Domain of Life

Classification of Living Organisms

The domain of life is the highest taxonomic rank in the classification of 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, including animals, plants, fungi, and protists.

Example: Humans belong to the domain Eukarya.

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): Network of membranes; rough ER has ribosomes (protein synthesis), smooth ER (lipid synthesis).

• Golgi Apparatus: Modifies, sorts, and packages proteins; stack of flattened sacs.

• Lysosomes: Contain digestive enzymes; spherical vesicles.

• Ribosomes: Protein synthesis; small, round structures, free or attached to ER.

• Plasma Membrane: Phospholipid bilayer; flexible boundary of the cell.

• Cytoskeleton: Network of protein fibers; maintains cell shape and assists movement.

Example: The mitochondrion is often called the "powerhouse of the cell."

Hierarchy of Living Organisms

Levels of Biological Organization

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

Example: Muscle tissue is made of muscle cells, which contain mitochondria (organelles).

Cell Size and Surface Area

Relationship and Importance

• 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 and Uses

• Light Microscope: Views living cells; lower magnification.

• Transmission Electron Microscope (TEM): Views internal structures; high magnification.

• Scanning Electron Microscope (SEM): Views cell surfaces in 3D.

Elements of Humanity

Most Abundant Elements

• Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N)

• These elements make up over 96% of the human body.

Reductionism

Importance in Biology

• Reductionism is the approach of studying complex systems by breaking them into simpler components.

• Helps understand biological processes at molecular and cellular levels.

DNA

Importance

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

• Directs synthesis of proteins.

Chemical Bonds

Types and Properties

• Ionic Bonds: Transfer of electrons between atoms (e.g., NaCl).

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

• Hydrogen Bonds: Weak attraction between polar molecules (e.g., between water molecules).

Polarity

Polar vs. Nonpolar 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).

Ions and Charges

Interactions

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

pH Levels

Acids and Bases

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Formula:

Scientific Method

Steps in Order

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Analysis

6. Conclusion

Homeostasis

Definition

• Maintenance of a stable internal environment despite external changes.

Elements vs. Molecules

Differences

• Element: Pure substance of one type of atom (e.g., O2).

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

Living vs. Nonliving

Shared Characteristics

• Both made of matter and obey physical laws.

• Living things exhibit metabolism, growth, response to stimuli, and reproduction.

Radioisotope Technology

Importance

• Used in medical imaging, cancer treatment, and dating fossils.

Atomic Charge Changes

How Atoms Change Charge

• Atoms gain electrons (become negative, anions) or lose electrons (become positive, cations).

Diffusion

Process

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

ATP Production

Electron Transport Chain

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

Plasma Membrane Permeability

What Can and Cannot Pass

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

• Ions and large polar molecules require transport proteins.

Active Transport

Definition

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

Isotonic Solutions

Effect on Cells

• Isotonic solution: Solute concentration is equal inside and outside the cell; no net water movement; cell shape remains unchanged.

Glycolysis

PURPOSE

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

Electron Carriers in Citric Acid Cycle

Types and Electron Sources

• NAD+ and FAD are electron carriers.

• They gain electrons from the oxidation of substrates in the citric acid cycle.

Plasma Membrane Structure

Components

• Phospholipid bilayer, proteins, cholesterol, and carbohydrates.

Connective Tissues

Types

• Loose connective tissue: Supports and binds tissues.

• Dense connective tissue: Forms tendons and ligaments.

• Adipose tissue: Stores fat.

• Cartilage: Flexible support.

• Bone: Rigid support.

• Blood: Transports substances.

Locations of Tissue Types

Examples

• Loose connective: Under skin

• Dense connective: Tendons

• Adipose: Under skin, around organs

• Cartilage: Joints, ear

• Bone: Skeleton

• Blood: Circulatory system

Muscle Type in the Stomach

Type

• Smooth muscle is found in the stomach wall.

Tissue Types and Functions

Overview

• Epithelial tissue: Covers surfaces, lines cavities.

• Connective tissue: Supports, binds, stores energy.

• Muscle tissue: Movement.

• Nervous tissue: Transmits signals.

Cell Junctions

Types

• Tight junctions: Seal cells together.

• Desmosomes: Anchor cells together.

• Gap junctions: Allow communication between cells.

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