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The Chemical Context of Life: Foundations for General Biology

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The Chemical Context of Life

Introduction

Understanding biology requires a foundation in chemistry and physics, as living organisms are composed of matter and governed by chemical principles. This section introduces the chemical basis of life, focusing on the elements, atomic structure, and chemical bonds essential for biological processes.

Biology as a Multidisciplinary Science

Integration of Chemistry, Physics, and Math

  • Biology is deeply interconnected with chemistry, physics, and mathematics.

  • Biological phenomena are explained by chemical reactions, physical laws, and mathematical models.

  • Examples: Cellular respiration involves chemical reactions; diffusion is governed by physical principles; population growth is modeled mathematically.

Composition of Living Things

Matter, Elements, and Compounds

  • Matter: Anything that takes up space and has mass.

  • Element: A substance that cannot be broken down to other substances by chemical reactions (e.g., Oxygen, Carbon).

  • Compound: A substance consisting of two or more elements in a fixed ratio (e.g., Sodium chloride).

  • Example: Sodium (Na) and Chlorine (Cl) combine to form Sodium chloride (NaCl), a compound essential for life.

Elements of Life

Major and Trace Elements in the Human Body

Living organisms are primarily composed of a small subset of elements, with a few making up the majority of body mass.

Element

Symbol

Percentage of Body Mass (including water)

Oxygen

O

65.0%

Carbon

C

18.5%

Hydrogen

H

9.5%

Nitrogen

N

3.3%

Calcium

Ca

1.5%

Phosphorus

P

1.0%

Potassium

K

0.4%

Sulfur

S

0.3%

Sodium

Na

0.2%

Chlorine

Cl

0.2%

Magnesium

Mg

0.1%

  • Trace elements (less than 0.01%): Boron, Chromium, Cobalt, Copper, Fluorine, Iodine, Iron, Manganese, Molybdenum, Selenium, Silicon, Tin, Vanadium, Zinc.

  • These elements are essential for various biological functions, such as enzyme activity and hormone production.

Atomic Structure

Atoms, Subatomic Particles, and Isotopes

  • Atom: The smallest unit of an element, composed of protons, neutrons, and electrons.

  • Proton: Positively charged particle in the nucleus.

  • Neutron: Neutral particle in the nucleus.

  • Electron: Negatively charged particle orbiting the nucleus.

  • Atomic number: Number of protons in the nucleus.

  • Mass number: Sum of protons and neutrons.

  • Isotopes: Atoms of the same element with different numbers of neutrons. Some are radioactive and decay spontaneously, emitting particles and energy.

Electron Distribution and Chemical Properties

Energy Shells and Valence Electrons

  • Electrons are arranged in energy levels or shells around the nucleus.

  • Valence electrons: Electrons in the outermost shell, determining chemical reactivity.

  • Atoms with incomplete valence shells tend to share or transfer electrons to achieve stability.

Chemical Bonds

Types of Chemical Bonds

  • Covalent bond: Sharing of valence electrons between atoms.

  • Single covalent bond: Sharing of one pair of electrons.

  • Double covalent bond: Sharing of two pairs of electrons.

  • Molecule: Two or more atoms held together by covalent bonds.

  • Polar covalent bond: Unequal sharing of electrons due to differences in electronegativity, resulting in partial charges.

  • Nonpolar covalent bond: Equal sharing of electrons.

  • Ionic bond: Attraction between oppositely charged ions (cation and anion). Example: Formation of sodium chloride (NaCl).

  • Hydrogen bond: Weak attraction between a hydrogen atom covalently bonded to an electronegative atom (usually O or N) and another electronegative atom.

Importance of Molecular Shape

Shape Determines Function

  • The three-dimensional shape of molecules is determined by the arrangement of chemical bonds.

  • Molecular shape is critical for biological function, such as enzyme activity and cell signaling.

Chemical Reactions

Reactants, Products, and Equilibrium

  • Chemical reaction: The making and breaking of chemical bonds, transforming reactants into products.

  • Reactants: Starting substances in a chemical reaction.

  • Products: Substances formed as a result of the reaction.

  • Reactions are often reversible, reaching chemical equilibrium when the rates of forward and reverse reactions are equal.

Example Equation:

This reaction shows the formation of water from hydrogen and oxygen.

Important Chemical Reactions for Life

  • Cellular respiration: The breakdown of glucose to produce energy.

  • Photosynthesis: The process by which plants convert carbon dioxide and water into glucose and oxygen using energy from sunlight.

Additional info: The above equations are central to metabolism and energy flow in living systems.

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