8.1 Photosynthesis uses light energy to make food

1. 8.1 Photosynthesis uses light energy to make food

2. I. The Structure of Chloroplasts A. Photosynthesis takes place in the chloroplast B. Chloroplasts contain compounds called pigments that give leaves their color (chlorophyll). C. Leaves contain the most chloroplasts. (fig. 8-2) D. Stoma are tiny pores that allow carbon dioxide to enter and oxygen to leave the plant cell.

3. Structure of chloroplast E. Veins (xylem) carry CO2 and H2O from the plants roots to the leaves and deliver (phloem) organic compounds to other parts of the plant. F. The inner membrane of a chloroplast encloses a thick fluid called stroma. G. Suspended in the stroma are many disk shaped sacs called thylakoids which are arranged in stacks called grana. H. These stacks organize the series of reactions that make up photosynthesis.

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6. Transparency 8A-5 1. In which part of a leaf are most chloroplasts located? Cells containing chloroplasts are concentrated in the mesophyll.

7. Transparency 8A-6 2. How is a thylakoid related to a granum? A granum is a stack of thylakoids within a chloroplast.

8. II. Overview of Photosynthesis A. In cellular respiration, electrons “fall” from glucose to O2 to release energy. B. In photosynthesis, electrons from water are boosted “uphill” (potential) by the energy of sunlight. C. These excited electrons, along with carbon dioxide and hydrogen ions to produce C6H12O6 molecules D. Photosynthesis occurs in two main steps: Light and Calvin Cycle (Dark Reaction).

9. III. The Light Reactions A. Light Reactions convert the energy in sunlight to chemical energy. B. Chloroplasts use captured light energy to remove electrons from H2O, splitting it into oxygen and hydrogen ions. C. The electrons and hydrogen ions are used to make NADPH, which is an electron carrier. D. Chloroplasts also use the captured light energy to generate ATP. E. The overall result of the light reactions is the conversion of light energy to chemical energy stored in NADPH and ATP

10. IV. The Calvin Cycle • Calvin Cycle makes sugar from the atoms in carbon dioxide plus the hydrogen ions and high energy electrons carried in NADP B. The ATP made in the light reactions provides the energy to make sugar. C. The Calvin cycle is sometimes referred to as the “light-independent reactions” because it does not require light energy to begin. See Overview fig. 8-4

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14. Transparency 8B-4 1. For each of the two main stages of photosynthesis, identify the inputs. Inputs of the light reactions are light and water, and ADP, P, and NADP+ from the Calvin cycle. Inputs of the Calvin cycle are CO2, and ATP and NADPH from the light reactions.

15. Transparency 8B-5 2. Identify the outputs for each stage, and tell how each is used. Outputs of the light reactions are oxygen, which is released to the atmosphere, and ATP and NADPH, which go into the Calvin cycle. Outputs of the Calvin cycle are ADP, P, and NADP+, which go into the light reactions, and sugar, which is used by the plant.

16. 8.2 The light reaction convert light energy to chemical energy

17. I. Light Energy and Pigments A. Light is a form of electromagnetic energy that travels in waves and the distance between adjacent waves is called a wavelength. B. The range of wavelengths is called the electromagnetic spectrum. (fig. 8-5 C. Visible light only makes up a small portion of the electromagnetic spectrum.

18. II. Pigments and Color A. A substances color is due to chemical compounds called pigments. B. Waves of light shining on a material can be absorbed, transmitted or reflected C. Leaves absorb blue-violet and red-orange light very well but either reflect or transmit green light and that is why leaves look green.

19. III. Identifying Chloroplast Pigments • Using a technique called chromatography different pigments in a leaf can be observed. (fig. 88-7) • Chlorophyll a absorbs mainly blue-violet light while chlorophyll b absorbs mainly red light.

20. IV. Harvesting Light Energy A. Within the thykaloid membrane, chlorophyll and other molecules are arranged in clusters called photosystems. (fig. 8-8) B. Each photosystem contains a few hundred pigment molecules, including chlorophyll a and b as well as carotenoids. C. Each time a pigment molecule absorbs light energy electrons are raised from a “ground state” to an “excited state”.

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26. Transparency 8C-6 1. What does a photosystem consist of? clusters of chlorophyll and other molecules embedded in the thylakoid membrane

27. Transparency 8C-7 2. How are electrons in chlorophyll and other pigment molecules affected by light striking the photosystem? Electrons become “excited”—that is, they gain energy when the photosystem absorbs sunlight.

28. Harvesting light energy D. This electron “jumps” from molecule to molecule until it arrives at the reaction center. E. The reaction center consists of chlorophyll a and a primary electron carrier. Other teams of molecules are also used to make ATP and NADPH

29. V. Chemical Products of Light Reactions A. 2 photosystems are involved in the light reactions. B. The first photosystem traps light energy and transfers the light-excited electrons to the electron transport chain, this can be referred to as the “water splitting photosystem”. (figs.8-10,11)

30. Light reaction products C. The second photosystem can be thought of as the “NADPH- producing photosystem” This system produces NADPH by transferring excited electrons and hydrogen ions to NAD+ D. The light reactions convert light energy to the chemical energy of ATP and NADPH, NO SUGAR has been produced, which is the job of the CALVIN CYCLE.

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36. Transparency 8D-6 1. What happens to water molecules in the first photosystem? Water molecules are split into H+ ions, electrons, and oxygen.

37. Transparency 8D-7 2. What is the overall result of the light reactions? Energy in sunlight is converted to chemical energy in the form of ATP and NADPH.

38. 8.3 Calvin Cycle makes sugar from carbon dioxide

39. I. A Trip Around the Calvin Cycle A. The Calvin Cycle is the sugar factory within the chloroplasts. B. The starting material for the Calvin cycle is regenerated each time the process occurs, the starting material is called RuBP, (a sugar with five carbons).

40. Calvin cycle C. The inputs for the Calvin cycle are ATP, CO2 and NADPH. (from light reaction and air thus no light) D. The cycles output is an energy rich sugar molecule called G3P which is not quite glucose but is used as the raw material to make glucose as the plant needs to.

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48. Transparency 8D-8 1. In what forms does carbon enter and exit the Calvin cycle? Carbon enters the cycle in the form of three CO2 molecules and exits as one molecule of G3P.

49. Transparency 8D-9 2. What is the source of the energy-rich ATP and NADPH molecules used in the cycle? ATP and NADPH are produced during the light reactions.

50. II. Summary of Photosynthesis • The equation (unbalanced) for photosynthesis is Carbon Dioxide + Water --> Glucose + Oxygen CO2 + H2O --> C6H12O6 + O2 B. The lightreactions take place in the thylakoidmembranes and convert light energy into chemical energy in the form of ATP and NADPH. (fig. 8-14) C. The light reactions use the reactantH2O and release the productO2.