Essential Chemistry for Biology: Foundations for Life

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Essential Chemistry for Biology

Biology and Society: The Importance of Water

Water is fundamental to all life on Earth. Droughts, or periods of abnormally dry weather, can have devastating effects on ecosystems and human societies, leading to crop failure, water shortages, and even the collapse of civilizations. Life cannot exist without water, making it more precious than gold.

Cracked dry earth, illustrating drought Desert landscape with dead trees, illustrating habitat loss due to drought

Some Basic Chemistry

All biological systems are composed of chemical substances. Understanding biology requires a foundation in chemistry, as chemical reactions are constantly occurring within living organisms.

Summary diagram of metabolic pathways

Matter: Elements and Compounds

Matter is anything that occupies space and has mass. It exists in three physical states: solid, liquid, and gas. All matter is composed of chemical elements, which are substances that cannot be broken down into other substances by chemical reactions. There are 92 naturally occurring elements, all listed in the periodic table.

Diagram showing solid, liquid, and gas states of matter Periodic table of elements

Elements and Compounds

Element: A pure substance consisting of only one kind of atom.
Compound: A substance containing two or more elements in a fixed ratio (e.g., H2O, NaCl).

Elements Essential to Life

Twenty-five elements are essential for human life. Four elements—oxygen (O), carbon (C), hydrogen (H), and nitrogen (N)—make up about 96% of the weight of most cells. Other elements, such as calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl), and magnesium (Mg), are also important. Trace elements are required in very small amounts but are essential for life (e.g., iron, iodine, fluorine).

Diagram showing the elemental composition of the human body

Trace Elements

Fluorine: Added to dental products and drinking water to maintain healthy bones and teeth.
Iodine: Essential for thyroid function; deficiency can cause goiter.

Diagram showing fluoride protecting tooth enamel Photograph of a person with goiter due to iodine deficiency Dietary sources of iodine: iodized salt, milk, eggs, spinach, strawberries

The Structure of Atoms

Atoms are the smallest units of matter that retain the properties of an element. They are composed of subatomic particles: protons (positive charge), neutrons (no charge), and electrons (negative charge). Protons and neutrons are packed into the nucleus, while electrons orbit the nucleus in electron shells.

Diagram of an atom showing nucleus and electron orbits

Atomic Number and Mass Number

Atomic number: Number of protons in the nucleus; defines the element.
Mass number: Sum of protons and neutrons in the nucleus.

Isotopes

Isotopes are forms of an element with the same number of protons but different numbers of neutrons. Some isotopes are stable, while others are radioactive and decay over time, releasing particles and energy.

	Carbon-12	Carbon-13	Carbon-14
Protons	6	6	6
Neutrons	6	7	8
Electrons	6	6	6

Table of carbon isotopes

Radioactive Isotopes and Their Uses

Radiometric dating: Used to estimate the age of fossils by measuring the decay of radioactive isotopes (e.g., carbon-14).
Medical applications: Used in PET scans to diagnose diseases.

Graph showing radioactive decay of carbon-14

Electron Arrangement and Chemical Properties

Electrons are arranged in shells around the nucleus. The chemical properties of an atom are determined by the number of electrons in its outermost shell (valence shell). Atoms with incomplete outer shells tend to react with other atoms to achieve stability.

Electron shells of hydrogen and carbon Electron shells of nitrogen and oxygen

Chemical Bonding and Molecules

Chemical bonds form when atoms interact to complete their outer electron shells. The main types of chemical bonds are ionic, covalent, and hydrogen bonds.

Ionic Bonds

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

Formation of sodium chloride (NaCl) through ionic bonding

Covalent Bonds

Covalent bonds form when two atoms share one or more pairs of electrons. These are the strongest chemical bonds and are responsible for holding atoms together in molecules (e.g., H2, O2, CH4).

Models of covalent bonding in H2, O2, and CH4

Hydrogen Bonds

Hydrogen bonds are weak attractions between the slightly positive hydrogen atom of one molecule and the slightly negative atom of another molecule. Water molecules form hydrogen bonds due to their polarity, which is crucial for many of water's unique properties.

Polarity of water molecule and hydrogen bonding Hydrogen bonds between water molecules

Chemical Reactions

Chemical reactions involve the breaking and forming of chemical bonds, resulting in the rearrangement of atoms. Reactants are the starting materials, and products are the end materials. Chemical reactions do not create or destroy matter but rearrange it.

Chemical reaction between hydrogen and oxygen to form water

Water and Life

Water is essential for life, making up 70–95% of cells. Its abundance on Earth is a key reason for the planet's habitability. Water's unique properties are due to its polarity and hydrogen bonding.

Water’s Life-Supporting Properties

Cohesion: Water molecules stick together, aiding in the transport of water in plants.
Surface tension: Water has a high surface tension due to hydrogen bonding.
Temperature moderation: Water resists temperature changes, helping to stabilize environments.
Ice floats: Solid water (ice) is less dense than liquid water, allowing aquatic life to survive under ice layers.
Solvent properties: Water dissolves many substances, making it the solvent of life.

Cohesion of water molecules in plant transport Hydrogen bonding in ice and liquid water

Acids, Bases, and pH

Acids are substances that release hydrogen ions (H+) in solution, while bases accept H+ ions. The pH scale measures the concentration of H+ ions, ranging from 0 (most acidic) to 14 (most basic), with 7 being neutral. Buffers help maintain stable pH in biological systems by accepting or donating H+ ions as needed.

pH scale showing acidic, neutral, and basic solutions Diagram illustrating buffer action in solution

Environmental Impact: Ocean Acidification

Increases in atmospheric CO2 can lead to ocean acidification, threatening marine ecosystems and biodiversity.

Evolution Connection: The Search for Extraterrestrial Life

Water is considered essential for life as we know it. The search for extraterrestrial life often focuses on finding water on other planets, such as Mars, where evidence suggests water was once abundant.