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Photosynthesis

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Biology · Grade 9 · 19 responses · analysed
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How to explore
  1. 1. Read the field note on the right — what’s stable, what’s diverging, what to do next.
  2. 2. Hover or click a concept in the landscape to see its evidence and typical reasoning.
  3. 3. Open a reasoning pattern below to read the students’ own words and their thinking profiles.

Understanding landscape

How ideas are connecting across your class — evidence, not scores.

StableFormingLimited evidenceShared pattern

Reasoning patterns

① Plant mass comes from the soil?

6 answersunconfirmed
“the roots suck up the dirt nutrients and thats what makes the plant bigger”
“if you grow a plant without soil it wont grow so the soil must be what its made of”

If this rings true — let the soil answer fail in public~5 min

Write the two numbers on the board: tree +4.0 kg, soil −0.05 kg. Ask everyone to commit to a source for the 4 kg before you say anything. Then ask the soil group directly: “If the plant ate 4 kg of soil, what should the pot look like?” Let them see the mismatch themselves, then ask what else went into the leaf.

Why this: The soil idea is not careless — it fits everything students can see. It only breaks against a measurement, so the measurement has to do the arguing, not you.

  • Mayafelt certain

    “the mass comes from the soil. the roots suck up the dirt nutrients and thats what makes the plant bigger”

    Understands ·
    Roots take things up from the soil
    Connects incorrectly ·
    Treats soil minerals as the bulk material of the plant rather than a trace input
    Next ·
    Let the soil answer fail in public
  • Jonasfelt certain

    “plants eat soil basically. thats why you need good soil or the plant dies”

    Understands ·
    Soil quality affects growth
    Connects incorrectly ·
    Uses an animal-feeding model — roots as a mouth, soil as the meal
    Next ·
    Show a plant grown without soil
  • Priya

    “It gets heavier because it takes minerals out of the ground through the roots.”

    Understands ·
    Minerals are absorbed through roots
    Connects incorrectly ·
    Scales a real but tiny input up to the whole 4 kg
    Next ·
    Compare the size of the mineral input to the mass gained
  • Tomas

    “soil. if you grow a plant without soil it wont grow so the soil must be what its made of”

    Understands ·
    Reasons from a controlled comparison
    Connects incorrectly ·
    Treats “necessary for growth” as “is the material of”
    Next ·
    Introduce hydroponics as the counter-case
  • Aishafelt certain

    “the dirt goes into the plant slowly. thats why the pot soil goes down over time”

    Understands ·
    Looks for physical evidence in the pot
    Connects incorrectly ·
    Explains settling soil as soil being consumed
    Next ·
    Weigh the pot: 0.05 kg vs 4.0 kg
  • Ruben

    “from fertilizer and soil, thats plant food”

    Understands ·
    Knows fertiliser supports growth
    Connects incorrectly ·
    Reads the word “plant food” literally as the plant’s substance
    Next ·
    Separate nutrients from building material

② The water becomes the plant’s mass?

3 answersunconfirmed
“plants are like 90% water so the mass is the water it drank”
“the water it absorbs turns into the plant body”

If this rings true — separate fresh mass from dry mass~4 min

Ask: “If we dried this tree completely in an oven, would it still be heavier than in spring?” Establish that the 4 kg is dry mass too. Then trace the atoms: water supplies hydrogen, CO₂ supplies the carbon skeleton that makes up most of the dry weight.

Why this: This group is right that plants are mostly water — they just haven’t separated water content from where the built material came from. Drying the plant makes that distinction concrete.

③ Sunlight itself turns into plant material?

2 answersunconfirmed
“sunlight gets absorbed and turns into the plant’s material”

If this rings true — name what light actually does~3 min

Ask: “Does a torch shining on a rock make the rock heavier?” Then: light carries energy, not atoms. Have a student restate the sentence with the roles fixed: light powers the reaction, CO₂ supplies the matter.

Why this: Energy and matter get blended when both are described as “going into” the plant. One quick, absurd case pulls them apart without dismissing the student’s point that light is essential.

④ Solid reasoning

4 answers
“The soil barely lost any mass but the tree gained 4 kg, so it can’t be from the soil.”
“Water gives the hydrogen but the carbon skeleton comes from the air, that’s where the mass is.”

If this rings true — extend — design the experiment that proves it~5 min

Challenge this group: “Design an experiment that would convince a sceptic the carbon came from the air.” Ask them to say what they’d label, how they’d detect it, and what result would settle it. Share the cleanest design with the class.

Why this: These students already hold the target idea. Pushing into experimental design is the next layer of the same concept, and their designs make good material for the rest of the class.

⑤ Working on it — no clear pattern

2 answers

Couldn’t read (2)

Too short or off-topic. Prism shows them raw rather than guessing:

  • Ben “idk”
  • Zara “we did this last week”

Prism sorts. You diagnose.
Everything above is a guess with the evidence attached — about today’s answers, never about students.

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