1. Photosynthesis

2. How is energy being obtained by the organisms in this picture?

3. Autotrophs & Heterotrophs (Review)  Plants are able to use light energy from the sun to produce food. - Autotrophs  Organisms that obtain energy from the foods they eat. - Heterotrophs

4. Photosynthesis  Definition:  Photosynthesis is the process by which light energy is converted to chemical energy in form of glucose.

5. Energy  Energy is the ability to do work and there’s always work to be done by the cell

6. First Law of Thermodynamics  Energy cannot be created or destroyed—it can only be changed in form. Energy is changed from potential energy to kinetic energy (the energy of motion) Light energy is changed to chemical energy

7. Jan Van Helmont’s Experiment-1600s  Question: When a seedling with a mass of only a few grams grows into a tree with a mass of several tons, where does the tree’s increase in mass come from? From the soil? The air? The water?

8. Jan Van Helmont’s Experiment  Hypothesis: Since a plant’s roots are in the soil, perhaps the tree is eating the soil and therefore, its’ mass comes from the soil. He imagined tiny faces on the ends of roots “eating” the soil.

9. Jan Van Helmont’s Experiment  Procedure: Van Helmont carefully found the mass of a pot of dry soil and a small seedling.  He planted the seedling in the pot of soil, watering it regularly for 5 years.

10. Jan Van Helmont’s Experiment  Results: At the end of 5 years, the seedling had gained 75 kilograms.  The soil and the pot had only decreased a few grams.

11. Jan Van Helmont’s Experiment  Van Helmont’s Conclusion: He concluded that most of the mass of the tree must have come from the water because that was the only thing that was added to the pot. Trees are made of water??????

12. Van Helmont was incorrect!  Van Helmont’s experiment accounts for the hydrate or water portion of the carbohydrate produced by photosynthesis. But where does the carbon of the carbo portion come from? Glucose—the most common and important carbohydrate/sugar made by plants in photosynthesis

13. The Rest of the Story that Van Helmont didn’t know: CO 2 !  Although Van Helmont did not realize it, carbon dioxide in the air made a major contribution to the mass of his tree. It is the carbon in CO 2 that is used to make carbohydrates. Carbon Dioxide

14. Joseph Priestley’s Experiment-1780  Priestly took a candle, placed a glass jar over it, and watched as the flame gradually died out.  Something in the air was necessary to keep the candle burning.  Today we call that substance oxygen.

15. Plants Produce Oxygen  Priestley than found out that if he put a sprig of mint under the jar and allowed a few days to pass, the candle could be re-lighted and would remain lighted longer.  The plant produced the substance needed for the candle to burn.  Later it was shown that this would only occur if the plant was placed in the light.

16. Requirements for Photosynthesis  Photosynthesis requires:  Carbon dioxide  Water  Light  Pigments such as chlorophyll to absorb the light energy

17. Formula For Photosynthesis:  6 CO 2 + 6 H 2 O + Sunlight → C 6 H 12 O 6 + 6 O 2  Carbon Dioxide + Water + Light→ Glucose + Oxygen

18. Sunlight  Nearly all organisms on Earth depend on the sun for energy.  Sunlight contains wavelengths of energy that can be absorbed by plants.

19. Electromagnetic Spectrum  Energy exists in different wavelengths.  Shorter wavelengths have more energy

20. Why are leaves green?  Leaves contain the pigment chlorophyll.  This pigment is green because it absorbs all other colors of light except green.  It reflects green light.

21. Pigments Absorb Light Energy  The process of photosynthesis begins when light is absorbed by pigments in the plant cell.  The most important pigment is chlorophyll-a green pigment. Chlorophyll

22. Energy-Storing Compounds  Light energy that is absorbed by chlorophyll is transferred to ATP molecules.

23. Photosynthesis: The Light and Dark Reactions  Photosynthesis occurs in 2 sets of reactions:  Light Reactions-trap sunlight energy and use it to make ATP (The “photo” part of photosynthesis)  Dark Reactions-use energy from ATP plus CO 2 and H 2 O to build glucose. (the “synthesis” part of photosynthesis).

24. Glucose

25. Chloroplast  Photosynthesis takes place in the chloroplast.  Light energy is trapped by chlorophyll molecules embedded in the membranes of the chloroplast. Draw and label all parts- color the thylakoid membranes green!

26. Summary of Dark Reactions  Also called the Light- Independent Reactions.  In these reactions (called the Calvin Cycle), CO 2 is used to build glucose.

27. Overview of Photosynthesis  In summary, light energy is changed to chemical energy that is stored in a molecule of glucose.  Plants and almost all other organisms use glucose to provide them with energy for cellular work.