Human Biology: Foundations, Cells, and Evolution – Structured Study Notes

Human Biology, Science, and Society

Introduction to Science and Biology

• Science is the systematic study of the natural world, encompassing both living and non-living things, and is based on matter and energy.

• Biology is the branch of science focused on living organisms and their life processes.

• All living things are composed of matter (substance of physical objects) and energy (capacity to cause change).

Characteristics of Life

• Composed of molecules (atoms) essential for life.

• Require energy and raw materials; metabolism refers to all chemical and physical processes that transform energy and molecules to sustain life.

• Carry out cellular respiration to produce ATP, the cellular energy currency.

• Composed of cells, the fundamental unit of life.

• Maintain homeostasis: a stable internal environment (e.g., regulated by hormones like epinephrine and cortisol).

• Respond to external stimuli.

• Grow and reproduce to pass on genetic information (DNA).

• Populations evolve over time through changes in genetic material.

Classification of Living Things

• Cells are classified as prokaryotic (no nucleus) or eukaryotic (with nucleus).

• Three domains: Bacteria, Archaea (both prokaryotic), and Eukarya (eukaryotic).

• Five kingdoms: Monera (Bacteria & Archaea), Animalia, Plantae, Protista, Fungi (Eukarya).

• Taxonomy is the science of classifying organisms: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.

• Scientific names: Genus species (e.g., Homo sapiens), italicized or underlined, genus capitalized.

• Humans are vertebrates, mammals, and classified as Homo sapiens.

• Species: groups of organisms that can interbreed and produce fertile offspring.

Defining Features of Humans

• Bipedalism (upright walking)

• Opposable thumbs

• Large brain relative to body size

• Complex language capacity

Evolution and the Origins of Life

Introduction to Evolution

• Evolution is the process by which populations of organisms change over time, explaining both the unity and diversity of life.

• It is driven by changes in genetic material and environmental pressures.

Evidence for Evolution

• Fossil Record: Preserved remains or impressions of organisms (bones, teeth, shells, spores, seeds). Soft tissues rarely fossilize due to rapid decay.

• Comparative Anatomy: Study of body structures to determine evolutionary relationships.

• Embryology: Comparison of embryo development among species; similar early development suggests common ancestry.

• Comparative Biochemistry: Analysis of similarities in proteins and genes; molecular similarities indicate relatedness.

• Biogeography: Study of the geographic distribution of organisms; geographic barriers can lead to speciation.

Fossil Record and Dating Methods

• Fossils form when organisms are buried by sediment, and minerals replace tissues over time.

• The fossil record is incomplete due to preservation biases (e.g., hard parts fossilize more easily).

• Stratification: Lower rock layers are older; upper layers are younger.

• Radiometric Dating: Uses radioactive isotopes to determine age of rocks/fossils.

• Potassium-Argon dating: Half-life = 1.3 billion years.

• Carbon-14 dating: Used for specimens <60,000 years old; half-life = 5,700 years.

Comparative Anatomy

• Homologous structures: Similar anatomy, different functions (e.g., human arm, bat wing, whale flipper); indicate common ancestry.

• Analogous structures: Similar function, different evolutionary origins (e.g., bird and insect wings).

• Vestigial structures: Reduced or nonfunctional structures (e.g., human coccyx, ear muscles); evidence of evolutionary history.

Comparative Embryology

• Vertebrate embryos share features such as notochord, somites, and pharyngeal arches.

• As development proceeds, differences emerge due to morphogenesis and differentiation.

Comparative Biochemistry

• Similarities in proteins (e.g., cytochrome c) and DNA sequences reflect evolutionary relationships.

• Greater molecular differences indicate earlier divergence from a common ancestor.

• Example: Human cytochrome c is identical to chimpanzee, differs by 1 amino acid from rhesus monkey, 16 from chicken, >50 from yeast.

Biogeography and Continental Drift

• Geographic barriers (oceans, mountains) isolate populations, leading to divergent evolution.

• Continental drift: Movement of Earth's plates; separation of continents (e.g., Pangaea) led to isolated evolution (e.g., marsupials in Australia).

Charles Darwin and Natural Selection

• Darwin's theory: Species show "descent with modification" from common ancestors; natural selection is the mechanism.

• Key observations:

  • Variation exists within populations; many traits are heritable.

  • More offspring are produced than survive; competition for resources is inevitable.

  • Individuals best suited to their environment are more likely to survive and reproduce.

  • Over time, advantageous traits become more common.

• Evolutionary relationships are often depicted as tree-like diagrams.

Hierarchy of Biological Organization

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

The Scientific Method and Critical Thinking

The Scientific Method

• Science is both a body of knowledge and a process for acquiring knowledge.

• Steps of the Scientific Method:

  1. Observe and generalize (inductive reasoning)

  2. Formulate a question

  3. Develop a hypothesis (tentative, testable statement)

  4. Make a testable prediction

  5. Experiment or observe to test the prediction (controlled experiments minimize variables)

  6. Modify hypothesis as necessary and repeat testing

• Findings are published in peer-reviewed journals for validation.

• A well-tested hypothesis may become a theory (e.g., Cell Theory).

Critical Thinking in Science

• Be skeptical and evaluate evidence critically.

• Understand the value of statistics for interpreting data.

• Learn to read graphs: X-axis (independent variable), Y-axis (dependent variable).

• Distinguish anecdotal evidence from scientific evidence.

• Differentiate between facts (verifiable) and conclusions (judgments based on facts).

• Remember: Correlation does not imply causation.

Science, Technology, and Society

• Science informs societal decisions; technology advances society and is influenced by science and societal needs.

• Science is limited to physical explanations for observable events and cannot answer all ethical, political, or social questions.

Structure and Function of Cells

Cell Doctrine

• All living things are composed of cells.

• The cell is the smallest unit exhibiting all characteristics of life.

• All cells arise from preexisting cells.

Types of Cells

• Prokaryotic cells: Small, simple, no nucleus, no true organelles (e.g., bacteria).

• Eukaryotic cells: Larger, complex, nucleus, membrane-bound organelles (e.g., human cells).

Cell Structure and Function

• Cell structure reflects function (e.g., muscle cells have many mitochondria; nerve cells are long and thin).

• Small cell size ensures efficient nutrient acquisition and waste disposal (high surface-to-volume ratio).

Microscopy

• Light microscope: up to 1000x, can view living cells.

• Transmission electron microscope: up to 100,000x, reveals internal structures.

• Scanning electron microscope: up to 100,000x, provides 3D surface views.

Major Cell Organelles and Their Functions

• Nucleus: Contains DNA, controls cell activities, has nuclear envelope, pores, nucleolus (site of ribosome assembly).

• Ribosomes: Sites of protein synthesis; free in cytoplasm (for internal use) or bound to rough ER (for export).

• Endoplasmic Reticulum (ER):

  • Rough ER: Has ribosomes, synthesizes proteins for secretion.

  • Smooth ER: No ribosomes, synthesizes lipids, detoxifies, stores calcium.

• Golgi Apparatus: Refines, packages, and ships products in vesicles.

• Vesicles:

  • Secretory: Export products.

  • Endocytic: Import substances.

  • Peroxisomes: Detoxify wastes (contain catalase).

  • Lysosomes: Digestive enzymes, recycle cell components.

• Mitochondria: "Powerhouse" of the cell, site of cellular respiration, generates ATP, has its own DNA.

• Fat (adipose tissue): Long-term energy storage (triglycerides).

• Glycogen: Short-term energy storage (in muscle and liver).

Support and Movement Structures

• Cytoskeleton: Internal scaffolding (microtubules, microfilaments, intermediate filaments) for shape and movement.

• Cilia: Short, many, move substances across cell surfaces (e.g., in airways).

• Flagella: Long, single, enable cell movement (e.g., sperm).

• Centrioles: Organize microtubules, important in cell division.

Plasma Membrane Structure and Function

• Lipid bilayer (phospholipids, cholesterol, proteins, carbohydrates), fluid mosaic model.

• Selective permeability: controls movement of substances in and out.

• Enables cell communication via receptor proteins.

Transport Across the Plasma Membrane

• Passive transport: No energy required.

  • Diffusion: Movement from high to low concentration.

  • Osmosis: Diffusion of water across a membrane (from low to high solute concentration).

  • Facilitated diffusion: Uses membrane proteins for specific molecules (e.g., glucose).

• Active transport: Requires energy (ATP), moves substances against concentration gradient (e.g., sodium-potassium pump).

• Bulk transport: Endocytosis (phagocytosis, pinocytosis, receptor-mediated), exocytosis.

Cell Volume and Tonicity

• Isotonic: Equal solute concentrations inside and outside; cell volume stable.

• Hypertonic: Higher solute outside; cell shrinks.

• Hypotonic: Lower solute outside; cell swells.

Metabolism and Energy

• Metabolism: All chemical reactions in a cell.

• Anabolism: Building larger molecules (requires energy).

• Catabolism: Breaking down molecules (releases energy).

• ATP is the main energy carrier.

Cellular Respiration

• Breakdown of glucose to produce ATP; requires oxygen.

• Four stages:

  1. Glycolysis (cytoplasm): Glucose → 2 pyruvate, 2 ATP (net), 2 NADH.

  2. Preparatory step (mitochondria): Pyruvate → Acetyl CoA, CO2, NADH.

  3. Citric Acid Cycle (Krebs, mitochondria): Acetyl CoA → CO2, NADH, FADH2, 2 ATP.

  4. Electron Transport System (inner mitochondrial membrane): NADH/FADH2 donate electrons, O2 is final acceptor, ATP produced by ATP synthase.

• Net yield: ~36 ATP per glucose.

• Without O2: Anaerobic glycolysis produces lactic acid (2 ATP per glucose).

From Cells to Organ Systems

Tissues: Groups of Cells with a Common Function

• Four primary tissue types:

  1. Epithelial: Covers surfaces, lines cavities, forms glands.

  2. Connective: Supports, connects, stores fat, produces blood cells.

  3. Muscle: Contracts for movement.

  4. Nervous: Transmits impulses.

Epithelial Tissue

• Shapes: Squamous (flat), cuboidal (cube), columnar (tall).

• Layers: Simple (single), stratified (multiple).

• Glandular: Exocrine (ducts), endocrine (hormones into blood).

• Basement membrane: Noncellular support layer.

• Cell junctions: Tight (seal), adhesion (stretch), gap (communication).

Connective Tissue

• Matrix: Nonliving material with fibers (collagen, elastic, reticular).

• Cells: Fibroblasts, macrophages, lymphocytes, neutrophils.

• Types:

  • Fibrous: Loose, dense, elastic, reticular.

  • Specialized: Cartilage, bone, blood, adipose (fat).

Muscle Tissue

• Skeletal: Voluntary, moves body parts, multinucleated.

• Cardiac: Involuntary, heart, single nucleus.

• Smooth: Involuntary, hollow organs, single nucleus.

Nervous Tissue

• Neurons: Generate and transmit electrical impulses (cell body, dendrites, axon).

• Glial cells: Support, protect, and nourish neurons.

Organs and Organ Systems

• Organs: Two or more tissue types working together for specific functions.

• Organ systems: Groups of organs with a common function (e.g., digestive, lymphatic).

Body Cavities and Membranes

• Anterior cavity: Thoracic (pleural, pericardial), abdominal.

• Posterior cavity: Cranial, spinal.

• Membranes:

  • Serous: Line and lubricate internal cavities.

  • Mucous: Line airways, digestive, reproductive tracts.

  • Synovial: Line movable joints.

  • Cutaneous: Skin.

Describing Body Position

• Planes: Midsagittal (left/right), frontal (front/back), transverse (top/bottom).

• Terms: Anterior (front), posterior (back), proximal (near trunk), distal (far from trunk), superior (above), inferior (below).

The Integumentary System (Skin)

• Functions: Protection, temperature regulation, vitamin D synthesis, sensation.

• Layers:

  • Epidermis: Stratified squamous epithelium, keratinocytes (keratin), melanocytes (melanin), no blood vessels.

  • Dermis: Dense connective tissue, collagen/elastic fibers, fibroblasts, mast cells, WBCs, fat cells.

• Accessory structures: Hair, smooth muscle, sebaceous (oil) glands, sweat glands, blood vessels, sensory nerves.

Homeostasis

• Maintaining a stable internal environment.

• Negative feedback: Detects and counteracts deviations from normal (e.g., body temperature regulation).

• Components: Controlled variable, sensor, control center, effector.

• Positive feedback: Amplifies changes (e.g., childbirth); not for homeostasis.

Summary Table: Cell Types and Features

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	No	Yes
Organelles	No true organelles	Membrane-bound organelles
Size	Small	Larger
Examples	Bacteria, Archaea	Animals, Plants, Fungi, Protists

Summary Table: Types of Muscle Tissue

Type	Location	Control	Nuclei
Skeletal	Attached to bones	Voluntary	Multinucleated
Cardiac	Heart	Involuntary	Single nucleus
Smooth	Walls of hollow organs	Involuntary	Single nucleus

Key Equations

• ATP Hydrolysis: $ATP \rightarrow ADP + P_i + \text{energy}$

• Cellular Respiration (overall): $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$

• Osmosis (osmotic pressure): $\Pi = iMRT$ where $\Pi$ is osmotic pressure, $i$ is the van 't Hoff factor, $M$ is molarity, $R$ is the gas constant, $T$ is temperature in Kelvin.

• Half-life (radioactive decay): $N_t = N_0 \left( \frac{1}{2} \right)^{t/t_{1/2}}$ where $N_t$ is the amount remaining after time $t$, $N_0$ is the initial amount, $t_{1/2}$ is the half-life.

Additional info: Some explanations and examples have been expanded for clarity and completeness, following standard academic biology textbooks.