Human Biology, Science, and Society

The Domains of Life

The domains of life are the highest taxonomic rank in the classification of living organisms. There are three domains:

• 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.

The Scientific Method

The scientific method is a systematic approach to inquiry in science. The steps are:

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Analysis

7. Conclusion

Example: Testing the effect of sunlight on plant growth by comparing plants grown in sunlight versus shade.

Reductionism

Reductionism is the approach of understanding complex systems by studying their simpler components. It is important in biology for breaking down processes to their molecular or cellular levels.

Homeostasis

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

• Example: Regulation of body temperature in humans.

Characteristics of Living vs. Nonliving Things

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

• Nonliving things: Do not exhibit all the above characteristics.

The Chemistry of Living Things

Most Abundant Elements in Humans

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

Atoms, Elements, and Molecules

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

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

Atomic Structure and Charge

• Atoms can change charge 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: Transfer of electrons from one atom to another.

• Covalent Bonds: Sharing of electrons between atoms.

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

Polarity of Molecules

• Polar molecules: Unequal sharing of electrons, resulting in partial charges (e.g., H2O).

• Nonpolar molecules: Equal sharing of electrons, no partial charges (e.g., O2).

pH, Acids, and Bases

• pH scale: Measures hydrogen ion concentration.

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Radioisotope Technology

Radioisotopes are unstable isotopes that emit radiation. They are important in medical imaging, cancer treatment, and biological research.

Structure and Function of Cells

Hierarchy of Living Organisms

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism

Cell Size and Surface Area

• As cell size increases, volume increases faster than surface area.

• Smaller cells have a higher surface area-to-volume ratio, facilitating efficient exchange of materials.

Formula for surface area of a sphere:

Formula for volume of a sphere:

Microscopy Types

• Light Microscopy: Observes living cells, limited resolution.

• Electron Microscopy: Higher resolution, observes cell ultrastructure (TEM for internal, SEM for surface).

Cell Organelles: Names, Functions, and Shapes

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.

Transport Across the Plasma Membrane

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

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

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

• What cannot pass: Large, polar molecules and ions (e.g., glucose, Na+).

Osmosis and Tonicity

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

• Cells retain normal shape in isotonic solutions.

Cellular Respiration and ATP Production

• Glycolysis: First step in glucose breakdown; occurs in cytoplasm; produces ATP and NADH.

• Citric Acid Cycle: Occurs in mitochondria; produces electron carriers (NADH, FADH2).

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

From Cells to Organ Systems

Types of Tissues and Their Functions

• Epithelial Tissue: Covers body surfaces, lines cavities, forms glands.

• Connective Tissue: Supports, binds, and protects organs.

• Muscle Tissue: Enables movement (skeletal, cardiac, smooth).

• Nervous Tissue: Transmits electrical impulses.

Types of Connective Tissues

• Loose Connective Tissue: Binds organs, holds tissue fluids.

• Dense Connective Tissue: Forms tendons and ligaments.

• Adipose Tissue: Stores fat.

• Cartilage: Supports, cushions joints.

• Bone: Supports, protects, stores minerals.

• Blood: Transports substances.

Locations of Tissue Types

• Epithelial: Skin, lining of digestive tract.

• Connective: Tendons, fat, bone, blood.

• Muscle: Skeletal muscles, heart (cardiac), walls of stomach (smooth muscle).

• Nervous: Brain, spinal cord, nerves.

Muscle Type in the Stomach

• The stomach contains smooth muscle, which contracts involuntarily to mix and propel food.

Cell Junctions

• Tight Junctions: Seal cells together, prevent leakage.

• Desmosomes: Anchor cells together, provide mechanical strength.

• Gap Junctions: Allow communication between cells via small channels.

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard introductory human biology content.