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

The Scientific Method

Overview of the Scientific Method

The scientific method is a systematic approach used in biology and other sciences to investigate phenomena, acquire new knowledge, or correct and integrate previous knowledge. It relies on observation, hypothesis formation, experimentation, and analysis.

• 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

• Hypotheses: 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."

  • Not 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: change only 1 variable.

  • Groups:

    • Control (placebo, no treatment)

    • Experimental (gets treatment)

  • Double blind: researchers + participants unaware of groups.

• Correlation vs. Causation:

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

  • Doesn’t mean causation; may be coincidental or other factors.

• Statistics:

  • Statistical significance: determines if results due to chance.

  • Null hypothesis = assumption no difference exists.

  • To increase 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: who supports site, ads = bias risk.

  • Look for frequent updates, peer-reviewed sources.

  • Best: find and read primary sources.

What Defines Life?

Properties and Organization of Living Things

Biologists define life by a set of properties and organizational levels that distinguish living organisms from non-living matter.

• Properties of Living Things:

  • Organized (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 and Molecules

All living things are composed of atoms, which combine to form molecules essential for life. Understanding atomic structure is fundamental to biology.

• Atoms:

  • Smallest unit of an element, made of protons (+), neutrons (0), electrons (-).

  • Protons + neutrons = nucleus.

  • Electrons orbit nucleus in shells.

  • Atoms reactive if outer shell 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 (vitamin C, E) donate electrons, neutralize.

Bonds and Properties of Water

Chemical bonds hold atoms together and give molecules their properties. Water is essential for life due to its unique chemical characteristics.

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

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

• Hydrogen bonds: weak attractions, important in water & DNA.

• Properties of Water:

  • Universal solvent

  • Cohesion/surface tension

  • Resist temperature changes

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

  • Nonpolar molecules (oil) = hydrophobic

Organic vs Inorganic Molecules

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

• Organic: carbon-based (C-C bonds)

Macromolecules

Major Biological Macromolecules

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

• Lipids: hydrophobic molecules.

  • Fats: store energy

  • Enzymes: speed reactions, end in -ase

  • Phospholipids: cell 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

Cell Types and Organelles

Cells are the basic units of life. They are classified as prokaryotic or eukaryotic, each with distinct structures and functions.

• Prokaryotic Cells:

  • Bacteria

  • No nucleus or organelles

  • Have DNA/RNA, ribosomes, cytoplasm, plasma membrane, cell wall

  • Smaller than eukaryotes

  • Some have cell walls (plants, fungi)

• Eukaryotic Cells:

  • Plants, animals, fungi, protists

  • Have nucleus + organelles

  • 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: protein/lipid production

  • Golgi apparatus: modify, sort, 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 and Transport

Diffusion is a fundamental process for movement of molecules in and out of cells. Enzymes are biological catalysts that speed up chemical reactions.

• Diffusion: Movement of molecules from high → 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?