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Investigations with immobilised algae
Paul Beaumont/Jenny Edrich
Science & Plants for Schools
Homerton College, Cambridge
BackgroundBackground
Debbie Eldridge
A novel approach to photosynthesis practicals
School Sci. Rev. (2004), 85, 37-45.
Photosynthesis Photosynthesis - problems- problems
understanding experimental procedures
– controlled experiments with conditions or materials missing followed by iodine test for starch.
with motivation – pupils have ‘done it before’ or see plants as
tedious.
Photosynthesis Photosynthesis - problems- problems
obtaining data – difficulty getting enough reliable data to illustrate change
in rates – Elodea bubbling rates notoriously unreliable.
keeping a range of photosynthetic organisms in school for use over the year.
New practical ideasNew practical ideas
Photosynthetic organisms easy to grow and culture.
The ability to be able to measure – either oxygen evolution – or carbon dioxide uptake so that rates can be
determined.
A novel species.
AlgaeAlgae
Scenedesmus quadricauda
calcium alginate(insoluble)
Algae suspended in + calcium chloridesodium alginate solution
A report on the bioscience curriculum by a working group established by the Biosciences Federation
Enthusing the next generation
Hydrogencarbonate indicatorHydrogencarbonate indicator
• Used to measure [CO2].
• Orange/red in air.
• Increasingly yellow as [CO2] increases .
• Orange red magenta deep purple as [CO2 ] decreases.
pH 7.6 9.2 (in 0.2 increments)
Hydrogencarbonate indicatorHydrogencarbonate indicator
Light SourcesLight Sources
£30 each from:Ring Lighting, Ring House, Gelderd Road, Leeds LS12 6NBTel: 0113 2767565
What might you observe?
Dark control
60-90 min irradiation
Variables?Variables?
• Colour of light• Light Intensity
• Distance from lamp• Neutral density experiment
• Number of balls• Ball size• Concentration of algae• Temperature
Colour of lightColour of light
'Red Filter''
Lamp Hydrogencarbonate indicator containing
algal balls
100% 0%Red Green Blue
Light Intensity ILight Intensity I
Light Intensity IILight Intensity II
Neutral density filter
Transmission dataTransmission data
Filter No Absorbance %T
298 0.15 71
209 0.30 50
210 0.60 25
211 0.90 12.5
299 1.20 6.25
100% 71% 50% 25% 12.5% 6.25%
Dark control
60-90 min irradiation
CO 2 loss as a function of time as measured by absorbance
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50 60 70
Time (min)
Absorbance (550 nm)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 50 100 150 200 250 300 350 400
Time (min)
Absorbance (550 nm)
Lamp off
CO2 appearance as a function of time
FiltersFilters
• LEE Filters – range of filters• Different colours available• Neutral density options• LEE Filters, Central Way,
Walworth Industrial Estate, Andover, Hants SP10 5AN. Tel 01264 366245; www.leefilters.com
Can we quantify Can we quantify the colour change?the colour change?
• By measuring the absorbance using a colorimeter
• By comparing the colours to a range of prepared buffer solutions.
ColorimeterColorimeter
R = Reference T = Test
Direction of Beam
pH 7.6 9.2 (in 0.2 increments)
Hydrogencarbonate indicatorHydrogencarbonate indicator
No access to a colorimeter?