Integrated Study Materials: Memory, Cell Biology, and Chemistry Summary & Study Notes

🧠 Overview of Human Memory

Memory is the mental process that enables encoding, storage, and retrieval of information. It underpins learning, decision-making, and daily functioning and is commonly divided into three stages.

🧠 Stages of Memory

Sensory memory is a very brief buffer that holds incoming sensory information for a fraction of a second. Short-term (working) memory holds information actively for about 15–30 seconds and is limited to roughly 7 ± 2 items. Long-term memory is effectively large and long-lasting, storing information from hours to a lifetime.

🧠 Types of Long-Term Memory

Explicit memory (conscious) includes episodic (personal experiences) and semantic (facts and knowledge). Implicit memory (unconscious) includes skills and habits (e.g., riding a bike) that are recalled without conscious effort.

🧠 Encoding and Retention

Encoding is the transformation of information for storage. Deeper processing—like making personal connections, creating imagery, organizing into meaningful categories, and generating examples—produces stronger memory traces. Repetition, visualization, and self-explanation improve encoding.

🧠 Why Memory Fails

Common causes of forgetting include decay (unused traces fade), interference (new and old information conflict), and retrieval failure (memory exists but cues are missing). For example, interference can cause someone to recall an old phone number instead of a new one.

🧠 Evidence-Based Study Tips

Space out study sessions (spacing effect), use self-testing over passive rereading, explain concepts in your own words, use visual tools (mind maps, diagrams), and teach others to strengthen retention.

🧫 Carbon and Biomolecules

Carbon is the backbone of life; all organic molecules in living organisms contain carbon. Carbon's tetravalence allows chains and diverse 3D shapes, which are crucial for molecular function. Abiotic synthesis experiments (e.g., Stanley Miller) support that organic molecules could form on early Earth.

🧫 Lipids and Membranes

Fats (triacylglycerols) are glycerol + fatty acids linked by ester linkages and mainly serve energy storage. Phospholipids (2 fatty acids + glycerol + phosphate + head group) are amphipathic and self-assemble into bilayers to form plasma membranes. Steroids have four fused rings and function in membranes and as signaling molecules (e.g., hormones).

🧫 Carbohydrates & Polymers

Monosaccharides (3–7 carbons) like glucose are building blocks for energy and biosynthesis. Disaccharides (e.g., sucrose, maltose) and polysaccharides (starch, glycogen, cellulose, chitin) differ in branching and linkage (e.g., $\beta$ vs $\alpha$ linkages) and serve storage or structural roles.

🧫 Proteins & Nucleic Acids

Amino acids form polypeptides via peptide bonds; protein function depends on primary → quaternary structures. Nucleic acids (DNA/RNA) are polynucleotides built from nucleotides (base + sugar + phosphate). DNA → transcription → RNA → translation → protein; nitrogenous bases include pyrimidines (C, T, U) and purines (A, G).

🧫 Organelles & Cell Types

All life is cellular: prokaryotes (bacteria, archaea) lack membrane-bound organelles; eukaryotes have organelles (nucleus, ER, Golgi, mitochondria, chloroplasts). Mitochondria and chloroplasts have double membranes and their own DNA and ribosomes; mitochondria catalyze cellular respiration, while chloroplasts perform photosynthesis ($\text{light} + CO_2 + H_2O \rightarrow \text{sugar} + O_2$).

🧫 Cytoskeleton & Extracellular Structures

The cytoskeleton has microtubules, actin filaments, and intermediate filaments for shape, motility, and intracellular transport. Plants have cell walls (primary, secondary) and plasmodesmata; animals have extracellular matrix (ECM) with collagen and proteoglycans and junctions like tight junctions, desmosomes, and gap junctions.

🧫 Membrane Transport

Membranes follow the fluid mosaic model; lipid composition (saturated vs unsaturated tails) controls fluidity. Transport includes passive diffusion, facilitated diffusion (channels, carriers), osmosis (water across semipermeable membrane), and active transport (energy-dependent pumps like Na⁺/K⁺ ATPase and proton pumps). Bulk transport involves endocytosis (phagocytosis, pinocytosis) and exocytosis.

⚛️ Matter and States

Matter occupies space and has mass; it exists as solids, liquids, gases, and plasma. Solids have fixed shape and volume, liquids have fixed volume but flow, gases have neither fixed volume nor shape, and plasma is ionized gas created at high energy.

⚛️ Atoms, Molecules, and Mass

Atoms consist of protons, neutrons, and electrons; elements are defined by proton number. Molecules are bonded atoms; compounds have fixed elemental ratios per the Law of Definite Composition. Atomic mass units (amu) and the mole (6.02 × 10^{23}) allow conversion between mass and particle count.

⚛️ Electronic Structure and Periodic Trends

Atomic orbitals (s, p, d) have characteristic shapes; electron configuration follows the Aufbau and Pauli principles. Periodic trends include atomic radius (increases down a group, decreases across a period) and ionization energy (opposite trend) as well as electronegativity.

⚛️ Chemical Bonding and Intermolecular Forces

Covalent bonds share electrons (polar vs nonpolar); ionic bonds form by electron transfer; metallic bonds involve delocalized electrons. Intermolecular forces (London dispersion, dipole-dipole, hydrogen bonding) influence physical properties like boiling point.

⚛️ Acids, Bases, and Electrolytes

Acids donate protons (Arrhenius/Bronsted-Lowry definitions); bases donate OH⁻ or accept protons. Electrolytes (strong vs weak) dissociate to ions in water; water's polarity enables hydration of ions (e.g., $NaCl$ dissociates into $Na^+$ and $Cl^-$). Neutralization yields salts and water.

⚛️ Chemical Reactions and Energy

Redox reactions involve electron transfer; nuclear reactions produce different elements. Thermodynamics: first law (energy conservation) and second law (entropy increases). Gibbs free energy ($\triangle G$) predicts spontaneity: $\triangle G < 0$ is exergonic (spontaneous), $\triangle G > 0$ is endergonic (non-spontaneous).

⚛️ Stoichiometry and Gas Laws

The mole and Avogadro's number link macroscopic mass to particle counts. Gas behavior follows laws like Boyle's, Charles', and Avogadro's; at STP a mole of ideal gas occupies about 22.4 L.