2.1 Atom to Organism & Metabolism

2.1.1 Levels of Organization

Biological systems are organized in a hierarchy from the simplest to the most complex structures. Understanding these levels helps explain how life is structured and functions.

• Organism: An individual living entity.

• System: Groups of organs working together (e.g., digestive system).

• Organ: Structures composed of different tissues performing specific functions.

• Tissue: Groups of similar cells performing a common function.

• Cell: Basic unit of life.

• Organelle: Specialized structures within cells (e.g., mitochondria).

• Compound: Chemical combinations of elements.

• Atom/Element: Basic unit of matter; elements are pure substances.

• Electron, proton, neutron: Subatomic particles making up atoms.

2.1.2 Definitions: Matter, Energy, Atom, Element, Electron, Proton, Neutron

• Matter: Anything that occupies space and has mass.

• Energy: The ability to do work; does not occupy space or have mass.

• Atom: The smallest unit of matter, made of protons, neutrons, and electrons.

• Element: A pure substance consisting of one type of atom, defined by its number of protons.

• Electron: Negatively charged subatomic particle found in energy levels around the nucleus; determines chemical reactivity.

• Proton: Positively charged subatomic particle found in the nucleus; determines the element's identity.

• Neutron: Neutral subatomic particle in the nucleus; contributes to atomic mass and isotopes.

2.1.3 The Four Most Common Elements in Living Things: CHON

• CHON: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N) are the most abundant elements in living organisms.

2.1.4 Other Essential Elements

Living organisms also require other elements in smaller amounts:

• Na+ (Sodium)

• K+ (Potassium)

• Cl- (Chloride)

• Ca2+ (Calcium)

2.1.5 The 2-8-8 Rule for Electron Arrangement

Electrons are arranged in energy levels (shells) around the nucleus:

• The first shell holds up to 2 electrons.

• The second and third shells can each hold up to 8 electrons.

• Electrons in the outermost shell are called valence electrons and are involved in chemical bonding.

• Atoms are most stable when their outer shell is full.

Nucleus: The center of the atom containing protons and neutrons.

2.1.6 The Importance of Carbon

• Carbon can form four covalent bonds, allowing for a variety of complex molecules.

• Carbon-based molecules include proteins, lipids, carbohydrates, and nucleic acids.

2.1.7 Chemical Bonds

Chemical bonds are attractions between atoms that allow the formation of chemical substances.

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

• Covalent bonds: Sharing of electrons between atoms.

• Covalent bonds can be further divided into:

  • Polar covalent: Unequal sharing of electrons, leading to partial charges (e.g., H2O).

  • Nonpolar covalent: Equal sharing of electrons, no charge separation (e.g., O2).

2.1.8 Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties.

Hydrophilic means water-loving (carries a charge); hydrophobic means water-repelling (no charge).

2.2 Water

2.2.1 Importance of Water

• All living things require water to survive.

2.2.3 Polar Covalent Bonds vs. Weak Hydrogen Bonds in Water

Water's unique properties arise from its molecular structure and bonding:

• Polar covalent bonds form between H and O within a water molecule, causing unequal sharing of electrons.

• This creates a dipole: O is slightly negative (δ-), H is slightly positive (δ+).

• Hydrogen bonds are weak attractions between the δ+ H of one water molecule and the δ- O of another.

• These interactions make water cohesive and give it a high boiling point.

2.2.4 Polar Covalent Bonds, Weak H Bonds, and Cohesion

• Weak H bonds cause water molecules to be attracted to each other (cohesion).

• Polar covalent bonds within water molecules allow for the formation of H bonds between molecules.

• Cohesion leads to surface tension, allowing water to form droplets and support small objects.

2.2.5 Adhesion of Water

• Adhesion: Water's attraction to other substances, such as the walls of plant vessels or blood vessels.

• Adhesion helps water move against gravity in plants (capillary action).

2.2.6 Dipole, Solvent Properties, and Transport

• Water's polarity allows it to dissolve many substances, making it an excellent solvent.

• Hydrophilic substances dissolve easily in water; hydrophobic substances do not.

• Water's solvent properties are essential for metabolism and transport of particles in living organisms.

2.3 Macromolecules

2.3.1 The Four Macromolecules

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

2.3.2 Universal Monomers of Macromolecules

• Carbohydrates: Monosaccharides (simple sugars)

• Lipids: Fatty acids + glycerol

• Nucleic acids: Nucleotides

• Proteins: Amino acids

2.3.3 Universal Monomer vs. Species-Specific Polymer

• Universal monomer: Building blocks used by all organisms to build macromolecules (e.g., amino acids for proteins).

• Species-specific polymer: The sequence and structure of polymers (e.g., proteins) are unique to each species.

• Universal monomers allow organisms to digest and reuse molecules from other organisms.

2.3.4 Condensation vs. Hydrolysis

• Condensation (Dehydration Synthesis): Joins monomers by removing water to form a bond.

• Hydrolysis: Breaks bonds between monomers by adding water.

Equation for condensation:

Equation for hydrolysis:

2.3.5 Carbohydrates: Size, Function, and Examples

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose); formula .

• Pentoses: 5-carbon sugars (e.g., ribose, deoxyribose).

• Hexoses: 6-carbon sugars (e.g., glucose, fructose, galactose).

• Functions: Quick energy source, building blocks for larger carbohydrates.

Examples:

• Glucose: Main energy source for cells.

• Fructose: Found in fruits.

• Galactose: Found in milk.