Domains of Life and Hierarchy of Living Organisms

Domains of Life

The three domains of life classify all living organisms based on cellular organization and genetics.

• 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 (with a nucleus), including animals, plants, fungi, and protists.

Hierarchy of Living Organisms

Biological organization is structured from smallest to largest:

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

Example: Muscle cell → Muscle tissue → Heart (organ) → Circulatory system → Human (organism)

Cell Structure and Function

Cell Organelles: Names, Functions, and Shapes

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

• Mitochondria: Site of ATP 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; stack of flattened sacs.

• Lysosomes: Contain digestive enzymes; spherical vesicles.

• Ribosomes: Synthesize proteins; small, round structures (free or attached to ER).

• Plasma Membrane: Phospholipid bilayer; controls entry/exit of substances.

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

Example: The mitochondrion is often called the "powerhouse" of the cell due to its role in energy production.

Cell Size and Surface Area

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

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

Formula: Surface area of a sphere: Volume of a sphere:

Chemistry of Living Things

Most Abundant Elements in Humans

• Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), Phosphorus (P)

Types of Chemical Bonds

• Ionic Bonds: Transfer of electrons from one atom to another (e.g., NaCl).

• Covalent Bonds: Sharing of electrons between atoms (e.g., H2O).

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

Polarity of Molecules

• Polar Molecules: Unequal sharing of electrons; have partial charges (e.g., water).

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

pH Scale: Acids and Bases

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Formula:

Elements, Atoms, and Molecules

• Element: Pure substance consisting of one type of atom.

• Molecule: Two or more atoms bonded together.

Radioisotope Technology

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

Atoms Changing Charge

• Atoms gain or lose electrons to become ions (charged particles).

• Negatively charged ions (anions) attract positively charged ions (cations).

Scientific Method and Reductionism

Scientific Method (in order)

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Analysis

6. Conclusion

Reductionism

• Understanding complex systems by studying their simpler components.

Homeostasis

• Maintenance of a stable internal environment despite external changes.

• Example: Regulation of body temperature.

Characteristics of Living vs. Nonliving Things

• Living things: Organization, metabolism, responsiveness, growth, reproduction, adaptation.

• Nonliving things: Lack one or more of these characteristics.

Microscopy

Types of Microscopy

• Light Microscopy: Uses light to view cells and tissues; limited resolution.

• Electron Microscopy: Uses electrons for higher resolution; can view organelles and macromolecules.

Example: Transmission electron microscopy (TEM) reveals internal cell structures.

Cell Membrane and Transport

Plasma Membrane Structure

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

Membrane Permeability

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

• Large or charged molecules require transport proteins.

Diffusion

• Movement of molecules from high to low concentration.

Active Transport

• Movement of substances against their concentration gradient using energy (ATP).

Isotonic Solutions

• Same solute concentration as the cell; no net water movement; cell shape remains unchanged.

Cellular Respiration and ATP Production

Glycolysis

• First step in cellular respiration; breaks down glucose into pyruvate, producing ATP and NADH.

Citric Acid Cycle (Krebs Cycle)

• Generates electron carriers (NADH, FADH2) by oxidizing acetyl-CoA.

• Electron carriers transfer electrons to the electron transport chain.

Electron Transport Chain (ETC)

• Most ATP is produced by ATP synthase, a protein complex in the inner mitochondrial membrane.

Tissues and Their Functions

Types of Tissues

• Epithelial Tissue: Covers surfaces; protection, absorption, secretion.

• Connective Tissue: Supports and binds other tissues; includes bone, blood, cartilage, adipose.

• Muscle Tissue: Movement; includes skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Conducts electrical impulses; found in brain, spinal cord, nerves.

Types of Connective Tissue and Locations

• Loose Connective Tissue: Under skin, between organs.

• Dense Connective Tissue: Tendons, ligaments.

• Cartilage: Joints, ear, nose.

• Bone: Skeleton.

• Blood: Circulatory system.

• Adipose Tissue: Fat storage under skin, around organs.

Muscle Type in the Stomach

• Smooth muscle is found in the stomach and other internal organs; responsible for involuntary movements.

Types of Cell Junctions

• Tight Junctions: Seal cells together to prevent leakage.

• Desmosomes: Anchor cells together, providing mechanical strength.

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

DNA and Its Importance

• DNA stores genetic information necessary for cell function, growth, and reproduction.

• It is the blueprint for protein synthesis.

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