Introduction to Biology

Levels of Biological Organization

Biological systems are organized from the simplest to the most complex, both within an individual organism and beyond.

• Molecules: Chemical components that make up cells.

• Cells: The smallest unit of life, composed of molecules.

• Tissues: Groups of similar cells performing specific functions.

• Organs: Structures made of different tissues working together for a specific function.

• Organ Systems: Two or more organs working together to perform specific functions (humans have 11 organ systems).

• Population: Individuals of the same species living in a distinct geographic area.

• Community: All living species that can potentially interact in a particular area.

• Ecosystem: A community plus its physical environment, viewed as relatively self-contained.

• Biosphere: All Earth’s living organisms and their habitats; the thin zone of Earth where life exists.

Basic Characteristics of Living Things

• Living things contain nucleic acids, proteins, carbohydrates, and lipids.

• They are made of cells, grow and reproduce, metabolize, detect and respond to stimuli, and maintain homeostasis.

• Populations of living things evolve over long periods of time.

Evolution: A Unifying Theme

• Classification reflects evolutionary relationships.

• Three domains: Bacteria, Archaea, and Eukarya.

• Domain Eukarya includes four kingdoms: protists, fungi, plants, and animals.

• Humans are classified as animals, vertebrates, mammals, and primates.

The Scientific Method

• Steps: Observations → Question → Hypothesis (testable explanation) → Experiment (with controls) → Conclusion.

• Related hypotheses supported by evidence may become a theory.

• Inductive reasoning: From specific observations to general conclusions.

• Deductive reasoning: From general principles to specific predictions ("if-then" logic).

• Human and animal experiments follow strict ethical rules, including informed consent and phased clinical trials (Phase I: safety, Phase II: efficacy, Phase III: comparison to existing treatments).

• Double-blind experiments prevent bias; epidemiological studies look for correlations in populations.

Critical Thinking in Science

• Involves questioning, hypothesizing, gathering information, and evaluating evidence and sources before drawing conclusions.

Chemistry of Life

The Nature of Atoms

• Atoms consist of protons (positive charge), neutrons (no charge), and electrons (negative charge).

• Protons and neutrons are in the nucleus; electrons orbit in shells.

• Atomic number: Number of protons.

• Atomic mass: Number of protons plus neutrons.

• Isotopes: Atoms with the same number of protons but different numbers of neutrons; radioisotopes emit radiation.

Chemical Bonds and Compounds

• Elements combine to form compounds held together by chemical bonds.

• Covalent bonds: Atoms share electrons.

• Ionic bonds: Attraction between oppositely charged ions (formed when atoms lose or gain electrons).

The Role of Water in Life

• Polar covalent bonds: Unequal sharing of electrons, resulting in polar molecules (e.g., water).

• Hydrogen bonds: Weak attractions between charged regions of polar molecules.

• Water’s polarity makes it an excellent solvent; hydrogen bonds give it high heat capacity and heat of vaporization.

• Acids increase H+ concentration; bases decrease it. The pH scale measures acidity/basicity.

• Buffers prevent dramatic changes in pH.

Major Molecules of Life

• Polymers: Large molecules made of repeating monomers; formed by dehydration synthesis, broken by hydrolysis.

• Carbohydrates: Sugars and starches; monosaccharides (simple sugars) and polysaccharides (complex carbohydrates).

• Lipids: Nonpolar molecules (e.g., triglycerides, phospholipids, steroids); function in energy storage and membrane structure.

• Proteins: Polymers of 20 amino acids; roles include structure, transport, movement, regulation, and catalysis (enzymes).

• Nucleic acids: DNA and RNA; polymers of nucleotides. DNA stores genetic information; RNA helps express it.

Cell Structure and Function

Eukaryotic vs. Prokaryotic Cells

• Prokaryotic cells: (Bacteria, Archaea) Lack membrane-bound organelles.

• Eukaryotic cells: (Protists, fungi, plants, animals) Have membrane-bound organelles.

Cell Size and Microscopy

• Cell volume increases faster than surface area; small size is necessary for efficient exchange with the environment.

• Light microscopes use light; electron microscopes use electrons for higher resolution.

Cell Structure and Function

• All eukaryotic cells have a plasma membrane and membrane-bound organelles.

• Structural differences reflect functional differences.

Plasma Membrane

• Composed of a phospholipid bilayer with proteins, cholesterol, and carbohydrates.

• Functions: Maintains integrity, regulates substance movement, cell recognition, communication, and tissue formation.

• Transport mechanisms: Simple diffusion, facilitated diffusion, active transport, osmosis, endocytosis, exocytosis.

Organelles

• Nucleus: Contains genetic material.

• Endoplasmic reticulum (ER): Rough ER (with ribosomes) synthesizes proteins; smooth ER synthesizes lipids.

• Golgi complex: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Digestive organelles.

• Mitochondria: Site of ATP production.

• Ribosomes: Non-membrane-bound; synthesize proteins.

Cytoskeleton

• Network of fibers: Microtubules, microfilaments, and intermediate filaments.

• Provides structure, shape, and facilitates movement within the cell.

Cellular Respiration and Fermentation

• Cells break down glucose to produce ATP via two pathways:

  • Cellular respiration: Requires oxygen; yields up to 36 ATP per glucose.

  • Fermentation: Anaerobic; yields 2 ATP per glucose.

• Phases of cellular respiration:

  1. Glycolysis (cytoplasm)

  2. Transition reaction (mitochondria)

  3. Citric acid cycle (mitochondria)

  4. Electron transport chain (mitochondria)

From Cells to Organ Systems

Tissues

• Epithelial tissue: Covers surfaces, forms glands, lines cavities and organs.

• Connective tissue: Storage, immunity, transport, protection, and support. Contains cells in an extracellular matrix (protein fibers and ground substance).

• Muscle tissue: Generates movement; three types: skeletal, cardiac, smooth.

• Nervous tissue: Coordinates activities via nerve impulses; consists of neurons and neuroglia.

Connective Tissue Types

• Connective tissue proper: Loose and dense connective tissue.

• Specialized connective tissue: Cartilage, bone, blood.

• Blood: Formed elements (red cells, white cells, platelets) in plasma; functions in transport and immunity.

Muscle Tissue Types

• Skeletal muscle: Voluntary, striated, multinucleate, attached to bones.

• Cardiac muscle: Involuntary, striated, single nucleus, found in heart walls.

• Smooth muscle: Involuntary, non-striated, single nucleus, found in walls of organs and vessels.

Nervous Tissue

• Neurons: Transmit nerve impulses.

• Neuroglia: Support, nourish, and insulate neurons; facilitate communication.

Specialized Junctions

• Tight junctions: Prevent passage of materials between cells.

• Adhesion junctions: Link cells via filaments and membrane thickenings.

• Gap junctions: Allow communication via small pores.

Organs and Organ Systems

• Organ: Structure composed of two or more tissues with a specialized function.

• Organ system: Two or more organs working together for a common function (11 major systems in humans).

Body Cavities

• Dorsal cavity: Cranial (brain) and spinal (spinal cord).

• Ventral cavity: Thoracic (chest) and abdominal cavities.

• Thoracic cavity subdivided into pleural (lungs) and pericardial (heart) cavities.

• Membranes line cavities and organ spaces.

Integumentary System (Skin)

Functions of the Integumentary System

• Protection from abrasion and dehydration.

• Regulation of body temperature.

• Synthesis of vitamin D.

• Detection of stimuli (touch, temperature, pain).

• Initiation of defense mechanisms.

Skin Structure

• Epidermis: Outermost layer; epithelial cells that die and wear away.

• Dermis: Thicker, connective tissue; contains nerves, blood vessels, glands.

• Hypodermis: Loose connective tissue anchoring skin to underlying tissues.

Skin Color and Derivatives

• Melanin: Pigment from melanocytes; determines skin color.

• Blood flow and oxygen content also affect color.

• Hair: Protection; derivative of skin.

• Nails: Modified skin tissue; protect and aid manipulation.

• Oil (sebaceous) glands: Secrete sebum; lubricates and inhibits bacteria.

• Sweat glands: Aid in temperature regulation.

Homeostasis

Definition and Mechanisms

• Homeostasis: Maintenance of a relatively constant internal environment.

• Dynamic state with small fluctuations around a set point.

• Maintained primarily through negative feedback mechanisms.

• Components: Receptors (detect changes), control center (processes information), effectors (carry out responses).

Skeletal System

Bone Functions

• Support and protection of organs.

• Movement (with muscles).

• Mineral (calcium, phosphorus) and fat storage.

• Blood cell production in red marrow.

Bone Structure

• Compact bone: Dense, outer layer; covered by periosteum (nourishes bone).

• Spongy bone: Latticework inside flat bones and ends of long bones.

• Marrow: Yellow (fatty, in shaft); red (blood cell production, in spongy bone).

Bone as Living Tissue

• Osteon: Structural unit; central canal surrounded by concentric rings of osteocytes in a hard matrix.

• Matrix: Hardened by calcium and phosphorus salts, strengthened by collagen.

• Embryonic skeleton forms as cartilage, replaced by bone via osteoblasts.

• Growth hormone and sex hormones regulate bone growth and maturation.

Bone Repair and Remodeling

• Fracture repair: Blood clot → cartilaginous callus → bone replacement.

• Remodeling: Osteoblasts build bone in response to stress; osteoclasts break down bone when not stressed.

Axial and Appendicular Skeleton

• Axial skeleton: Skull, backbone, rib cage, sternum; protects and supports organs.

• Appendicular skeleton: Shoulders, pelvis, arms, legs; enables movement.

Joints

• Classified by composition and movement allowed.

• Immovable joints: Sutures of the skull.

• Synovial joints: Freely movable; cartilage covers bone ends, synovial fluid lubricates, ligaments stabilize.

• Sprain: Ligament damage.

• Arthritis: Joint inflammation; osteoarthritis (wear and tear), rheumatoid arthritis (autoimmune).

Muscular System

Muscle Types and Characteristics

• Three types: Skeletal, smooth, cardiac.

• All muscle cells are excitable, contractile, extensible, and elastic.

Skeletal Muscles Working in Pairs

• Arranged in antagonistic pairs: one causes flexion, the other extension.

• Attached to bones by tendons.

• Origin: Attachment to stationary bone; insertion: Attachment to moving bone.

Muscle Contraction

• Muscle cells contain myofibrils composed of myofilaments (actin and myosin).

• Contraction results from interactions between actin and myosin filaments.

Table: Comparison of Muscle Tissue Types

Additional info:

• Some explanations and examples were expanded for clarity and completeness, such as the phases of cellular respiration and the functions of organelles.

• Table comparing muscle tissue types was constructed based on standard biological knowledge.