Ch. 8 Sec. 2

1. Ch. 8 Sec. 2 Photosynthesis: An Overview

2. Review • The key cellular process identified with energy production is photosynthesis. • 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.

3. I. Investigating Photosynthesis A. Jan Van Helmont’s Experiment (1600’s) • Planted a seedling in a pot and watered it regularly a. After five years, the seedling was a small tree and had gained 75 kg b. Soil’s mass was almost unchanged

4. 2. Concluded that the gain in mass came from water 3. Accounts for the “hydrate,” or water, portion of the carbohydrate produced by photosynthesis

5. B. Joseph Priestley’s Experiment (1700’s) • Priestley took a candle, placed a glass jar over it, and watched as the flame gradually died out 2. Priestley then placed a live sprig of mint under the jar and allowed a few days to pass • He found that the candle could be relit and would remain lit for a while • The mint plant had produced released oxygen

6. C. Jan Ingenhousz (Late 1700’s) • Showed that Priestley’s results occurred only when the plant was exposed to light

7. The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists who finally discovered that, in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen

8. II. The Photosynthesis Equation The equation for photosynthesis is: 6CO2 + 6H2O C6H12O6 + 6O2 carbon dioxide + water sugars + oxygen Light Light

9. Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.Plants release the oxygen and use the sugars to produce starches (complex carbohydrates)

10. Light energy O2 Light-Dependent Reactions (thylakoids) H2O ADPNADP+ ATPNADPH CO2+H20 Sugar Calvin Cycle (stroma) Fig. 8-4 page 206 Photosynthesis is a series of reactions that uses light energy from the sun to convert water and carbon dioxide into sugars and oxygen.

11. III. Light and Pigments A. In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll

12. B. Sunlight 1. Mixture of different wavelengths of light 2. Gathered by pigments (light absorbing molecules) a. Two main types of chlorophyll: chlorophyll a chlorophyll b

13. Page 207 Fig. 8-5 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.

14. 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.

15. C. Chlorophyll absorbs light 1. Energy is transferred to electrons in the chlorophyll 2. The energy levels of these electrons is raised These high-energy electrons are what make photosynthesis work

16. 8–2 Photosynthesis: An Overview The equation for photosynthesis is: 6CO2 + 6H2O C6H12O6 + 6O2 carbon dioxide + water sugars + oxygen Research into photosynthesis began centuries ago. The experiments of van Helmont, Priestly, and Ingenhousz led to work by other scientists. These scientists found that in the presence of light, plants change carbon dioxide and water into carbohydrates and give off oxygen. This process is called photosynthesis. Light Light

17. Photosynthesis uses the energy of sunlight to convert waterand carbon dioxide into high-energy sugars and oxygen. Plantsget the carbon dioxide needed for photosynthesis from the airor from the water in which they grow. Plants use the sugars produced during photosynthesis to make complex carbohydrates such as starches.

18. Photosynthesis also requires light and chlorophyll. Plants gather the sun’s energy with light-absorbing molecules called pigments. The main pigment in plants is chlorophyll. A compound that absorbs light also absorbs the light’s energy. When chlorophyll absorbs sunlight, much of the light energy is sent directly to electrons in the chlorophyll molecules. This raises the energy levels of the electrons.

19. The visible spectrum is made up of wavelengths of light youcan see. This spectrum contains all the colors. Chlorophyll absorbslight in the blue-violet and red regions of the visible spectrumwell. Chlorophyll does not absorb light in the green region well.Plants look green because their leaves reflect this green light.