Biology 1 - Lesson 2: Chemical Foundations of Life
Overview
Biological systems depend on chemical elements and compounds to sustain life. This lesson explores the chemical context of life, focusing on atoms, molecules, chemical bonds, and the special properties of water that make it indispensable for organisms. By understanding these chemical underpinnings, you will gain insight into how complex biological processes emerge from fundamental chemical interactions.
1. Atoms, Elements, and Compounds
1.1 Structure of an Atom
Protons: Positively charged particles located in the nucleus.
Neutrons: Electrically neutral particles, also in the nucleus.
Electrons: Negatively charged particles found in orbitals surrounding the nucleus.
The atomic number is the number of protons in an atom, which defines the element. The mass number is the total of protons plus neutrons. An element can have variants called isotopes, which differ in neutron number but retain the same number of protons.
1.2 Elements Essential to Life
Although there are 118 known elements, only about 25 are essential for most life forms. The four most common in living organisms are:
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Together, they make up approximately 96% of the human body’s mass. Additional elements such as phosphorus (P), sulfur (S), calcium (Ca), and potassium (K) are also crucial for various biological functions (e.g., ATP production, bone structure, nerve signaling).
1.3 Formation of Compounds
A compound is a substance consisting of two or more elements combined in a fixed ratio. Common examples include:
Water (H₂O): Two hydrogens bound to one oxygen.
Carbon Dioxide (CO₂): One carbon bound to two oxygens.
Biological systems use myriad compounds, both inorganic (like water and mineral salts) and organic (containing carbon-hydrogen bonds, like glucose).
2. Chemical Bonds
2.1 Ionic Bonds
Occur when electrons are transferred from one atom to another, creating ions (charged atoms or molecules).
Example: Sodium chloride (NaCl) forms when sodium (Na⁺) donates an electron to chlorine (Cl⁻).
2.2 Covalent Bonds
Form when electrons are shared between atoms.
Covalent bonds are stronger in biological contexts compared to ionic interactions in aqueous environments.
Example: Water (H₂O) has polar covalent bonds, with electrons shared unequally between O and H.
2.3 Hydrogen Bonds
Weak attractions between a partially positive hydrogen atom in one molecule and a partially negative atom (often oxygen or nitrogen) in another.
Critical in maintaining the structure of large biomolecules such as DNA (holding the two strands together) and proteins.
| Bond Type | Key Characteristics |
|---|---|
| Ionic Bond |
|
| Covalent Bond |
|
| Hydrogen Bond |
|
3. Water: The Essential Molecule for Life
3.1 Polarity of Water
Water’s molecular structure (H₂O) is bent, causing an uneven charge distribution:
The oxygen end is partially negative (δ−).
Each hydrogen end is partially positive (δ+).
This polarity leads to hydrogen bonding between water molecules, granting water many unique properties essential to life.
3.2 Properties of Water
Cohesion and Adhesion
Cohesion: Water molecules stick to each other (surface tension).
Adhesion: Water molecules stick to other substances (capillary action in plants).
High Specific Heat
Water can absorb or release large amounts of heat with only a slight change in its own temperature, moderating Earth’s climate and helping organisms regulate body temperature.
High Heat of Vaporization
Evaporation of water (e.g., sweat) cools surfaces significantly due to the high energy required to break hydrogen bonds.
Expansion Upon Freezing
Ice is less dense than liquid water (hydrogen bonds become rigid and form a lattice), allowing ice to float and insulate aquatic life in cold climates.
Excellent Solvent
Water’s polarity can dissolve many ionic and polar substances, enabling chemical reactions and transport of nutrients in organisms.
3.3 Biological Significance
Cellular Environment: Most biochemical reactions take place in an aqueous environment inside cells.
Transport: Blood plasma is mostly water; plants use water-based xylem sap to transport nutrients.
Temperature Regulation: Sweating in mammals and transpiration in plants illustrate water’s role in thermoregulation.
4. Real-Life Applications
Medical IV Solutions: Carefully balanced aqueous solutions maintain patients’ ion and fluid balance.
Agriculture: Soil moisture content critically impacts plant growth; irrigation strategies revolve around water’s properties.
Climate Science: Large bodies of water stabilize regional temperatures, influencing weather and climate patterns.
5. Exercise: Exploring Water Properties at Home
Objective: Investigate how water’s cohesion and adhesion properties work.
Materials:
Two clear glasses or jars
Paper towels
Water
Food coloring (optional)
Procedure:
Fill one glass with water, leaving the other empty.
Twist or fold a paper towel into a long strip.
Place one end of the paper towel in the glass with water and the other end in the empty glass.
[Optional] Add food coloring to the water for a more visible effect.
Observation:
Over time, water will “walk” through the paper towel from the full glass into the empty one. This illustrates capillary action (a combination of cohesion and adhesion).
Analysis:
Note how the adhesion of water to the paper towel fibers and the cohesion between water molecules enable water to move upward against gravity.
6. Additional Learning Components
6.1 Historical Anecdote: Linus Pauling’s Contribution
Linus Pauling (1901–1994) was instrumental in describing the nature of the chemical bond. His work on electronegativity and bond formation set the stage for modern chemistry and structural biology. He received two unshared Nobel Prizes (one in Chemistry and one in Peace).
6.2 Researcher Spotlight: Rosalind Franklin’s Early Work
Before her critical involvement with DNA structure, Rosalind Franklin studied the arrangement of water molecules in coals and carbons. Her precision in experimental work paved the way for deeper understanding of molecular structures.
6.3 Advanced Reading Suggestions
“The Nature of the Chemical Bond” by Linus Pauling: A seminal book on bonding principles.
Articles in Biochemistry Journal: Look for research on the structure-function relationships in proteins and how hydrogen bonding is crucial.
6.4 Notable Breakthrough: Discovery of Water’s Role in Origin-of-Life Studies
Recent research in astrobiology examines the presence of liquid water on moons like Europa and Enceladus, suggesting that water’s universal properties could support life beyond Earth.
7. Recall Questions
Atoms and Bonds: Describe the difference between an ionic bond and a covalent bond. Which type of bond is typically stronger in biological systems?
Water’s Properties: Name two special properties of water that emerge from hydrogen bonding and explain their significance in living organisms.
Elements of Life: Which four elements make up the majority of living matter, and why are they so important?
Home Experiment: If you tried the paper towel experiment, what did you observe, and how does it relate to cohesion and adhesion?
Historical Context: What was Linus Pauling’s major contribution to our understanding of chemical bonding?
Use these questions to check your comprehension of the chemical foundations that underpin biological processes.
