Water and Carbon: The Basis of Life (General Biology Study Notes)

Chapter 2: Water and Carbon – The Basis of Life

Overview

This chapter explores how chemistry underpins the evolution and function of life, focusing on the roles of water and carbon. Key concepts include the structure of atoms, ions, and molecules, the nature of chemical reactions, energy transformations, and the unique properties of water and carbon in biological systems.

The Structure of Atoms, Ions, and Molecules

Atoms and Molecules

• Atom: The smallest unit of an element, composed of protons, neutrons, and electrons.

• Molecule: Two or more atoms bonded together.

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

Atoms combine to form molecules through chemical bonds, which can be ionic (transfer of electrons) or covalent (sharing of electrons).

Chemical Reactions

Types of Chemical Reactions

• Reversible Reaction: The products can revert to reactants. Example: $\mathrm{H_2O} \rightleftharpoons \mathrm{CH_2O_3}$

• Irreversible Reaction: The reaction proceeds in one direction only. Example: $\mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{H_2O}$

Chemical reactions involve the breaking and formation of chemical bonds, resulting in the transformation of substances.

Example: Cellular Respiration

• Cellular Respiration: A process by which cells convert glucose and oxygen into carbon dioxide, water, and energy (ATP).

General equation:

$\mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} + 30\mathrm{ADP} + 30\mathrm{Pi} \rightarrow 6\mathrm{CO_2} + 6\mathrm{H_2O} + 30\mathrm{ATP}$

This reaction demonstrates the transfer of energy required for chemical reactions in living organisms.

Energy in Biological Systems

What Is Energy?

• Energy: The capacity to do work or supply heat.

• Exists in two main forms:

  • Potential Energy: Stored energy due to position or structure (e.g., energy stored in chemical bonds).

  • Kinetic Energy: Active energy of movement.

Energy transformations are essential for biological processes such as metabolism and growth.

Potential Energy in Covalent Bonds

Bond Strength and Energy

• Polar Covalent Bonds: Unequal sharing of electrons (e.g., O–H), shortest and strongest bonds, lower potential energy.

• Nonpolar Covalent Bonds: Equal sharing of electrons (e.g., C–H), longest and weakest bonds, higher potential energy.

Polar covalent bonds are more easily broken, releasing energy that can be harnessed by cells.

Spontaneous Processes, Potential Energy, and Entropy

Spontaneity and Disorder

• Spontaneous Processes: Tend to result in lower potential energy and increased disorder (higher entropy).

• Entropy: A measure of disorder or randomness in a system.

Example: The combustion of glucose increases entropy and releases energy as heat.

$\mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \rightarrow 6\mathrm{CO_2} + 6\mathrm{H_2O} + \text{Heat}$

Organic Molecules and Carbon’s Role in Life

Importance of Organic Molecules

• Organic Compounds: Molecules containing carbon and other elements (e.g., hydrogen, oxygen, nitrogen).

• Carbon atoms provide a versatile backbone for molecular structure and function.

• The chemical behavior of organic compounds is dictated by their functional groups (e.g., hydroxyl, carboxyl, amino, phosphate).

Functional Groups

• Functional Group: A specific group of atoms within a molecule that is responsible for characteristic chemical reactions.

• Examples include hydroxyl (–OH), carboxyl (–COOH), amino (–NH2), and phosphate (–PO4).

• Functional groups influence molecular properties such as acidity, polarity, and reactivity.

Macromolecules and Their Building Blocks

Monomers and Polymers

• Monomer: A small molecule that can join with others to form a polymer.

• Polymer: A large molecule made of repeating monomer units.

• Polymerization requires energy and decreases molecular disorder.

Major Families of Organic Molecules

Building Block (Monomer)	Macromolecule (Polymer)	Function
Monosaccharide	Polysaccharide	Energy storage, structural support
Fatty acid	Lipid	Membrane structure, energy storage
Amino acid	Protein	Catalysis, structure, signaling
Nucleotide	Nucleic acid	Genetic information storage and transfer

Example: Glucose (a monosaccharide) polymerizes to form starch or glycogen (polysaccharides).

Additional info: The notes infer the importance of energy transformations and molecular structure in the origin and maintenance of life, as well as the central role of carbon in organic chemistry.