Scientific Method

Overview

The scientific method is a systematic approach used in scientific investigation to acquire, test, and apply knowledge about the natural world.

• Observation: Gathering information about phenomena.

• Question: Formulating a question based on observations.

• Hypothesis: Proposing a testable explanation.

• Experiment: Designing and conducting tests to support or refute the hypothesis.

• Data Analysis: Interpreting results to draw conclusions.

• Conclusion: Accepting, rejecting, or modifying the hypothesis.

Periodic Table and Atomic Structure

Subatomic Particles and Atomic Properties

Atoms are composed of three main subatomic particles, each with distinct properties.

• Protons: Positively charged particles found in the nucleus; determine the atomic number.

• Neutrons: Neutral particles in the nucleus; contribute to atomic mass.

• Electrons: Negatively charged particles orbiting the nucleus; involved in chemical bonding.

• Atomic Number (Z): Number of protons in an atom; defines the element.

• Atomic Mass (A): Sum of protons and neutrons in the nucleus.

Example: Carbon has 6 protons, 6 neutrons, and 6 electrons; atomic number = 6, atomic mass ≈ 12.

Molecular Bonding

Covalent, Ionic, and Hydrogen Bonds

Atoms bond to achieve stable electron configurations, forming molecules and compounds.

• Covalent Bonds: Atoms share electron pairs (e.g., H2O).

• Ionic Bonds: Transfer of electrons from one atom to another, creating charged ions (e.g., NaCl).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Why Atoms Bond: Atoms bond to achieve a full outer electron shell (octet rule), increasing stability.

Biological Macromolecules

Types, Structure, and Function

Living organisms are built from four major classes of macromolecules, each with unique monomers and functions.

• Proteins: Polymers of amino acids; perform structural, enzymatic, and regulatory roles.

• Carbohydrates: Polymers of monosaccharides; provide energy and structural support.

• Lipids: Not true polymers; include fats, oils, and phospholipids; store energy and form membranes.

• Nucleic Acids: Polymers of nucleotides (DNA, RNA); store and transmit genetic information.

Monomer vs. Polymer: Monomers are single subunits; polymers are chains of monomers.

Dehydration Synthesis: Joins monomers by removing water.

Hydrolysis: Breaks polymers into monomers by adding water.

Protein Folding: Determines protein function; misfolding can cause diseases.

Plasma Membrane: Structure and Function

Membrane Transport Methods

The plasma membrane controls the movement of substances into and out of the cell.

• Passive Transport: Movement down a concentration gradient without energy input (e.g., diffusion, osmosis, facilitated diffusion).

• Active Transport: Movement against a concentration gradient using energy (ATP) (e.g., sodium-potassium pump).

• Movement: Can increase, decrease, or remain the same depending on gradients and membrane properties.

Enzymes

Enzyme Cycle and Catalyzed Reactions

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

• Enzyme Cycle: Substrate binds to enzyme's active site, reaction occurs, products are released, enzyme is reused.

• Enzyme-Catalyzed Reactions: Follow specific pathways; enzymes are highly specific for their substrates.

• Prediction: Understanding the pathway allows prediction of outcomes if substrates or enzymes are altered.

Cellular Respiration

Overview of Process: Inputs and Outputs

Cellular respiration is the process by which cells convert glucose and oxygen into energy (ATP), carbon dioxide, and water.

• Inputs: Glucose (C6H12O6), O2

• Outputs: ATP, CO2, H2O

Overall Equation:

Cell Division

Mitosis and Meiosis

Cell division is essential for growth, repair, and reproduction. Two main types are mitosis and meiosis.

• Mitosis: Produces two genetically identical diploid cells; used for growth and repair.

• Meiosis: Produces four genetically unique haploid cells (gametes); used in sexual reproduction.

• Compare and Contrast: Mitosis involves one division, meiosis involves two; meiosis increases genetic diversity.

Cell Signaling

Signal Transduction Pathway

Cells communicate using chemical signals that trigger a series of events inside the cell, known as the signal transduction pathway.

• Why? Allows cells to respond to their environment and coordinate activities.

• Pathway: Signal molecule (ligand) binds to receptor → intracellular signaling cascade → cellular response.

DNA vs. RNA Structure and Function

Comparison and Universality of DNA

DNA and RNA are nucleic acids with distinct structures and functions.

Universality of DNA: All living organisms use DNA as their genetic material, highlighting the unity of life.

Example: The genetic code is nearly universal across species.

Gene Expression

Transcription, Translation, and Differential Expression

Gene expression is the process by which information from DNA is used to synthesize functional products like proteins.

• Transcription: DNA is copied into messenger RNA (mRNA).

• Translation: mRNA is decoded by ribosomes to build proteins.

• Differentiation: Cells express different genes, leading to specialized cell types.

• Differential Gene Expression: Regulates development and function in multicellular organisms.