Domains of Life and Hierarchy of Living Organisms

Domains of Life

The domains of life represent the highest taxonomic rank in the classification of living organisms. There are three domains:

• Bacteria: Single-celled prokaryotes with no 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.

Hierarchy of Living Organisms

Living organisms are organized in a hierarchical structure:

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

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

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.

• 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; controls entry and exit of substances.

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

Formula:

Key Point: Smaller cells have a higher surface area-to-volume ratio, facilitating efficient exchange.

Microscopy Types

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

• Transmission Electron Microscopy (TEM): Views internal cell structures at high resolution.

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

Chemistry of Living Things

Most Abundant Elements in Humans

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Calcium (Ca)

• Phosphorus (P)

Together, these elements make up over 99% of the human body mass.

Reductionism

• Reductionism is the approach of understanding complex systems by studying their simpler components.

• It is important in biology for analyzing functions at the molecular or cellular level.

DNA Importance

• DNA (Deoxyribonucleic Acid) stores genetic information necessary for growth, development, and reproduction.

• It is the blueprint for protein synthesis.

Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another (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 of Molecules

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

• Nonpolar Molecules: Electrons are shared equally; no partial charges (e.g., O2).

Interactions of Charged Elements

• Negatively charged elements (anions) attract positively charged elements (cations) to form ionic bonds.

pH Levels: Acids and Bases

• pH measures hydrogen ion concentration.

• Acidic: pH < 7

• Neutral: pH = 7

• Basic (Alkaline): pH > 7

Elements vs. Molecules

• Element: A pure substance consisting of one type of atom (e.g., O2).

• Molecule: Two or more atoms bonded together (can be same or different elements; e.g., H2O).

Radioisotope Technology

• Radioisotopes are unstable isotopes that emit radiation.

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

Changing Atomic Charges

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

• Loss of electrons: Becomes a cation (+ charge).

• Gain of electrons: Becomes an anion (– charge).

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

• Homeostasis is the maintenance of a stable internal environment despite external changes.

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

Shared Characteristics of Living and Nonliving Things

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

• Nonliving things may have organization but lack metabolism and reproduction.

Cell Membrane and Transport

Plasma Membrane Structure

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

• Functions as a selective barrier.

Diffusion

• Movement of molecules from an area of higher concentration to lower concentration.

• Does not require energy (passive transport).

Active Transport

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

• Example: Sodium-potassium pump.

Plasma Membrane Permeability

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

• Large or charged molecules require transport proteins.

Isotonic Solutions

• Isotonic solution: Solute concentration is equal inside and outside the cell.

• No net movement of water; cell maintains its shape.

Cellular Respiration and ATP Production

Glycolysis

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

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

Electron Transport Chain (ETC) and ATP Synthesis

• Most ATP is produced by the ATP synthase protein complex during the ETC in mitochondria.

Electron Carriers in the Citric Acid Cycle

• NADH and FADH2 are electron carriers.

• They receive electrons from metabolic intermediates during the citric acid cycle.

Tissues and Their Functions

Types of Tissues

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

• Connective Tissue: Supports, binds, and protects organs; includes bone, blood, cartilage, adipose.

• Muscle Tissue: Responsible for movement; types include skeletal, cardiac, and smooth muscle.

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

Types of Connective Tissues and Locations

• Loose Connective Tissue: Underlies skin, surrounds 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

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

Types of Cell Junctions

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

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

• Gap Junctions: Allow communication between cells via channels (e.g., heart muscle).

Summary Table: Types of Tissues and Their Functions

Additional info: Academic context and examples have been added to expand on the brief review points and ensure the notes are self-contained for exam preparation.