Chemistry of Life

Elements Essential to Life

Living organisms are primarily composed of a small number of chemical elements. These elements are found in similar proportions across most forms of life and are essential for biological processes.

• Major elements: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg)

• Trace elements: Required in smaller amounts (e.g., Fe, Zn, I, Mn, Cu, Co, Mo, Se, F, Cr, V, Si, Sn)

Table: Major Elements in Living Organisms

• Abiotic forms: Elements are often found in nature as minerals, ions, or simple molecules (e.g., O2, CO2, H2O).

• Animals: Obtain elements in chemical forms such as ions (Na+, K+), molecules (glucose, amino acids), or as part of food.

• Plants: Absorb elements as ions from soil (e.g., NO3-, PO43-), CO2 from air, and water from soil.

Atoms and Elements

An element is a substance that cannot be broken down into other substances by chemical reactions. Each element is defined by its atomic number (number of protons).

• Atomic structure: Atoms consist of protons, neutrons, and electrons.

• Example: Sodium (Na) has 11 protons, 12 neutrons, and 11 electrons.

Properties of Water

Structure and Polarity

Water (H2O) is a polar molecule, with a partial negative charge near the oxygen atom and partial positive charges near the hydrogen atoms. This polarity allows water molecules to form hydrogen bonds with each other and with other polar molecules.

• Hydrophilic: Substances that dissolve in water (water-loving).

• Hydrophobic: Substances that do not dissolve in water (water-fearing).

Hydrogen Bonding and Properties

• Cohesion: Water molecules stick to each other via hydrogen bonds.

• Adhesion: Water molecules stick to other polar surfaces.

• High specific heat: Water can absorb or release large amounts of heat with little temperature change.

• High heat of vaporization: Large amounts of energy are required to convert water from liquid to gas.

• Density anomaly: Water is less dense as a solid (ice) than as a liquid; ice floats.

• Solvent properties: Water dissolves many ionic and polar substances.

Biological Significance of Water's Properties

• Temperature regulation: High specific heat and evaporative cooling help maintain stable temperatures in organisms and environments.

• Ice floats: Aquatic life survives under ice during winter because ice insulates the water below.

• Capillary action: Cohesion and adhesion allow water to move up plant vessels and paper towels.

• Surface tension: Water forms rounded drops and supports small objects on its surface.

Chemical Bonds

Types of Chemical Bonds

• Nonpolar covalent bonds: Electrons are shared equally between atoms (e.g., O2, H2).

• Polar covalent bonds: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

• Ionic bonds: Electrons are transferred from one atom to another, forming ions (e.g., NaCl).

• Hydrogen bonds: Weak attractions between a hydrogen atom (attached to O or N) and another electronegative atom.

• Van der Waals interactions: Weak, transient attractions between molecules due to temporary dipoles.

Organic Macromolecules

Identifying Organic Macromolecules

Organic macromolecules are large, carbon-based molecules essential for life. The four major classes are carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates: Approximate C:H:O ratio is 1:2:1 (e.g., C6H12O6).

• Lipids: Contain C, H, and O, but with much less O than carbohydrates; often hydrophobic.

• Proteins: Contain C, H, O, N, and sometimes S; made of amino acids.

• Nucleic acids: Contain C, H, O, N, and P; made of nucleotides.

Functional Groups in Organic Molecules

Functional groups determine the chemical properties of organic molecules. They can be polar or nonpolar, hydrophilic or hydrophobic, and are found in different classes of biomolecules.

Additional info: The table above is inferred and expanded for clarity based on standard biology knowledge.

Identifying Macromolecules by Structure

• Lipid (fat or triglyceride): Composed of glycerol and three fatty acids; hydrophobic.

• Amino acid: Contains amino (–NH2) and carboxyl (–COOH) groups; monomer of proteins.

• Tripeptide: Three amino acids linked by peptide bonds; short protein fragment.

• DNA strand: Polymer of nucleotides; contains bases A, T, C, G.

• Disaccharide: Two monosaccharides joined by a glycosidic bond (e.g., sucrose).

• Fatty acid: Long hydrocarbon chain with a carboxyl group; component of lipids.

• Ribonucleotide: Monomer of RNA; contains ribose, phosphate, and nitrogenous base.

• Polysaccharide: Long chain of monosaccharides (e.g., starch, cellulose).

• Carbon sugar: Monosaccharide (e.g., glucose, fructose).

Scientific Method and Experimental Design

Steps in the Scientific Method

• Observation

• Question

• Hypothesis

• Experiment

• Data collection

• Analysis

• Conclusion

Experimental Variables

• Independent variable: The factor that is changed or controlled by the experimenter (e.g., amount of ammonium nitrate, amount of light).

• Dependent variable: The factor that is measured (e.g., height of the plants).

• Control group: The group that does not receive the experimental treatment; used for comparison.

• Placebo: An inert substance given to the control group to mimic the experimental treatment.

Example: Plant Growth Experiment

• 16 pots of strawberry plants divided into groups with different amounts of ammonium nitrate and light exposure.

• Independent variables: Amount of ammonium nitrate, amount of light.

• Dependent variable: Height of the plants.

Summary Table: Macromolecule Identification