Unit 3 – AOS 2: Photosynthesis & Cellular Respiration

Biochemical Pathway

Series of enzyme-catalysed reactions where the product of one reaction is the substrate for the next.

Enzyme Role in Pathways

Catalyse each step, lowering activation energy.

Coenzyme Role in Pathways

Assist enzymes by carrying energy, electrons, or protons.

ATP

Energy carrier molecule used in cells.

NADP⁺/NADPH

Electron and proton carrier in photosynthesis.

NAD⁺/NADH

Electron carrier in cellular respiration.

FAD/FADH₂

Electron carrier in cellular respiration.

Photosynthesis Overall Equation

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

Photosynthesis Location

Chloroplasts.

Light-Dependent Stage Location

Thylakoid membranes.

Light-Dependent Stage Inputs

H₂O, ADP + Pi, NADP⁺.

Light-Dependent Stage Outputs

O₂, ATP, NADPH.

Light-Independent Stage Location

Stroma.

Light-Independent Stage Inputs

CO₂, ATP, NADPH.

Light-Independent Stage Outputs

Glucose, ADP + Pi, NADP⁺.

Rubisco

Enzyme that catalyses carbon fixation in Calvin cycle.

Rubisco Inefficiency

Can bind O₂ instead of CO₂, causing photorespiration.

Photorespiration

Process where O₂ binds Rubisco, wasting ATP and producing no glucose.

Photorespiration Favoured By

High temperatures, low CO₂, high O₂ (stomata closed).

C₃ Photosynthesis

Standard photosynthesis pathway, occurs in most plants.

C₄ Photosynthesis

Spatial separation of steps, adapted for hot, humid environments.

C₄ Mesophyll

PEP carboxylase fixes CO₂ into 4C compound.

C₄ Bundle Sheath

CO₂ released near Rubisco, increasing concentration.

CAM Photosynthesis

Temporal separation of steps, adapted for hot, arid environments.

CAM Night

Stomata open, CO₂ fixed into malate.

CAM Day

Stomata closed, malate releases CO₂ for Calvin cycle.

Light Intensity Effect on Photosynthesis

Increases rate until another factor becomes limiting.

CO₂ Concentration Effect on Photosynthesis

Increases rate until saturation point.

Temperature Effect on Photosynthesis

Rate rises to optimum

Water Availability Effect on Photosynthesis

Low water causes stomata closure, reducing CO₂ intake.

Light Wavelength Effect on Photosynthesis

Most efficient under red and blue light, least under green light.

CRISPR in Photosynthesis

Modify Rubisco to prefer CO₂ over O₂.

CRISPR Photosynthetic Traits

Engineer C₃ plants with C₄ or CAM traits.

CRISPR Stress Tolerance

Improve heat, drought, or frost tolerance.

Aerobic Respiration Overall Equation

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP.

Aerobic Respiration Location

Cytosol and mitochondria.

Glycolysis Location

Cytosol.

Glycolysis Inputs

Glucose, ADP + Pi, NAD⁺.

Glycolysis Outputs

2 pyruvate, 2 ATP (net), 2 NADH.

Krebs Cycle Location

Mitochondrial matrix.

Krebs Cycle Inputs

Acetyl-CoA, ADP + Pi, NAD⁺, FAD.

Krebs Cycle Outputs

CO₂, 2 ATP, NADH, FADH₂.

Electron Transport Chain Location

Cristae (inner mitochondrial membrane).

Electron Transport Chain Inputs

NADH, FADH₂, O₂, ADP + Pi.

Electron Transport Chain Outputs

H₂O, ~26–28 ATP, NAD⁺, FAD.

Anaerobic Respiration Role

Occurs without O₂ to regenerate NAD⁺ for glycolysis.

Lactic Acid Fermentation Location

Cytosol (animals).

Lactic Acid Fermentation Inputs

Pyruvate, NADH.

Lactic Acid Fermentation Outputs

Lactic acid, NAD⁺.

Alcoholic Fermentation Location

Cytosol (yeast).

Alcoholic Fermentation Inputs

Pyruvate, NADH.

Alcoholic Fermentation Outputs

Ethanol, CO₂, NAD⁺.

Glucose Availability Effect on Respiration

More glucose increases rate until limiting factor reached.

Oxygen Availability Effect on Respiration

Required for ETC

Temperature Effect on Respiration

Rate rises to optimum

Mitochondria Cristae

Inner membrane folds, site of ETC.

Mitochondria Matrix

Fluid interior, site of Krebs cycle.

Bioethanol Production Step 1

Hydrolysis – enzymes break biomass into glucose.

Bioethanol Production Step 2

Fermentation – yeast ferments glucose to ethanol + CO₂ (anaerobic).

Bioethanol Production Step 3

Distillation – ethanol purified for use as fuel.