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Lecture 3

BIOL 1000 Lecture Notes - Lecture 3: Chlorophyll, Photon, Chemical EquationExam

Course Code
BIOL 1000
Nicole Nivillac

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Effect of Green Light vs White Light on Photosynthetic Rate of Aquatic Plant Cabomba
Shiyanuka Raveendrakumar
Section B 05
Manvir Virdi

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The photosynthetic rate measured by the cumulative oxygen production per gram
overtime of the aquatic plant Cabomba caroliniana under white light will be greater in
comparison to the aquatic plant under green light. Photosynthesis in plants occur in their
chloroplasts, specifically in the thylakoid membrane. The thylakoid membrane contains
specialized molecules called pigments that proficiently absorb a specific wavelength of visible
light because of their conjugated system of alternating carbon double and single bonds (Wilson et
al. 2016). Light travels in variable wavelengths and when it encounters a pigment, dependent on
the wavelength the pigment will either reflect or transmit or absorb the photon (Wilson et al.
2016). Only when the energy of a photon is absorbed by a pigment molecule the plant can use the
energy to drive the process of photosynthesis. Hence external factors, one being different
coloured light affect the rate of photosynthesis because pigments absorb light at specific
wavelengths (Vaz et al. 2012). The pigments found in chloroplasts are chlorophyll and
carotenoids. Chlorophyll a and b can strongly absorb red and blue light (Vaz et al. 2012). The
absorption of green light is very little, it is usually reflected from the pigment which is why most
plants are green in colour and so photons of this wavelength is not used as energy for
photosynthesis. White light is a mixture of all the wavelengths in visible light, so when all
wavelengths are absorbed by chlorophyll a and b, more energy is being absorbed and
photosynthesis will occur at a faster rate. The balanced chemical equation of photosynthesis can
be represented as: 6 H2O + 6 CO2 6 O2 + C6H12O6. Through this equation it is shown that the
rate of photosynthesis can be measured by either the intake of carbon dioxide or the production of
oxygen. The aquatic plant will be under both treatments (white and green light) in the closed
manometric system in which the cumulative oxygen production will recorded and analyzed to
prove which colour of light will result in the greater photosynthetic rate.

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The results show that the aquatic plant has a greater photosynthetic rate (mL O2/g/hour)
when it was under white light in comparison to being under green light. The cumulative oxygen
production (mL O2) was recorded in intervals of 0.03 hours over a time period of 0.27 hours
(Table 1,2). The slope (mL O2/hour) was the line of best fit calculated in reference to each test
tube and trial. In both white and green light, the slopes are positive showing an accumulation of
oxygen overtime but white light demonstrated this with great extent.
The experimental tubes that were under white light had photosynthetic rates ranging from
a minimum of 0.168 mL O2/g/hour to a maximum of 0.344 mL O2/g/hour (Table 1). Whereas the
experimental tubes under green light ranged from a minimum of 0.034 mL O2/g/hour to a
maximum of 0.057 mL O2/g/hour (Table 2). The aquatic plant under either white or green light
both resulted in a positive correlation in all three trials ensuring that photons of different
wavelengths are still absorbed but at different rates (Table 1, 2). The slope of the oxygen
production relative to white light in all three trials ranged from 0.681 mL O2/hour to 1.402 mL
O2/hour (Table 1). The slope of the oxygen production relative to green light in all three trials
ranged from 0.1395 mL O2/hour to 0.2285 mL O2/hour (Table 2). The mean of the photosynthetic
rate for white light is 0.243 mL O2/g/hour whereas for green light is 0.045 mL O2/g/hour which
means that the photosynthetic rate of the aquatic plant under white light is ~5.4 times higher than
when it was under green light (Figure 3).
All experimental tubes contained ~4g of the aquatic plant Cabomba caroliniana, and this
small sample is an accurate representation of its whole population because the error bars validate
this assumption (Figure 3). Control tubes were in the same conditions as experimental tubes but
did not contain the plant and were used to ensure that there were no other influences that may
have affected the photosynthetic rates (mL O2/g/hour). Although the control tubes under white
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