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, distinct from bacteria, often found in extreme environments.

• Eukarya: Organisms with eukaryotic cells (with a nucleus), including animals, plants, fungi, and protists.

Hierarchy of Living Organisms

Living organisms are organized in a hierarchical structure:

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → 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 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" because it produces most of the cell's ATP.

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:

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), and Phosphorus (P) are the most abundant elements in the human body.

Reductionism

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

DNA Importance

• DNA (deoxyribonucleic acid) stores genetic information and directs cell activities.

Chemical Bonds

• Ionic Bonds: Formed when electrons are transferred from one atom to another.

• Covalent Bonds: Formed when atoms share electrons.

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

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., oxygen gas).

Interactions of Charged Elements

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

pH Levels

• Acidic: pH < 7

• Neutral: pH = 7

• Basic (Alkaline): pH > 7

Formula:

Elements vs. Molecules

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

• Molecule: Two or more atoms bonded together (e.g., H2O).

Radioisotope Technology

• Radioisotopes are used in medical imaging, cancer treatment, and as tracers in biological research.

Changing Atomic Charges

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

Scientific Method and Homeostasis

Scientific Method (in order)

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Conclusion

Homeostasis

• Homeostasis is the maintenance of a stable internal environment in an organism.

• 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.

Diffusion

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

Active Transport

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

What Can and Can’t Pass Through the Plasma Membrane

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

• Ions and large polar molecules require transport proteins.

Isotonic Solution

• An isotonic solution has the same solute concentration as the cell; no net water movement; cell shape remains unchanged.

Cellular Respiration

Glycolysis

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

Electron Transport Chain (ETC) and ATP Production

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

Electron Carriers in the Citric Acid Cycle

• NAD+ and FAD are electron carriers; they gain electrons during the cycle to become NADH and FADH2.

Tissues and Their Types

Types of Tissues and Their Functions

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

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

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

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

Types of Connective Tissues

• Loose Connective Tissue: Supports and binds other tissues; found under skin.

• Dense Connective Tissue: Forms tendons and ligaments.

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

• Bone: Rigid support and protection.

• Blood: Transports substances throughout the body.

• Adipose Tissue: Stores fat for energy and insulation.

Locations of Tissue Types

• Epithelial: Skin, lining of digestive tract.

• Connective: Tendons, ligaments, bone, blood.

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

• Nervous: Brain, spinal cord, nerves.

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.

• Desmosomes: Anchor cells together, providing mechanical strength.

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

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard Human Biology curriculum.