Domains of Life and Hierarchy of Living Organisms

Domains of Life

The domains of life are 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 tissue is made of muscle cells, which contain mitochondria (an organelle), which are made of molecules and atoms.

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 has ribosomes and synthesizes proteins; smooth ER synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

• Lysosomes: Contain digestive enzymes to break down waste.

• Ribosomes: Sites of protein synthesis; can be free or attached to rough ER.

• Plasma Membrane: Phospholipid bilayer that controls what enters and exits the cell.

• Cytoskeleton: Network of protein fibers that maintain cell shape and assist in 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:

Microscopy Types

• 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

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

• A molecule is polar if it has an uneven distribution of charge (e.g., water).

• A molecule is nonpolar if charge is evenly distributed (e.g., oxygen gas).

Interactions of Charged Elements

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

pH Levels

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Formula:

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 used in medical imaging, cancer treatment, and as tracers in biochemical research.

Changing Atomic Charges

• Atoms change charge by gaining or losing electrons, forming ions.

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.

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.

Diffusion

• Movement of molecules from high to low concentration until equilibrium is reached.

Active Transport

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

Isotonic Solution

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

Cellular Respiration and Energy Production

Glycolysis

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

Electron Transport Chain and ATP Production

• Most ATP is produced by the ATP synthase protein complex during the electron transport chain in mitochondria.

Electron Carriers in the Citric Acid Cycle

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

Tissues and Their Functions

Types of Tissues

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

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

• Muscle Tissue: Responsible for movement; includes 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 (e.g., under skin).

• Dense connective tissue: Forms tendons and ligaments.

• Adipose tissue: Stores fat.

• Cartilage: Provides flexible support (e.g., nose, joints).

• Bone: Rigid support and protection.

• Blood: Transports substances.

Locations of Tissue Types

• Epithelial: Skin, lining of digestive tract.

• Connective: Tendons, fat, bone, blood.

• Muscle: Skeletal muscles, heart, walls of hollow organs (e.g., stomach).

• 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 (e.g., in intestines).

• Desmosomes: Anchor cells together, providing mechanical strength.

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

Table: Types of Tissues and Their Functions

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