Measuring Photosynthesis: Leaf Disk Assay

[@Tiagomed96]

Can you use filters to change the wavelength of the light reaching the leaf disks? Then I can setup an experiment with my students to exemplify which wavelengths are most optimal for photosyntehsis.

[@LabXchange]

Using colored filters to change the wavelength of light reaching the leaf disks is an effective experimental setup for testing which wavelengths are most optimal for photosynthesis. Be sure to keep all other variables constant such as watts of the light bulbs, distance of the light source to the leaf disks, angle of the light source to the leaf disks, and translucency of filters for example. As a bonus, this experimental setup is nicely aligned to the AP Biology standards!

[@kristashahmooradian2732]

Hi i did a similar experiment in class and we used purple light, white light and no light. Im confused which light should be the most efficient. My experiment showed all the spinach leaves going up with purple light and none with white light. I think there could have been an error with the white light but is purple light more efficient than white light? in my hypothesis i assumed purple light would be most efficient but now I am not sure given some research says white light and others say purple light is most efficient.

[@JORGEPATRICIOORTEGAVALENCIA]

Excellent, thanks.

[@hannanhassan149]

Hello! Great video by the way😊 I was wondering whether I could use temperature as my independent variable instead of light, is that possible? Thank you!

[@LabXchange]

Yes, a leaf disk assay can be used to measure the effect temperature has on rate of photosynthesis!

[@alexisyu8946]

Also if I were to use leaves with red parts, why shouldn’t I cut leaf discs there?

[@LabXchange]

While you could use red portions of the leaves to cut the leaf discs, it is not recommended as the chlorophyll composition may differ from the green parts of the leaf and therefore, this would introduce another extraneous variable into the experiment.

[@nonixbelargo7414]

How many leaf disks do i need?

[@yoshakodagoda7866]

5

[@LabXchange]

We recommend about 20 leaf disks per trial.

[@yoshakodagoda7866]

@@LabXchange oh our teacher told 5

[@1nabee]

Can I use malabar nightshade for this experiment?

[@LabXchange]

Malabar spinach can be used for this experiment. We recommend using green shades and leaves that are not too waxy on the surface as the waxy cuticle can make it difficult to extract the gasses from the leaf disks.

[@Soo.hannah]

Why we are creating vaccum?

[@LabXchange]

A vacuum is necessary to extract the gases from the leaves. As the plant photosynthesizes, the gas oxygen will be produced within the leaves which will cause the leaf disks to float. Therefore, we are able to visually measure photosynthesis as the amount of floating leaf disks per minute. If we did not extract the gases from the leaves through the use of a vacuum, we would not be able to track oxygen production as a measure of photosynthesis.

[@Soo.hannah]

@LabXchange thankyou.

[@thiagohenrique9200]

Awesome!

[@anitadas3368]

Can we perform this expt. In sun light

[@LabXchange]

It is likely not feasible to perform this experimental set-up in direct sunlight and obtain reliable results due to the fluctuations in light intensity or amount of sunlight at different times of the day. To obtain consistent results we recommend using a controlled light source (same wattage on all light bulbs) and ensuring all other variables are also controlled (distance of the light source to the beaker containing the leaf disks, same type of plant, same amount of bicarbonate etc).

[@iPad-un2mu]

what would the leaves happen if it didnt vacuum well?

[@LabXchange]

If the vacuum doesn't work the first time, you can try again with the same leaves. However, after a few tries, the leaves would likely be damaged and we recommend starting with new disks. Adding soap is also an important step for breaking through the waxy cuticle of the plant in order to extract the oxygen.

[@alexisyu8946]

Why can’t we cut the leaves at the big veins?

[@LabXchange]

The structure of the large veins makes it much more challenging to extract gasses via the vacuum mechanism rather than the flatter parts of the leaf. As the plant photosynthesizes, the gas oxygen will be produced within the leaves which will cause the leaf disks to float. Therefore, we are able to visually measure photosynthesis as the amount of floating leaf disks per minute. If we did not extract the gases from the leaves through the use of a vacuum, we would not be able to track oxygen production as a measure of photosynthesis.

[@alexisyu8946]

But why is it harder extract gasses in areas with large veins?

[@LabXchange]

@@alexisyu8946 Large veins are structured to tunnel gasses and nutrients throughout the leaf and therefore are not as flat as the rest of the leaf. The structure of the large veins makes it much more challenging to extract gasses via the vacuum mechanism rather than the flatter parts of the leaf. Thus, leaf disks cut from veins will typically float. Remember that to visually measure photosynthesis we need to first sink the leaf disks by extracting gasses via the vacuum method and then use the amount of floating leaf disks per minute as a measure of photosynthesis.