1. Photosynthesis: An Overview 8-2

2. The key cellular process identified with energy production is photosynthesis The key cellular process identified with energy production is photosynthesis During photosynthesis, plants convert H 2 O and CO 2 into high-energy sugars and O 2 During photosynthesis, plants convert H 2 O and CO 2 into high-energy sugars and O 2 The investigations of many scientists have contributed to the current understanding of the process of photosynthesis The investigations of many scientists have contributed to the current understanding of the process of photosynthesis

3. Jan van Helmont’s Experiment Belgian physician, 1600’s Belgian physician, 1600’s Wondered where the mass of a plant came from - water? Soil? Air? Wondered where the mass of a plant came from - water? Soil? Air? Devised an experiment to determine if plants grew by taking material out of soil Devised an experiment to determine if plants grew by taking material out of soil

4. Determined mass of a pot of dry soil and a small seedling Determined mass of a pot of dry soil and a small seedling Planted seedling in pot of soil Planted seedling in pot of soil Watered plant regularly Watered plant regularly At the end of 5 years, the seedling, now a tree, had gained 75 kg At the end of 5 years, the seedling, now a tree, had gained 75 kg

5. The mass of the soil had remained virtually unchanged The mass of the soil had remained virtually unchanged He concluded that most of the gain in mass had come from water He concluded that most of the gain in mass had come from water Van Helmont’s experiment accounts for the “hydrate” portion of the carbohydrate produced during photosynthesis Van Helmont’s experiment accounts for the “hydrate” portion of the carbohydrate produced during photosynthesis

6. Van Helmont did not realize that carbon dioxide in the air also made a major contribution to the mass of the tree Van Helmont did not realize that carbon dioxide in the air also made a major contribution to the mass of the tree Despite this shortcoming, van Helmont made a major contribution to science Despite this shortcoming, van Helmont made a major contribution to science

7. Joseph Priestley’s Experiment English minister, 100 years after van Helmont English minister, 100 years after van Helmont Took a candle and placed a glass jar over it, and watched the flame gradually go out Took a candle and placed a glass jar over it, and watched the flame gradually go out He reasoned that something in the air was needed to keep flame burning He reasoned that something in the air was needed to keep flame burning

8. When that substance was used up, the flame would go out When that substance was used up, the flame would go out Substance was oxygen Substance was oxygen Repeated the experiment by placing a sprig of live mint under jar for a few days, and then adding a lit candle Repeated the experiment by placing a sprig of live mint under jar for a few days, and then adding a lit candle

9. The candle remained lit for a while The candle remained lit for a while The mint produced the substance required to keep the candle burning The mint produced the substance required to keep the candle burning It released oxygen It released oxygen

10. Jan Ingenhousz Dutch scientist Dutch scientist Showed that the effect observed by Priestley happened only when the plant was exposed to light Showed that the effect observed by Priestley happened only when the plant was exposed to light The results of both Priestley and Ingenhousz showed light is necessary for photosynthesis The results of both Priestley and Ingenhousz showed light is necessary for photosynthesis

11. The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists that showed that The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists that showed that In the presence of light, plants transform CO 2 and H 2 O into carbohydrates and O 2 In the presence of light, plants transform CO 2 and H 2 O into carbohydrates and O 2

12. The Photosynthesis Equation light light 6CO 2 + 6H 2 O ---> 6O 2 + C 6 H 12 O 6 6CO 2 + 6H 2 O ---> 6O 2 + C 6 H 12 O 6 Carbon dioxide + water --> oxygen + sugars Carbon dioxide + water --> oxygen + sugars Plants use sugars to make complex carbs. like starches Plants use sugars to make complex carbs. like starches

13. Light and Pigments In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll Energy from the sun travels as light Energy from the sun travels as light It appears as “white” light, but is a mixture of different wavelengths of light It appears as “white” light, but is a mixture of different wavelengths of light

14. Many wavelengths are visible to your eyes - you see them as different colors Many wavelengths are visible to your eyes - you see them as different colors Plants gather the sun’s energy with light absorbing molecules called pigments Plants gather the sun’s energy with light absorbing molecules called pigments Principal pigment is chlorophyll Principal pigment is chlorophyll Two types chlorophyll a and chlorophyll b Two types chlorophyll a and chlorophyll b Absorbs light very well in blue-violet and red regions of visible spectrum Absorbs light very well in blue-violet and red regions of visible spectrum

15. Chlorophyll does not absorb light well in the green region of the spectrum Chlorophyll does not absorb light well in the green region of the spectrum Green light is reflected - why plants look green Green light is reflected - why plants look green Plants also contain red and orange pigments that absorb other wavelengths of light Plants also contain red and orange pigments that absorb other wavelengths of light

16. Because light is a form of energy, any compound that absorbs light also absorbs the energy from that light Because light is a form of energy, any compound that absorbs light also absorbs the energy from that light When chlorophyll absorbs light, that energy is transferred to electrons in chlorophyll When chlorophyll absorbs light, that energy is transferred to electrons in chlorophyll Raises energy levels of electrons Raises energy levels of electrons High-energy electrons make photosynthesis work High-energy electrons make photosynthesis work