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Science lesson plan · 8th grade (Year 9 in England) · 45 minutes

DNA, genes and chromosomes

Cells, genetics and evolution

CCSS NGSS.MS-LS3-1CCSS NGSS.HS-LS1-1CCSS NGSS.HS-LS3-1England: KS3 Biology: Genetics and evolutionEngland: KS4 Combined Science: Evolution, inheritance and variation

Objective and success criteria

Students will: DNA, genes and chromosomes.

  • 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: Plant and animal cells

Leads to: Genetic crosses and Punnett squares; Mitosis and meiosis; Natural selection and resistance

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 (Plant and animal cells). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Which part of a cell is a thin layer around the cytoplasm? (chloroplasts / nucleus / cell wall / cell membrane) → cell membranePrompt: Think about which parts are only in plant cells.
  2. Cells: which statement is NOT true? (Plant cells have a cell wall but animal cells do not. / Only animal cells have mitochondria. / Chloroplasts are found in plant cells, not animal cells. / Bacterial cells have no nucleus.) → Only animal cells have mitochondria.Prompt: Do plant cells respire?
  3. Which part of a cell absorbs light for photosynthesis? (chloroplasts / cell membrane / nucleus / cell wall) → chloroplastsPrompt: Think about which parts are only in plant cells.

Hook · 5 min

  • Show a microscope image of cells and ask what students think they are looking at.
  • Share the objective: DNA, genes and chromosomes. 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: What is a gene?
  • Step 1: A gene is a short section of DNA carrying the code for one protein.
  • Step 2: So the answer is: a section of DNA that codes for a protein
  • Answer: a section of DNA that codes for a protein
  • 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. Rosalind Franklin's X-ray image helped scientists discover… (the first vaccine / penicillin / the shape of the Earth / the structure of DNA) → the structure of DNAPrompt: Watson and Crick used her data.
  2. Human body cells have 23 pairs of chromosomes. How many chromosomes are in a skin cell? → 46Prompt: Is this a gamete (sex cell) or a body cell?

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. How many chromosomes are in a normal human body cell? (23 / 46 (23 pairs) / 12 / 92) → 46 (23 pairs)Prompt: They come in pairs, one of each pair from each parent.
  2. Human body cells have 23 pairs of chromosomes. How many chromosomes are in a sperm cell? → 23Prompt: Is this a gamete (sex cell) or a body 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: Plant and animal cells.
  • 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: Genetic crosses and Punnett squares; Mitosis and meiosis; Natural selection and resistance.
  • 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-8.

Free lesson plan from eurekami.com/lesson-plan-builder

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DNA, genes and chromosomes

Name

Date

Score/ 8

  1. Question 1

    How many chromosomes are in a normal human body cell?

    • A. 92
    • B. 23
    • C. 12
    • D. 46 (23 pairs)

  2. Question 2

    Human body cells have 23 pairs of chromosomes. How many chromosomes are in a sperm cell?

    Answer

  3. Question 3

    Rosalind Franklin's X-ray image helped scientists discover…

    • A. penicillin
    • B. the first vaccine
    • C. the shape of the Earth
    • D. the structure of DNA

  4. Question 4

    What is a gene?

    • A. a type of cell
    • B. a whole chromosome
    • C. a section of DNA that codes for a protein
    • D. a disease

  5. Question 5

    Human body cells have 23 pairs of chromosomes. How many chromosomes are in a skin cell?

    Answer

  6. Question 6

    What shape is a DNA molecule?

    • A. a double helix
    • B. a single straight line
    • C. a cube
    • D. a ring of six atoms

  7. Question 7

    Where is DNA found in an animal cell?

    • A. outside the cell
    • B. in the chloroplasts
    • C. mainly in the nucleus
    • D. in the cell wall

  8. Question 8

    Human body cells have 23 pairs of chromosomes. How many chromosomes are in an egg cell?

    Answer

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Answer key: DNA, genes and chromosomes

  1. 1. D. 46 (23 pairs)

  2. 2. 23

  3. 3. D. the structure of DNA

  4. 4. C. a section of DNA that codes for a protein

  5. 5. 46

  6. 6. A. a double helix

  7. 7. C. mainly in the nucleus

  8. 8. 23