1. Photosynthesis: An Overview
Formula of Photosynthesis
History
Light
Pigments
Photo Credit: ©Stone
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2. The Photosynthesis Equation
6CO2 + 6H2O C6H12O6 + 6O2
carbon dioxide + water sugars + oxygen
Photosynthesis is the process in which green plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates and oxygen.
The key cellular process identified with energy production is photosynthesis.
Light
Light
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3. Investigating Photosynthesis
Research into photosynthesis began centuries ago.
Scientists who made contributions to understanding Photosynthesis: van Helmont, Priestley, and Ingenhousz.
Van Helmont’s Experiment:
In the 1600s, van Helmont investigated plants growing by taking material out of the soil.
He determined & repotted the mass of a pot of dry soil and a small seedling then watered it regularly.
After five years, the seedling was a small tree gained 75 kg, but the soil’s mass was almost unchanged.
He concluded the gain in mass came from water because water was the only thing he had added.

4. Investigating Photosynthesis
van Helmont did not realize carbon dioxide ‘s role in photosynthesis, he still made a major contribution to understanding the mass of his tree.
In photosynthesis, the carbon in carbon dioxide is used to make sugars and other carbohydrates. (This happens in the Calvin Cycle & is known as Carbon Fixation.)
Van Helmont had only part of the story, but he made a major contribution to science.
Video 1 (The impact of CO2 on a plant.)
Isolated for 42 days in chambers of ambient and elevated CO2 concentrations, we periodically document the growth of cowpea plants (Vigna unguiculata) via time-lapse photography. (**The end of the video there is a political statement to try to convince un-educated people away from other affects of CO2.** An educated student is our best globally aware student!)
Video 2 (The impact of CO2 on a plant, Scientist walking us through how it is being done.)
The CO2 fertilization effect on trees and plants from increased levels of carbon dioxide.

5. Investigating Photosynthesis
Priestley’s Experiment
More than 100 years after van Helmont’s experiment, Joseph Priestley provided another insight into the process of photosynthesis.
He took a candle, placed a glass jar over it, and watched as the flame gradually died out.
He reasoned that the flame needed something in the air to keep it burning. That substance was oxygen.
He then placed a live sprig of mint under the jar and allowed a few days to pass: the candle re-lighted and remained light for a while.
The mint plant had produced a substance required for burning.
In other words, it had released oxygen.
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6. Investigating Photosynthesis
Jan Ingenhousz
Ingenhousz showed that the effect observed by Priestley only happened when the plant was exposed to light.
Both Priestley’s and Ingenhousz’s experiments showed that light is necessary for plants to produce oxygen.
In Summary:
The experiments performed by van Helmont, Priestley, and Ingenhousz led to more work by other scientists. All their working together brought us to this: in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen.
Video (Overview of all three scientists.)
Segment from the program Photosynthesis: Transforming Light to Life. To purchase this program please visit (**This is part of a video set that is up for purchase.)

7. The Photosynthesis Equation
Light energy
H2O
Light-Dependent Reactions (thylakoids) O2
ADP NADP+
ATP NADPH
Photosynthesis is a series of reactions that uses light energy from the sun to convert water and carbon dioxide into sugars and oxygen.
CO2 + H20
Sugar
Calvin Cycle (stroma)
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8. Tying it all together!
Nice PPT – (I’m still reviewing this, but check it out and let me know your thoughts! Cellular Respiration

9. Light and Pigments How do plants capture the energy of sunlight?
In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll.
Plants gather the sun's energy with light-absorbing molecules called pigments.
The main pigment in plants is chlorophyll.
There are two main types of chlorophyll:
chlorophyll a
chlorophyll b
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10. Light and Pigments
Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum.
100 80 60 40 20
Chlorophyll b
Estimated Absorption (%)
Chlorophyll a
Photosynthesis requires light and chlorophyll. In the graph above, notice how chlorophyll a absorbs light mostly in the blue-violet and red regions of the visible spectrum, whereas chlorophyll b absorbs light in the blue and red regions of the visible spectrum.
Wavelength (nm)
Wavelength (nm)
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11. Light and Pigments
Chlorophyll does not absorb light will in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green.
100 80 60 40 20
Chlorophyll b
Estimated Absorption (%)
Chlorophyll a
Photosynthesis requires light and chlorophyll. In the graph above, notice how chlorophyll a absorbs light mostly in the blue-violet and red regions of the visible spectrum, whereas chlorophyll b absorbs light in the blue and red regions of the visible spectrum.
Wavelength (nm)
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12. Light and Pigments
Light is a form of energy, so any compound that absorbs light also absorbs energy from that light.
When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons.
These high-energy electrons are what make photosynthesis work.
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13. In van Helmont's experiment, most of the added mass of the tree came from
soil and carbon dioxide.
water and carbon dioxide.
oxygen and carbon dioxide.
soil and oxygen.
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14. Plants use the sugars produced in photosynthesis to make
oxygen.
starches.
carbon dioxide.
protein.
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15. The raw materials required for plants to carry out photosynthesis are
carbon dioxide and oxygen.
oxygen and sugars.
carbon dioxide and water.
oxygen and water.
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16. The principal pigment in plants is
chloroplast.
chlorophyll.
carotene.
carbohydrate.
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17. The colors of light that are absorbed by chlorophylls are
green and yellow.
green, blue, and violet.
blue, violet, and red.
red and yellow.
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