Domains of Life

Classification of Living Organisms

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

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: Stacks of flattened sacs; modifies, sorts, and packages proteins and lipids.

• Lysosomes: Spherical vesicles containing digestive enzymes; break down waste.

• Ribosomes: Small, round structures; site of protein synthesis.

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

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

• Chloroplasts (plants): Site of photosynthesis; contains chlorophyll.

• Cell Wall (plants, fungi, some protists): Rigid outer layer; provides support.

Hierarchy of Living Organisms

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

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 a larger cell cannot efficiently exchange materials with its environment.

• Surface area-to-volume ratio is critical for nutrient uptake and waste removal.

Microscopy

Types and Uses

• Light Microscope: Uses light to view cells and tissues; up to 1000x magnification.

• Electron Microscope: Uses electrons for higher resolution; includes Transmission (TEM) and Scanning (SEM) types.

• Fluorescence Microscope: Uses fluorescent dyes to label and visualize specific cell components.

Chemistry of Living Things

Most Abundant Elements in Humans

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

Reductionism

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

• Helps in understanding biological processes at the molecular or cellular level.

Importance of DNA

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

• Acts as a blueprint for protein synthesis.

Chemical Bonds

• Ionic Bonds: Transfer of electrons from one atom to another, forming charged ions.

• Covalent Bonds: Sharing of electron pairs between atoms.

• Hydrogen Bonds: Weak attraction between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Polarity

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

• A molecule is nonpolar if electrons are shared equally (e.g., oxygen gas).

Interactions of Charged Elements

• Negatively charged elements (anions) are attracted to positively charged elements (cations), forming ionic bonds.

pH Levels

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

The Scientific Method

• Observation → Question → Hypothesis → Experiment → Data Collection → Conclusion → Communication

Homeostasis

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

• Examples: Body temperature regulation, blood glucose levels.

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).

Characteristics of Living vs. Nonliving Things

• Living things: Organization, metabolism, homeostasis, growth, reproduction, response to stimuli, adaptation.

• Nonliving things do not exhibit all these characteristics.

Radioisotope Technology

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

Atomic Charge Changes

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

• Loss of electrons: Cation (positive ion); Gain of electrons: Anion (negative ion).

Diffusion

• Diffusion is the movement of molecules from an area of higher concentration to lower concentration.

• Does not require energy (passive transport).

ATP Production and Electron Transport Chain

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

Plasma Membrane Permeability

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

• Large or charged molecules (e.g., ions, glucose) require transport proteins.

Active Transport

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

• Example: Sodium-potassium pump.

Isotonic Solutions

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

Glycolysis

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

Electron Carriers in the Citric Acid Cycle

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

Plasma Membrane Structure

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

Connective Tissues

• Loose connective tissue: Supports and binds other tissues.

• Dense connective tissue: Provides strength (e.g., tendons, ligaments).

• Adipose tissue: Stores fat.

• Cartilage: Flexible support.

• Bone: Rigid support.

• Blood: Transports substances.

Locations of Tissue Types

• Epithelial tissue: Covers body surfaces and lines cavities.

• Connective tissue: Found throughout the body (e.g., under skin, in bones, blood).

• Muscle tissue: Attached to bones, in the heart, and in walls of hollow organs.

• Nervous tissue: Brain, spinal cord, nerves.

Muscle Type in the Stomach

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

Tissue Types and Functions

• Epithelial: Protection, absorption, secretion.

• Connective: Support, binding, transport.

• Muscle: Movement.

• Nervous: Communication, control.

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.

Summary Table: Types of Cell Junctions

Key Equations

• Surface Area to Volume Ratio (for a sphere):

• Cellular Respiration (Overall):

• pH Equation:

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