Human Biology, Science, and Society

The Domains of Life

The classification of life is organized into three domains, which represent the broadest categories of living organisms.

• Bacteria: Single-celled prokaryotes without a nucleus.

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

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

Hierarchy of Living Organisms describes the levels of biological organization:

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

Scientific Method (in order):

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Conclusion

7. Peer Review/Publication

Homeostasis is the maintenance of a stable internal environment despite external changes.

Reductionism is 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, development, 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), and 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 the charge is evenly distributed (e.g., O2).

Acids and Bases (pH):

• Acidic: pH < 7

• Neutral: pH = 7

• Basic (Alkaline): pH > 7

Radioisotope Technology: Used in medical imaging, cancer treatment, and as tracers in biochemical research.

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); usually spherical.

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

• Endoplasmic Reticulum (ER): Network of membranes; rough ER has ribosomes (protein synthesis), smooth ER (lipid synthesis).

• Golgi Apparatus: Stack of flattened sacs; modifies, sorts, and packages proteins.

• Lysosomes: Spherical vesicles containing digestive enzymes.

• Ribosomes: Small, round structures; sites of protein synthesis.

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

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

Microscopy Types:

• Light Microscopy: For viewing live cells and tissues.

• Transmission Electron Microscopy (TEM): For detailed internal structures.

• Scanning Electron Microscopy (SEM): For surface details of cells.

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

Diffusion: The movement of molecules from an area of higher concentration to lower concentration.

Plasma Membrane Structure: Composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

What Can and Can’t Pass Through the Plasma Membrane?

• Can Pass: Small, nonpolar molecules (e.g., O2, CO2), water (via aquaporins).

• Cannot Pass Easily: Large, polar molecules and ions (e.g., glucose, Na+).

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

Isotonic Solution: A solution with the same solute concentration as the cell; no net water movement, cell remains unchanged.

ATP Production: Most ATP is produced by the ATP synthase protein complex during the electron transport chain in mitochondria.

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

Electron Carriers in the Citric Acid Cycle: NAD+ and FAD collect electrons from metabolic reactions and transfer them to the electron transport chain.

From Cells to Organ Systems

Tissues and Their 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.

Types of Connective Tissues:

• Loose Connective Tissue: Binds organs together, found beneath skin.

• Dense Connective Tissue: Forms tendons and ligaments.

• Adipose Tissue: Stores fat, insulates body.

• Cartilage: Provides flexible support (e.g., nose, joints).

• Bone: Rigid support and protection.

• Blood: Transports substances throughout the body.

Locations of Tissues:

• Epithelial: Skin, lining of digestive tract.

• Connective: Tendons, fat, bone, blood.

• Muscle: Skeletal muscles, heart (cardiac), walls of hollow organs (smooth).

• Nervous: Brain, spinal cord, nerves.

Type of Muscle in the Stomach: Smooth muscle.

Types of Cell Junctions:

• Tight Junctions: Seal cells together to prevent leakage.

• Desmosomes: Anchor cells together, providing mechanical strength.

• Gap Junctions: Allow communication between cells via channels.

Table: Types of Tissues and Their Functions

Examples and Applications

• Example: The sodium-potassium pump is an example of active transport, moving Na+ out and K+ into the cell using ATP.

• Example: Radioisotopes such as Technetium-99m are used in medical imaging to diagnose heart disease.

Additional info: Academic context and definitions have been expanded for clarity and completeness.