Photosynthesis and Cellular Respiration

Overview

Photosynthesis and cellular respiration are fundamental biological processes that allow organisms to convert energy for life. Photosynthesis transforms light energy into chemical energy, while cellular respiration releases energy from organic molecules. Understanding these processes is essential for connecting concepts across biology, including cell transport, energy transfer, and metabolism.

Photosynthesis

General Equation and Reactants/Products

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.

• General Equation:

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

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

Main Events in Photosynthesis

• 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 synthesize glucose from CO2.

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: CO2, 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

Pigments and Energy Capture

• Chlorophyll: The main pigment in plants that absorbs light energy, primarily in the blue and red wavelengths.

• Accessory pigments: Carotenoids and others help capture additional light energy.

ATP and NADPH in the Calvin Cycle

• ATP: Provides energy for the synthesis of glucose.

• NADPH: Provides reducing power (electrons) for the reduction of CO2 to glucose.

Structure of the Chloroplast

• Thylakoids: Membranous sacs where light reactions occur.

• Stroma: Fluid surrounding thylakoids; site of the Calvin Cycle.

• Granum: Stack of thylakoids.

Redox Reactions in Photosynthesis and Respiration

Definition and Application

• Redox Reaction: A chemical reaction involving the transfer of electrons between two substances.

• Photosynthesis: Water is oxidized (loses electrons), CO2 is reduced (gains electrons).

• Respiration: Glucose is oxidized, oxygen is reduced.

• Electron Donors/Acceptors: NADP+ (photosynthesis), NAD+ and FAD (respiration)

Cellular Respiration

General Equation and Reactants/Products

Cellular respiration is the process by which cells extract energy from glucose to produce 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 glucose breakdown; 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 per glucose

• Role: First step in cellular respiration; produces pyruvic acid

Citric Acid Cycle

• Location: Mitochondrial matrix

• Net ATP Produced: 2 ATP per glucose

• Role: Completes oxidation of glucose; produces NADH and FADH2

Oxidative Phosphorylation

• Location: Inner mitochondrial membrane

• Net ATP Produced: Up to 34 ATP per glucose

• Role: Uses NADH and FADH2 to drive ATP synthesis via the electron transport chain

Fermentation

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

• Purpose: Allows ATP production without oxygen

Pyruvic Acid

• Produced: During glycolysis

• Purpose: Entry point for citric acid cycle or fermentation

ATP Synthase and Electron Transport Chain

• ATP Synthase: Enzyme that synthesizes ATP using the H+ gradient

• Used in: Light-dependent reactions (photosynthesis) and oxidative phosphorylation (respiration)

• H+ Gradient: Drives ATP production; created by electron transport chain

Oxygen as Final Electron Acceptor

• Importance: Allows electron transport chain to function; prevents backup of electrons

• Result: Formation of water

NADH and Electron Transport

• NADH: Carries electrons to the electron transport chain

• "Dumping" Electrons: Essential for continued ATP production

ATP Production in Cellular Processes

• Processes: Glycolysis, citric acid cycle, oxidative phosphorylation, fermentation

Organisms Requiring Cellular Respiration

• All aerobic organisms: Animals, plants, fungi, many protists and bacteria

Phosphorylation

• Definition: Addition of a phosphate group to a molecule

• Energy Source: Energy from electron transport chain or light reactions

Comparison Table: Photosynthesis vs. Cellular Respiration

Key Activities and Applications

• Photosynthesis Exploration: Magic bead bracelet, algae beads, floating spinach disks, bloody chlorophyll

• Respiration Activities: Barf bag (fermentation), bromothymol blue, earthworms and spinach lab

Sample Concept Questions

• Recognize and write equations for photosynthesis and respiration

• Identify reactants and products for each process and phase

• Describe the main events and locations of photosynthesis and respiration

• Explain the importance of ATP, NADPH, and electron transport

• Compare fermentation types and their products

• Discuss the role of oxygen and H+ gradients in energy production

Additional Resources

• Dynamic Study Modules (Pearson)

• HHMI Photosynthesis (Canvas)

• Bozeman Science YouTube videos: Photosynthesis, Cellular Respiration

Additional info: Academic context and explanations have been expanded for clarity and completeness. This guide covers all major concepts listed in the review, suitable for exam preparation in General Biology.