Investigations with immobilised algae Paul Beaumont/Jenny Edrich Science & Plants for Schools Homerton College, Cambridge

A novel approach to photosynthesis practicals Background Debbie Eldridge A novel approach to photosynthesis practicals School Sci. Rev. (2004), 85, 37-45.

Photosynthesis - 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 - 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 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 quadricauda

Enthusing the next generation A report on the bioscience curriculum by a working group established by the Biosciences Federation

Hydrogencarbonate indicator Used to measure [CO2]. Orange/red in air. Increasingly yellow as [CO2] increases . Orange  red  magenta  deep purple as [CO2 ] decreases.

Hydrogencarbonate indicator Buffers 7.6 –9.2

Light Sources Buffers 7.6 –9.2

£30 each from: Ring Lighting, Ring House, Gelderd Road, Leeds LS12 6NB Tel: 0113 2767565

What might you observe? The colorimeter we recommend for key stage 4 use is the WPA colorimeter

Dark control 60-90 min irradiation

Variables? Colour of light Light Intensity Number of balls Ball size Distance from lamp Neutral density experiment Number of balls Ball size Concentration of algae Temperature The colorimeter we recommend for key stage 4 use is the WPA colorimeter

Colour of light The colorimeter we recommend for key stage 4 use is the WPA colorimeter

0% 100% Red Green Blue

Light Intensity I The colorimeter we recommend for key stage 4 use is the WPA colorimeter

Light Intensity II The colorimeter we recommend for key stage 4 use is the WPA colorimeter

Transmission 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 The colorimeter we recommend for key stage 4 use is the WPA colorimeter

100% 71% 50% 25% 12.5% 6.25%

Dark control 60-90 min irradiation

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 The colorimeter we recommend for key stage 4 use is the WPA colorimeter

Can we quantify the colour change? By measuring the absorbance using a colorimeter By comparing the colours to a range of prepared buffer solutions. The colorimeter we recommend for key stage 4 use is the WPA colorimeter

Colorimeter Direction of Beam R = Reference T = Test

Hydrogencarbonate indicator No access to a colorimeter? Buffers 7.6 –9.2