Chapter 8 - Photosynthesis

1. ATP Components

• ATP consists of:

  • Ribose (a sugar)

  • Adenine (a nitrogenous base)

  • Three phosphate groups. These phosphates make ATP negatively charged.

2. Photosynthesis: Reactants and Products

• Reactants:

  • Water (H_2O)

  • Carbon dioxide (CO_2)

  • Sunlight energy

• Products:

  • Glucose (C6H12O6)

  • Oxygen (O_2)

• Equation:

  H2o+CO2+Light+C6H2O6+O2

• Photosynthesis uses light energy to convert water and carbon dioxide into glucose and oxygen. Water and carbon dioxide are the reactants/substrates, while glucose (sugar) and oxygen are the products.

3. Chloroplast Structure and Reactions

• Chloroplasts have double membranes, similar to mitochondria.

• Thylakoid Membrane:

  • An internal membrane within the chloroplast, formed by a phospholipid bilayer.

  • Location of the light-dependent reactions, including the electron transport chain (ETC).

  • Thylakoids are disk-shaped.

• Granum:

  • A stack of thylakoids.

• Stroma:

  • The space between the grana and the outer membrane of the chloroplast.

  • Location of the light-independent reactions, also known as the Calvin cycle (or carbon cycle).

4. Chlorophyll

• Found embedded in the thylakoid membrane, specifically within photosystems II and I.

• Chlorophyll molecules absorb light energy to initiate photosynthesis.

• They absorb most wavelengths of light, especially blue and red, but reflect green wavelengths, which is why plants appear green.

5. Light-Dependent Reactions

• Location: Thylakoid membrane

• Key Components:

  • Photosystem II (PSII)

  • Photosystem I (PSI)

  • ATP synthase

• Process:

  • Chlorophyll molecules in photosystems absorb light energy.

  • The energy initiates the electron transport chain (ETC).

• Molecules Used:

  • Light

  • Water (H_2O)

• Molecule Produced:

  • Oxygen (O_2) is produced as a byproduct.

  • ATP and NADPH are also generated, which are used in the Calvin cycle.

6. ATP Synthase

• A membrane protein found in both chloroplasts and mitochondria.

• In the thylakoid membrane (in chloroplasts), ATP synthase generates ATP via chemiosmosis.

• Chemiosmosis: Hydrogen ions (H^+) move from a high concentration to a low concentration through ATP synthase, providing the energy for ATP production.

7. Calvin Cycle (Light-Independent Reactions)

• Location: Stroma

• Key Enzyme: Rubisco

• Process:

  • ATP and NADPH (generated during the light-dependent reactions) are used to power the cycle.

  • Carbon dioxide (CO_2) is captured from the atmosphere by the enzyme Rubisco.

  • Carbon fixation occurs: Inorganic carbon from CO_2 is incorporated into an organic molecule.

  • The cycle produces a 3-carbon unit called glyceraldehyde-3-phosphate (G3P).

  • Two G3P molecules combine to form a 6-carbon glucose molecule (C6H{12}O_6).

• For every turn of the Calvin Cycle one G3P molecule is produced.

• Another cycle of Calvin is combined, finally, two G3P becomes a 6-carbon glucose

8. Photorespiration

• Occurs on hot days when plants close their stomata to conserve water.

• Closing stomata prevents CO2 from entering and O2 from exiting the leaf.

• Instead of using CO2 RuBisCO uses oxygen O2 in the Calvin cycle, which is an inefficient process, generating less sugar.

9. Comparison of C3, C4, and CAM Plants

• C3 Plants:

  • "Normal" plants where the light-dependent reactions and Calvin cycle occur in mesophyll cells.

  • RuBisCO directly fixes CO2

• C4 Plants (e.g., corn, sugarcane):

  • Light-dependent reactions occur as in C3 plants, but the Calvin cycle has two steps in different cells.

  • CO_2 is initially fixed in mesophyll cells and then transferred as an organic molecule to bundle sheath cells, where the actual Calvin cycle occurs to produce glucose.

• CAM Plants (e.g., cactus, succulents):

  • Close stomata during the day and open them at night to conserve water.

  • CO_2 is fixed into organic molecules during the night.

  • The Calvin cycle occurs during the daytime.

10. Photosynthesis Diagram and Cellular Respiration Equation

• Photosynthesis Equation:

  • H2O + CO2 + Light + C6H2O6 + O2

• Cellular Respiration Equation:

  • Note: The transcript does not include. Standard equation for cellular respiration should be included here.

  • C6H12O6 + O2 ———> CO2 + H2O + Energy (ATP) This equation shows how glucose and oxygen are converted into carbon dioxide, water, and energy, highlighting the relationship between photosynthesis and cellular respiration.

11. Differences Between Light-Dependent and Light-Independent Reactions

• Light-Dependent Reactions:

  • Require light.

  • Occur in the thylakoid membrane.

  • Use water H2O to produce oxygen O2 ATP, and NADPH.

• Light-Independent Reactions (Calvin Cycle):

  • Do not directly require light.

  • Occur in the stroma.

  • Use CO2, ATP, AND NADPH to produce glucose 6H{12}O6).

12. End Products of Light-Dependent Reactions

• ATP

• NADPH

• Oxygen (O_2)

13. Location of Light-Independent Reactions

• Stroma of the chloroplast.

14. Carbon Fixation

• The process by which inorganic carbon (from CO_2$$) is incorporated into organic molecules.

• Rubisco enzyme plays a key role in this process.

15. Chlorophyll Absorption Spectrum

• Chlorophyll absorbs most light in the blue and red wavelengths.

• Chlorophyll reflects (does not absorb) green wavelengths.

16. RuBisCo Enzyme Function

• In the Calvin cycle, RuBisCo takes carbon from carbon dioxide and puts it into an organic molecule, facilitating carbon fixation.

Additional Notes/Equations (From Last Page)

• Photosynthesis Summary:

  • Light + H2O ——→ O2

  • CO2 + ATP + NADPH ——→ Glucose

  • Overall Equation:

  • 6CO2 + 6H2O +LIGHT+C6H12O6 +6O2 This equation summarizes the entire process of photosynthesis, illustrating how carbon dioxide and water, in the presence of light energy, are transformed into glucose and oxygen.

  • Products: NADH, ETC, ATP

• Cellular Respiration Summary:

  • Glycolysis

  • Pyruvate

  • Krebs Cycle

  • ETC

  • Overall: C6H12O6+O2———>CO2+H20+ATP