Photosynthesis rate – light, CO₂, temperature and the compensation point
BiologyPlant PhysiologyAges 16–17Virtual lab
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Plant Physiology
A sprig of pondweed under a lamp releases O₂ bubbles faster or slower with light intensity, CO₂ concentration and temperature, while a graph plots gross photosynthesis, respiration and net photosynthesis and marks the light compensation point. A Light & dark bottles screen measures the primary productivity of pond water under shade screens (GPP = NPP + R) and compares NPP across biomes; a Litter bags screen measures how fast leaf litter decomposes with temperature, moisture, mesh size and the lignin : nitrogen ratio.
Lesson: Photosynthesis and respiration in plants; primary productivity of ecosystems; decomposition
What it shows
Photosynthesis can be followed by counting the oxygen bubbles a pondweed gives off: net photosynthesis is gross photosynthesis minus respiration, and the two are equal at the light compensation point. In a lake the same idea is measured with light and dark bottles of water: the dark bottle shows respiration (R), the light bottle net primary productivity (NPP), and GPP = NPP + R. NPP differs between biomes because light, water, warmth and nutrients limit growth. Decomposition returns nutrients to the soil: litter rots faster when it is warm, moist and rich in nitrogen, and slower when it is high in lignin or soil animals are kept out.
How to use
On Photosynthesis rate, change Light, CO₂ concentration and Temperature and choose the graph axis. On Light & dark bottles, choose the Water sample, the Light reaching the bottles, the Water temperature and the Incubation time, press Incubate and read the oxygen in each bottle; the table and graph collect your runs. On Litter bags, choose the Litter and conditions, press Run and dig up a bag every few months to weigh it.
Parameters you can change
- Light intensity 0–2000 µmol photon/m²/s
- CO₂ concentration 50–1500 ppm
- Temperature 0–50 °C
- Graph x-axis Light intensity, CO₂ concentration, Temperature
- Screen Photosynthesis rate, Light & dark bottles, Litter bags
- Water sample Clear lake (few algae), Pond (some algae), Green pond (many algae)
- Light reaching the bottles 0–100 %
- Water temperature 5–35 °C
- Incubation time 1–24 h
- Biome NPP chart Per m², Global total
- Litter Clover leaves (legume), Maple leaves, Oak leaves, Pine needles
- Soil temperature 0–35 °C
- Soil moisture (% of capacity) 10–100 %
- Mesh size Coarse (5 mm), Fine (1 mm)
Questions to explore
- Why are no O₂ bubbles released at the light compensation point, even though the plant is still photosynthesising?
- Why does the dark bottle measure respiration, and how do both bottles together give gross primary productivity?
- Why does oak or pine litter decompose more slowly than clover leaves in the same soil?
Teaching ideas
All guides- Group Activities with Simulations: Roles and RoutinesGroup activities with simulations that keep every student working: four roles, five routines, one link per group, and two worked examples with real data.
- 5E Lesson Plan with Interactive SimulationsA 5E lesson plan with interactive simulations: what each E looks like, a timed photosynthesis lesson with real data, a reusable template and adaptations.
- Osmosis Virtual Lab: Potato Strips in Sugar SolutionsOsmosis virtual lab: soak potato strips in 0–1.0 mol/dm³ sugar solutions, calculate the percentage change in mass and find where the mass stays the same.
- Photosynthesis Virtual Lab: Light Intensity and RatePhotosynthesis virtual lab: count oxygen bubbles from pondweed at seven light levels, plot the rate, then raise CO₂ to find the limiting factor.
