SCIENCE · INVESTIGATE AND EXPLAIN

Separate carbon gain, water loss and an efficiency ratio

Stomata connect internal leaf gas spaces to the atmosphere. Guard-cell osmotic and turgor changes alter pore opening, affecting CO2 entry and water-vapor escape. The same opening can therefore support carbon uptake and impose a water cost. Cuticle, boundary layers and leaf structure also influence exchange.

Learning outcome: Compare g = 0.2, 0.6 and 1 at D = 2, retaining A, E and their ratio separately. Then change D at fixed g and identify which feedback the imposed static comparison prevents.

Starting recap

Connect plant tissues, transport, developmental signals and reproductive origins to complete quantitative evidence with explicit resource and model boundaries.

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Try

At g = 0.6 and D = 2, A = 12/0.8 = 15 µmol CO2/m²/s and E = 6 mmol H2O/m²/s. A/E = 2.5 µmol CO2/mmol H2O. At D = 3 with g unchanged, E becomes 9 and the ratio falls to about 1.667.

Open the experiment

Predict

Does a higher carbon-per-water ratio necessarily imply more total carbon gained?

Your prediction and reason

Experiment

Compare g = 0.2, 0.6 and 1 at D = 2, retaining A, E and their ratio separately. Then change D at fixed g and identify which feedback the imposed static comparison prevents.

Compare carbon uptake and water loss under a changed atmosphere

Worked teaching model · synthetic values · Original steady comparison: net assimilation A=20 g/(0.2+g)µmol CO2/m²/s and transpiration E=5 gD mmolH2O/m²/s. Temperature/light/CO2 fixed; no true optimal-control or universal species response implied.

Relative stomatal conductance: 0.6 relative Vapor-pressure deficit: 2 kPa

Reset keeps your prediction, captures and practice history.

Opening stomata can raise carbon uptake while increasing water loss under the stated atmosphere.

At fixed conductance, a larger vapor-pressure deficit raises modeled water loss without changing the supplied carbon curve. Actual stomata can respond, and ABA, hydraulics, temperature and light complicate this static comparison. Ratio efficiency is not automatically maximum growth.

Solid: Supplied saturating carbon response. Axes rescale to the current range; use labeled values rather than comparing graph heights across settings.

Original model curve values
Relative conductance	Supplied saturating carbon response (Assimilation µmol CO2/m²/s)
0.2	10.00000
0.4	13.33333
0.6000000000000001	15.00000
0.8	16.00000
1	16.66667

Calculated quantities under stated assumptions
Quantity	Value	Unit
Net carbon assimilation	15	µmol CO2/m²/s
Water loss	6	mmolH2O/m²/s
Instantaneous assimilation / water loss	2.500000	µmol CO2/mmolH2O

Retain prior predictions, settings and quantities in the notebook. These are original supplied/calculated comparisons, not physical specimen observations or laboratory participation.

Opening stomata can raise carbon uptake while increasing water loss under the stated atmosphere.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

1. Orient: Separate carbon gain, water loss and an efficiency ratio

2. Connect plant structure and mechanism

The original static comparison supplies assimilation A = 20g/(0.2+g) µmol CO2/m²/s and transpiration E = 5gD mmol H2O/m²/s, where g is relative conductance and D is vapor-pressure deficit in kPa. The saturating carbon response and linear water response are illustrative functions, not a calibrated species model.

At fixed g, a larger atmospheric deficit increases modeled water loss while leaving the supplied carbon curve unchanged. Actual stomata may respond to water status and ABA signaling, and leaf temperature can change. Holding a control fixed is a hypothetical contrast, not a claim that the organism ignores feedback.

The ratio A/E is instantaneous carbon uptake per water lost, with µmol/mmol units here. Maximizing that ratio is not the same objective as maximizing total carbon gain, reproduction or survival. A plant can conserve water by closing stomata while also limiting growth; decisions require time-dependent resources and organismal context.

3. Work a complete evidence example

At g = 0.6 and D = 2, A = 12/0.8 = 15 µmol CO2/m²/s and E = 6 mmol H2O/m²/s. A/E = 2.5 µmol CO2/mmol H2O. At D = 3 with g unchanged, E becomes 9 and the ratio falls to about 1.667.

4. Predict and investigate

Predict first: Does a higher carbon-per-water ratio necessarily imply more total carbon gained?

Compare g = 0.2, 0.6 and 1 at D = 2, retaining A, E and their ratio separately. Then change D at fixed g and identify which feedback the imposed static comparison prevents.

Retain the original first prediction, stated controls, complete ledger and a conflicting or null comparison. Original supplied calculations are not measured plant specimens or completed practical work.

5. Transfer to a changed plant case

Apply the mechanism to a changed case

At g = 0.4 and D = 1, calculate A, E and A/E.

Retain your calculation, units and assumptions in the lesson notebook before opening this public practice response.

Compare a worked response

A = 8/0.6 ≈ 13.333 µmol CO2/m²/s; E = 2 mmol H2O/m²/s; ratio ≈ 6.667 µmol CO2/mmol H2O. This is not a universal optimum or a long-term growth prediction.

6. Reflect and defend a bounded conclusion

Connect a tissue or developmental mechanism to the evidence, identify an omitted alternative and propose an independent discriminating observation. Preserve a first report and human critique in the General Biology II workspace. Public practice does not establish independently assessed practical skill, and these conceptual models do not prescribe hormone, fertilizer or field interventions.

Supporting scientific reference, checked 30 October 2026. Original prose, numerical packets and diagrams; no source exercise or figure reproduced. Actual calibrated plant transport or specimen work requires separate supervised evidence.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

At g = 0.4 and D = 1, calculate A, E and A/E.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Compare xylem conduit geometry with loss of functional paths Next: Connect sugar loading to pressure-driven source–sink transport

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