Science 7–10 · Year 8

Yeast respiration: carbon dioxide output against temperature

Science understanding: Biological sciences (AC9S8U01 is about cell structure and the plant and animal cell comparison, and yeast is neither; the only ACARA v9 content description that names respiration is AC9S9U03, a Year 9 Earth and space sciences description of the carbon cycle, so the ACARA side is coded to Year 8 science inquiry only; the NSW side carries the concept in Stage 4 Cells and classification, whose content point asks learners to identify cellular respiration via mitochondria)

PracticalLow risk

The idea

Living cells release carbon dioxide as they respire sugar, and the rate depends on temperature.

What you need

Dried baker's yeast, three 7 g sachets (3.5 g for each of six bottles)
White sugar, 5 g for each of the five bottles that get sugar (25 g)
Six 250 mL plastic bottles, each with a delivery tube to an inverted 100 mL measuring cylinder of water: one for each of the five temperatures and one for the no-sugar control at 35 °C
Water at 10, 25, 35, 45 and 60 °C in baths that hold each bottle; thermometer; timer

How to do it

Put 3.5 g of yeast and 5 g of sugar into each of five bottles and add 100 mL of water at that bottle's set temperature. Swirl, then fit the delivery tube at once.
Keep each bottle in its bath. Every five minutes for 30 minutes read the volume of gas collected in the measuring cylinder.
Set up the sixth bottle the same way at 35 °C but without sugar, as a control.
Plot gas volume against time for each temperature and read the gradient of the straight part as the rate in mL per minute.
Plot rate against temperature.
Test the gas from one bottle with limewater.

What you should see

Gas collects faster in the warm bottles than at 10 °C, and little or none collects at 60 °C because the heat kills the yeast; the no-sugar control gives little gas. Warming or cooling the air in each bottle also changes the gas volume in the first few minutes, so read the rate from the straight part of the curve after the first five minutes. Limewater turns milky, identifying carbon dioxide. The learner knows it worked when the 35 °C bottle produces a measurable volume within ten minutes and the rate plot rises then falls.

What changes

What you change: Temperature (°C)
What you measure: Volume of carbon dioxide collected per minute
What you keep the same: Yeast mass
Sugar mass
Water volume
Bottle and collection method
Timing

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Yeast is not alive because it comes dry in a packet.
The gas is air pushed out by bubbling.
Warmer is always faster; the rate falls again at high temperatures, and at 60 °C the yeast is killed.

Safety card

Low riskLearners carry it out

Hazards

Hot water at 60 °C
Pressure if a bottle is sealed without an outlet

Controls

Tongs or gloves for the hot bath
Open delivery tubes only; never a stoppered bottle

Note

No hazardous chemicals; record a RiskAssess risk assessment for the activity as school procedure requires.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7–10 Syllabus (2023)SC4-CLS-01 SC4-WS-03 SC4-WS-05 SC4-WS-06
Australian Curriculum v9AC9S8I02AC9S8I04AC9S8I05

Sources

The pages the author read to write this activity.

All Concept Studio activities