General Biology Study Guide: The Working Cell, Cellular Respiration & Fermentation, Photosynthesis, and Cell Cycle & Division

Chapter 5 – The Working Cell

Membrane Structure and Function

The cell membrane is a dynamic structure that regulates the movement of substances into and out of the cell, maintaining homeostasis and enabling communication.

• Fluid-Mosaic Model: Describes the membrane as a mosaic of proteins floating in or on the fluid lipid bilayer. The membrane is selectively permeable, allowing certain molecules to pass while restricting others.

• Selective Permeability: The ability of the membrane to allow some substances to cross more easily than others.

• Examples: Small nonpolar molecules (e.g., O2, CO2) can diffuse freely; ions and large polar molecules require transport proteins.

Transport Mechanisms

Cells use various mechanisms to move substances across membranes, either passively or actively.

• Passive Transport: Movement of substances down their concentration gradient without energy input. Includes diffusion and facilitated diffusion.

• Active Transport: Movement of substances against their concentration gradient, requiring energy (usually ATP).

• Facilitated Diffusion: Passive movement of molecules via transport proteins.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Concentration Gradient: Difference in concentration of a substance across a space.

• Types of Solutions: Isotonic (equal solute), hypotonic (lower solute outside), hypertonic (higher solute outside).

Energy Transformation in Cells

Cells transform energy to perform work, following the laws of thermodynamics.

• Kinetic vs. Potential Energy: Kinetic energy is energy of motion; potential energy is stored energy.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Second Law of Thermodynamics: Energy transformations increase entropy (disorder).

Metabolic Pathways and Enzymes

Metabolism involves anabolic (building) and catabolic (breaking down) pathways, regulated by enzymes.

• Anabolic Pathways: Synthesize complex molecules from simpler ones (e.g., protein synthesis).

• Catabolic Pathways: Break down complex molecules into simpler ones (e.g., cellular respiration).

• ATP & ADP: ATP (adenosine triphosphate) is the main energy currency; ADP (adenosine diphosphate) is formed when ATP loses a phosphate.

• Enzyme Activity: Enzymes lower activation energy, increasing reaction rates. Factors affecting activity include temperature, pH, and substrate concentration.

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

Equation for ATP hydrolysis:

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Chapter 6 – Cellular Respiration & Fermentation

Overview of Cellular Respiration

Cellular respiration is the process by which cells extract energy from organic molecules, primarily glucose, to produce ATP.

• Breathing vs. Cellular Respiration: Breathing is gas exchange; cellular respiration is the breakdown of glucose to produce ATP.

• Redox Reactions: Oxidation is loss of electrons; reduction is gain of electrons. These reactions transfer energy in cells.

• Electron Carriers: NAD+ and FAD are molecules that carry electrons during cellular respiration.

• Stages of Cellular Respiration: Glycolysis, Krebs Cycle (Citric Acid Cycle), Electron Transport Chain.

• Summary Equation:

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

• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP to form ATP.

• Oxidative Phosphorylation: ATP production using energy from electrons transferred to oxygen.

• Chemiosmosis: Movement of ions across a membrane to generate ATP.

• ATP Synthase: Enzyme that synthesizes ATP from ADP and inorganic phosphate.

Chapter 7 – Photosynthesis

Photosynthesis Overview

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

• Sites of Photosynthesis: Occurs in chloroplasts, mainly in leaf cells.

• Photosynthesis Equation:

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

• Reactants: CO2, H2O, light energy

• Products: Glucose, O2

• Light Reactions: Convert light energy to chemical energy (ATP, NADPH).

• Calvin Cycle: Uses ATP and NADPH to synthesize glucose from CO2.

• Chlorophyll: Main pigment absorbing light energy.

• Electromagnetic Spectrum: Range of wavelengths of light; visible light is used in photosynthesis.

• Photophosphorylation: ATP production during light reactions.

• Comparison: ATP synthesis in photosynthesis vs. cellular respiration.

Chapter 8 – Cell Cycle & Division

Cell Division in Prokaryotes and Eukaryotes

Cell division is essential for growth, repair, and reproduction. Prokaryotes divide by binary fission; eukaryotes by mitosis and meiosis.

• Binary Fission: Prokaryotic cell division producing two identical cells.

• Mitosis: Eukaryotic cell division producing genetically identical daughter cells.

• Meiosis: Eukaryotic cell division producing gametes with half the chromosome number.

• Chromosome Terms: DNA, chromatin, sister chromatids, centromere, duplicated chromosome.

• Cell Cycle Phases: Interphase (G1, S, G2), M phase (mitosis, cytokinesis).

• Mitosis Stages: Prophase, metaphase, anaphase, telophase.

• Meiosis Stages: Meiosis I and II, each with prophase, metaphase, anaphase, telophase.

• Genetic Variation: Crossing over, independent assortment, random fertilization.

• Nondisjunction: Error in meiosis leading to abnormal chromosome numbers.

Process	Purpose	Result
Mitosis	Growth, repair, asexual reproduction	2 identical diploid cells
Meiosis	Sexual reproduction	4 non-identical haploid cells

Example: Human somatic cells undergo mitosis; gametes (sperm and egg) are produced by meiosis.

Additional info: Key figures referenced in the notes (e.g., 5.1, 6.6, 7.2, 8.4) correspond to textbook diagrams illustrating these processes. Students should review these figures for visual understanding.