Photosynthesis - Plant Gas Exchange
Biology: Cambridge International GCSE Supplement, topic 6.1.2
Detecting Plant Gas Exchange
Plants carry out both photosynthesis and respiration.
Hydrogencarbonate indicator
- Hydrogencarbonate indicator changes colour depending on how much carbon dioxide is in a solution.
- It can be used to show how much photosynthesis and respiration an aquatic plant (like pondweed) is doing, by adding it to the water the plant is in.
High CO2
- Hydrogencarbonate indicator turns yellow in high levels of carbon dioxide.
- Since CO2 is produced in respiration and used up in photosynthesis, this suggests the plant is respiring more than it is photosynthesising.
- This result can be seen if the plant is kept in the dark.
Low CO2
- Hydrogencarbonate indicator turns purple in low levels of carbon dioxide.
- Since CO2 is produced in respiration and used up in photosynthesis, this suggests the plant is photosynthesising more than it is respiring.
- This result can be seen if the plant is kept in bright light.
Normal atmospheric CO2
- Hydrogencarbonate indicator turns red in normal atmospheric levels of carbon dioxide.
- Since CO2 is produced in respiration and used up in photosynthesis, this suggests the plant is respiring at the same rate that it is photosynthesising.
Test yourself on Photosynthesis - Plant Gas Exchange
What colour would hydrogencarbonate indicator turn when added to pondweed in bright light?