The Chemical Level of Organization

Introduction to Chemistry in Biology

Living organisms and their environments are fundamentally composed of chemicals, which are organized into molecules and higher levels of biological structure. Understanding basic chemistry is essential for comprehending the processes of life.

• Chemicals form the basis of biological organization.

• Atoms are ordered into molecules, representing the lowest level of biological organization.

• Biological structure and function depend on the arrangement and interaction of these chemicals.

Elements, Atoms, and Molecules

Elements are the simplest forms of matter and cannot be broken down further. Atoms are the smallest units of elements, and molecules are combinations of atoms.

• Element: A pure substance consisting of only one type of atom.

• There are 92 naturally occurring elements; about 25 are essential for life.

• Trace elements are required in minute amounts but are vital for health.

Trace Elements and Their Importance

Trace elements are added to food and water to prevent disease and support physiological functions.

• Iron (Fe): Essential for oxygen transport in blood.

• Iodine (I): Required for thyroid hormone production; deficiency can cause goiter.

Compounds

Compounds are substances formed from two or more elements in fixed ratios. Their properties differ from the individual elements.

• Example: Sodium chloride (NaCl) is formed from sodium (a metal) and chlorine (a poisonous gas), but together they make edible table salt.

• Most biological compounds contain carbon, hydrogen, oxygen, and nitrogen.

Atomic Structure and Properties

Atoms and Subatomic Particles

Atoms consist of protons, neutrons, and electrons. These subatomic particles determine the chemical properties of elements.

• Proton: Positive charge

• Neutron: No charge

• Electron: Negative charge

Element Information and Atomic Number

Each element is defined by its atomic number (number of protons) and atomic mass (sum of protons and neutrons).

• Atomic Number: Number of protons in the nucleus

• Atomic Mass: Weighted average mass based on isotopes

• Element Symbol: Abbreviation from common or Latin name

Isotopes and Atomic Mass

Isotopes are variants of elements with different numbers of neutrons. Atomic mass reflects the average mass of all isotopes.

• Example: Hydrogen has three isotopes: 1H (protium), 2H (deuterium), 3H (tritium).

• Atomic mass is calculated based on the abundance of each isotope.

Isotopes of Carbon

Radioactive Isotopes

Some isotopes are unstable and emit energy, which can be useful or harmful.

• Medical uses: Radioactive tracers for imaging (e.g., PET scans).

• Dangers: Uncontrolled exposure can damage DNA and cellular molecules.

Electron Arrangement and Chemical Bonds

Electron Shells and Chemical Properties

Electrons occupy energy levels called shells. The arrangement of electrons determines how atoms interact and form bonds.

• First shell holds 2 electrons; second and third hold up to 8.

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

Ionic Bonds

Ionic bonds form when atoms transfer electrons, resulting in charged ions that attract each other.

• Example: Sodium (Na) donates an electron to chlorine (Cl), forming Na+ and Cl– ions, which combine to make NaCl.

Covalent Bonds

Covalent bonds form when atoms share electrons. These bonds are essential for forming molecules.

• Atoms follow the octet rule, seeking to fill their outer shell.

• Electronegativity: The ability of an atom to attract shared electrons.

Polar and Nonpolar Covalent Bonds

• Nonpolar covalent bonds: Electrons are shared equally (e.g., H2, O2).

• Polar covalent bonds: Electrons are shared unequally, creating partial charges (e.g., H2O).

Hydrogen Bonds

Hydrogen bonds are weak attractions between polar molecules, especially important in water and biological molecules.

• Hydrogen bonds contribute to water's cohesion, surface tension, and temperature moderation.

Cohesion and Surface Tension

Water molecules stick together due to hydrogen bonding, resulting in high cohesion and surface tension.

• Surface tension allows insects to walk on water.

Water's Role in Temperature Regulation

Hydrogen bonds allow water to resist temperature changes, supporting life by stabilizing environments and organisms.

• Evaporative cooling (perspiration) is an example of water's temperature regulation.

Density of Ice vs. Liquid Water

Water is less dense as a solid (ice) than as a liquid, due to stable hydrogen bonds forming a crystal structure.

• Ice floats on water, which is crucial for aquatic life.

Water as the Solvent of Life

Solutions, Solutes, and Solvents

Water is the universal solvent, dissolving many substances essential for biological processes.

• Solute: Substance dissolved

• Solvent: Substance doing the dissolving (water in biological systems)

Chemical Reactions and Energy

Types of Energy

• Potential energy: Stored energy, such as chemical energy in bonds.

• Kinetic energy: Energy of motion, used to perform work.

ATP: The Energy Molecule

ATP stores chemical energy in phosphate bonds, which is released during hydrolysis to power cellular processes.

• ATP (adenosine triphosphate) is the primary energy carrier in cells.

Types of Chemical Reactions

• Synthesis:

• Decomposition:

• Exchange:

• Reversible:

Activation Energy

Chemical reactions require activation energy to start. Enzymes lower this energy barrier, allowing reactions to proceed efficiently in cells.

Acidic and Basic Conditions

Acids, Bases, and pH

Water can dissociate into hydrogen ions (H+) and hydroxide ions (OH–). The balance of these ions determines acidity or basicity.

• Acid: Increases H+ concentration

• Base: Reduces H+ concentration, increases OH–

• pH scale: Measures acidity/basicity from 0 (acidic) to 14 (basic); 7 is neutral.

Summary Table: Elements in the Human Body

Summary Table: Isotopes of Carbon

Key Takeaways

• Understanding the chemical basis of life is foundational for anatomy and physiology.

• Elements, atoms, and molecules form the structural and functional basis of living organisms.

• Chemical bonds and reactions drive biological processes, including energy transfer and regulation of pH.