Respiration and Photosynthesis Demonstrations

Respiration and photosynthesis demonstrations show how organisms obtain and use energy, whether by releasing it from food or capturing it from sunlight. They are essential for understanding life processes, yet seeing them happen makes the concepts far more concrete.

Demonstration	Materials	Difficulty	Safety	Summary
Bell Jar Breathing Model	★★☆	★★☆	★☆☆	A bell jar model can be used to demonstrate how breathing works by showing how changes in chest cavity volume and pressure cause air to move in and out of the lungs. Pulling on a rubber sheet represents diaphragm contraction (inhalation), while pushing it up represents diaphragm relaxation (exhalation).
Leaf Chromatography	★★☆	★★☆	★★☆	Chromatography is used to separate pigments in green leaves. By dissolving leaf pigments in alcohol and drawing them up filter paper, students can see hidden colors like carotenoids and anthocyanins that are usually masked by chlorophyll.
Measuring Oxygen Use by Germinating Seeds	★★☆	★★☆	★☆☆	Germinating seeds use oxygen and release carbon dioxide during respiration. Using a respirometer with limewater and detergent, oxygen consumption can be measured by observing the movement of a liquid drop inside a sealed tube.
Leaf Disk Photosynthesis	★★☆	★★☆	★☆☆	In this investigation, leaf disks are vacuum-infiltrated with a baking soda solution so they sink. When exposed to light, oxygen from photosynthesis causes the disks to float, and the time until half of them float (ET50) indicates the photosynthesis rate.
Test for Starch in Leaves	★★☆	★★☆	★★☆	Leaves from a plant kept in light and one kept in darkness are boiled briefly, decolorized in hot ethyl alcohol, and stained with iodine. A blue-black color indicates starch, showing that photosynthesis in light produced stored carbohydrate.
Bubbling Plants: Quantifying Photosynthesis	★★★	★★☆	★☆☆	Students place Elodea in baking-soda water and count gas bubbles produced in low light and bright light for fixed time intervals. Comparing bubble counts provides an indirect, simple measure of photosynthesis under different light intensities.
Build a Model Lung	★☆☆	★☆☆	★☆☆	This demonstration uses balloons, straws, and a plastic bottle to create a working model of the lungs and diaphragm. Pulling on the bottom balloon increases the chest cavity volume, causing the lung balloons to inflate, while releasing it decreases the volume, causing them to deflate.
Carbon Dioxide in Breath	★★☆	★★☆	★★☆	This experiment compares the carbon dioxide content of inhaled and exhaled air by passing a person’s breath through tubes into test solutions. Limewater is used to detect carbon dioxide, showing the difference between inhaled and exhaled air.
Aerobic vs. Anaerobic Yeast Respiration	★★☆	★☆☆	★☆☆	This experiment demonstrates yeast respiration by placing yeast, sugar, and warm water in bottles sealed with balloons. Under aerobic conditions, yeast uses oxygen to produce carbon dioxide rapidly, inflating the balloon more. Under anaerobic conditions, yeast ferments sugar into ethanol and carbon dioxide, inflating the balloon more slowly.
Lung Capacity Test	★☆☆	★☆☆	★☆☆	Use an inverted, water-filled bottle and a tube to capture the volume of exhaled air by water displacement. Counting marked volume intervals on the bottle estimates vital lung capacity.

Materials
★☆☆ Easy to get from supermarket or hardware store
★★☆ Available in most school laboratories or specialist stores
★★★ Requires materials not commonly found in school laboratories

Difficulty
★☆☆ Can be easily done by most teenagers
★★☆ Available in most school laboratories or specialist stores
★★★ Requires a more experienced teacher

Safety
★☆☆ Minimal safety procedures required
★★☆ Some safety precautions required to perform safely
★★★ Only to be attempted with adequate safety procedures and trained staff