Chemistry of the Human Body: Chapter 2A Study Guide

Chemistry Comes Alive

Overview of the Chemical Level of Organization

The chemical level is the smallest and least complex level of organization in the human body. Understanding chemistry is essential for grasping how biological processes occur at the molecular level. This section covers matter, elements, chemical reactions, energy, inorganic compounds, water, salts/electrolytes, and acids and bases.

Matter and Mass

Definitions and Differences

• Matter: Anything that has mass and takes up space. Examples include humans, animals, water, and all living things.

• Mass: A measure of the amount of matter in an object. It is constant and only changes with significant physical changes (e.g., gaining/losing muscle, fat, or bone density).

• Weight: The force exerted by gravity on an object. It can vary depending on location due to changes in gravity.

Example: Weighing yourself on different floors of a building yields slightly different weights, but your mass remains unchanged.

Elements

Definition and Importance

• Elements: The simplest substances that cannot be broken down further by chemical reactions.

• There are 92 natural elements, but only a few are crucial for human biology.

Major Elements in the Human Body

CHON Elements

• Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N): These four elements make up approximately 96% of the human body.

• Memory Trick: "CHON" helps recall the major elements.

Trace Elements

Essential Minor Elements

• Trace elements: Present in smaller amounts but essential for life.

• Calcium (Ca) and Phosphorus (P): Form salts that strengthen bones and teeth.

• Sodium (Na) and Potassium (K): Necessary for muscle contraction, nervous system function, and electrical signaling.

Additional info: Sodium and potassium are critical for nerve communication via electrical signals.

Chemical Reactions

Reactants and Products

• Chemical reactions: Processes that build or break down compounds.

• Reactants: Starting materials in a reaction.

• Products: Substances formed after the reaction.

Example: Baking a cake: ingredients (reactants) become the finished cake (product). Hydrogen and oxygen combine to form water.

Types of Chemical Reactions

Decomposition (Catabolic) Reactions

• Definition: Break large compounds into smaller parts.

• Exergonic: Energy is released when bonds break. Memory Trick: Exergonic = Energy EXITS.

• Catabolic: Catastrophic destruction; breaking apart molecules.

Example: Large Lego castle broken into individual pieces.

Synthesis (Anabolic) Reactions

• Definition: Build larger compounds from smaller ones.

• Endergonic: Energy must be added to form bonds. Memory Trick: Endergonic = Energy ENTERS.

• Anabolic: Building/growth; muscles get bigger.

Example: $A + B \rightarrow AB$

Equilibrium Reactions

• Definition: Reactions that can build or break down compounds depending on the body's needs.

• Homeostasis: The body constantly maintains equilibrium and balance.

Example: The body adjusts synthesis or decomposition to restore balance, like a seesaw.

Energy

Types and Importance

• Energy: The capacity to do work or put matter into motion. Cells require energy to function.

Kinetic vs Potential Energy

• Kinetic energy: Energy in motion (e.g., moving muscles).

• Potential energy: Stored energy that can become kinetic (e.g., students sitting, ready to stand).

Kinetic Energy	Potential Energy
Energy in action	Stored energy
Moving	Not moving
Active	Can become active

Other Forms of Energy

• Chemical energy: Stored in chemical bonds; ATP is the main energy source for cells. ATP releases energy when broken apart.

• Electrical energy: From moving charged particles (ions like sodium and calcium); creates electrical signals in cells.

• Mechanical energy: Used to move body parts (e.g., muscle contraction).

• Radiant/Electromagnetic energy: Light energy (visible light, UV, X-rays); important for vision.

Biochemistry

Definition

• Biochemistry: The study of chemistry in living organisms.

Organic vs Inorganic Compounds

Classification

• Organic compounds: Contain carbon. Examples: carbohydrates, fats, proteins, nucleic acids.

• Inorganic compounds: Do not contain carbon. Examples: water, salts, acids, bases.

Memory Hint: Foods are organic compounds.

Water

Properties and Importance

• 60–80% of cells are made of water; body fluids are mixtures/solutions, not pure water.

High Heat Capacity

• Water absorbs large amounts of heat before changing temperature, distributing heat evenly throughout the body.

Example: Microwaved coffee mug is hot, but liquid is lukewarm; water absorbs heat slowly.

High Heat of Vaporization

• Water absorbs heat and removes it through evaporation (sweating), helping maintain body temperature (~98°F).

Solvent Properties

• Solvent: The liquid portion (e.g., water).

• Solute: The substance dissolved (e.g., salt).

• Water is an excellent transport medium; it does not alter solutes.

Example: Saltwater: water is the solvent, salt is the solute.

Reactivity

• Water participates in reactions such as hydrolysis (breaking compounds apart using water) and dehydration synthesis (removing water to build compounds).

Example: Digestion requires water for hydrolysis.

Cushioning

• Water protects organs and lubricates joints.

• The body does not make water; hydration is essential.

Example: Dehydration can lead to joint pain as water is removed from joints for vital functions.

Salts/Electrolytes

Definitions and Functions

• Electrolytes: Salts that conduct electricity.

• Cations: Positively charged ions ("T" resembles +).

• Anions: Negatively charged ions ("N" = negative).

Electrolyte	Importance
Sodium chloride	Fluid/electrical balance
Potassium chloride	Muscle & nerve function
Calcium carbonate	Bone support
Calcium phosphate	Strengthens bones & teeth (most abundant salt in the body)

Acids and Bases

pH Scale and Concepts

• pH scale: Ranges from 0 to 14.

• pH 7: Neutral

• Below 7: Acidic

• Above 7: Basic/alkaline

Relationship between pH and hydrogen: Hydrogen concentration and pH move in opposite directions.

Hydrogen	pH
High hydrogen	Low pH
Low hydrogen	High pH

• Acids: More hydrogen ions, pH below 7 (e.g., milk, pH 6.3).

• Bases: Fewer hydrogen ions, pH above 7 (e.g., blood, pH 7.4).

Example: Heartburn is caused by excess acid; treatments (Tums, Nexium, Pepto-Bismol) are basic substances that absorb hydrogen and raise pH.

High Priority Exam Focuses

• Chemistry Basics: Matter, mass vs weight, elements, CHON elements

• Reactions: Catabolic vs anabolic, exergonic vs endergonic, equilibrium reactions

• Water Properties: High heat capacity, high heat of vaporization, solvent properties, hydrolysis vs dehydration synthesis, cushioning

• Electrolytes: Sodium, potassium, calcium, calcium phosphate

• pH Concepts: Acids vs bases, pH scale, hydrogen relationship to pH

Memory Tricks from Lecture

Concept	Memory Trick
CHON	Major body elements
Exergonic	Energy exits
Endergonic	Energy enters
Catabolic	Catastrophic destruction
Anabolic	Muscles get bigger
Hydrolysis	Water breaks apart
Cations	"T" resembles +
Anions	"N" = negative