Domains of Life and Hierarchy of Living Organisms

Classification of Life

The domain is 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 hierarchy of living organisms (from smallest to largest):

• Atom

• Molecule

• Organelle

• Cell

• Tissue

• Organ

• Organ system

• Organism

Shared characteristics between living and nonliving things include the presence of matter and energy, but only living things exhibit metabolism, growth, reproduction, and response to stimuli.

Cell Structure and Function

Cell Organelles: Names, Functions, and Shapes

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

• Mitochondria: Site of ATP production via cellular respiration; 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-floating or attached to rough ER.

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

• Cytoskeleton: Network of protein filaments; provides structure and facilitates movement.

Labeling and identification of organelles is a common exam task. Practice with diagrams and be able to match functions to structures.

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.

• Surface area to volume ratio is critical for efficient nutrient uptake and waste removal.

Formula for surface area of a sphere:

Formula for volume of a sphere:

Microscopy

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

• Electron Microscopy: Higher resolution; used for detailed images of organelles and cell structures.

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

• Transmission Electron Microscopy (TEM): Provides detailed images of internal cell structures.

Chemistry of Living Things

Most Abundant Elements in Humans

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Other important elements: Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg)

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).

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

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

• Polar Molecules: Have unequal sharing of electrons, resulting in partial charges (e.g., H2O).

• Nonpolar Molecules: Have equal sharing of electrons; no partial charges (e.g., O2).

Acids, Bases, and pH

• pH Scale: Measures hydrogen ion concentration; ranges from 0 (acidic) to 14 (basic).

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Formula for pH:

Radioisotope Technology

• Radioisotopes are unstable isotopes that emit radiation.

• Used in medical imaging, cancer treatment, and biological research.

Scientific Method and Homeostasis

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.

• Examples: Regulation of body temperature, blood glucose levels.

Reductionism

• Breaking down complex systems into simpler components for study.

• Helps in understanding biological processes at the molecular or cellular level.

DNA and Its Importance

• DNA (Deoxyribonucleic Acid) stores genetic information necessary for the development, functioning, and reproduction of living organisms.

• DNA is inherited from parent to offspring and directs protein synthesis.

Cell Membrane Structure and Transport

Plasma Membrane Structure

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

• Functions as a selective barrier, controlling what enters and exits the cell.

Transport Across the Membrane

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

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

• Facilitated Diffusion: Passive transport using membrane proteins.

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

• What cannot pass: Large, polar molecules and ions without transport proteins.

Osmosis and Tonicity

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

• Hypotonic Solution: Lower solute concentration outside; water enters cell; cell may swell.

• Hypertonic Solution: Higher solute concentration outside; water leaves cell; cell shrinks.

Cellular Respiration and ATP Production

Glycolysis

• First step in cellular respiration; occurs in the cytoplasm.

• Breaks down glucose into two molecules of pyruvate, producing ATP and NADH.

Citric Acid Cycle (Krebs Cycle)

• Occurs in mitochondria; completes the breakdown of glucose derivatives.

• Electron carriers NADH and FADH2 are produced by transferring electrons from metabolic intermediates.

Electron Transport Chain (ETC)

• Located in the inner mitochondrial membrane.

• Most ATP is produced by the ATP synthase protein complex during oxidative phosphorylation.

Tissues and Their Types

Types of Tissues

• 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.

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: Skeleton.

• Blood: Circulatory system.

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

Muscle in the Stomach

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

Cell Junctions

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

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

• Gap Junctions: Allow communication between cells via direct transfer of ions and molecules (e.g., in cardiac muscle).

Summary Table: Types of Tissues and Their Functions

Additional info: Some explanations and examples have been expanded for clarity and completeness, based on standard human biology curricula.