It is possible to determine rates of CO2 assimilation and water loss (transpiration) by measuring the flux of CO2 and water vapour from a leaf in a sealed chamber. This process, termed gas exchange (because CO2 is going in and water vapour is coming out) is more complicated than might be initially imagined. During photosynthesis, plants take up CO2 (which is converted to sugar) and produce oxygen. All the while they are respiring and releasing CO2 back into the cells. To make matters more complex, the enzyme that fixes CO2 (Rubisco) also ‘fixes’ oxygen, a reaction called photorespiration that releases CO2, but does not produce energy. Gas exchange is also influenced by light levels, because when more light is available, generally, more CO2 can be fixed.
Production of CO2>02 during the day
Plan and complete an experiment
Plan an experiment to investigate the effect of light on net gas exchange
Understand HCIS and its response to CO2
2.43 Describe a simple controlled experiment to investigate the effect of light on net gas exchange from a leaf, using hydrogen carbonate indicator
Under the graphs, describe what is happening at a, b and c.
Write it as X>Y etc...
Complete P1 and P2 Plant Nutrition NEAB worksheets for Thursday
Planning an experiment
How do we plan an experiment?
We need to follow a pattern.
An experiment needs:
Introduction: This is where we introduce the science behind the experiment
Aim: what the experiment will investigate
Hypothesis: what we expect will happen and why
Method: how the experiment was carried out
Results: a table displaying what was found in the experiment
Conclusion: what we found from our results and how it compares to the science from our introduction
Evaluation: how we could have made the experiment more reliable
What could we use to measure the change in gas levels around a leaf?
We will be using:
Hydrogen Carbonate Indicator Solution (HCIS)
HCIS is an indicator for Carbon Dioxide.
Under normal atmospheric conditions (0.04% CO2) HCIS is
When the concentration of CO2 INCREASES, HCIS turns
When the concentration of CO2 DECREASES, HCIS turns
Plan Your Experiment
Complete the HCIS IGCSE exam questions and stick them into your book
How does gas get in and out of leaves?
09/01/2018 · Gas exchange in plants
Using pages 29 onwards, explain how the alveoli are adapted for gas exchange by diffusion.
2.42 Describe the role of stomata in gas exchange.
Apply what you have learnt about stomata and gas exchange in a leaf, to consolidate the new(ish) information
Human gas exchange system
What are these?
They are found on specialised cells called CILIATED EPITHELIAL CELLS.
Plants obtain the gases they need through their leaves
Even though alveoli are so small there are huge numbers of them which results in a large surface area for gas exchange. Also the wall of the alveoli is made up of a single layer of thin cells and so are the capillaries, this creates a short diffusion distance for the gases. Therefore this allows rapid gas exchange. The alveoli are covered by a dense network of blood capillaries which have a low oxygen and high carbon dioxide concentrations. This allows oxygen to diffuse into the blood and carbon dioxide to diffuse out of the blood. Finally, there are cells in the alveolar walls which secrete a fluid that keeps the inner surface of the alveoli moist, allowing gases to dissolve. This fluid also contains a natural detergent that prevents the sides of the alveoli from sticking together.
IB Biology Notes - 6.4 Gas exchange
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Gas exchange is the process of swapping one gas for another. It occurs in the alveoli of the lungs. Oxygen diffuses into the capillaries from the air in the alveoli and carbon dioxide diffuses out of the capillaries and into the air in the alveoli.