Skip to 0 minutes and 6 secondsBEVERLY GOODGER: In mammals and many other animals, the heat generated by respiration is used to maintain body temperature. In plants, this energy dissipates as heat. This practical shows that plants, in this case, germinating seeds are respiring by showing that they are giving off heat. This practical works well with both peas and wheat seeds. We're going to use 25 germinating pea seeds, 25 boiled and cooled germinating peas, made up to an equal volume with glass beads if needed, and another equal volume of glass beads. We've already shown how you can work out the volume of the germinating pea seeds, and work out equivalent volumes for the other setups.
Skip to 0 minutes and 51 secondsYou will also need three vacuum flasks of the same volume labelled germinating peas, boiled and cooled peas, and glass beads, three generous cotton wool bungs to fit the necks of the vacuum flasks, a data logger, and three temperature probes or three thermometers. Carefully place the germinating peas in the labelled flask. Insert a cotton wool bung into the flask and insert the temperature probe through the bung into the germinating peas. Alternatively, you may wish to wrap the cotton wool around the temperature probe before pushing the bung into the neck of the flask. Repeat this process for the boiled and cold peas and for the glass beads, adding the glass beads to the flask very carefully to avoid smashing it.
Skip to 1 minute and 42 secondsTurn on the data logger and record the initial temperature. The investigation can be carried out using a thermometer instead of a data logger. Leave the flasks in the same conditions for between two and five days. The set up should be placed away from direct sources of light and heat to maintain as constant external conditions as possible. It's important not to leave the experiment running for longer than seven days for two reasons. Temperatures can increase to a point that they will affect the living respiring seeds. And microbes on the surface of the seeds will increase in number. Microbial respiration will generate a further heating effect, confounding the data.
Skip to 2 minutes and 27 secondsYou should find that the temperature inside the flask containing live germinating seeds increases over time. The temperature inside the flask containing the boiled cooled seeds and the glass beads should not change.
Germinating seeds in flasks
This video demonstrates how to set up an investigation into heat production by living and non-living pea seeds. The experiment uses the observation that respiring organisms release heat, to investigate aerobic respiration in living, germinating pea seeds and germinating pea seeds that have been killed by boiling them to denature enzymes. The vacuum flasks used in the investigation trap any heat produced by the seeds. The use of temperature probes attached to data loggers allows continuous monitoring of temperature changes inside the flasks over several days.
As in the last step, note down the possible misconceptions that this practical could be used to help address with your students.
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