Seeing Stomata – Measuring Gas Exchange Under the Microscope 

When students learn about photosynthesis, respiration, and gas exchange, it can feel abstract — a list of processes hidden inside leaves. That’s why looking at stomata under the microscope is such a powerful lesson.

🔍 What Are Stomata?

Stomata are tiny pores on the surface of leaves. They open and close to control the exchange of gases:

• Carbon dioxide in for photosynthesis

• Oxygen out as a by-product

• Water vapour out in transpiration

🧪 In the Lab

Using nail varnish impressions or clear acetate peels, students can view stomata under the microscope. Counting how many are open or closed lets us see how plants balance gas exchange and water conservation.

We can then link this to experiments with PASCO CO₂ and O₂ sensors to measure changes in gas concentration, showing stomata “in action” as plants photosynthesise or respire.

🌡 Environmental Factors

Students quickly realise that stomatal behaviour is affected by:

• Light (more open in daylight for photosynthesis)

• Humidity (close in dry conditions to prevent water loss)

• Carbon dioxide concentration (feedback control for efficiency)

🎓 Why It Works in Teaching

Seeing stomata with their own eyes makes the invisible visible. Linking microscopic structures to whole-leaf gas exchange helps students understand how plants adapt and survive — and why stomata are at the centre of the GCSE and A-Level biology story.

Measuring Gas Exchange in Plants Using CO₂ and O₂ Sensors 🌿⚗️

Photosynthesis and respiration are often taught as equations on the board — but students learn best when they see the process happening in real time. That’s where CO₂ and O₂ sensors make all the difference.

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🧪 The Setup

We place a living plant (often pondweed like Elodea or a small leafy shoot) inside an enclosed vessel. With PASCO CO₂ and O₂ sensors linked to a data logger, we can monitor changes in gas concentrations second by second.

By adjusting the conditions — light on/off, intensity, or adding a lamp with a filter — students can track how the plant switches between:

• Photosynthesis dominating (CO₂ falls, O₂ rises).

• Respiration dominating (O₂ falls, CO₂ rises) when the light is removed.

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📊 What Students See

• In bright light, CO₂ concentration decreases as the plant takes it in for photosynthesis, while O₂ rises as a by-product.

• In darkness, photosynthesis stops, but respiration continues — so O₂ decreases and CO₂ increases.

• By plotting graphs, students can calculate rates of photosynthesis and respiration under different conditions.

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🌡 Variables to Explore

• Light intensity (move lamp closer/further).

• Temperature (compare room vs warm water bath).

• CO₂ availability (add sodium hydrogen carbonate solution).

These simple changes make the experiment highly interactive and link directly to GCSE and A-Level exam questions.

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🎓 Why It Works in Teaching

Sensors make the invisible visible. Instead of being told what gases are moving, students watch the data change live. The graphs bring equations like:

$$6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂$$

to life, showing that photosynthesis isn’t just words in a book but a process happening in front of them.