Lesson Overview

1. Lesson Overview 8.2 Photosynthesis: An Overview

2. Light • Energy from the sun travels to Earth in the form of light. • Sunlight is a mixture of different wavelengths • visible spectrum- different wavelengths that we differentiate as different colors: red, orange, yellow, green, blue, indigo, and violet.

3. Pigments • pigments- light-absorbing molecules • A red apple appears red because the molecule of pigment in the apple’s skin absorbs blue light, not red. Thus, we see red. • Chlorophyll molecules absorb blue light & some red light. other colors reflected resulting in the green color of plants.

4. Pigments • Two types of chlorophyll in plants: • chlorophyll a & chlorophyll b, absorb light very well in the blue-violet and red regions of the visible spectrum, but not in the green region, as shown in the graph. • .

5. Pigments • Plants also contain carotenoids- red, orange, or yellow pigments, and include the familiar compound carotene, which gives carrots their color. • Carotenoids cannot transfer sunlight energy directly to the photosynthetic pathway, but must pass their absorbed energy to chlorophyll. For this reason, they are called accessory pigments.

6. Pigments • Most of the time chlorophyll overwhelms the other pigments- as temperatures drop, chlorophyll molecules break down and red and orange pigments appear. • In some trees, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves to turn this glucose into a red color. • The brown color of trees like oaks is made from wastes left in the leaves.

7. Chloroplasts • Photosynthesis takes place inside chloroplasts. • thylakoids- saclike photosynthetic membranes which are interconnected • Grana- stacks of thylakoids

8. Chloroplasts • Pigments are located in the thylakoid membranes. • Stroma- fluid portion outside of the thylakoids

9. Energy Collection • Light is a form of energy • Compounds that absorb light absorb energy • Chlorophyll absorbs visible light especially well. • When chlorophyll absorbs light, a large fraction of the light energy is transferred to electrons. These high-energy electrons make photosynthesis work.

10. High-Energy Electrons • NADP+(nicotinamide adenine dinucleotide phosphate) is a carrier molecule. • NADP+ accepts and holds two high-energy electrons, along with a hydrogen ion (H+). In this way, it is converted into NADPH. • The NADPH can then carry the high-energy electrons to chemical reactions elsewhere in the cell.

11. An Overview of Photosynthesis • Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen.

12. An Overview of Photosynthesis • Plants use sugars generated by photosynthesis to produce complex carbohydrates such as starches, and to provide energy for the synthesis of other compounds, including proteins and lipids.

13. Light-Dependent Reactions • Photosynthesis involves two sets of reactions. • Light-dependent reactions- require the direct involvement of light and light-absorbing pigments.

14. Light-Dependent Reactions • The light-dependent reactions use energy from sunlight to produce ATP and NADPH. • These reactions take place within the thylakoid membranes of the chloroplast.

15. Light-Dependent Reactions • Water is required as a source of electrons and hydrogen ions. • Oxygen is released as a byproduct.

16. Light-Independent Reactions • Plants absorb carbon dioxide from the atmosphere and complete the process of photosynthesis by producing sugars and other carbohydrates. • Light-independent reactions use ATP and NADPH molecules produced in the light-dependent reactions to produce high-energy sugars from carbon dioxide.

17. Light-Independent Reactions • No light is required to power the light-independent reactions. • The light-independent reactions take place in the stroma.