General Biology 101 — Comprehensive Study Notes

Big Ideas in Biology

Levels of Organization

• Life is organized: Biological systems are structured hierarchically: molecules → cells → tissues → organs → organ systems → organisms → populations → ecosystems.

• Structure relates to function: The shape and structure of proteins and other molecules affect their function in biological systems.

• Information flow: DNA stores genetic information; cells read it to build proteins.

• Energy flow: Organisms obtain and use energy, with energy transformations occurring as heat, motion, or chemical energy.

• Evolution explains unity and diversity: Shared traits and differences among organisms arise from common ancestry and change over time.

Scientific Method & Experimental Design

Key Terms and Concepts

• Hypothesis: A testable explanation for an observation, often based on prior knowledge.

• Prediction: What you expect to observe if the hypothesis is correct.

• Independent variable: The factor you change in an experiment.

• Dependent variable: The factor you measure in response to changes.

• Control variables: Factors kept the same to ensure results are meaningful.

Good Experimental Practice

• Replication: Repeating experiments increases reliability.

• Randomization: Reduces bias.

• Sample size: Larger sample sizes increase statistical power.

• Correlation vs. causation: Correlation does not imply causation; further testing is needed to establish cause-effect relationships.

Interpreting Data

• Read data carefully; identify outliers and trends.

• Statistical tests help determine if differences are meaningful or due to chance.

Chemistry of Life (Water, pH, Bonds)

Properties of Water

• Polarity: Water is a polar molecule, forming hydrogen bonds that give it unique properties.

• Cohesion/Adhesion: Water molecules stick to each other and to other substances, aiding in transport.

• High heat capacity: Water resists temperature changes, stabilizing environments.

• Solvent: Water dissolves many polar molecules, making it a universal solvent.

pH and Acids/Bases

• pH scale: Measures hydrogen ion concentration; $\text{pH} = -\log_{10} [\text{H}^+]$

• Low pH = more H+ (acidic); high pH = fewer H+ (basic).

• Buffers: Resist changes in pH, important for enzyme and blood chemistry.

Chemical Bonds

• Covalent bonds: Atoms share electrons (strong, within molecules).

• Ionic bonds: Electrons are transferred; ions form and dissolve in water.

• Hydrogen bonds: Weak individually, but strong collectively (e.g., DNA base pairing, water properties).

Macromolecules & Enzymes

Macromolecules

• Carbohydrates: Quick energy, structural support. Monomer = monosaccharide.

• Lipids: Energy storage, insulation, hormones. Not true polymers.

• Proteins: Enzymes, structure, transport, signaling. Monomer = amino acid.

• Nucleic acids: DNA/RNA. Monomer = nucleotide.

Enzymes (Biological Catalysts)

• Speed up reactions by lowering activation energy (do not change $\Delta G$).

• Have an active site; affected by temperature, pH, and substrate concentration.

• Denaturation: Loss of shape = loss of function.

• Inhibitors: Competitive inhibitors block active sites; noncompetitive inhibitors change enzyme shape.

Cells: Structure & Function

Cell Types

• Prokaryotes: No nucleus (bacteria, archaea); DNA in nucleoid region.

• Eukaryotes: Nucleus and membrane-bound organelles (animals, plants, fungi, protists).

Major Organelles

• Nucleus: Stores DNA; transcription occurs here (in eukaryotes).

• Mitochondria: Site of cellular respiration, ATP production.

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

• Ribosomes: Protein synthesis.

• Endoplasmic reticulum: Protein and lipid synthesis.

• Golgi apparatus: Modifies and ships proteins.

• Lysosomes: Digestion/recycling (common in animal cells).

• Cell wall: Plants (cellulose), fungi (chitin), bacteria (peptidoglycan).

Cell Membranes & Transport

Membrane Structure

• Phospholipid bilayer: Hydrophilic heads, hydrophobic tails.

• Fluid mosaic model: Proteins float in lipid 'sea'.

• Membrane is selectively permeable; controls what enters/leaves the cell.

Transport Mechanisms

• Passive transport: No energy required.

  • Diffusion: Movement from high to low concentration.

  • Osmosis: Diffusion of water across a membrane.

  • Facilitated diffusion: Uses transport proteins (channels/carriers), still high → low.

• Active transport: Requires energy (ATP).

  • Moves substances against gradient (low → high), e.g., sodium-potassium pump.

  • Bulk transport: Endocytosis/exocytosis for large materials.

• Osmotic terms:

  • Hypotonic: Outside cell has lower solute; water enters cell (animal cells may lyse).

  • Hypertonic: Outside cell has higher solute; water leaves cell (cell shrinks).

  • Isotonic: No net water movement.

Energy in Cells: Respiration & Photosynthesis

Cellular Respiration

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

• Major steps:

  • Glycolysis: Cytoplasm; glucose → pyruvate + a little ATP + NADH.

  • Krebs cycle: Mitochondria; produces CO2, ATP, NADH, FADH2.

  • ETC (Electron Transport Chain): Mitochondria; most ATP produced, oxygen is final electron acceptor.

Photosynthesis

• Occurs in plants/algae.

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

• Light reactions: Capture energy, make ATP + NADPH, release O2.

• Calvin cycle: Uses ATP + NADPH to build sugars from CO2.

• Key connection: Photosynthesis stores energy in glucose; respiration releases it for cellular work.

DNA, Gene Expression, and Genetics

DNA Basics

• Double helix with base pairing: A-T, G-C.

• Replication is semi-conservative (each new DNA has one old strand + one new).

Central Dogma

• DNA → RNA → Protein (transcription in nucleus, translation in cytoplasm).

Mutations

• Types: Substitution, insertion, deletion (can cause frameshifts).

Mendelian Genetics

• Genes have alleles (AA, Aa, aa); phenotype is the trait you see.

• Dominant/recessive: Recessive masked in heterozygote (Aa shows dominant trait).

• Punnett squares: Predict probabilities of offspring genotypes.

Beyond Mendel

• Incomplete dominance: Blending of traits.

• Codominance: Both alleles expressed.

• Polygenic traits: Many genes affect one trait.

• Linked genes: Inherited together if close on chromosome.

Evolution & Biodiversity

Natural Selection

• Requires:

  1. Variation in traits

  2. Traits are heritable

  3. Differential survival/reproduction

Mechanisms of Evolution

• Natural selection: Traits that improve survival/reproduction increase in frequency.

• Genetic drift: Random changes, stronger in small populations.

• Gene flow: Migration; movement of alleles between populations.

• Mutation: Source of new alleles.

Hardy-Weinberg Equilibrium

• Describes non-evolving populations; allele frequencies stay constant.

Equation: $p^2 + 2pq + q^2 = 1$ $p + q = 1$ where p and q are allele frequencies.

Phylogenetic Trees

• Show evolutionary relationships; nodes = common ancestors.

• Closer branches = more recent shared ancestor.

Ecology (How Living Things Interact)

Levels of Organization

• Population: Same species in an area.

• Community: All species in an area.

• Ecosystem: All living and nonliving components in an area.

Energy Flow

• Producers capture energy; consumers eat producers; decomposers recycle matter.

• Energy decreases at higher trophic levels (often ~10% transfer).

Cycles

• Matter cycles (carbon, nitrogen, water) move atoms through living/nonliving parts of Earth.

Human Impacts

• Habitat loss, climate change, pollution, invasive species, overharvesting.

• Conservation focuses on biodiversity, ecosystem services, sustainability.

Quick "High-Yield" Checklist (Exam-Friendly)

• Define hypothesis vs. theory; independent vs. dependent variable.

• Compare prokaryotes vs. eukaryotes; plant vs. animal cells.

• Explain macromolecules and what affects enzyme activity.

• List major organelles and their functions.

• Know differences: DNA vs. RNA; genotype vs. phenotype.

• Use Punnett squares to predict probability (genetics).

• Explain how natural selection & 3-step chain (variation → heritability → differential success) drive evolution.

• Interpret a simple phylogenetic tree and an energy pyramid.