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:

• Atoms → Molecules → Organelles → Cells → Tissues → Organs → Organ Systems → 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: The maintenance of a stable internal environment despite changes in external conditions.

Reductionism: The approach of understanding complex systems by breaking them down into their simpler components.

Shared Characteristics of Living and Nonliving Things:

• Living things: Composed of cells, grow, reproduce, respond to stimuli, maintain homeostasis, evolve, and use energy.

• Nonliving things: May have structure and organization but do not exhibit all characteristics of life.

Radioisotope Technology: Used in medical imaging, cancer treatment, and as tracers in biochemical research due to the emission of detectable radiation.

The Chemistry of Living Things

Elements, Atoms, and Molecules

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

• Molecule: Two or more atoms bonded together (e.g., H2O, O2).

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

Atoms and Charges:

• Atoms can change their charges by gaining or losing electrons, forming ions.

• Negatively charged elements (anions) attract positively charged elements (cations) to form ionic bonds.

Types of Chemical Bonds:

• Ionic Bonds: Formed when electrons are transferred from one atom to another.

• Covalent Bonds: Formed when atoms share electrons.

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

Polarity:

• A molecule is polar if it has an uneven distribution of charge (e.g., water).

• A molecule is nonpolar if electrons are shared equally (e.g., O2).

pH Scale:

• Measures the concentration of hydrogen ions (H+) in a solution.

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Importance of DNA:

• DNA stores genetic information essential for inheritance, coding for proteins, and guiding cellular activities.

Structure and Function of Cells

Cell Organelles: Names, Functions, and Shapes

• Nucleus: Contains genetic material (DNA); controls cell activities; usually spherical.

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

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery.

• Lysosomes: Contain digestive enzymes; break down waste and cellular debris.

• Ribosomes: Sites of protein synthesis; can be free or attached to ER.

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

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

• Centrioles: Involved in cell division in animal cells.

Cell Size and Surface Area:

• As a cell increases in size, its volume grows faster than its surface area.

• This limits cell size because the surface area must be sufficient for exchange of materials.

Microscopy Types:

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

• Transmission Electron Microscopy (TEM): Views internal cell structures at high resolution.

• Scanning Electron Microscopy (SEM): Provides detailed 3D images of cell surfaces.

Plasma Membrane Structure and Function

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

• Regulates movement of substances in and out of the cell.

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

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

• Large or charged molecules (e.g., ions, glucose) require transport proteins.

Types of Transport:

• Diffusion: Movement of molecules from high to low concentration.

• Active Transport: Movement against concentration gradient; requires energy (ATP).

• Isotonic Solution: Solute concentration is equal inside and outside the cell; no net water movement; cell remains unchanged.

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, binds, and protects organs; includes bone, blood, cartilage, adipose tissue.

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

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

Types of Connective Tissues:

• Loose connective tissue

• Dense connective tissue

• Cartilage

• Bone

• Blood

• Adipose (fat) tissue

Locations of Tissues:

• Epithelial: Skin, lining of digestive tract

• Connective: Tendons, ligaments, 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 (involuntary, non-striated).

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 small channels.

Cellular Respiration and Energy Production

ATP Production and Metabolic Pathways

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

• Citric Acid Cycle (Krebs Cycle): Completes the breakdown of glucose; produces electron carriers NADH and FADH2 by transferring electrons from acetyl-CoA.

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

Electron Carriers:

• NADH and FADH2 carry electrons from glycolysis and the citric acid cycle to the ETC.

Summary Table: Types of Tissues and Their Functions of

Key Equations

• Cellular Respiration (Overall):

• pH Calculation:

Example Applications

• Radioisotope Technology: PET scans use radioisotopes to detect cancerous tissues.

• Diffusion: Oxygen moves from the lungs into the blood by diffusion.

• Active Transport: Sodium-potassium pump maintains nerve cell function by moving ions against their gradients.

Additional info: Academic context and explanations have been expanded for clarity and completeness based on standard Human Biology curriculum.