General Biology Study Guide: Cell Structure, Metabolism, Respiration, Photosynthesis, and Cell Division

Chapter 5 – The Working Cell

Fluid-Mosaic Model of Membrane Structure

The Fluid-Mosaic Model describes the structure of cell membranes as a mosaic of diverse protein molecules embedded in a fluid bilayer of phospholipids. This model explains how membranes are selectively permeable and dynamic.

• Selectively permeable: Allows certain molecules to pass while restricting others.

• Examples: Water, oxygen, and carbon dioxide can diffuse freely; ions and large polar molecules require transport proteins.

Membrane Transport Mechanisms

Cells regulate the movement of substances across membranes using various transport mechanisms.

• Passive Transport: Movement of molecules down their concentration gradient without energy input.

• Facilitated Diffusion: Passive transport aided by membrane proteins.

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

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

Comparing Solutions: Tonicity

Tonicity describes the relative concentration of solutes in solutions separated by a membrane.

• Hypotonic: Lower solute concentration than the cell; water enters the cell.

• Isotonic: Equal solute concentration; no net water movement.

• Hypertonic: Higher solute concentration than the cell; water leaves the cell.

Kinetic and Potential Energy in Cells

Cells use energy in various forms to drive biological processes.

• Kinetic Energy: Energy of motion (e.g., movement of molecules).

• Potential Energy: Stored energy (e.g., chemical bonds in ATP).

• Exergonic Reactions: Release energy (e.g., cellular respiration).

• Endergonic Reactions: Require energy input (e.g., photosynthesis).

Enzymes and Catalysis

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• Active Site: Region on the enzyme where substrate binds.

• Substrate: The reactant acted upon by the enzyme.

• Product: The result of the enzymatic reaction.

• Factors Affecting Enzyme Activity: Temperature, pH, substrate concentration.

ATP and ADP

ATP (adenosine triphosphate) is the primary energy carrier in cells.

• ATP Hydrolysis: $ATP + H_2O \rightarrow ADP + P_i + \text{energy}$

• Role: Provides energy for cellular processes.

Chapter 6 – Cellular Respiration & Fermentation

Cellular Respiration Overview

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

• Breathing vs. Cellular Respiration: Breathing exchanges gases; cellular respiration uses oxygen to produce ATP.

• Redox Reactions: Transfer of electrons; oxidation (loss of electrons), reduction (gain of electrons).

Stages of Cellular Respiration

• Glycolysis: Glucose is split into two pyruvate molecules.

• Krebs Cycle (Citric Acid Cycle): Completes the breakdown of glucose, producing NADH and FADH2.

• Electron Transport Chain: Uses NADH and FADH2 to produce ATP via oxidative phosphorylation.

Summary Equation

The overall reaction for cellular respiration is:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$

• Reactants: Glucose, oxygen

• Products: Carbon dioxide, water, ATP

Electron Carriers

• NAD+ and FAD: Accept electrons during glycolysis and the Krebs cycle.

• ATP Synthase: Enzyme that synthesizes ATP during chemiosmosis.

Fermentation

Fermentation allows cells to produce ATP without oxygen.

• Lactic Acid Fermentation: Produces lactate in muscle cells.

• Alcoholic Fermentation: Produces ethanol and CO2 in yeast.

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.

• Photosynthesis vs. Cellular Respiration: Photosynthesis stores energy; respiration releases energy.

Summary Equation

The overall reaction for photosynthesis is:

$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$

• Reactants: Carbon dioxide, water, light energy

• Products: Glucose, oxygen

Stages of Photosynthesis

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

• Calvin Cycle: Occurs in the stroma; uses ATP and NADPH to synthesize glucose from CO2.

Leaf Structure and Pigments

• Stomata: Pores for gas exchange.

• Chlorophyll: Primary pigment absorbing light energy.

• Accessory Pigments: Carotenoids, xanthophylls (absorb additional wavelengths).

Photophosphorylation

• Non-cyclic Photophosphorylation: Produces ATP and NADPH.

• Cyclic Photophosphorylation: Produces only ATP.

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.

• Mitosis: Produces two genetically identical daughter cells.

• Meiosis: Produces four genetically unique gametes.

Chromosome Structure

• Chromatin: DNA and protein complex.

• Sister Chromatids: Identical copies joined at the centromere.

• Homologous Chromosomes: Chromosome pairs with the same genes.

Cell Cycle Phases

• Interphase: G1, S, G2 phases; cell growth and DNA replication.

• M Phase: Mitosis and cytokinesis.

Mitosis Stages

• Prophase: Chromosomes condense, spindle forms.

• Metaphase: Chromosomes align at the cell equator.

• Anaphase: Sister chromatids separate.

• Telophase: Nuclear envelope reforms.

Meiosis Stages

• Meiosis I: Homologous chromosomes separate.

• Meiosis II: Sister chromatids separate.

• Genetic Variation: Crossing over, independent assortment.

Non-disjunction

• Definition: Failure of chromosomes to separate properly during meiosis.

• Consequence: Can lead to genetic disorders (e.g., Down syndrome).

Comparison Table: Mitosis vs. Meiosis

Feature	Mitosis	Meiosis
Number of Divisions	1	2
Number of Daughter Cells	2	4
Genetic Identity	Identical	Unique
Function	Growth, repair	Sexual reproduction

Additional info: These notes expand on the original outline by providing definitions, examples, and context for each topic, ensuring a comprehensive review for exam preparation.