Biological Organization and the Foundations of Biology

Levels of Biological Organization

The study of biology involves understanding life at different levels of organization, from the largest to the smallest. Each level builds upon the previous, exhibiting new properties called emergent properties.

• Biosphere: All life on Earth and all the places where life exists.

• Ecosystem: All living things in a particular area, along with nonliving components.

• Community: Array of organisms inhabiting a particular ecosystem.

• Population: All individuals of a species living within the bounds of a specified area.

• Organism: Individual living thing.

• Organ and Organ Systems: Body parts that carry out particular functions in the organism.

• Tissues: Groups of cells that work together to perform a specialized function.

• Cells: Life's fundamental unit of structure and function. The cell is considered the basic unit of life because it can perform all activities required for life.

• Organelles: Functional components within cells.

• Molecules: Chemical structures consisting of two or more atoms.

Emergent Properties

Emergent properties are new characteristics that arise at each level of organization, due to the arrangement and interactions of parts as complexity increases. For example, a functioning bicycle emerges only when all necessary parts are connected in the correct way.

Structure and Function

There is a close relationship between the structure of a biological molecule or organ and its function. For example, the shape of a bird's wing is adapted for flight, and the structure of DNA enables it to store genetic information.

Unifying Themes of Life

• Organization: Life is highly ordered, from molecules to the biosphere.

• Information: Life processes involve the expression and transmission of genetic information (e.g., DNA).

• Energy and Matter: Life requires the transfer and transformation of energy and matter (e.g., photosynthesis).

• Interactions: Organisms interact with each other and their environment.

• Evolution: The core theme of biology, explaining both the unity and diversity of life.

Example: The structure of hemoglobin (a protein) allows it to bind and transport oxygen in the blood.

Unity and Diversity of Life; Natural Selection

• Unity: All living things share certain characteristics (e.g., genetic code, cell structure).

• Diversity: Life is incredibly diverse, with millions of species.

• Natural Selection: The process by which populations adapt and evolve. Individuals with advantageous traits survive and reproduce, leading to changes in populations over time.

The Scientific Process

The scientific method is a systematic approach to understanding the natural world.

1. Observation

2. Question

3. Hypothesis

4. Prediction

5. Experiment

6. Analysis

7. Conclusion

• Inductive reasoning: Drawing general conclusions from specific observations.

• Deductive reasoning: Making specific predictions based on general principles or hypotheses.

The Chemical Context of Life

Atomic Structure

• Atomic Number: Number of protons in an atom.

• Mass Number: Sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons. Example: Carbon-12, Carbon-13, Carbon-14.

Chemical Bonds

• Covalent Bonds: Atoms share electrons. Can be nonpolar (equal sharing) or polar (unequal sharing).

• Ionic Bonds: Electrons are transferred from one atom to another, forming ions (charged atoms).

• Hydrogen Bonds: Weak bonds between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

• Atoms vs. Ions: Atoms are neutral; ions are charged due to loss or gain of electrons.

Electronegativity and Bond Polarity

• Electronegativity: The ability of an atom to attract electrons in a covalent bond.

• Differences in electronegativity create polar covalent bonds (e.g., in water), leading to partial charges.

• Hydrogen bonds form between polar molecules.

Reactivity and Valence

• Reactivity: Determined by the number of electrons in the outermost shell (valence electrons).

• Valence: The bonding capacity of an atom, usually equal to the number of unpaired electrons in the outer shell.

• When electrons gain energy, they move to higher energy levels; when they lose energy, they fall to lower levels.

Properties of Water

Water is essential for life due to its unique properties:

• Cohesion and Adhesion: Water molecules stick to each other (cohesion) and to other substances (adhesion).

• High Specific Heat: Water can absorb a lot of heat before changing temperature.

• High Heat of Vaporization: Takes a lot of energy to convert water from liquid to gas.

• Expansion upon Freezing: Ice is less dense than liquid water.

• Versatile Solvent: Water dissolves many substances, facilitating chemical reactions in cells.

Impact on Life: These properties help regulate Earth's climate, support aquatic life, and enable biological processes.

Carbon and the Molecular Diversity of Life

Carbon Skeletons and Organic Molecules

• Organic Molecule: A molecule containing carbon and usually hydrogen.

• Carbon has 4 valence electrons, allowing it to form up to 4 covalent bonds, making it highly versatile.

• Carbon skeletons can vary in length, branching, double bond position, and ring structure.

Isomers

• Isomers: Compounds with the same molecular formula but different structures.

• Types:

  • Structural isomers: Differ in covalent arrangement.

  • Cis-trans isomers: Differ in arrangement around a double bond.

  • Enantiomers: Mirror images of each other.

Major Biological Molecules

There are four major classes of biological macromolecules: carbohydrates, proteins, lipids, and nucleic acids.

Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose).

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

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose, glycogen).

• Function: Energy storage and structural support.

Proteins

• Monomer: Amino acids.

• Structure: Four levels:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (alpha helix, beta sheet).

  • Tertiary: Overall 3D shape.

  • Quaternary: Association of multiple polypeptides.

• Function: Enzymes, structural support, transport, signaling, etc.

Lipids

• Types: Triglycerides, phospholipids, sterols.

• Triglycerides: Glycerol + 3 fatty acids; energy storage.

• Phospholipids: Glycerol + 2 fatty acids + phosphate group; major component of cell membranes.

• Sterols: Four fused carbon rings (e.g., cholesterol).

• Saturated fats: No double bonds; solid at room temperature.

• Unsaturated fats: One or more double bonds; liquid at room temperature.

Nucleic Acids

• Types: DNA and RNA.

• Monomer: Nucleotide (sugar, phosphate, nitrogenous base).

• Function: Store and transmit genetic information.

• DNA: Double-stranded, deoxyribose sugar, bases A, T, C, G.

• RNA: Single-stranded, ribose sugar, bases A, U, C, G.

Dehydration Synthesis and Hydrolysis

• Dehydration synthesis: Monomers are joined by removing a water molecule.

• Hydrolysis: Polymers are broken down by adding a water molecule.

Example: The breakdown of starch into glucose monomers during digestion is a hydrolysis reaction.