saps - photosynthesis with algal balls
TRANSCRIPT
Photosynthesis
with algal balls
Background
Debbie Eldridge
King Ecgbert School, Sheffield
‘A novel approach to photosynthesis practicals’
School Sci. Rev. (2004), 85, 37-45.
Photosynthesis KS4 - 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.• 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 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.
Algae
Scenedesmus and Chlorella -successfully cultured in the laboratory
Algae
• Immobilised algae to demonstrate rates of photosynthesis
• Algae ‘trapped’ in sodium alginate so that:• numbers can be regulated • they can be separated from the medium
Hydrogencarbonate indicator
Hydrogen carbonate indicator:
• routinely used to measure CO2 levels in aquatic systems.
• red in equilibrium with atmospheric air • becomes more orange/yellow with increased CO2
• changes from red through magenta to deep purple as CO2 is removed.
pH 7.6 9.2 (in 0.2 increments)
Hydrogencarbonate indicatorHydrogencarbonate indicator
Variables?• Colour of light• Light Intensity
• Distance from lamp• Neutral density experiment
• Number of balls• Ball size• Concentration of algae• Temperature • Starting [CO2] etc...
Filters
• 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
FiltersData from www.saps.org.uk (coming soon…):
Wavelength
(nm)
Absorbance Transmittance Transmittance (%)
402 0.87 0.14 14.0
406 0.79 0.16 16.0
410 0.72 0.19 19.0
etc etc etc etc
730 0.41 0.39 39.0
FiltersSpectrum from www.saps.org.uk (coming soon…):
Filter 124, Dark Green
0.000.501.001.502.002.503.003.50
400 450 500 550 600 650 700 750
Wavelength / nm
Abs
orba
nce
FiltersSpectrum from www.saps.org.uk (coming soon…):
Filter 124, Dark Green
0
20
40
60
80
400 500 600 700
Wavelength / nm
Tra
ns
mis
sio
n /
%
FiltersSpectrum from www.saps.org.uk (coming soon…):
Filter 210, 0.6 Neutral Density
0
20
40
60
80
400 500 600 700
Wavelength / nm
Tra
ns
mis
sio
n /
%
Can we quantify the colour change?
Yes!• By measuring the absorbance using a
colorimeter
• By comparing the colours to a range of prepared buffer solutions.
Quantifying colour change
No access to a colorimeter?
• compare the colour change to a series of ready made buffer solutions.
• borax/boric acid buffers in pH range 7.6-9.2.
• 9 cm3 buffer + 1 cm3 concentrated indicator prepared freshly.