Friday, July 24, 2026

Photosynthesis UPCAT Reviewer: Lesson and Practice

TEACHER ABI UPCAT SCIENCE

Photosynthesis

Follow matter and energy through the chloroplast, then use evidence to identify what limits the rate.

5-10 minute lesson27 original questionsAdaptive practiceSaves progress
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Photosynthesis

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Photosynthesis transfers light energy into chemical energy

Light reactionsthylakoid membranesCalvin cyclestromalight + H₂OO₂CO₂sugarsATP + NADPHChloroplast: light energy → chemical energy

The light reactions in thylakoid membranes use light and water, releasing O₂ and producing ATP and NADPH. The Calvin cycle in the stroma uses CO₂, ATP, and NADPH to build carbon compounds that can become sugars.

Rate questions usually depend on limiting factors: light, CO₂, temperature, water availability, or pigment condition.

Track atoms

Carbon in sugars comes from CO₂; released oxygen gas comes from water.

Read the whole experiment

Separate the manipulated variable, measured response, controlled variables, and justified conclusion.

DO IT FAST

Stage → location → input → output

Problem: A chemical blocks electron flow in thylakoids.

Recognize: The light reactions occur there.

Do it fast: ATP and NADPH production falls, so the Calvin cycle loses its energy and reducing power.

Why it works

Mapping each stage prevents confusing where oxygen, carbon, ATP, and sugars originate.

WORKED EXAMPLES

Five forms you should recognize

1. Light reactions

Thylakoids use light and H₂O; O₂, ATP, and NADPH result.

2. Calvin cycle

The stroma uses CO₂, ATP, and NADPH to build carbon compounds.

3. Light saturation

A plateau under increasing light means another factor has become limiting.

4. Stomata

Closing stomata saves water but restricts CO₂ entry.

5. Isotope evidence

Labeling water oxygen can demonstrate that released O₂ comes from H₂O.

COMMON TRAPS

Check before you commit

  • Saying plants obtain most biomass from soil
  • Saying released O₂ comes directly from CO₂
  • Assuming respiration stops in light
  • Treating every bubble as exact proof
  • Ignoring limiting factors
  • Confusing thylakoids and stroma
FIVE-FORM SKILL CHECK

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CHOOSE YOUR PRACTICE

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Foundations

Build the core procedure with immediate explanations.

Core Practice

Use mixed forms with less scaffolding.

UPCAT-Style Transfer

Apply the competency in unfamiliar representations.

FRESH MASTERY CHECK

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QUICK ANSWERS

Photosynthesis FAQ

Do plants respire?

Yes. Plant cells perform cellular respiration day and night.

Does the Calvin cycle occur only at night?

No. It is light-independent in the sense that it does not directly absorb light, but it normally depends on products of the light reactions.

RELATED COMPETENCIES

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