Human Biology, Science, and Society

The Scientific Method

The scientific method is a systematic approach used to investigate natural phenomena. It ensures that scientific inquiry is logical, repeatable, and objective.

• Steps of the Scientific Method:

  1. Observation

  2. Question

  3. Hypothesis

  4. Experiment

  5. Data Collection

  6. Analysis

  7. Conclusion

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

• Homeostasis: The maintenance of a stable internal environment despite external changes.

Example: Body temperature regulation is an example of homeostasis.

The Chemistry of Living Things

Elements and Molecules

All matter is composed of elements, which are substances that cannot be broken down by chemical means. Molecules are combinations of two or more atoms held together by chemical bonds.

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

• Difference between Element and Molecule: An element is a pure substance of one type of atom; a molecule consists of two or more atoms bonded together.

Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in charged ions.

• Covalent Bonds: Formed when atoms share electrons.

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Polarity

• Polar Molecules: Have unequal sharing of electrons, resulting in partial charges (e.g., water).

• Nonpolar Molecules: Have equal sharing of electrons and no charge separation (e.g., oxygen gas).

Acids, Bases, and pH

• pH Scale: Measures hydrogen ion concentration; ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

• Acidic Substances: pH less than 7.

• Basic Substances: pH greater than 7.

Atoms and Ions

• Atoms: Basic units of matter, composed of protons, neutrons, and electrons.

• Ions: Atoms that have gained or lost electrons, acquiring a charge.

• How Atoms Change Charge: By gaining electrons (becoming negatively charged, anions) or losing electrons (becoming positively charged, cations).

• Interaction of Charged Elements: Negatively charged ions attract positively charged ions, forming ionic bonds.

Radioisotope Technology

• Radioisotopes: Unstable isotopes that emit radiation; used in medical imaging, cancer treatment, and biological research.

Structure and Function of Cells

Hierarchy of Living Organisms

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

Domains of Life

• Bacteria

• Archaea

• Eukarya (includes plants, animals, fungi, and protists)

Cell Organelles: Names, Functions, and Shapes

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

• Mitochondria: Site of ATP production; oval-shaped.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins.

• Lysosomes: Contain digestive enzymes; break down waste.

• Ribosomes: Synthesize proteins; small, round structures.

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

Cell Size and Surface Area

• As cells increase in size, their volume increases faster than their surface area.

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

Formula for Surface Area to Volume Ratio:

Microscopy

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

• Electron Microscopy: Used for high-resolution images of cell structures.

DNA

• Importance: DNA stores genetic information necessary for cell function and inheritance.

From Cells to Organ Systems

Plasma Membrane Structure and Function

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

• Function: Regulates movement of substances into and out of the cell.

Transport Across the Plasma Membrane

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

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

• What Can Pass: Small, nonpolar molecules (e.g., O2, CO2).

• What Cannot Pass: Large or charged molecules (e.g., ions, glucose) require transport proteins.

Osmosis and Tonicity

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

Cellular Respiration

• Glycolysis: The breakdown of glucose to pyruvate, producing ATP and NADH.

• Citric Acid Cycle: Produces electron carriers (NADH, FADH2) by oxidizing acetyl-CoA.

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

Equation for Cellular Respiration:

Electron Carriers

• NADH and FADH2: Carry electrons from glycolysis and the citric acid cycle to the electron transport chain.

Tissues and Their Types

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

• Connective Tissue: Supports and binds other tissues; 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 the brain, spinal cord, and nerves.

Connective Tissue Types and Locations

• Loose Connective Tissue: Underlies skin and surrounds organs.

• Dense Connective Tissue: Found in tendons and ligaments.

• Cartilage: Found in joints, ear, nose.

• Bone: Forms the skeleton.

• Blood: Circulates in blood vessels.

• Adipose Tissue: Stores fat under the skin and around organs.

Muscle in the Stomach

• Smooth Muscle: Involuntary muscle found in the walls of the stomach and other hollow organs.

Cell Junctions

• Tight Junctions: Seal cells together to prevent leakage.

• Desmosomes: Anchor cells together, providing mechanical strength.

• Gap Junctions: Allow communication between adjacent cells.

Shared Characteristics of Living and Nonliving Things

• Living things exhibit organization, metabolism, homeostasis, growth, reproduction, and response to stimuli.

• Nonliving things may have organization but do not exhibit all characteristics of life.

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