Study sheet: Photosynthesis

📋 Course Outline

1. Photosynthesis Purpose and Equation
2. Chloroplast Structure and Organization
3. Calvin Cycle Carbon Fixation
4. Rubisco and Carbon Acceptance
5. Photosystems and Light Capture
6. Electron Flow and ATP Production
7. CAM and C4 Plant Consequences

📖 1. Photosynthesis Purpose and Equation

🔑 Key Concepts & Definitions

• Photosynthesis : The synthesis of sugars from CO2, H2O, and light, converting light energy into chemical energy.

📝 Essential Points

📐 Formula — The overall reaction of photosynthesis is $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$.

📌 The light reactions produce ATP and NADPH, whereas the light-independent reactions, called the Calvin cycle, use them to make sugar by fixing carbon.

💡 Memory Hook

Sunlight → chemical energy → sugar

📖 2. Chloroplast Structure and Organization

🔑 Key Concepts & Definitions

• Grana : Stacks of thylakoids within the chloroplast.
• Stroma : The fluid surrounding the grana in a chloroplast.

📝 Essential Points

• Photosynthesis takes place in the chloroplast, an organelle with two membranes.

💡 Memory Hook

Stacks of thylakoids floating like grana in the stroma

📖 3. Calvin Cycle Carbon Fixation

★ Must-know

• 🔄 The Calvin cycle proceeds through three phases:

  1. Fixation
  2. Reduction
  3. Regeneration

• During fixation, CO2 is used to make 3PG when RuBP accepts carbon.

• During reduction, 3PG is reduced to G3P.

Further detail

• During regeneration, RuMP is regenerated to RuBP, the CO2 acceptor used in fixation.

💡 Memory Hook

Fixation → reduction → regeneration

📖 4. Rubisco and Carbon Acceptance

🔑 Key Concepts & Definitions

• Rubisco : The key enzyme that fixes carbon by removing carbon from CO2 and connecting it to another molecule.

★ Must-know

• Rubisco has eight active sites and has ten times greater affinity for CO2 than for O2.

Further detail

• Rubisco is the most abundant enzyme on the planet and accounts for 10–50% of total leaf protein.

📌 O2 competes with CO2 for Rubisco binding sites, producing consequences for C4 and CAM plants.

💡 Memory Hook

Rubisco binds CO2 more readily than O2

📖 5. Photosystems and Light Capture

🔑 Key Concepts & Definitions

• Photosystem : A light-harvesting complex in which pigments direct energy to a reaction center containing two special chlorophyll a molecules and an electron acceptor.

★ Must-know

• Plants have two kinds of photosystems, Photosystem II and Photosystem I.

Further detail

• Chlorophyll a is the most abundant pigment in plants, and its long tail anchors it in a photosystem spanning the thylakoid membrane.

💡 Memory Hook

Pigments form an antenna funneling energy toward a reaction center

📖 6. Electron Flow and ATP Production

★ Must-know

• In the light reactions, light excites electrons, and electron transport establishes a proton gradient that ATP synthase uses to produce ATP.

• Photosystem II produces ATP, whereas Photosystem I produces NADPH for use in the Calvin cycle.

• After Photosystem II chlorophyll a gives up an electron, it takes replacement electrons from water by splitting the water molecule.

• The oxygen we breathe comes from the splitting of water during the light reactions.

Further detail

📌 In mitochondria, energy derived from glucose establishes the proton gradient, whereas in thylakoids, light energy excites electrons to establish the gradient.

💡 Memory Hook

Light excites electrons → proton gradient → ATP and NADPH

📖 7. CAM and C4 Plant Consequences

📝 Essential Points

• The competition between O2 and CO2 for Rubisco binding sites has interesting consequences for C4 and CAM plants.

📊 Synthesis Tables

Photosynthesis Reaction Stages

Stage	Main purpose	Key products or inputs
Light reactions	Convert light energy into chemical energy	ATP and NADPH; O2 comes from H2O
Calvin cycle	Fix carbon and make sugar	Uses CO2, ATP, and NADPH