How To Calculate The Rate Of Photosynthesis

Without photosynthesis life as we know it would not exist. It's worth a moment's reflection…

There would be no biology without photosynthesis. Plant biomass is the food and fuel for all animals. Plants are the master producers. These amazing organisms are capable of capturing the energy of sunlight and fixing it in the grade of potential chemical energy in organic compounds. The organic compounds are synthetic from 2 principle raw materials; carbon dioxide and water (which is a source of hydrogen). These compounds are stable and can be stored until required for life processes. Hence animals, fungi and non-photosynthetic leaner depend on these for the maintenance of life.

But how can we mensurate the rates at which photosynthesis takes place?

The quantities are mind boggling. A hectare (e.g. a field 100 m by 100 k) of wheat tin convert as much as 10,000 kg of carbon from carbon dioxide into the carbon of sugar in a year, giving a total yield of 25,000 kg of sugar per year.

There is a total of 7000 x 109 tonnes of carbon dioxide in the atmosphere and photosynthesis fixes 100 ten 109 tonnes per year. So 15% of the full carbon dioxide in the atmosphere moves into photosynthetic organisms each twelvemonth.

Photo by Jeremy Bezanger on Unsplash

What are the different methods of measuring the rate of photosynthesis?

There are a few key methods to calculate the rate of photosynthesis. These include:

1. Measuring the uptake of CO2
2. Measuring the production of O2
3. Measuring the production of carbohydrates
4. Measuring the increase in dry mass

As the equation for respiration is almost the opposite of the one for photosynthesis, you will demand to remember whether these methods measure out photosynthesis alone or whether they are measuring the balance between photosynthesis and respiration.

Measuring photosynthesis via the uptake of carbon dioxide

Using 'immobilised algae' – Information technology's easy and accurate to measure the rate of photosynthesis and respiration using immobilised algae in hydrogen carbonate indicator solution – known equally the 'algal balls' technique. Read the full protocol on using immobilsed algae to measure photosynthesis.

Using an IRGA – Uptake of CO2 tin be measured with the means of an IRGA (Infra-Red Gas Analyser) which can compare the CO2 concentration in gas passing into a bedroom surrounding a leaf/establish and the CO2 leaving the chamber.

Using a CO2 monitor – More simply, you could put a constitute in a plastic bag and monitor the CO2 concentration in the pocketbook using a CO2 monitor. Naturally, the soil and roots must Non be in the bag (as they respire). Alternatively, you lot could identify some Bicarbonate Indicator Solution in the pocketbook with the plant and picket the colour alter. This would best exist done with a reference colour chart to try to make the end-point less subjective. This could requite a comparison between several plants. There are difficulties with this method, as I'g sure yous tin can appreciate. The leaf area of the plants should be measured so you lot can compensate for plant size. Atmospheric air is only 400ppm CO2, so there is not much CO2 to monitor and the institute will presently run out of CO2 to gear up.

Measuring photosynthesis via the production of oxygen

Oxygen tin can be measured by counting bubbles evolved from pondweed, or by using the Audus apparatus to measure the amount of gas evolved over a menstruum of time. To practice this, place Cabomba pondweed in an upside downward syringe in a h2o bathroom connected to a capillary tube (yous can too use Elodea, but we observe Cabomba more than reliable). Put the weed in a solution of NaHCO3 solution. You tin can so investigate the amount of gas produced at different distances from a lamp. Read a full protocol on how to investigate photosynthesis using pondweed.

Measuring photosynthesis via the production of carbohydrates

There is a crude method where a disc is cut out of ane side of a leaf (using a cork borer against a rubber bung) and weighed after drying. Some days (or even weeks later), a disk is cut out of the other half of the leaf, dried and weighed. Increase in mass of the disc is an indication of the extra mass that has been stored in the leaf. This is very simple to practice and enables you to investigate plants growing in the wild. Still, yous can probably think of several inaccuracies in this method.

Measuring photosynthesis via the increase in dry mass

Dry mass is often monitored past the technique of 'serial harvests' where several plants are harvested, dried to constant weight and weighed – this is repeated over the elapsing of the experiment. If you harvest several plants and record how much mass they take accumulated you will accept an authentic measure of the surplus photosynthesis over and above the respiration that has taken identify. As with most methods, you demand several plants and then you have replicate measurements and you can notice an average and a standard departure if necessary.

Investigating the light-dependent reaction in photosynthesis

The charge per unit of decolourisation of DCPIP in the Hill Reaction is a measure of the rate of the light-requiring stages of photosynthesis

Source: https://www.saps.org.uk/teaching-resources/resources/157/measuring-the-rate-of-photosynthesis/

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