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, distinct from bacteria, often found in extreme environments.

• Eukarya: Organisms with eukaryotic cells (with 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 (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 to other organelles.

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

• Ribosomes: Sites of protein synthesis; can be free in cytoplasm 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.

Cell size and surface area: As a cell increases in size, its volume grows faster than its surface area, limiting the rate of material exchange with the environment. This is why cells are typically small.

Microscopy

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

• Electron Microscopy: Higher resolution; used to view organelles and detailed cell structures.

Chemistry of Living Things

Elements, Atoms, and Molecules

• 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.

• Molecule: Two or more atoms bonded together.

Atomic Structure and Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating 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: A molecule is polar if it has an uneven distribution of charge (e.g., water), and nonpolar if charge is evenly distributed (e.g., oxygen gas).

Negatively charged elements (anions) are attracted to positively charged elements (cations).

Atoms can change their charges by gaining or losing electrons.

pH and Acidity

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

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Radioisotope Technology

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

Scientific Method and Reductionism

Scientific Method (in order)

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Conclusion

7. Peer Review/Publication

Reductionism: The approach of understanding complex systems by studying their simpler components.

Cell Membrane and Transport

Plasma Membrane Structure

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

Transport Mechanisms

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

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

• What can/can't pass through the plasma membrane:

  • Can: Small, nonpolar molecules (e.g., O2, CO2), some small polar molecules (e.g., water).

  • Cannot: Large molecules, ions, and most polar molecules without transport proteins.

• Isotonic Solution: Has the same solute concentration as the cell; no net water movement; cell remains unchanged.

Cellular Respiration and Energy Production

ATP Production

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

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

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

Electron carriers (NADH and FADH2) donate electrons to the electron transport chain, which ultimately produces ATP.

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite external changes. It is essential for proper cell and organ function.

Tissues and Their Types

Types of Tissues and Their 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, and tendons.

• 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: 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.

• Desmosomes: Anchor cells together, providing mechanical strength.

• Gap Junctions: Allow communication and passage of small molecules between cells.

Summary Table: Types of Tissues and Their Functions

Additional info:

• Some explanations (e.g., for reductionism, radioisotopes, and the scientific method) were expanded for clarity.

• Table entries and tissue locations were inferred based on standard human biology knowledge.