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The Reactions of Photosynthesis 8-3

Explore the intricate processes of photosynthesis within chloroplasts, from light-dependent reactions in thylakoids to the Calvin Cycle in the stroma. Learn how factors like water, temperature, and light intensity affect this vital plant function.

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The Reactions of Photosynthesis 8-3

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  1. The Reactions of Photosynthesis8-3 Flora Biology 1004

  2. Inside the Chloroplast • Chloroplast contains thylakoid (sac-like membranes) • Thylakoids are arranged in stacks called “grana” • Area outside the thylakoids is called the “stroma” • Proteins in thylakoids organize chlorophyll/pigments into clusters known as photosystems • These are the light collection centers of the chloroplast.

  3. Chloroplast

  4. 2 Types of Reactions • Light Dependent • Light Independent • A.K.A. – Calvin Cycle

  5. Light Dependent • Occurs in the thylakoids • Requires light • Converts ADP and NADP to ATP and NADPH • Water is split to form: • Oxygen gas (released) • 2 Hydrogen Ions • 2 electrons

  6. Light Dependent Process • 1 – pigments in photosystem II absorb light • 2 – Energy in light is absorbed by electrons. • New electrons are provided by the splitting of water • 3 – High energy electrons move through ETC from photosystem II to photosystem I • 4 – Energy carried by electrons is used to pump Hydrogen ions from stroma to inner thylakoid • 5 – Pigments in Photosystem I use energy from light to re-energize electrons, NADP picks up these electrons and becomes NADPH.

  7. Light Dependent Cont. • As more NADPH is made, more hydrogen is pumped into the inner membrane. • Outside becomes negatively charged, inside is positively charged – difference in charges provides energy to turn ADP into ATP (used in calvin cycle) • Hydrogen ions pass through membranes using ATP synthase – a protein

  8. Calvin Cycle/Light Independent • Takes place in the stroma • During this process plants use the energy in ATP and NADPH (from dependent reactions) to build glucose • Does not require light • 6 CO2 molecules produce ONE, six-carbon sugar • Main product of Calvin Cycle is SUGAR

  9. Process of Calvin Cycle • Six carbon dioxide molecules enter the cycle • Each molecule combines with six 5-carbon molecules producing 12 3-carbon molecules. • Each molecule then absorbs energy • 2 of molecules leave the cycle using them to produce sugars, lipids, amino acids, etc. • The remaining 10 molecules are converted back into 5-carbon molecules and then combine with 6 new carbon dioxide molecules to begin the next cycle.

  10. The use of sugars made • The plant uses the sugars to meet its energy needs and to build more complex macromolecules such as cellulose that it needs for growth and development.

  11. Factors Affecting Photosynthesis Rate • Shortage of Water • Temperature • Intensity of Light • Increase light intensity results in increase in the rate of photosynthesis.

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