• 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. Mary Anning was famous for… (landing on the Moon / inventing the telescope / finding important fossils, such as ichthyosaurs / discovering electricity) → finding important fossils, such as ichthyosaursPrompt: She searched the cliffs of the Jurassic Coast in England.
2. How many chromosomes are in a normal human body cell? (12 / 23 / 92 / 46 (23 pairs)) → 46 (23 pairs)Prompt: They come in pairs, one of each pair from each parent.
3. Evolution: which statement is true? (Dinosaurs and early humans lived at the same time. / Individual animals evolve during their own lifetime. / Species can become extinct. / Humans evolved from modern chimpanzees.) → 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. Before the Industrial Revolution most peppered moths were pale. Soot darkened tree bark, and dark moths became common. Why? (Soot changed the moths' genes directly / Dark moths were better camouflaged, so fewer were eaten by birds / Birds prefer to eat dark moths / Pale moths painted themselves dark) → Dark moths were better camouflaged, so fewer were eaten by birdsPrompt: Which moths could birds see more easily on dark bark?
2. A population of 500 bacteria contains 1% that are resistant to an antibiotic. The antibiotic kills all the others. How many bacteria survive? → 5Prompt: 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. Why should patients finish a course of antibiotics? (To make the antibiotic taste better / To kill all the bacteria, so resistant ones are less likely to survive and spread / To make their immune system weaker / Because antibiotics kill viruses) → 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 1% that are resistant to an antibiotic. The antibiotic kills all the others. How many bacteria survive? → 1Prompt: Only the resistant ones survive.

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