Photosynthesis

1. Photosynthesis

2. Life in the Sun • Light is central to the life of a plant. • Photosynthesis is the most important chemical process on Earth. • Autotrophs are the producers of the biosphere. • Plants, some protists, and some bacteria are photosynthetic autotrophs. • They produce the O2 for the atmosphere. • They provide food consumed by virtually all organisms. • Autotrophs convert light energy into chemical signals.

3. Life in the Sun • Light can influence the architecture of a plant. • Plants that get adequate light are often bushy with deep green leaves. • Without enough light, plants become tall and spindly with small pale leaves. • Too much sun can damage a plant.

4. Photosynthesis Overview • Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide. Carbondioxide Water Glucose Oxygengas PHOTOSYNTHESIS

5. Photosynthesis- The Cell Structure • In most plants, photosynthesis occurs primarily in the chloroplasts of the leaf cells. • A chloroplast contains: • Stroma (a fluid) • Grana (stacks of thylakoids) • Thylakoids (contain chlorophyll) • Chlorophyll (green pigment that captures certain wavelengths of light for energy)

6. Photosynthesis- The Process sunlight • CO2 + H2O  C6H12O6 + O2 • Two linked sets of reactions: • Light Reactions • Convert light energy into chemical energy using water • Produce O2 • Calvin Cycle • Use chemical energy from light reaction • Produce sugar molecules from CO2

7. Phase 1 – Light Reactions • Take place in the thylakoids which are stacked into grana • Light-absorbing pigments (chlorophyll) are found in the thylakoids.

8. Phase 1 – Light ReactionsThylakoids GOAL: CHANGE LIGHT ENERGY INTO CHEMICAL ENERGY • Absorption of light is the first step in photosynthesis. • Pigments in the thylakoid capture light energy. The light energy causes: • Electrons to become excited in Photosystem II. • A water molecule to split. • An electron to be released for use later. • H+ to be released for use later. • O2 to be released as a waste product.

9. Phase 1 – Light ReactionsThylakoids • Following the electrons: • Excited electrons move to an electron-acceptor molecule in the thylakoid membrane. • The acceptor molecule moves the electrons along a series of carriers to Photosystem I. • Photosystem I moves the electrons to a protein, which transfers the electrons to a final carrier: NADP+ • An energy-storing molecule NADPH is formed. • Another energy-storing molecule ATP is also formed.

10. Phase 2 – The Calvin CycleStroma GOAL: USE CHEMICAL ENERGY TO PRODUCE SUGAR • Carbon fixation: 6 CO2 molecules combine with 6 5-carbon compounds to form 12 3-carbon molecules called 3-phosphoglycerate (3-PGA). • Chemical energy from ATP and NADPH is transferred to the 3-PGA molecules to form 12 high energy molecules called glyceraldehyde 3-phosphates (G3P). • Two G3P molecules leave the cycle to be used for sugar production. • Finally, an enzyme called rubisco converts the remaining 10 G3P into 5-carbon molecules to combine with future CO2 to continue the cycle.

11. Phase 2 – The Calvin CycleStroma

12. An overview of photosynthesis H2O CO2 Chloroplast Light NADP+ ADP+ P LIGHTREACTIONS(in grana) CALVINCYCLE(in stroma) ATP Electrons NADPH O2 Sugar