CP

Biology Unit 2 Study Guide

5 Characteristics of All Living Things

  1. Made of cells (basic unit of life).

    • Ex: Humans (cells), bacteria (single cell).

  2. Reproduce.

    • Ex: Plants make seeds; animals have offspring.

  3. Respond to environment.

    • Ex: Plants grow toward sunlight.

  4. Grow and develop.

    • Ex: Caterpillar → butterfly.

  5. Use energy (metabolism).

    • Ex: Humans eat food for energy.

Living vs. Nonliving

  • Living: dog, tree, bacteria.

  • Nonliving: rock, water, chair.

⚠ Sometimes the 5 characteristics aren’t perfect → viruses reproduce but don’t have cells, so scientists debate if they’re truly “living.”

Atoms & Molecules

  • Atom: Smallest unit of matter.

  • Element: Pure substance made of one type of atom (ex: Oxygen, Carbon).

  • Electrons: Negatively charged particles around the nucleus.

  • Atomic Number: Number of protons in an atom.

  • Molecule: Two or more atoms bonded together (H₂O).

  • Covalent Bond: Atoms share electrons (ex: water molecules).

👉 These are all connected: atoms → elements → combine into molecules → bonds hold them together.

Carbon: The Element of Life

  • Carbon is versatile because it can form 4 bonds with other atoms.

  • Can make chains, rings, or branched structures.

  • Forms backbone of all major macromolecules (carbs, lipids, proteins, nucleic acids).

4 Macromolecules of Life

Monomer vs. Polymer

  • Monomer = building block.

  • Polymer = many monomers joined.

1. Carbohydrates

  • Monomer: Monosaccharide (glucose).

  • Function: Quick energy, structure.

  • Examples: Bread, pasta, cellulose (plant cell walls).

  • Structure: Carbon rings.

2. Proteins

  • Monomer: Amino acids.

  • Function: Enzymes, muscle, transport.

  • Examples: Meat, beans, enzymes.

  • Structure: Chains folded into 3D shapes.

3. Nucleic Acids

  • Monomer: Nucleotide.

  • Function: Store genetic info.

  • Examples: DNA, RNA.

  • Structure: Long chains (sugar-phosphate backbone + nitrogen base).

4. Lipids

  • No true monomer.

  • Examples: fats, oils, waxes, steroids.

  • Function: Long-term energy, insulation, hormones.

  • Structure: Long hydrocarbon chains.

Polarity of Water

  • Polar = uneven sharing of electrons → molecule has charged sides.

  • In water:

    • Oxygen side = negative (electrons spend more time here).

    • Hydrogen side = positive.

  • Covalent bond: holds H and O together inside one water molecule.

  • Hydrogen bond: weak attraction between different water molecules.

6 Properties of Water

  1. Polarity: Allows water to dissolve many substances.

  2. Cohesion: Water sticks to water → surface tension.

  3. Adhesion: Water sticks to other things → capillary action in plants.

  4. High heat capacity: Water absorbs lots of heat → stabilizes body/earth temp.

  5. Ice less dense: Ice floats → insulates aquatic life.

  6. Universal solvent: Dissolves many substances → allows reactions in cells.

Water as a Universal Solvent

  • Solute = substance being dissolved (salt).

  • Solvent = substance doing the dissolving (water).

  • Solution = solute + solvent (saltwater).

Ionic Bonds

  • One atom gives electrons to another → creates charged ions.

  • Example: Na⁺ + Cl⁻ → NaCl (salt).

When salt dissolves in water

  • Positive side of water (H) pulls negative ions (Cl⁻).

  • Negative side of water (O) pulls positive ions (Na⁺).

  • Water molecules surround ions → salt dissolves.