system weaker) → To kill all the bacteria, so resistant ones are less likely to survive and spreadPrompt: Stopping early can leave the toughest bacteria alive.
2. A population of 100 bacteria contains 2% that are resistant to an antibiotic. The antibiotic kills all the others. How many bacteria survive? → 2Prompt: Only the resistant ones survive.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. A population of 100 bacteria contains 2% that are resistant to an antibiotic. The antibiotic kills all the others. How many bacteria survive? → 2Prompt: Only the resistant ones survive.
2. What is the original source of new variation in a population? (exercise / learning new skills / injuries / mutations in DNA) → mutations in DNAPrompt: It is a change in the genetic code.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.