Science lesson plan · 9th grade (Year 10 in England) · 45 minutes
Count chromosomes after mitosis, meiosis and fertilisation
Cells, genetics and evolution
CCSS NGSS.HS-LS1-4CCSS NGSS.HS-LS3-2England: GCSE Combined Science: Inheritance, variation and evolutionEngland: GCSE Combined Science: Cell biology
Objective and success criteria
Students will: Count chromosomes after mitosis, meiosis and fertilisation.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Mitosis and meiosis
Leads to: Sex chromosomes and the chance of a boy or a girl
Materials: Microscope images or slides, Cell diagrams, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Mitosis and meiosis). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Mitosis or meiosis? It used in asexual reproduction. (mitosis / meiosis) → mitosisPrompt: Which one makes sex cells (gametes)?
- A bacterium divides into two every 30 minutes. Starting with one cell, how many cells are there after 2.5 hours (if none die)? → 32Prompt: How many divisions happen in that time?
- Why must gametes have half the normal number of chromosomes? (So the fertilised egg has the full number again / So they can swim faster / Because they are smaller / So the baby has no chromosomes) → So the fertilised egg has the full number againPrompt: What happens when an egg and sperm join?
Hook · 5 min
- Show a microscope image of cells and ask what students think they are looking at.
- Share the objective: Count chromosomes after mitosis, meiosis and fertilisation. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A body cell of a cat has 38 chromosomes. It divides by mitosis. How many chromosomes are in each new cell?
- Step 1: Mitosis keeps the number the same: 38
- Step 2: So the answer is: 38
- Answer: 38
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A body cell of a fruit fly has 8 chromosomes. How many chromosomes are in one of its gametes (sex cells)? → 4Prompt: Mitosis makes cells identical to the parent cell.
- A potato plant sperm cell has 24 chromosomes. It fertilises an egg cell from the same species. How many chromosomes does the zygote (fertilised egg) have? → 48Prompt: How many chromosomes does the egg cell have?
You do: independent practice · 10 min
- 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.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- How many cells are produced when one cell divides by meiosis? (4, genetically different / 2, genetically different / 2, genetically identical / 4, genetically identical) → 4, genetically differentPrompt: Do the new cells need to be identical to the parent cell, or genetically different?
- A body cell of a potato plant has 48 chromosomes. How many chromosomes are in one of its gametes (sex cells)? → 24Prompt: Mitosis makes cells identical to the parent cell.
Watch out for
- Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
- Remembering facts without the reason: ask "why?" and "what is the evidence?"
Support and stretch
Support
- Review first: Mitosis and meiosis.
- Use concrete materials: microscope images or slides.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Sex chromosomes and the chance of a boy or a girl.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.
Free lesson plan from eurekami.com/lesson-plan-builder