Unit 2 Study Guide

Unit 1: Foundations of Biology

Levels of Organization in the Living World

Biological systems are organized in a hierarchy from the simplest to the most complex structures.

• Atom → Molecule → Macromolecule → Organelle → Cell → Tissue → Organism → Community → Ecosystem → Biosphere

Energy Flow (Trophic Pyramid) & Biogeochemical Cycles

Energy and matter move through ecosystems in distinct ways.

• Energy Flow: Energy decreases by ~90% at each trophic level. For example:

$\text{Grass} = 100\% \rightarrow \text{Grasshopper} = 10\% \rightarrow \text{Bird} = 1\% \rightarrow \text{Hawk} = 0.1\%$

• Biogeochemical Cycles: Elements like carbon, water, nitrogen, and phosphorus cycle through ecosystems, but energy does not cycle.

Homeostasis

Homeostasis provides a stable internal environment for organisms to thrive.

Three Domains of Life

All living organisms are classified into three domains based on cellular structure.

• Bacteria: Prokaryotic, no nucleus, unicellular.

• Archaea: Prokaryotic, often extremophiles, unicellular.

• Eukarya: Eukaryotic, with a nucleus (includes animals, plants, fungi, and protists).

Community vs. Ecosystem

• Community: Focuses only on living organisms.

• Ecosystem: Includes both living (biotic) and non-living (abiotic) components.

Natural Selection

Natural selection acts at the population level, favoring traits that increase survival and reproduction.

Hypothesis vs. Theory

• Hypothesis: A testable prediction.

• Theory: A well-substantiated explanation of some aspect of the natural world.

Independent & Dependent Variables

• Independent variable: What you change in the experiment.

• Dependent variable: What you measure or observe.

Scientific Inquiry Steps

• Steps: Observation → Hypothesis → Experiment → Data Analysis → Conclusion.

• Critical Thinking: Evaluate evidence and make logical conclusions.

Unit 2: Basic Knowledge

Atoms, Isotopes, and Ions

Understanding atomic structure is fundamental to biology and chemistry.

• Atom: Smallest unit of an element.

• Isotope: Same element, different number of neutrons (e.g., 14C).

• Ion: Charged atom (unequal protons and electrons).

Formation of Ions

• Ions form when atoms gain or lose electrons to become stable (full outer electron shell).

• Example: Cl- (gains an electron, becomes negative).

Chemical Bonds

Atoms interact through different types of chemical bonds.

• Ionic Bonds: Electrons are transferred between atoms (e.g., NaCl).

• Covalent Bonds: Electrons are shared between atoms (e.g., H2O).

• Hydrogen Bonds: Weak bonds between polar molecules (e.g., between water molecules).

Electronegativity & Polarity

• Electronegativity: An atom's attraction for electrons.

• Polar covalent bonds: Uneven electron sharing, causing partial charges (e.g., H2O).

• Nonpolar covalent bonds: Even sharing of electrons (e.g., O2).

Acids, Bases, and Buffers

• Acids: Release H+ ions (e.g., lemon juice).

• Bases: Release OH- ions (e.g., ammonia).

• Buffer: Stabilizes pH by absorbing or releasing H+ ions.

• pH scale: Acidic (pH < 7), Neutral (pH = 7), Basic (pH > 7).

NaCl & pH

• NaCl dissolves in water because ionic bonds are broken.

• It slightly affects pH by increasing ion concentration, but not significantly.

Macromolecules and Organic Chemistry

What Makes a Molecule Organic?

• Contains carbon-hydrogen bonds (e.g., methane).

Hydrolysis Reaction

• Breaks down polymers by adding water.

Macromolecules and Their Monomers

• Carbohydrates: Monosaccharides (e.g., glucose).

• Lipids: Fatty acids (e.g., triglycerides).

• Proteins: Amino acids (e.g., enzymes).

• Nucleic acids: Nucleotides (e.g., DNA).

Functional Groups

• COOH (carboxyl) group: Found in fatty acids and amino acids.

• NH2 (amino) group: Found in amino acids.

• OH (hydroxyl) group: Found in alcohols and carbohydrates.

Sugars

• Monosaccharides: One sugar ring (e.g., glucose).

• Disaccharides: Two sugar rings (e.g., sucrose = glucose + fructose).

• Polysaccharides: Many sugar rings (e.g., starch, glycogen, cellulose).

Fatty Acids & Lipids

• Saturated fats: No double bonds, solid at room temperature (e.g., butter).

• Unsaturated fats: At least one double bond, liquid at room temperature (e.g., olive oil).

Proteins

Protein Structure

• Primary structure: Sequence of amino acids.

• Secondary structure: Folding into alpha helices or beta sheets.

• Tertiary structure: Further folding due to R-group interactions.

• Quaternary structure: Multiple polypeptides come together.

Quick Reference for Macromolecule Functions

Macromolecule	Main Function
Carbohydrates	Energy source
Lipids	Energy storage, cell membranes
Proteins	Enzymes, structure, transport
Nucleic acids	Genetic information (DNA/RNA)

Other Key Points

• R-groups: Part of amino acids that determine the protein's function.

• Lipids & Water: Lipids are hydrophobic (repel water).

Why Are Amino Acids Important?

• Proteins do all kinds of jobs in the body. The sequence and folding of amino acids determine what a protein can do.

• Examples of protein functions:

  • Enzymes: Speed up chemical reactions.

  • Collagen: Provides structure in skin and bones.

Important Terms to Know

1. Peptide Bond: The bond that connects amino acids in a protein.

2. R-group: The part of the amino acid that gives it its properties (hydrophobic, polar, etc.).

3. Polypeptide: A long chain of amino acids that forms a protein.

4. Denaturation: When a protein loses its shape and function due to changes in its environment (e.g., heat, pH).

Quick Recap

• Amino acids are the building blocks of proteins.

• They are linked together to form a polypeptide chain, which folds into a specific 3D shape to create a functional protein.

• The sequence of amino acids and the way they fold determine what the protein will do in the body.