Fundamental Chemistry Concepts in General Biology

Chapter 1: The Study of Life Reveals Unifying Themes

Biology is the scientific study of life, encompassing a wide range of topics from the molecular to the ecosystem level. Understanding the chemical basis of life is essential for exploring biological processes.

Chapter 2: The Chemical Context of Life

2.1: Matter Consists of Chemical Elements in Pure Form and in Combinations Called Compounds

• Element: A substance that cannot be broken down into other substances by chemical reactions. Examples: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N).

• Compound: A substance consisting of two or more elements combined in a fixed ratio. Example: Water (H2O).

• Essential elements: Elements required for an organism to survive, grow, and reproduce. In humans, these include O, C, H, N, and others in smaller amounts.

• Trace elements: Elements required by an organism in minute quantities (e.g., iron, iodine).

2.2: An Element’s Properties Depend on the Structure of Its Atoms

• Atom: The smallest unit of matter that retains the properties of an element.

• Subatomic particles: Atoms are composed of protons (positive charge), neutrons (neutral), and electrons (negative charge).

• Atomic number (Z): Number of protons in the nucleus of an atom. Determines the element.

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

• Isotopes: Atoms of the same element with different numbers of neutrons. Example: Carbon-12 (6 protons, 6 neutrons) vs. Carbon-14 (6 protons, 8 neutrons).

• Radioactive isotopes: Unstable isotopes that decay spontaneously, emitting radiation. Used in biological research and medicine (e.g., PET scans).

• Electron shells: Electrons are arranged in shells around the nucleus. The chemical behavior of an atom depends on the number of electrons in its outermost shell (valence electrons).

2.3: The Formation and Function of Molecules Depend on Chemical Bonding Between Atoms

• Chemical bonds: Atoms with incomplete valence shells can share or transfer electrons, resulting in chemical bonds.

• Covalent bond: Sharing of a pair of valence electrons by two atoms. Can be single, double, or triple bonds.

• Polar covalent bond: Electrons are shared unequally, resulting in partial charges (e.g., in water molecules).

• Nonpolar covalent bond: Electrons are shared equally between atoms.

• Ionic bond: Transfer of electrons from one atom to another, resulting in oppositely charged ions that attract each other (e.g., NaCl).

• Hydrogen bond: Weak attraction between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom.

• Van der Waals interactions: Weak attractions between molecules or parts of molecules that result from transient local partial charges.

2.4: Chemical Reactions Make and Break Chemical Bonds

• Chemical reaction: The making and breaking of chemical bonds, leading to changes in the composition of matter.

• Reactants: Starting materials in a chemical reaction.

• Products: Resulting materials after the reaction.

• Conservation of mass: Matter is neither created nor destroyed in a chemical reaction.

Chapter 3: Water and Life

3.1: Polar Covalent Bonds in Water Molecules Result in Hydrogen Bonding

• Polarity of water: Water is a polar molecule due to the unequal sharing of electrons between oxygen and hydrogen atoms, resulting in a partial negative charge near oxygen and partial positive charges near hydrogens.

• Hydrogen bonding: The polarity of water molecules allows them to form hydrogen bonds with each other, leading to unique properties.

3.2: Four Emergent Properties of Water Contribute to Earth’s Suitability for Life

• Cohesion: Water molecules stick together due to hydrogen bonding, contributing to phenomena like surface tension.

• Adhesion: Water molecules can also stick to other substances, aiding processes like capillary action in plants.

• Moderation of temperature: Water has a high specific heat, allowing it to absorb or release large amounts of heat with little temperature change. This stabilizes temperatures in organisms and environments.

• Expansion upon freezing: Ice is less dense than liquid water due to the formation of a crystalline structure, causing ice to float and insulate bodies of water.

• Versatility as a solvent: Water’s polarity allows it to dissolve many substances, making it an excellent solvent for biological reactions.

3.3: Acidic and Basic Conditions Affect Living Organisms

• Acid: A substance that increases the hydrogen ion concentration of a solution (pH < 7).

• Base: A substance that reduces the hydrogen ion concentration (pH > 7).

• pH scale: Measures the concentration of hydrogen ions in a solution. Defined as .

• Buffers: Substances that minimize changes in pH by accepting or donating H+ ions. Example: Bicarbonate buffer system in blood.

• Hydrophilic substances: Substances that have an affinity for water (e.g., salts, sugars).

• Hydrophobic substances: Substances that do not have an affinity for water (e.g., oils, fats).

Table: Comparison of Covalent, Ionic, and Hydrogen Bonds

Additional Key Concepts

• Atomic mass: The total mass of an atom, approximately equal to the mass number (protons + neutrons).

• Valence: The bonding capacity of an atom, usually equal to the number of unpaired electrons in the valence shell.

• Electronegativity: The attraction of a particular atom for the electrons of a covalent bond.

• Hydration shell: The sphere of water molecules around each dissolved ion in an aqueous solution.

Example: The bicarbonate buffer system in blood helps maintain a stable pH by the following equilibrium:

Example: Ice floats on water, insulating aquatic life in winter and preventing bodies of water from freezing solid.

Additional info: These notes synthesize key learning objectives and concepts from introductory chapters in Campbell's Biology, 11th edition, focusing on the chemical foundations of life and the unique properties of water essential for biological systems.