Human Biology, Science, and Society

The Domains of Life

The classification of life is organized into three domains based on cellular organization and genetics:

• Bacteria: Single-celled prokaryotes without a nucleus.

• Archaea: Single-celled prokaryotes, distinct from bacteria, often found in extreme environments.

• Eukarya: Organisms with eukaryotic cells (with a nucleus), including animals, plants, fungi, and protists.

Hierarchy of Living Organisms:

• Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → Organism

Scientific Method (in order):

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Conclusion

7. Peer Review/Publication

Homeostasis: The maintenance of a stable internal environment despite external changes. Example: Regulation of body temperature.

Reductionism: The approach of understanding complex systems by studying their simpler components.

Shared Characteristics of Living and Nonliving Things: Living things exhibit organization, metabolism, responsiveness, growth, reproduction, and adaptation. Nonliving things do not possess all these characteristics.

The Chemistry of Living Things

Elements, Molecules, and Bonds

• Most Abundant Elements in Humans: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), Phosphorus (P)

• Element: A pure substance consisting of one type of atom (e.g., O2).

• Molecule: Two or more atoms bonded together (e.g., H2O).

Types of Chemical Bonds:

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating charged ions (e.g., NaCl).

• Covalent Bonds: Formed when atoms share electrons (e.g., H2O).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

Polarity: A molecule is polar if it has an uneven distribution of charge (e.g., water), and nonpolar if charges are evenly distributed (e.g., O2).

Acids, Bases, and pH:

• Acidic: pH < 7

• Neutral: pH = 7

• Basic (Alkaline): pH > 7

Radioisotope Technology: Used in medical imaging and cancer treatment due to the emission of radiation from unstable isotopes.

How Atoms Change Charge: By gaining or losing electrons, atoms become ions (cations are positive, anions are negative).

What Do Negatively Charged Elements Do to Positively Charged Elements? They attract each other, forming ionic bonds.

Structure and Function of Cells

Cell Organelles: Names, Functions, and Shapes

• Nucleus: Contains genetic material (DNA); spherical shape.

• Mitochondria: Site of ATP production; oval-shaped with inner folds (cristae).

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins; stack of flattened sacs.

• Lysosomes: Contain digestive enzymes; spherical vesicles.

• Ribosomes: Sites of protein synthesis; small, round structures.

• Plasma Membrane: Phospholipid bilayer; controls entry and exit of substances.

• Cytoskeleton: Network of protein fibers; provides cell shape and movement.

Cell Size and Surface Area: As a cell increases in size, its volume grows faster than its surface area, limiting efficient exchange of materials.

Microscopy Types:

• Light Microscopy: Used for viewing live cells and tissues.

• Electron Microscopy: Used for high-resolution images of cell structures (TEM for internal, SEM for surface).

DNA Importance: DNA stores genetic information, directs protein synthesis, and is essential for inheritance.

Cell Membrane Structure and Function

• Plasma Membrane Composition: Phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• What Can and Can’t Pass Through:

  • Small, nonpolar molecules (e.g., O2, CO2) can pass freely.

  • Ions and large polar molecules require transport proteins.

Diffusion: Movement of molecules from high to low concentration without energy input.

Active Transport: Movement of substances against their concentration gradient, requiring energy (ATP).

Isotonic Solution: Has the same solute concentration as the cell; no net water movement, so cell shape is maintained.

Cellular Respiration and ATP Production

• Glycolysis: The breakdown of glucose into pyruvate, producing ATP and NADH; occurs in the cytoplasm.

• Citric Acid Cycle (Krebs Cycle): Produces electron carriers (NADH, FADH2) by oxidizing acetyl-CoA; occurs in mitochondria.

• Electron Transport Chain: Most ATP is produced here, specifically at the ATP synthase protein complex.

Electron Carriers: NAD+ and FAD collect electrons during glycolysis and the citric acid cycle and deliver them to the electron transport chain.

From Cells to Organ Systems

Tissues: Types, Locations, and Functions

• Epithelial Tissue: Covers body surfaces and lines cavities; functions in protection, absorption, and secretion.

• Connective Tissue: Supports and binds other tissues; types include loose, dense, adipose, cartilage, bone, and blood.

• Muscle Tissue: Responsible for movement; types include skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Conducts electrical impulses; found in the brain, spinal cord, and nerves.

Locations of Tissue Types:

• Epithelial: Skin, lining of digestive tract

• Connective: Tendons, ligaments, fat, bone, blood

• Muscle: Skeletal muscles, heart (cardiac), walls of stomach and intestines (smooth)

• Nervous: Brain, spinal cord, peripheral nerves

Type of Muscle in the Stomach: Smooth muscle

Cell Junctions

• Tight Junctions: Seal cells together to prevent leakage (e.g., in the intestines).

• Desmosomes: Anchor cells together, providing mechanical strength (e.g., in skin).

• Gap Junctions: Allow communication between cells via channels (e.g., in cardiac muscle).

Connective Tissue Types

Summary Table: Cell Organelles and Functions

Additional info: Academic context and examples have been added to ensure completeness and clarity for exam preparation.