Cellular Respiration and Photosynthesis: Key Concepts and Processes (Chapters 7-8)

Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is the process by which cells convert biochemical energy from nutrients into ATP, releasing waste products. It involves a series of metabolic pathways that break down glucose and other molecules.

• ATP (Adenosine Triphosphate): The main energy currency of the cell.

• Redox (Reduction-Oxidation) Reactions: Chemical reactions involving the transfer of electrons between molecules.

• NADH and FADH2: Electron carriers that transport electrons to the electron transport chain.

• Electron Transport Chain (ETC): Series of protein complexes that transfer electrons and pump protons to generate ATP.

• Glycolysis: The breakdown of glucose into pyruvate, producing ATP and NADH.

• Pyruvate: The end product of glycolysis, which enters the mitochondria for further oxidation.

• Krebs Cycle (Citric Acid Cycle): A cycle of reactions that generates electron carriers and CO2 from acetyl-CoA.

• Oxidative Phosphorylation: The production of ATP using energy derived from the transfer of electrons in the ETC.

• Fermentation: An anaerobic process that allows glycolysis to continue in the absence of oxygen.

Equation for Cellular Respiration:

• $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Key Concepts:

• Cells specialize for particular functions, including energy production.

• Electron carriers (NADH, FADH2) are crucial for transferring electrons in metabolic pathways.

• The electron transport chain uses oxygen as the final electron acceptor.

• Fermentation occurs when oxygen is not available, producing less ATP.

Major Steps in Cellular Respiration

• Glycolysis: Occurs in the cytoplasm; breaks down glucose into pyruvate.

• Krebs Cycle: Occurs in the mitochondrial matrix; oxidizes acetyl-CoA to CO2 and generates NADH and FADH2.

• Electron Transport Chain: Occurs in the inner mitochondrial membrane; uses electrons from NADH and FADH2 to create a proton gradient for ATP synthesis.

Example: Muscle cells use fermentation during intense exercise when oxygen is limited, producing lactic acid.

Photosynthesis

Overview of Photosynthesis

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

• Chloroplast: The organelle where photosynthesis occurs.

• Thylakoid: Membranous structures within chloroplasts where light-dependent reactions take place.

• Stroma: The fluid-filled space surrounding thylakoids, where the Calvin cycle occurs.

• Light-dependent Reactions: Use light energy to produce ATP and NADPH.

• Light-independent Reactions (Calvin Cycle): Use ATP and NADPH to fix carbon dioxide into glucose.

• Photosystems I and II: Protein complexes that absorb light and transfer electrons.

• NADPH: Electron carrier produced in the light-dependent reactions.

Equation for Photosynthesis:

• $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

Key Concepts:

• Photosynthesis consists of two main stages: light-dependent and light-independent reactions.

• Photosystems I and II work together to transfer electrons and produce ATP and NADPH.

• The Calvin cycle uses ATP and NADPH to synthesize glucose from CO2.

• Chlorophyll is the main pigment that absorbs light energy.

Major Steps in Photosynthesis

• Light-dependent Reactions: Occur in the thylakoid membrane; produce ATP and NADPH.

• Calvin Cycle (Light-independent Reactions): Occur in the stroma; fix CO2 into organic molecules.

Example: In C3 plants, the Calvin cycle is the primary pathway for carbon fixation.

Comparison of Cellular Respiration and Photosynthesis

Key Differences and Complementary Roles

Cellular respiration and photosynthesis are complementary processes in the global carbon and energy cycles. Photosynthesis stores energy in glucose, while cellular respiration releases energy from glucose.

Process	Location	Reactants	Products	Main Purpose
Cellular Respiration	Mitochondria	Glucose, O2	CO2, H2O, ATP	Energy release
Photosynthesis	Chloroplast	CO2, H2O, Light	Glucose, O2	Energy storage

Sample Test Question Analysis

Electron Transport and Photosystem Function

Disruption of electron transport in photosynthesis can prevent ATP and NADPH formation, affecting the Calvin cycle and overall energy production. If NADP+ is unavailable, electrons cannot be accepted, halting photosystem I and the Calvin cycle.

• Example: If a bacterial toxin blocks electron transport in the thylakoid membrane, ATP and NADPH production would cease, and photosynthesis would be impaired.

Additional info: The notes reference the importance of electron acceptors in both cellular respiration (oxygen) and photosynthesis (NADP+), highlighting how disruptions can affect energy production.