General Biology Study Notes: Foundations, Chemistry, Cells, and Metabolism

Introduction to Biology

Shared Characteristics of Living Systems

• Reproduction: Ability to produce offspring.

• Homeostasis: Regulation of internal environment to maintain stability.

• Evolution & Adaptation: Populations change over time through natural selection.

• Cells: Basic unit of life; all organisms are composed of cells.

• DNA: Genetic material that stores information.

• Energy Metabolism: Obtain and use energy for growth and maintenance.

• Response to Stimuli: Ability to sense and react to environmental changes.

Levels of Biological Organization

• Biosphere → Ecosystem → Communities → Populations → Organisms → Organ Systems → Tissues → Cells → Organelles → Molecules

Theory of Evolution by Natural Selection

• Natural selection explains how evolution occurs: individuals with advantageous traits survive and reproduce more successfully.

• Populations evolve as the frequency of beneficial traits increases over generations.

Scientific Method

• Make observations and ask questions.

• Formulate a hypothesis.

• Design and conduct experiments to test the hypothesis.

• Collect and analyze data.

• Draw conclusions and communicate results.

Chemistry of Life

Elements, Atoms, and Molecules

• Element: Substance that cannot be broken down further.

• Atom: Smallest unit of an element, composed of protons, neutrons, and electrons.

• Isotope: Atoms of the same element with different numbers of neutrons (e.g., Carbon-12 & Carbon-14).

• Ion: Atom with a net charge due to loss or gain of electrons.

• Molecule: Two or more atoms bonded together.

• Compound: Substance formed from two or more elements in a fixed ratio.

Atomic Structure

• Nucleus: Contains protons and neutrons.

• Electrons: Orbit the nucleus in energy shells.

Chemical Bonds

• Ionic Bonds: Transfer of electrons between atoms (e.g., NaCl).

• Covalent Bonds: Sharing of electrons between atoms.

• Polar Covalent Bonds: Unequal sharing of electrons (e.g., H2O).

• Hydrogen Bonds: Weak attractions between polar molecules (e.g., water molecules).

Water and Its Properties

• Polarity allows water to form hydrogen bonds, making it an excellent solvent.

• High specific heat, cohesion, adhesion, and surface tension.

• pH scale measures acidity/basicity; water is neutral (pH 7).

Biomolecules

Carbohydrates

• Monomers: Monosaccharides (e.g., glucose, fructose, galactose).

• Functions: Energy storage (starch, glycogen), structural support (cellulose, chitin).

• Formula: $C_6H_{12}O_6$ (glucose)

Lipids

• Monomers: Glycerol and fatty acids.

• Functions: Energy storage, insulation, cell membrane structure (phospholipids), hormones.

• Saturated vs. Unsaturated: Saturated fats have no double bonds; unsaturated fats have one or more double bonds.

Proteins

• Monomers: Amino acids.

• Levels of Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets.

  • Tertiary: 3D folding due to R-group interactions.

  • Quaternary: Multiple polypeptide chains.

• Functions: Enzymes, structural proteins, transport, signaling, defense (antibodies).

Nucleic Acids

• Monomers: Nucleotides (phosphate group, five-carbon sugar, nitrogenous base).

• Types: DNA and RNA.

• Function: Store and transmit genetic information.

Cell Structure and Function

Cell Theory

• All living things are made of cells.

• Cells are the basic unit of structure and function.

• All cells arise from pre-existing cells.

Microscopy

• Microscopes allow visualization of cell structure and organelles.

Prokaryotic vs. Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound organelles	Absent	Present
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Plant vs. Animal Cells

• Both: Mitochondria, cytosol/cytoplasm, chromatin, ER, nucleus, Golgi apparatus, ribosomes, peroxisomes.

• Plant Cells: Vacuole, cell wall, chloroplast, plasma membrane, vesicle.

• Animal Cells: Nuclear envelope, cilia, cytoskeleton, lysosome, centromere.

Cell Organelles and Their Functions

• Nucleus: Contains DNA, controls cell activities.

• Ribosomes: Protein synthesis.

• Endomembrane System: Includes ER, Golgi apparatus, lysosomes, vesicles.

• Mitochondria: Site of cellular respiration, ATP production.

• Chloroplasts: Site of photosynthesis (plants and algae).

• Cell Wall: Provides structure and support (plants, fungi, some protists).

• Cytoskeleton: Maintains cell shape, enables movement.

The Membrane

Plasma Membrane Structure

• Composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Selective permeability regulates movement of substances in and out of the cell.

Cellular Junctions

• Tight Junctions: Seal gaps between cells.

• Desmosomes: Anchor cells together.

• Gap Junctions: Allow communication between cells.

Transport Across Membranes

• Diffusion: Movement of molecules from high to low concentration.

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

• Facilitated Diffusion: Transport via membrane proteins.

• Active Transport: Movement against concentration gradient using ATP.

• Endocytosis/Exocytosis: Bulk transport via vesicles.

Energy and Metabolism

ATP Cycle and Metabolic Reactions

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

• ATP is produced by cellular respiration and used for cellular work.

• ATP hydrolysis releases energy: $ATP \rightarrow ADP + P_i + \text{energy}$

• Anabolic Reactions: Build complex molecules (require energy).

• Catabolic Reactions: Break down molecules (release energy).

Enzymes

• Biological catalysts that speed up chemical reactions by lowering activation energy.

• Affected by temperature, pH, substrate concentration, and inhibitors.

Redox Reactions

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Important in cellular respiration and photosynthesis.

Respiration and Photosynthesis

Cellular Respiration

• Overall equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

• Stages: Glycolysis, Krebs cycle, Electron Transport Chain (ETC).

• Produces up to 36 ATP per glucose molecule.

• Aerobic Respiration: Requires oxygen.

• Anaerobic Respiration: Does not require oxygen; less efficient (e.g., fermentation).

Photosynthesis

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

• Occurs in chloroplasts of plant cells.

• Light-dependent reactions: Convert light energy to chemical energy (ATP, NADPH).

• Light-independent reactions (Calvin cycle): Use ATP and NADPH to synthesize glucose.

• Photosystems I and II, electron transport chain, and chemiosmosis are key steps.

Comparison of Cellular Respiration and Photosynthesis

• Cellular respiration breaks down glucose to release energy; photosynthesis builds glucose using energy from sunlight.

• Equations are essentially the reverse of each other.