Cellular Respiration and Photosynthesis: Key Concepts and Processes

Cellular Respiration and Photosynthesis: Key Concepts and Processes

Overview

This study guide covers essential vocabulary, concepts, and processes related to cellular respiration and photosynthesis, as discussed in General Biology. It includes definitions, mechanisms, and applications relevant for exam preparation.

Key Terminology

Definitions and Examples

• Entropy: A measure of disorder or randomness in a system. In biological systems, entropy tends to increase as energy is transformed.

• Kinetic Energy: The energy of motion. Example: Movement of molecules during diffusion.

• Gibbs Free Energy (G): The energy available to do work in a system. $\Delta G = \Delta H - T\Delta S$

• Endergonic Reaction: A reaction that absorbs energy; $\Delta G > 0$.

• Exergonic Reaction: A reaction that releases energy; $\Delta G < 0$.

• ATP (Adenosine Triphosphate): The primary energy carrier in cells.

• AMP (Adenosine Monophosphate): A nucleotide involved in cellular energy transfer.

• GTP (Guanosine Triphosphate): Another energy-carrying molecule.

• Substrate: The molecule upon which an enzyme acts.

• Activation Energy: The minimum energy required to start a chemical reaction.

• Aerobic/Cellular Respiration: The process by which cells convert glucose and oxygen into ATP, CO2, and water.

• Citrate/Citric Acid Cycle: A series of reactions that generate energy through the oxidation of acetyl-CoA.

• Oxidative Phosphorylation: The production of ATP using energy derived from the electron transport chain.

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

• Glucose: A simple sugar and primary energy source for cells.

• Acetyl CoA: A molecule that enters the citric acid cycle.

• NAD+/NADH, FAD/FADH2: Electron carriers involved in cellular respiration.

• Chemiosmosis: The movement of ions across a semipermeable membrane, producing ATP.

• Intermembrane Space: The space between the inner and outer membranes of mitochondria.

• Lactic Acid Fermentation: Anaerobic process producing lactic acid and ATP.

• Chloroplast: Organelle where photosynthesis occurs.

• Stroma: The fluid-filled space inside a chloroplast.

• Thylakoid: Membranous structures within chloroplasts where light reactions occur.

• Photosystem I and II: Protein complexes involved in the light reactions of photosynthesis.

• Rubisco: The enzyme that catalyzes the fixation of CO2 in the Calvin cycle.

• Photon: A particle of light energy.

• NADPH: An electron carrier used in photosynthesis.

• Excited State: A higher energy state of an electron after absorbing a photon.

• Mesophyll Cells: Photosynthetic cells in leaves.

• Calvin Cycle: The set of reactions that fix carbon dioxide into sugars during photosynthesis.

• Endosymbiotic Theory: The theory that mitochondria and chloroplasts originated from free-living bacteria.

Cellular Respiration

Overview and Steps

Cellular respiration is the process by which cells harvest energy from organic molecules, primarily glucose, to produce ATP. It consists of glycolysis, the citric acid cycle, and oxidative phosphorylation.

• Glycolysis: Occurs in the cytoplasm; breaks down glucose into two pyruvate molecules, producing ATP and NADH.

• Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondrial matrix; oxidizes acetyl-CoA to CO2, generating NADH and FADH2.

• Oxidative Phosphorylation: Uses electron transport chain and chemiosmosis to produce ATP from NADH and FADH2.

• Fermentation: Occurs when oxygen is absent; includes lactic acid and alcoholic fermentation.

Key Equations

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

• Glycolysis: $\text{Glucose} + 2\text{NAD}^+ + 2\text{ADP} + 2\text{P}_i \rightarrow 2\text{Pyruvate} + 2\text{NADH} + 2\text{ATP} + 2\text{H}_2\text{O}$

Regulation and Alternative Pathways

• AMP and ATP: High AMP levels activate glycolysis; high ATP inhibits it.

• Alternative Pathways: When oxygen is limited, fermentation pathways are activated to regenerate NAD+.

Photosynthesis

Overview and Steps

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

• Light Reactions: Occur in the thylakoid membranes; convert light energy into ATP and NADPH.

• Calvin Cycle: Occurs in the stroma; uses ATP and NADPH to fix CO2 into sugars.

• Electron Transport: Involves movement of electrons from water to NADP+, producing NADPH and releasing O2.

Key Equations

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

Experimental Evidence

• Van Niel's Hypothesis: Oxygen released during photosynthesis comes from water, not CO2. Supported by experiments using isotopes of oxygen.

• Purple Sulfur Bacteria: Use H2S instead of H2O, releasing sulfur as a waste product.

Enzyme Function and Energy Coupling

Mechanisms and Applications

• Enzymes: Biological catalysts that lower activation energy and increase reaction rates.

• Energy Coupling: Endergonic reactions are driven by exergonic reactions, such as ATP hydrolysis.

• ATP Synthase: Enzyme that synthesizes ATP using the proton gradient across the mitochondrial or thylakoid membrane.

Table: Comparison of Cellular Respiration and Photosynthesis

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

Sample Questions and Explanations

Endergonic vs. Exergonic Reactions

• Endergonic Reaction Example: Synthesis of glutamine from glutamic acid and ammonia requires energy input.

• Energy Coupling: Endergonic reactions are often coupled to ATP hydrolysis, making the overall process exergonic.

Citric Acid Cycle and CO2 Release

• Two carbon atoms are released as CO2 in the citric acid cycle, but these are not the same carbon atoms added to the cycle from acetyl-CoA in each turn.

Regulation of Cellular Respiration

• AMP increases the rate of glycolysis by activating phosphofructokinase.

• Fermentation pathways are activated to regenerate NAD+ when oxygen is limited.

Photosynthesis: Source of Oxygen

• Oxygen released during photosynthesis originates from water, not CO2, as shown by isotope labeling experiments.

Electron Transport in Photosynthesis

• Electron transport between photosystem II and I is used to pump protons into the thylakoid space, creating a gradient for ATP synthesis via chemiosmosis.

Additional info:

• Some terms and processes were expanded for clarity and completeness.

• Experimental details and regulatory mechanisms were inferred from standard biology curriculum.