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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.
  1. Mitosis or meiosis? It keeps the full number of chromosomes (46 in humans). (mitosis / meiosis) → mitosisPrompt: Which one makes sex cells (gametes)?
  2. A bacterium divides into two every 60 minutes. Starting with one cell, how many cells are there after 4 hours (if none die)? → 16Prompt: How many divisions happen in that time?
  3. Why must gametes have half the normal number of chromosomes? (Because they are smaller / So the baby has no chromosomes / So they can swim faster / So the fertilised egg has the full number again) → 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.
  1. A body cell of a cat has 38 chromosomes. How many chromosomes are in one of its gametes (sex cells)? → 19Prompt: Mitosis makes cells identical to the parent cell.
  2. A onion plant sperm cell has 8 chromosomes. It fertilises an egg cell from the same species. How many chromosomes does the zygote (fertilised egg) have? → 16Prompt: 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.
  1. Which type of division makes egg and sperm cells? (mitosis / meiosis / binary fission / fertilisation) → meiosisPrompt: Do the new cells need to be identical to the parent cell, or genetically different?
  2. A human sperm cell has 23 chromosomes. It fertilises an egg cell from the same species. How many chromosomes does the zygote (fertilised egg) have? → 46Prompt: How many chromosomes does the egg cell have?

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

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Count chromosomes after mitosis, meiosis and fertilisation

Name

Date

Score/ 8

  1. Question 1

    A body cell of a horse has 64 chromosomes. How many chromosomes are in one of its gametes (sex cells)?

    Answer

  2. Question 2

    A chimpanzee sperm cell has 24 chromosomes. It fertilises an egg cell from the same species. How many chromosomes does the zygote (fertilised egg) have?

    Answer

  3. Question 3

    How many cells are produced when one cell divides by mitosis?

    • A. 4, genetically identical
    • B. 2, genetically different
    • C. 4, genetically different
    • D. 2, genetically identical

  4. Question 4

    A body cell of a onion plant has 16 chromosomes. How many chromosomes are in one of its gametes (sex cells)?

    Answer

  5. Question 5

    A dog sperm cell has 39 chromosomes. It fertilises an egg cell from the same species. How many chromosomes does the zygote (fertilised egg) have?

    Answer

  6. Question 6

    Which type of division makes the cells for growth and repair of skin?

    • A. mitosis
    • B. meiosis
    • C. fertilisation
    • D. binary fission

  7. Question 7

    A body cell of a fruit fly has 8 chromosomes. It divides by mitosis. How many chromosomes are in each new cell?

    Answer

  8. Question 8

    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?

    Answer

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Answer key: Count chromosomes after mitosis, meiosis and fertilisation

  1. 1. 32

  2. 2. 48

  3. 3. D. 2, genetically identical

  4. 4. 8

  5. 5. 78

  6. 6. A. mitosis

  7. 7. 8

  8. 8. 48