Retrieval Starter
Rosenshine Principle 1 · Prior knowledge activationYou may be asked to complete a table about the roles of minerals in plants. You may also need to write about the roles of minerals as part of a longer question about plant growth or plant physiology. Practise linking function → deficiency symptom → reason.
See – Think – Wonder
Harvard Project Zero · Visible Thinking RoutineObserve the mineral deficiency experiment below. Use the three lenses.
Consider: plants lacking nitrogen show yellowing of older leaves. Plants lacking magnesium show yellowing between leaf veins. Why might these two deficiencies produce similar-looking but slightly different symptoms?
Core Content
Spec 4.8 · Fully Addresses Learning ObjectivePlants are approximately 90% water (compared to ~65% in humans). Water is fundamental to nearly every process in a plant.
Photosynthesis
Water is a raw material — CO₂ + H₂O → glucose + O₂. Water molecules are split during the light-dependent reactions to release hydrogen ions and oxygen.
Structural Support (Turgor)
Water moves into vacuoles by osmosis, pushing the cytoplasm against the cell wall and making cells rigid (turgid). Non-woody plants wilt when water is lost.
Transport Medium
Mineral ions are carried dissolved in water through the xylem. Sugars are dissolved in water and transported in the phloem. Water drives the transpiration stream.
Thermoregulation (Cooling)
Evaporation of water from leaf surfaces requires energy (latent heat). This removes heat from the plant, preventing overheating in direct sunlight.
Although plants synthesise carbohydrates through photosynthesis, they cannot make proteins, DNA or chlorophyll without inorganic mineral ions absorbed from the soil via active transport.
🔵 NITRATES (NO₃⁻)
• Amino acids → proteins (including enzymes)
• DNA and many plant hormones
• A range of other nitrogen-containing compounds
🟡 CALCIUM (Ca²⁺)
• Calcium pectate in the middle lamella — holds plant cells together
• Important for membrane permeability and stability
🟢 MAGNESIUM (Mg²⁺)
• Chlorophyll — the green pigment that traps light energy
• Activates several plant enzymes
• Involved in the synthesis of nucleic acids (DNA/RNA)
| Mineral Ion | Key Functions | Deficiency Symptom | Why That Symptom? |
|---|---|---|---|
| NO₃⁻ Nitrate | Makes amino acids, proteins, enzymes, DNA, hormones | Yellowing of older leaves; stunted growth; eventual death | Nitrogen remobilised from older leaves to newer growing tissues |
| Ca²⁺ Calcium | Forms calcium pectate in middle lamella; membrane stability | Growing points die back; young leaves yellow and crinkly | Not remobilised — new growing tissue suffers most |
| Mg²⁺ Magnesium | Core of chlorophyll molecule; enzyme activation; nucleic acids | Interveinal chlorosis on older leaves; slower growth | Magnesium remobilised from older leaves to newer growth |
Always link the role of the mineral to its deficiency symptom. For example: "Magnesium is needed for chlorophyll synthesis. Without it, the plant cannot produce enough chlorophyll, so leaves turn yellow — particularly in older leaves from which magnesium is remobilised."
Dual Coding Tasks
Cognitive Science · Paivio's Dual-Coding TheoryResearch shows that combining visual representations with words strengthens memory encoding by activating two cognitive channels simultaneously. Complete these tasks in your exercise book.
Task A — Water in a Non-Woody Plant
Draw a simple plant and annotate it with four arrows showing where water is used: photosynthesis (leaf), turgor support (stem cell), transport (xylem vessel), evaporation/cooling (stomata). Label each with the biological process.
Task B — Mineral Function Flow
Create a concept map with "Mineral Ions" at the centre. Branch out to NO₃⁻, Ca²⁺, and Mg²⁺. For each, draw a box for its function and a separate box (in red) for its deficiency symptom. Draw an arrow labelled "leads to" connecting them.
Task C — The 5-Plant Experiment
Re-draw Figure A from the textbook (the 5 beakers). Label each solution and the condition of the plant. Then add an explanation sentence beneath each: "This plant lacks __ which is needed for __ and therefore…"
Task D — Deficiency Leaf Diagrams
Draw two leaf outlines. On one, shade the yellowing pattern for nitrate deficiency (whole leaf yellowing). On the other, shade the yellowing pattern for magnesium deficiency (interveinal — between the veins). Label and explain the difference.
Some plants hyperaccumulate metal ions — they absorb far more than usual. Alyssum species can absorb toxic heavy metals (thallium, lead) from contaminated soil in a process called phytoremediation. In California, Streptanthus polygaloides absorbs nickel from soil, making up to 1% of its dry mass. The plants are harvested and smelted, extracting the metal commercially.
❓ Consider: How does the active transport mechanism that plants use to absorb minerals from the soil make phytoremediation possible? What would you expect to happen to these plants if you grew them in a mineral-free solution?
Tiered Progress Checks
Scaffolded · Foundation → Core → Challenge + Struggle- For photosynthesis / as a raw material for photosynthesis
- For support / to maintain turgor pressure in cells
- As a transport medium / to carry mineral ions in the xylem
- For cooling / evaporation of water cools the plant
[Imagine a table: Row 1: Nitrate — function = make amino acids → deficiency = __; Row 2: __ ion — function = make chlorophyll → deficiency = yellow older leaves; Row 3: Calcium — function = __ → deficiency = growing points die back]
- Nitrate deficiency → older leaves yellow and die / stunted growth (1)
- Missing ion = Magnesium (Mg²⁺) (1)
- Calcium function = forms calcium pectate in middle lamella / holds cells together (1)
- Photosynthesis — without water, no glucose produced, growth stops (1)
- Turgor support — without water, vacuoles lose pressure, plant wilts (1)
- Transport — mineral ions cannot reach cells, enzyme function impaired (1)
- Cooling — plant overheats, enzymes denature, metabolic reactions fail (1)
- Nitrate is needed to make amino acids and therefore proteins/chlorophyll (1)
- Nitrate is remobilised by the plant — moved from older leaves to newer growing tissue (1)
- Therefore older leaves are depleted of nitrate first, lose chlorophyll, and turn yellow (1)
(a) Predict and explain the appearance of the plant grown in −Mg²⁺ solution. [3]
(b) Suggest why the distilled-water plant showed some growth initially but then stopped. [2]
- Leaves would show yellowing / interveinal chlorosis — particularly on older leaves (1)
- Because Mg²⁺ is needed to make chlorophyll (1)
- Without chlorophyll, the plant cannot photosynthesise effectively, so growth slows (1)
- The seed contained stored minerals / food reserves (e.g. starch, proteins) which could be used initially (1)
- Once seed reserves were exhausted and no minerals available from solution, the plant could no longer synthesise essential molecules and growth stopped (1)
- Nitrate and magnesium are mobile in the phloem — the plant can remobilise them from older leaves to younger, actively growing tissues (1)
- Calcium is immobile — once deposited in cell walls as calcium pectate, it cannot be remobilised and moved via the phloem (1)
- Therefore calcium deficiency always affects new growth / growing points, which rely on incoming Ca²⁺ from the xylem (1)
- Whereas nitrate and magnesium deficiency depletes older leaves first, as supply is redirected to new growth (1)
The Phytoremediation Problem
A scientist wants to use Alyssum plants to clean up a field contaminated with lead (Pb²⁺) ions. She hypothesises that the plants will absorb the lead via the same active transport mechanism used for mineral ion uptake in roots.
Design a controlled investigation to test whether lead concentration in the soil affects the rate at which Alyssum plants absorb lead. In your answer, identify the independent variable, dependent variable, three controlled variables, and explain how you would measure the dependent variable.
Lesson Checkpoint
Textbook Spec 4.8 · Self-AssessmentCan you now answer these? — The Spec's Three Questions
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