Foundations of Biology: Cells, Molecules, and the Basis of Life

Biology: The Nature of Life and How We Study It

Introduction to Biology

Biology is the scientific study of life, focusing on the structure, function, growth, origin, evolution, and distribution of living organisms. The cell is the fundamental unit of life, and understanding its properties is essential for anatomy and physiology.

• Robert Hooke: First observed cells using a microscope, identifying cell walls in cork tissue.

• Anton Van Leeuwenhoek: Discovered microorganisms, including bacteria and red blood cells.

• Cells: Highly organized compartments separated from the environment by a membrane barrier.

The Scientific Method in Biology

The scientific method is a systematic approach used to investigate biological phenomena.

Step	Description
Theory	Explanation for broad patterns
Hypothesis	Testable statement explaining observations
Experiment	Tests the effect of a single factor
Prediction	Measurable or observable results

• Independent variable: Variable changed by the experimenter

• Dependent variable: Variable measured, depends on the independent variable

• Control group: Baseline for comparison

• Key considerations: Environmental conditions must be constant, repeat experiments, use large sample sizes

Louis Pasteur's Experiment: Demonstrated that all cells come from pre-existing cells, not spontaneously generated.

Fundamental Characteristics of Organisms

Five Fundamental Characteristics

All living organisms share five key characteristics:

#	Characteristic	Description
1	Cells	Membrane-bound units
2	Replication	Cells arise from pre-existing cells
3	Information	Genetic material (DNA)
4	Energy	Photosynthesis/Cellular Respiration
5	Evolution	Natural selection

Three Unifying Theories in Biology

Theory	Description
The Cell Theory	All cells arise from pre-existing cells; all cells are connected by a common lineage
Chromosomal Theory of Inheritance	Genes are located on chromosomes made from DNA
Theory of Evolution by Natural Selection	Fitness, natural selection, adaptation

Genetic Information: DNA, RNA, and Proteins

The Central Dogma

Genetic information flows from DNA to RNA to protein, determining physical traits.

• DNA → RNA → Protein

• Genotype: Genetic makeup (genes)

• Phenotype: Physical traits

Structure of DNA

• Deoxyribonucleic acid (DNA): Hereditary material

• Chromosomes: Molecules of DNA

• Genes: Segments of DNA coding for cell products

• Base pairing: Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C)

This base pairing allows DNA to be copied during cell division.

RNA Structure and Function

• RNA: Ribonucleic acid, single-stranded

• Uracil (U) replaces Thymine (T) in RNA; U pairs with A

• Messenger RNA (mRNA): Carries genetic information from DNA to ribosomes for protein synthesis

Proteins

• Essential for biological functions

• Structural components

• Promote chemical reactions (enzymes)

Nutrition and Energy in Cells

Cellular Energy Needs

• Cells acquire energy in the form of adenosine triphosphate (ATP)

• ATP is produced by breaking down carbohydrates, fats, or proteins

• Plants use photosynthesis: Sunlight + Sugar → ATP

• Other organisms use cellular respiration

Evolution and Natural Selection

Darwin and Wallace's Theory

• Species are related by common ancestry

• Characteristics are modified from generation to generation

• Descent with modification

Natural Selection

• Acts on individuals with heritable traits

• Traits that increase reproductive success become more common

• Speciation occurs when populations diverge into new species

Fitness	Adaptation
Ability to produce offspring	Trait that increases fitness in a particular environment

Classification of Organisms

Major Groups of Organisms

Eukaryotes	Prokaryotes
Have nucleus, DNA, usually multicellular	Lack nucleus, usually unicellular
Eukarya	Bacteria and Archaea

Taxonomy and Nomenclature

• Taxonomy: Naming and classifying organisms

• Domain: Bacteria, Archaea, Eukarya

• Phylum: Major lineage within a domain

• Genus: Group of closely related species

• Species: Individuals that breed

• Scientific names: Genus capitalized, species lowercase, both italicized (e.g., Homo sapiens)

Basis of Life: Atoms, Elements, and Molecules

Atomic Structure

• Nucleus: Contains protons (positive charge) and neutrons (neutral charge)

• Electrons: Orbit the nucleus, negative charge

• Atomic number: Number of protons

• Mass number: Sum of protons and neutrons

• Isotopes: Same element, different number of neutrons

Major elements in the body: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur.

Electron Arrangement

• Orbitals: Regions around nucleus where electrons are found

• Electron shells: Groups of orbitals (numbered 1, 2, 3...)

• Electrons fill the innermost shells first

• Valence shell: Outermost shell, most stable when full (usually 8 electrons)

Molecules and Chemical Bonds

• Molecules: Atoms bonded together

• Chemical bonds: Attractions that bind atoms

Five important types of bonds exist in biological molecules (not detailed in the provided notes).

Additional info: Some explanations and definitions have been expanded for clarity and completeness, including the scientific method, taxonomy, and atomic structure.