Background Terminology

Matter and Its States

Matter is defined as anything that occupies space and has mass. It exists in three primary states:

• Solid – has a definite shape and volume.

• Liquid – has a definite volume but takes the shape of its container.

• Gas – has neither a definite shape nor a definite volume.

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

• Kinetic energy – energy in action.

• Potential energy – stored energy; has the capability to do work but is not currently doing so.

Forms of energy relevant to physiology include:

• Chemical energy – stored in the bonds of chemical substances (e.g., food molecules, ATP).

• Electrical energy – movement of charged particles.

• Mechanical energy – energy directly involved in moving matter.

• Radiant (electromagnetic) energy – energy that travels in waves (e.g., visible light, X-rays).

Basic Atomic Structure

Atoms and Elements

All matter is composed of elements, unique substances that cannot be broken down by ordinary chemical means. Each element is identified by its atomic symbol and is listed in the periodic table.

• An atom is the smallest particle of an element that retains its properties.

• Atoms consist of a central nucleus (containing protons and neutrons) and electrons that orbit the nucleus.

• Protons are positively charged, neutrons are neutral, and electrons are negatively charged.

• The atomic number is the number of protons in the nucleus; the mass number is the sum of protons and neutrons.

• Atoms are electrically neutral when the number of protons equals the number of electrons.

Isotopes are atoms of the same element with different numbers of neutrons.

Major Elements and Trace Elements in the Body

Essential Elements

The human body is primarily composed of four major elements:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

These elements make up about 96% of body weight. Other important minerals (trace elements) include calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium, and iron. Trace elements are required in very small amounts but are essential for normal body function.

Definitions: Molecule, Compound, Mixture, Solution, Solvent, and Solute

Key Terms

• Molecule – two or more atoms bonded together (e.g., O2).

• Compound – a substance formed when two or more different kinds of atoms bind together (e.g., H2O).

• Mixture – a physical combination of two or more substances (e.g., air, blood).

• Solution – a homogeneous mixture where the components are evenly distributed (e.g., salt water).

• Solvent – the substance present in the greatest amount in a solution (e.g., water in salt water).

• Solute – the substance present in smaller amounts and dissolved in the solvent (e.g., salt in salt water).

Chemical Bonds: Ionic, Covalent, and Hydrogen Bonds

Types of Chemical Bonds

• Ionic bonds – formed when one atom transfers electrons to another, resulting in oppositely charged ions that attract each other (e.g., NaCl).

• Covalent bonds – formed when two atoms share one or more pairs of electrons. Can be nonpolar (equal sharing) or polar (unequal sharing, as in water).

• Hydrogen bonds – weak attractions between a hydrogen atom (already covalently bonded to another atom) and an electronegative atom (e.g., oxygen or nitrogen) in another molecule. Important in water and biological molecules.

Example: Water (H2O) molecules are held together by polar covalent bonds, and hydrogen bonds form between adjacent water molecules, giving water its unique properties.

Properties of Water and Its Importance

Unique Properties of Water

• High heat capacity – absorbs and releases large amounts of heat with little temperature change.

• High heat of vaporization – requires significant energy to break hydrogen bonds for evaporation, aiding in cooling.

• Polar solvent properties – dissolves ionic and polar substances, making it the universal solvent.

• Reactivity – involved in hydrolysis and dehydration synthesis reactions.

• Cushioning – protects organs by forming a cushion (e.g., cerebrospinal fluid).

Acids, Bases, Buffers, and pH

Acids and Bases

• Acids – substances that release hydrogen ions (H+) in solution (e.g., HCl).

• Bases – substances that accept hydrogen ions or release hydroxide ions (OH-) (e.g., NaOH).

The pH scale measures the concentration of hydrogen ions in a solution:

• pH 7 is neutral; below 7 is acidic; above 7 is basic (alkaline).

• Blood pH is tightly regulated between 7.35 and 7.45.

Buffers are substances that minimize changes in pH by releasing or binding hydrogen ions as needed.

Major Biomolecules: Carbohydrates, Proteins, Lipids, and Nucleic Acids

Carbohydrates

• Composed of carbon, hydrogen, and oxygen.

• Main source of energy for cells.

• Include sugars (monosaccharides, disaccharides) and starches (polysaccharides).

• Example: Glucose (C6H12O6).

Proteins

• Made of amino acids joined by peptide bonds.

• There are 20 different amino acids; proteins may contain 100–10,000 amino acids.

• Serve as structural materials, enzymes, and hormones.

• Enzymes are biological catalysts that speed up chemical reactions.

Lipids

• Insoluble in water; include fats, oils, and steroids.

• Functions: energy storage, insulation, and cell membrane structure (phospholipids).

• Phospholipids form the bilayer of cell membranes.

Nucleic Acids

• Composed of nucleotides (phosphate, sugar, nitrogenous base).

• DNA (deoxyribonucleic acid) stores genetic information.

• RNA (ribonucleic acid) is involved in protein synthesis.

• ATP (adenosine triphosphate) is the energy currency of the cell.

Summary Table: Major Biomolecules

Key Equations

• pH calculation:

• General formula for carbohydrates:

• ATP hydrolysis:

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.