Untitled Flashcards Set

🌞 1. Light-Dependent Reactions (LDR)

Location: Thylakoid membranes of chloroplasts (mainly in grana)
Purpose: Convert light energy into chemical energy (ATP and NADPH)

🔬 Key Steps in AQA Detail:

1. Photoionisation of Chlorophyll

   • Light hits Photosystem II (PSII).

   • Electrons in chlorophyll are excited and leave the molecule.

   • Chlorophyll becomes oxidised.

2. Photolysis of Water

   • Electrons lost by PSII are replaced by splitting water:
     2H2O→4H++4e−+O22H₂O → 4H⁺ + 4e⁻ + O₂2H2​O→4H++4e−+O2​

   • Oxygen is released, protons (H⁺) used in ATP/NADPH formation.

3. Electron Transport Chain

   • Excited electrons move down the ETC from PSII to Photosystem I (PSI).

   • Energy from electrons is used to pump H⁺ ions into the thylakoid lumen, creating a proton gradient.

4. Chemiosmosis

   • Protons move down the concentration gradient through ATP synthase.

   • This drives phosphorylation of ADP → ATP (photophosphorylation).

5. Reduction of NADP⁺

   • Electrons reach PSI, get re-excited, and passed to NADP⁺, along with a proton, forming NADPH:
     NADP++2e−+H+→NADPHNADP⁺ + 2e⁻ + H⁺ → NADPHNADP++2e−+H+→NADPH

🔑 Products:

• ATP (energy for Calvin Cycle)

• NADPH (reducing power for Calvin Cycle)

• Oxygen (by-product)

🌿 2. Light-Independent Reactions (LIR / Calvin Cycle)

Location: Stroma of chloroplasts
Purpose: Use ATP and NADPH to fix carbon dioxide and make organic molecules like glucose.

🔬 AQA Step-by-Step:

1. Carbon Fixation

   • CO₂ (from air) combines with RuBP (5C).

   • Catalysed by the enzyme Rubisco.

   • Forms 2 molecules of GP (glycerate-3-phosphate, 3C).

2. Reduction of GP

   • Each GP molecule is reduced to TP (triose phosphate).

   • Requires:

     • 2 ATP (energy from LDR)

     • 2 NADPH (reducing power from LDR)

   • NADPH is oxidised to NADP⁺.

3. Regeneration of RuBP

   • 5 out of every 6 TP molecules are used to regenerate RuBP.

   • This process uses ATP.

   • The cycle must turn 6 times to make 1 glucose molecule (needs 6 CO₂).

🔁 Summary:

• Carbon dioxide + ATP + NADPH → Glucose (eventually)

• Regenerates RuBP to keep the cycle going.

🔢 For 1 glucose:

• 6 CO₂

• 18 ATP

• 12 NADPH

🌾 3. Nitrogen Cycle (AQA detail)

Purpose: Convert atmospheric N₂ into forms usable by plants and return it back.

🌀 Main Processes:

1. Nitrogen Fixation

   • Atmospheric N₂ → Ammonia (NH₃) or Ammonium ions (NH₄⁺).

   • By nitrogen-fixing bacteria (e.g., Rhizobium in root nodules).

   • Also occurs abiotically via lightning or Haber process.

2. Ammonification

   • Saprobionts (decomposers) break down organic nitrogen (e.g., proteins, urea) from dead organisms and waste.

   • Produce ammonia, which forms NH₄⁺ in soil.

3. Nitrification

   • Aerobic process.

   • Ammonium → nitrite (NO₂⁻) by Nitrosomonas.

   • Nitrite → nitrate (NO₃⁻) by Nitrobacter.

   • Nitrates are absorbed by plant roots via active transport.

4. Assimilation

   • Plants use nitrates to make amino acids and proteins.

   • Animals eat plants and assimilate nitrogen compounds into their own tissues.

5. Denitrification

   • Anaerobic bacteria convert NO₃⁻ → N₂ gas, returning nitrogen to the atmosphere.

   • Happens in waterlogged, low-oxygen soils.

📋 Summary Table: