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 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 or attached to rough ER.

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

• Cytoskeleton: Network of protein filaments for cell shape and movement.

Relationship between 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.

Microscopy

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

• Electron Microscopy: Higher resolution; used for detailed images of organelles (Transmission EM for internal structures, Scanning EM for surfaces).

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.

Chemical Bonds

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

• Covalent Bonds: Atoms share electrons; can be single, double, or triple bonds.

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

Polarity: A molecule is polar if it has an uneven distribution of charge (e.g., water), and nonpolar if charges are evenly distributed (e.g., oxygen gas).

Negatively charged elements (anions) attract positively charged elements (cations) due to electrostatic forces.

pH and Acidity

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

• pH < 7: Acidic; pH = 7: Neutral; pH > 7: Basic (alkaline).

Atoms and Ions

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

• Radioisotope technology: Uses unstable isotopes for medical imaging, cancer treatment, and dating fossils.

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 and Function

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

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

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:

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

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

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

Homeostasis

The maintenance of a stable internal environment despite external changes.

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, FADH2) by oxidizing acetyl-CoA.

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

• Electron carriers (NADH, FADH2) donate electrons to the ETC, which are originally obtained from glucose breakdown.

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, and loose connective 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.

Types of Connective Tissues

• Loose Connective Tissue: Binds organs together; found under the skin.

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

• Dense Connective Tissue: Forms tendons and ligaments.

• Cartilage: Provides support and flexibility; found in joints, ear, nose.

• Bone: Supports and protects; forms the skeleton.

• Blood: Transports substances; found in blood vessels.

Locations of Tissue Types

• Epithelial: Skin, lining of digestive tract, respiratory tract.

• Connective: Throughout the body (e.g., tendons, fat, bone, blood).

• Muscle: Skeletal muscles, heart (cardiac), walls of hollow organs (smooth).

• Nervous: Brain, spinal cord, peripheral nerves.

Type of muscle in the stomach: Smooth muscle.

Cell Junctions

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

• Desmosomes: Anchor cells together, providing mechanical strength.

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

Summary Table: Types of Tissues and Their Functions

Additional info:

• For diagrams, practice labeling organelles and identifying their functions.

• Review the steps of the scientific method and be able to apply them to experimental scenarios.

• Understand the importance of homeostasis in maintaining health.