General Biology Study Guide: Foundations, Chemistry of Life, Cells, and Enzymes

The Scientific Method

Overview

The scientific method is a systematic approach used by scientists to investigate natural phenomena, develop hypotheses, and test predictions through experimentation and observation.

• Steps:

  1. Observation

  2. Hypothesis

  3. Prediction

  4. Experiment (test prediction)

  5. Conclusion (true/false prediction?)

  6. Revise or reject hypothesis

  7. Additional tests or alternative hypotheses

• Hypothesis: A proposed explanation or possible solution to a problem (educated guess). Must be testable and falsifiable.

  • Example of testable: "Colds are caused by viruses." / "Echinacea reduces severity of colds."

  • Non-testable: "Spirits are watching you."

• Predictions: Use deductive reasoning (if/then).

  • Example: If vitamin C decreases colds, then people taking supplements will get fewer colds than those who do not.

• Experiments: Controlled tests that change only one variable at a time.

  • Control: placebo, no treatment

  • Experimental: gets treatment

  • Random assignment

  • Double blind: both researchers and participants unaware of group assignments

• Correlation vs. Causation:

  • Correlation: relationship (e.g., ice cream sales ↑ with drowning deaths)

  • Does not mean causation; may be coincidental or due to other factors

• Statistics:

  • Statistical significance: determines if results are due to chance

  • Null hypothesis: assumption of no difference exists

  • Statistical validity: large sample size, careful design, double blind, repetition, peer review

• Sources:

  • Primary: peer-reviewed journals (Science, Nature)

  • Secondary: books, news, ads

  • Anecdotal evidence: personal stories ("worked for me")

  • Avoid anecdotal infomercials

  • Use reputable sites (NIH, Mayo Clinic)

  • Check for supporting studies, peer-reviewed sources

  • Best: find and read primary sources

What Defines Life?

Properties of Living Things

Living organisms share several key characteristics that distinguish them from non-living matter.

• Organized (composed of cells)

• Metabolism (energy for growth, reproduction, response to stimuli, homeostasis)

• Reproduction

• Evolution/adaptation

Levels of Organization

• Molecule → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biome → Biosphere

Chemistry of Life

Atoms

Atoms are the smallest units of elements, consisting of subatomic particles.

• Made of protons (+), neutrons (0), electrons (−)

• Protons and neutrons: nucleus

• Electrons: orbit nucleus in shells

• Atoms are reactive if outer shell is not full

Electrons

• Transfer energy in cells

• Shells: 1st holds 2, 2nd/3rd hold 8

• Ions: different # of protons and electrons

Free Radicals & Antioxidants

• Free radicals: unstable, steal electrons, cause damage

• Antioxidants (vitamins C, E): donate electrons, neutralize

Valence & Bonds

• Ionic bonds: electron transfer (NaCl), weak, break in water

• Covalent bonds: electrons shared, strong, store energy (C6H12O6)

• Hydrogen bonds: weak attractions, important in water and DNA

Properties of Water

• Universal solvent

• Cohesion/surface tension

• Resists temperature changes

• pH scale: acids (↑ H+), bases (↓ H+)

• Nonpolar molecules (oil) = hydrophobic

Organic vs Inorganic

• Inorganic: no C–C bonds (H2O, O2, NaCl)

• Organic: carbon-based (C–C bonds)

Macromolecules

Overview

Macromolecules are large, complex molecules essential for life, including carbohydrates, proteins, lipids, and nucleic acids.

• Carbohydrates: energy & structure

  • Monosaccharides: simple sugars

  • Disaccharides: 2 sugars

  • Polysaccharides: long chains (starch, cellulose, glycogen)

• Proteins: built from amino acids

  • Structural: hair, muscle

  • Enzymes: speed reactions, end in -ase

  • Transport: hemoglobin

  • Shape = specific chemical function

• Lipids: hydrophobic molecules

  • Fats: store energy, insulation

  • Triglycerides: 3 fatty acids, energy storage

  • Phospholipids: double layer in membranes (hydrophilic head, hydrophobic tails)

• Nucleic Acids:

  • DNA: double helix of nucleotides (sugar-phosphate backbone, base pairs by H-bonds)

  • Stores genetic info

• ATP: high-energy compound, immediate energy for cells

Cells

Prokaryotic vs Eukaryotic Cells

• Prokaryotic: bacteria; no nucleus or organelles; have DNA/RNA, ribosomes, cytoplasm, plasma membrane, cell wall; smaller than eukaryotes

• Eukaryotic: plants, animals, fungi, protists; have nucleus and organelles; some have cell walls (plants, fungi)

Organelles

• Nucleus: stores DNA

• Cytoplasm: cytosol + organelles

• Mitochondria: aerobic respiration → ATP

• Chloroplasts: photosynthesis (plants/algae)

• Lysosomes: digestion

• Ribosomes: protein assembly (free or on ER)

• ER (endoplasmic reticulum): protein/lipid production

• Golgi apparatus: modify, store, package proteins

• Centrioles: cell division

• Central vacuole (plants): storage, pressure, rigidity

Membranes

• Fluid mosaic of lipids & proteins

• Regulate water:

  • Too much → swelling, burst

  • Too little → shrink

  • Plant/fungal cells use cell walls for protection

Diffusion & Enzymes

Diffusion

Diffusion is the movement of molecules from areas of high to low concentration, down a concentration gradient.

• Passive transport: does not require energy

• Osmosis: diffusion of water across a selectively permeable membrane

• Active transport: moves molecules against concentration gradient (low → high), requires energy (usually ATP)

• Facilitated diffusion: transport proteins help large or charged molecules move across membrane (still passive)

Enzymes

• Definition: proteins that speed up chemical reactions (biological catalysts)

• How they work:

  • Substrate binds to enzyme's active site (specific shape – lock-and-key or induced fit)

  • Reaction occurs → products released

  • Reusable: enzymes are not consumed in the reaction

Factors Affecting Enzyme Activity

• Temperature: too low = reaction slows; too high = enzyme denatures (loses shape)

• pH: each enzyme works best at an optimal pH; too high/low = denaturation

• Substrate concentration: higher substrate concentration = faster reaction (until saturation)

• Inhibitors: block or reduce enzyme activity

  • Competitive inhibitors: bind active site

  • Noncompetitive inhibitors: bind elsewhere, change enzyme shape

Quick Review Questions

• What makes a hypothesis scientific?

• How do experiments avoid bias?

• Why doesn't correlation mean causation?

• What are signs of credible vs non-credible sources?

• What properties define life?

• Difference between prokaryotic and eukaryotic cells?