Quick Answer: The respiration apparatus is a glass-and-tubing set-up used in biology practicals to show that living material, usually germinating seeds, takes in oxygen and gives out carbon dioxide during respiration. It demonstrates that respiration happens rather than measuring its rate.
What the Apparatus Demonstrates
Respiration is invisible, so school practicals rely on apparatus that makes its effects show up. In one widely taught version, germinating seeds are sealed in a conical flask with a small tube of potassium hydroxide solution hung inside, and a bent glass tube runs from the stopper into a beaker of water. The potassium hydroxide absorbs the carbon dioxide the seeds release, the gas volume in the flask falls as oxygen is used, and water rises up the tube. In another, air is drawn over the seeds and then through lime water, which turns milky when carbon dioxide is present.
Some respiration apparatus is built for people rather than seeds: two tubes of lime water share a mouthpiece so that inhaled air is drawn through one and exhaled air is blown through the other, showing that breathed-out air carries more carbon dioxide. The listing does not state which design this is or what glassware is included, so check the form of the apparatus against the practical in your syllabus.
Compared with a respirometer, which measures the rate of oxygen uptake on a graduated scale, a respiration apparatus is qualitative: it shows that respiration has taken place and what it produces. Many schools keep both, using the apparatus with younger classes and the respirometer for rate experiments.
Applications
- Showing that germinating seeds release carbon dioxide, with boiled seeds as a control
- Comparing the carbon dioxide in inhaled and exhaled air using lime water
- Introducing aerobic respiration before quantitative respirometer work
- Science exhibitions, where the lime water change is easy for visitors to see
Specifications
| Item | Demonstration apparatus for respiration |
| Shows | Carbon dioxide release and oxygen uptake by living material |
| Typical reagents | Lime water or potassium hydroxide solution, prepared separately |
| Typical material | Germinating seeds; exhaled air in the breathing version |
| Design and glassware included | Confirm at enquiry |
Care & Handling
- Potassium hydroxide is corrosive: wear eye protection and gloves when filling the absorbent tube, and read the SDS before preparing it.
- Check that stoppers and tubing joints are airtight before the class; a small leak stops the water from rising.
- For the breathing version, fit a fresh mouthpiece for each student and check the tube arrangement so that no one can draw lime water into the mouth.
- Rinse glassware soon after use; lime water leaves a white calcium carbonate film that is easiest to remove while fresh.
Why Choose LabEquip
A respiration apparatus is usually bought by secondary schools stocking their biology practical cupboard, often with a respirometer for senior classes. LabEquip supplies both in its Biology Lab Products range; tell us through the contact page which version of the practical you teach.
Frequently Asked Questions
Why does lime water turn milky?
Carbon dioxide reacts with the calcium hydroxide dissolved in lime water to form insoluble calcium carbonate, which appears as a white cloudiness.
Why is potassium hydroxide placed in the flask?
It absorbs carbon dioxide. When the seeds take in oxygen and their carbon dioxide is removed, the volume of gas in the flask falls and water is drawn up the tube.
Why are boiled seeds used as a control?
Boiled seeds are dead and cannot respire, so any change seen only with living seeds must come from respiration. Rinse the boiled seeds in a mild disinfectant so that microbes growing on them do not respire instead.
Can the apparatus measure how fast respiration happens?
Not accurately. It shows that respiration takes place. For rates, a respirometer with a graduated capillary and a coloured liquid index is used.
Which seeds work well?
Seeds that germinate quickly and respire strongly, such as gram, peas, mung or wheat, soaked overnight and kept moist for a day or two until the radicle appears.
Do germinating seeds also give out heat?
Yes. A separate practical places germinating seeds in a vacuum flask with a thermometer; over a day or two the temperature rises compared with a flask of boiled seeds.
Last Updated: September 2026
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