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?