The Chemistry of Life

Introduction

The study of anatomy and physiology begins with understanding the chemical basis of life. All living organisms are composed of matter and energy, which interact to sustain biological processes. This section introduces the essential chemical principles underlying human biology.

Matter

Definition and States of Matter

Matter is the "stuff" of the universe, defined as anything that has mass and occupies space. Matter exists in three primary states:

• Solid: Has a definite shape and volume.

• Liquid: Has a definite volume but a changeable shape.

• Gas: Has both changeable shape and volume.

Energy

Definition and Types of Energy

Energy is the capacity to do work or put matter into motion. It exists in two main forms:

• Kinetic Energy: Energy in action.

• Potential Energy: Stored energy due to position; inactive until released.

Forms of Energy

• Chemical Energy: Stored in the bonds of chemical substances.

• Electrical Energy: Results from the movement of charged particles.

• Mechanical Energy: Directly involved in moving matter.

• Radiant (Electromagnetic) Energy: Energy traveling in waves, such as visible light, ultraviolet light, and X-rays.

Energy Form Conversions

• Energy can be converted from one form to another, such as chemical energy to mechanical energy during muscle contraction.

• During conversion, some energy is "lost" as heat, increasing entropy.

Composition of Matter

Elements and Atoms

• Elements: Unique substances that cannot be broken down by ordinary chemical means.

• Atoms: The basic building blocks of each element, consisting of a nucleus and electrons.

• Atomic Symbol: One- or two-letter shorthand for each element (e.g., O for oxygen).

Properties of Elements

• Physical Properties: Characteristics detected with our senses (e.g., color, texture).

• Chemical Properties: Describe how atoms interact with one another (e.g., reactivity).

Elements of the Human Body

Major Elements

Four elements make up about 96% of the human body:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

Lesser and Trace Elements

• Lesser Elements: Make up 3.9% of the body and include calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl), magnesium (Mg), iodine (I), and iron (Fe).

• Trace Elements: Make up less than 0.01% of the body. They are required in minute amounts and are often found as part of enzymes.

Atomic Structure

Subatomic Particles

• Neutrons: No charge; mass of 1 atomic mass unit (amu).

• Protons: Positive charge; mass of 1 amu.

• Electrons: Negative charge; mass of approximately 1/2000 that of a proton (effectively 0 amu); found orbiting the nucleus.

Models of the Atom

Planetary Model

• Electrons move around the nucleus in fixed, circular orbits.

Orbital Model

• Electrons are found in regions (orbitals) around the nucleus where they are most likely to be located.

Summary Table: Major, Lesser, and Trace Elements of the Human Body

Example Applications

• Chemical energy in food is converted to mechanical energy for movement.

• Electrical energy is used to transmit nerve impulses.

• Oxygen is essential for cellular respiration, a process that releases energy from nutrients.

Key Equations

• Atomic Mass Number:

• Atomic Number:

Additional info:

• Understanding the chemical basis of life is essential for grasping physiological processes such as metabolism, nerve conduction, and muscle contraction.

• Trace elements, though present in minute quantities, are vital for enzyme function and overall health.