Foundations of General Biology: Levels of Organization, Scientific Method, Chemistry of Life, and Biological Molecules

Biological Levels of Organization

Hierarchy of Biological Organization

Biology studies life at various levels of organization, from the smallest chemical units to the entire biosphere.

• Atoms → Molecules → Cells → Tissues → Organs → Organ Systems → Organism → Species → Community → Population → Biosphere

Each level represents increasing complexity and integration of structure and function.

Characteristics of Life

Defining Life

Living things are defined by a set of characteristics that distinguish them from non-living matter.

• Acquire energy

• Maintain complexity (from unicellular to multicellular)

• Respond to stimuli

• Grow

• Reproduce

• Evolve (change over long periods of time)

All six characteristics must be present for an entity to be considered living.

The Scientific Method

Steps of the Scientific Method

The scientific method is a systematic approach to investigating questions and testing hypotheses.

1. Observation

2. Ask a question

3. Hypothesis (a testable explanation)

4. Prediction (often in "if...then" format)

5. Test/Experiment

6. Results

7. Interpret → Conclusion (accept or reject hypothesis)

Variables in Experiments

• Independent variable: The factor that is changed or manipulated (X axis).

• Dependent variable: The factor that is measured or affected (Y axis), depends on the independent variable.

• Constants: Factors kept the same to ensure a fair test.

Example: Hand Soap vs. Hand Sanitizer Experiment

• Hypothesis: Hand soap will reduce bacterial diversity; hand sanitizer will also reduce bacterial diversity.

• Prediction: If hand sanitizer/soap is effective, there will be less bacterial growth.

• Experiment: Three dishes—one with soap, one with sanitizer, one control (no treatment).

• Results: Both hand soap and sanitizer decreased the number of bacteria.

• Conclusion: Both methods are effective; further experiments can compare their relative effectiveness.

Viruses and Evolution

Are Viruses Alive?

Viruses exhibit some characteristics of life (e.g., reproduction, evolution) but lack others (e.g., independent metabolism). Scientists debate their classification.

• Viruses can evolve, respond to stimuli, and reproduce by infecting host cells.

• They require host cells for energy and reproduction.

Evolution and Disease

• Microbes: Small particles (often bacteria or viruses) that can cause disease.

• Tuberculosis (TB): Caused by bacteria, spread through the air; symptoms include cough, fever, and weight loss.

• Multidrug-resistant TB: TB that does not respond to standard antibiotics, requiring multiple drugs.

• Antibiotic resistance: Occurs when bacteria evolve to survive exposure to antibiotics, often due to incomplete or improper use of medications.

Atoms and Elements

Structure of Atoms

Atoms are the basic units of elements, which are substances that cannot be broken down into simpler substances.

• Composed of subatomic particles:

  • Protons: Positively charged

  • Neutrons: Uncharged

  • Electrons: Negatively charged

• Atoms are neutral when protons = electrons.

Isotopes and Ions

• Isotopes: Atoms of the same element with different numbers of neutrons (different mass numbers). Some are radioactive.

• Ions: Atoms that have gained or lost electrons, resulting in a net positive or negative charge.

Free Radicals and Antioxidants

• Free radicals: Highly reactive atoms or molecules with unpaired electrons; can damage cells and contribute to aging.

• Antioxidants: Molecules that neutralize free radicals.

Chemical Bonds

Types of Chemical Bonds

• Ionic bonds: Transfer of electrons between atoms, forming oppositely charged ions.

• Covalent bonds: Sharing of electrons between atoms.

  • Polar covalent: Unequal sharing (e.g., water)

  • Nonpolar covalent: Equal sharing

• Hydrogen bonds: Weak attractions between polar molecules, especially involving hydrogen and oxygen or nitrogen.

Properties of Water

Importance of Water in Biology

• Cohesion: Water molecules stick together via hydrogen bonds, leading to surface tension.

• Adhesion: Water molecules stick to other polar substances, enabling capillary action (movement through narrow spaces).

• Solvent properties: Water is an excellent solvent for polar and ionic substances, forming solutions.

• Hydrophilic: Water-loving substances dissolve in water.

• Hydrophobic: Water-fearing substances (e.g., fats, oils) do not dissolve in water.

• Temperature moderation: Water has a high specific heat (energy required to raise temperature), helping organisms maintain stable internal conditions.

• Ice density: Ice is less dense than liquid water, allowing it to float and insulate aquatic environments.

pH and Buffers

• pH scale: Measures hydrogen ion concentration; ranges from 0 (acidic) to 14 (basic), with 7 as neutral.

• Acids: Increase H+ concentration.

• Bases: Decrease H+ concentration (increase OH-).

• Buffers: Substances that help maintain a constant pH by accepting or releasing H+ ions.

Biological Molecules

Importance of Carbon

Carbon is the backbone of organic molecules due to its ability to form four covalent bonds, allowing for complex structures.

• Organic molecules: Contain carbon and usually hydrogen and oxygen; synthesized by organisms.

• Inorganic molecules: Generally lack carbon atoms.

Functional Groups

Functional groups are specific groups of atoms attached to the carbon backbone of organic molecules, influencing their chemical reactivity and interactions.

Polymers and Monomers

• Monomers: Small organic molecules (building blocks).

• Polymers: Chains of monomers.

• Dehydration synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Major Classes of Biological Molecules

There are four main classes of biological macromolecules, each with distinct structures and functions.

Class	Basic Structure	Complex Molecule	Functions	Examples
Carbohydrates	Monosaccharides (simple sugars)	Polysaccharides (starch, cellulose, glycogen)	Short-term energy, structural support	Glucose, ribose, deoxyribose, sucrose, starch, cellulose, chitin
Lipids	No true monomers; built from glycerol and fatty acids	Triglycerides, phospholipids, steroids	Long-term energy storage, waterproofing, membrane structure	Fats, oils, waxes, phospholipids, steroids
Nucleic acids	Nucleotides	DNA, RNA	Information storage, energy transfer	DNA, RNA, ATP
Proteins	Amino acids	Polypeptides	Enzymes, structure, transport, regulation	Enzymes, keratin, actin, myosin, insulin, hemoglobin

Examples and Applications

• Starch: Energy storage in plants.

• Glycogen: Energy storage in animals.

• Cellulose: Structural component of plant cell walls.

• Chitin: Structural component in fungi and arthropod exoskeletons.

• Phospholipids: Major component of cell membranes.

• ATP: Main energy currency of the cell.

Additional info: The notes also reference the importance of functional groups, dehydration synthesis, and hydrolysis in the formation and breakdown of biological macromolecules, as well as the role of carbon in organic chemistry.