Photosynthesis and Cellular Respiration

Overview

Photosynthesis and cellular respiration are fundamental biological processes that allow organisms to convert energy for cellular activities. Photosynthesis occurs in plants, algae, and some bacteria, while cellular respiration is performed by nearly all living organisms to extract energy from organic molecules.

Photosynthesis

General Equation and Reactants/Products

Photosynthesis is the process by which autotrophs convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.

• General Equation:

• Reactants: Carbon dioxide (CO2), water (H2O), light energy

• Products: Glucose (C6H12O6), oxygen (O2)

Main Events in Photosynthesis

Photosynthesis consists of two main stages:

• Light-dependent reactions: Occur in the thylakoid membranes; convert light energy to chemical energy (ATP and NADPH).

• Calvin Cycle (light-independent reactions): Occur in the stroma; use ATP and NADPH to fix carbon dioxide into glucose.

Light-dependent Reactions

• Reactants: Water, light energy, ADP, NADP+

• Products: Oxygen, ATP, NADPH

• Location: Thylakoid membranes of the chloroplast

• Oxygen Production: Oxygen is produced when water is split (photolysis) during the light reactions.

Calvin Cycle

• Reactants: Carbon dioxide, ATP, NADPH

• Products: Glucose (or G3P), ADP, NADP+

• Sugar Produced: Glyceraldehyde-3-phosphate (G3P), which is used to form glucose

• Location: Stroma of the chloroplast

Chloroplast Structure

• Thylakoids: Site of light-dependent reactions

• Stroma: Site of Calvin Cycle

• Chlorophyll: Main pigment that absorbs light energy; located in thylakoid membranes

Role of ATP and NADPH

• ATP and NADPH produced in the light reactions are used in the Calvin Cycle to drive the synthesis of glucose from CO2.

Redox Reactions in Photosynthesis

• Definition: Redox reactions involve the transfer of electrons between molecules.

• In photosynthesis, water is oxidized (loses electrons) and CO2 is reduced (gains electrons).

• Electron Donor: Water

• Electron Acceptor: NADP+ (becomes NADPH)

Cellular Respiration

General Equation and Reactants/Products

Cellular respiration is the process by which cells extract energy from glucose, producing carbon dioxide, water, and ATP.

• General Equation:

• Reactants: Glucose, oxygen

• Products: Carbon dioxide, water, ATP

Main Events in Cellular Respiration

• Glycolysis: Occurs in the cytoplasm; breaks glucose into pyruvate; produces 2 net ATP

• Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondrial matrix; completes breakdown of glucose; produces 2 ATP

• Oxidative Phosphorylation (Electron Transport Chain): Occurs in the inner mitochondrial membrane; produces up to 34 ATP

Glycolysis

• Location: Cytoplasm

• Aerobic or Anaerobic: Anaerobic (does not require oxygen)

• Net ATP Produced: 2 ATP

• Product: Pyruvic acid (pyruvate)

Aerobic Respiration

• Location: Mitochondria

• Includes: Citric Acid Cycle and Oxidative Phosphorylation

Fermentation

• Types: Alcoholic fermentation (produces ethanol and CO2), lactic acid fermentation (produces lactic acid)

• Occurs: When oxygen is not available

ATP Production in Cellular Respiration

• Glycolysis: 2 ATP

• Citric Acid Cycle: 2 ATP

• Oxidative Phosphorylation: Up to 34 ATP

• Total: Up to 38 ATP per glucose molecule

Electron Transport Chain (ETC) and ATP Synthase

• ETC: Series of protein complexes in the inner mitochondrial membrane; electrons from NADH and FADH2 are transferred, creating a proton (H+) gradient

• ATP Synthase: Enzyme that uses the H+ gradient to synthesize ATP from ADP and inorganic phosphate

• Oxygen: Final electron acceptor; essential for ETC function

Redox Reactions in Cellular Respiration

• Glucose is oxidized (loses electrons), oxygen is reduced (gains electrons)

• NADH and FADH2 carry electrons to the ETC

Importance of H+ Gradient

• Drives ATP synthesis via ATP synthase

• Maintained by electron transport and pumping of protons across the membrane

Phosphorylation

• Definition: Addition of a phosphate group to a molecule

• Energy Source: Energy from redox reactions and H+ gradient

Organisms and Cellular Respiration

• All organisms (plants, animals, fungi, protists, and most bacteria) require cellular respiration to produce ATP

Comparison Table: Photosynthesis vs. Cellular Respiration

Key Terms and Definitions

• ATP (Adenosine Triphosphate): Main energy currency of the cell

• NADPH: Electron carrier used in photosynthesis

• NADH: Electron carrier used in cellular respiration

• Redox Reaction: Chemical reaction involving electron transfer

• Fermentation: Anaerobic process producing ATP without oxygen

• Phosphorylation: Addition of a phosphate group to a molecule

• Electron Transport Chain: Series of proteins transferring electrons and creating a proton gradient

Examples and Applications

• Magic bead bracelet, algae beads, floating spinach disks, bloody chlorophyll: Demonstrate photosynthesis and pigment function

• Barf Bag Activity, Bromothymol Blue, Earthworms and Spinach Lab: Explore fermentation and cellular respiration

• Mystery of the Seven Deaths Case Study: Illustrates the importance of electron transport and NADH in respiration

Additional Info

• Connecting cell transport and ETC: The movement of ions (especially H+) across membranes is essential for ATP production.

• Hydrolysis and ATP phosphorylation: ATP is produced by adding a phosphate group to ADP, often powered by energy released from hydrolysis reactions.