Photosynthesis and Cellular Respiration - Detailed Notes

Photosynthesis

• What it is: Using sunlight to make energy (chemical).

  • Sunlight is captured by chlorophyll.

• What it uses: Carbon dioxide and water.

  • Carbon dioxide comes from the air.

  • Water is absorbed from the soil by the plant's roots.

• What it makes: Carbohydrates (like sugar) and oxygen.

  • Carbohydrates (glucose) are used for the plant's energy and growth.

  • Oxygen is released into the air.

• Equation: 6CO2 + 6H2O \xrightarrow{\text{Light}} C6H{12}O6 + 6O2

  • Carbon dioxide + Water -> Glucose + Oxygen

• Needs Chlorophyll

Chloroplast

• Photosynthesis happens here.

• Structure and Parts:

  • Leaf: The organ where photosynthesis primarily occurs.

  • Mesophyll: Tissue in the interior of the leaf where chloroplasts are concentrated.

  • Mesophyll Cell: A cell within the mesophyll containing chloroplasts.

  • Chloroplast: The organelle where photosynthesis takes place.

  • Outer Membrane: The outermost membrane of the chloroplast.

  • Inner Membrane: The inner membrane of the chloroplast that encloses the stroma.

  • Intermembrane Space: The space between the outer and inner membranes.

  • Stroma: The fluid-filled space within the chloroplast surrounding the grana, where the Calvin cycle occurs.

  • Granum: A stack of thylakoids.

  • Thylakoid: A flattened sac-like membrane structure inside the chloroplast used to convert light energy to chemical energy.

  • Thylakoid Membrane: The membrane enclosing the thylakoid lumen, where the light-dependent reactions of photosynthesis occur.

  • Thylakoid Space (Lumen): The space inside the thylakoid where H+ ions accumulate during the light-dependent reactions.

  • Vein: Vascular tissue that transports water and nutrients to the leaf and carries away photosynthetic products.

  • Stomata: Pores on the leaf surface that allow for gas exchange (CO2 intake and O2 release).

Light

• Plants use visible light (380-750 nm).

• Shorter light waves = more energy.

• Longer light waves = less energy.

Chlorophyll

• Has a head that grabs light.

• Magnesium in the center.

• Tail likes proteins in membranes.

• Electrons get excited by light.

• Doesn't mix well with water.

Light Energy

• Light turns into an excited electron.

• This moves H+ into thylakoid space.

• H+ makes ATP (energy).

• ATP helps make glucose in the Calvin Cycle.

Light Reactions

• Electrons in chlorophyll get excited.

• Oxygen is released.

• H+ makes ATP.

• NADP⁺ turns into NADPH.

• Electrons move through proteins.

• Water molecules are split.

• Happens in the thylakoid membrane.

• Creates power for the Calvin cycle.

• A used electron is replaced.

• Order:

  • Photosystem II → Electron transport chain → ATP formation → Photosystem I → NADPH formation

  The electron transport chain (ETC) in photosynthesis involves several key components:

  • Photosystem II (PSII): Captures light energy and initiates the electron transport chain by oxidizing water, releasing oxygen, and passing electrons to plastoquinone (Pq).

  • Plastocyanin (PC): A mobile electron carrier that transfers electrons from the cytochrome complex to Photosystem I (PSI).

  • Photosystem I (PSI): Absorbs light energy and uses it to re-energize the electrons, passing them to ferredoxin (Fd).

  • Ferredoxin (Fd): Transfers electrons to NADP+ reductase.

  • NADP+ Reductase: Catalyzes the transfer of electrons from Fd to NADP+, forming NADPH.

  • ATP Synthase: Uses the proton gradient created by the cytochrome complex to synthesize ATP from ADP and inorganic phosphate (Pi) through chemiosmosis.

Calvin Cycle

• CO2 molecules enter one by one.

• CO2 joins with RuBP (helped by Rubisco) to make 3-phosphoglycerate.

• 3-phosphoglycerate turns into G3P using ATP and NADPH.

• RuBP is made again to keep the cycle going.

• G3P (sugar) is made as output, which can be used to form glucose and other organic compounds.

Light vs. Calvin

• Light Reaction: chlorophyll, thylakoid membrane, ATP synthase, ETC, photon.

• Calvin Cycle: stroma, RUBISCO, carbon fixation, glucose, carbon dioxide.

Photosynthesis vs. Cellular Respiration

• Photosynthesis: 6CO2 + 6H2O \xrightarrow{\text{solar energy}} C6H{12}O6 + 6O2

• Cellular Respiration: C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O + \text{ATP} + \text{heat}

Cellular Respiration

• What it is: Breaking down nutrients to make energy (ATP).

  • Nutrients (glucose) are broken down.

  • ATP is the energy currency for the cell.

Overview

• Glycolysis, Krebs Cycle, and Electron Transport Chain.

Glycolysis

• Happens in the cytosol.

• Glucose + 2 ATP + 2 NAD+ -> 2 Pyruvate + 4 ATP + 2 NADH

Krebs Cycle

• Happens in the mitochondrial matrix.

• Pyruvate + NAD+ + Coenzyme A -> Acetyl CoA + NADH + H+ + CO2

• Acetyl CoA -> 3 NADH + H+ + 1 FADH2 + 2 CO2