Introduction to Biology

Domains of Life

The domain system classifies all living organisms into three major groups based on genetic and cellular differences.

• Bacteria: Prokaryotic, unicellular organisms lacking a nucleus.

• Archaea: Prokaryotic, often found in extreme environments, genetically distinct from bacteria.

• Eukarya: Eukaryotic organisms with membrane-bound nuclei; includes animals, plants, fungi, and protists.

Hierarchy of Living Organisms

Biological organization follows a hierarchical structure from smallest to largest.

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

Shared Characteristics of Living and Nonliving Things

• Living things: Composed of cells, capable of growth, reproduction, response to stimuli, metabolism, and homeostasis.

• Nonliving things: May have structure and mass but lack cellular organization and biological processes.

Scientific Method

The scientific method is a systematic approach to investigation.

1. Observation

2. Hypothesis

3. Experiment

4. Data Collection

5. Analysis

6. Conclusion

Homeostasis

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

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

Chemistry of Life

Most Abundant Elements in Humanity

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

• Phosphorus (P)

• Sulfur (S)

Reductionism

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

• Example: Studying cell organelles to understand cell function.

Importance of DNA

• DNA stores genetic information, directs protein synthesis, and enables inheritance.

Types of Chemical Bonds

• Ionic Bonds: Formed by transfer of electrons between atoms.

• Covalent Bonds: Formed by sharing electrons between atoms.

• Hydrogen Bonds: Weak attractions between partially charged atoms, important in water and DNA structure.

Polarity of Molecules

• Polar molecules: Unequal sharing of electrons, resulting in partial charges (e.g., water).

• Nonpolar molecules: Equal sharing of electrons, no charge separation (e.g., methane).

Acids, Bases, and pH

• Acidic: pH < 7

• Basic (Alkaline): pH > 7

• Neutral: pH = 7

Radioisotope Technology

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

Atoms and Charge

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

• Negatively charged elements (anions) attract positively charged elements (cations).

Elements vs. Molecules

• Element: Pure substance consisting of one type of atom.

• Molecule: Two or more atoms bonded together.

Structure & Function of Cells

Cell Organelles: Names, Functions, and Shapes

• Nucleus: Stores DNA; spherical.

• Mitochondria: Site of ATP production; oval-shaped.

• Ribosomes: Protein synthesis; small, round.

• Endoplasmic Reticulum (ER): Synthesis of proteins (rough ER) and lipids (smooth ER); tubular network.

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

• Lysosomes: Digestion of cellular waste; spherical.

• Plasma Membrane: Controls entry/exit; flexible, phospholipid bilayer.

Cell Size and Surface Area

Cell size is limited by the surface area-to-volume ratio, which affects nutrient and waste exchange.

• Smaller cells have higher surface area relative to volume, allowing efficient transport.

Microscopy Types

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

• Electron Microscopy: Used for high-resolution imaging of cell structures.

Cell Membrane & Transport

Plasma Membrane Structure

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

Diffusion

Diffusion is the passive movement of molecules from high to low concentration.

• Example: Oxygen entering cells.

Active Transport

Active transport moves substances against their concentration gradient using energy (ATP).

• Example: Sodium-potassium pump.

What Can and Can't Pass Through the Plasma Membrane

• Can pass: Small, nonpolar molecules (e.g., O2, CO2), some small polar molecules.

• Cannot pass: Large molecules, ions, and most polar molecules without transport proteins.

Isotonic Solutions

An isotonic solution has equal solute concentration as the cell, causing no net movement of water.

• Cells retain their shape in isotonic solutions.

Cellular Respiration

Glycolysis

Glycolysis is the first step in cellular respiration, breaking down glucose into pyruvate and producing ATP.

• Occurs in the cytoplasm.

Electron Transport Chain & ATP Production

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

Electron Carriers in Citric Acid Cycle

• NAD+ and FAD are electron carriers.

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

Tissues & Organ Systems

Types of Tissues and Their Functions

• Epithelial Tissue: Covers surfaces, lines cavities, protects, absorbs, and secretes.

• Connective Tissue: Supports, binds, and protects organs.

• Muscle Tissue: Contracts to produce movement.

• Nervous Tissue: Transmits electrical signals.

Types of Connective Tissues

• Loose connective tissue: Cushions organs.

• Dense connective tissue: Forms tendons and ligaments.

• Adipose tissue: Stores fat.

• Cartilage: Provides flexible support.

• Bone: Provides rigid support.

• Blood: Transports substances.

Locations of Tissue Types

• Epithelial: Skin, lining of digestive tract.

• Connective: Tendons, fat, bone, blood.

• Muscle: Skeletal muscles, heart, stomach.

• Nervous: Brain, spinal cord, nerves.

Muscle Type in the Stomach

• Smooth muscle is found in the stomach, responsible for involuntary contractions.

Types of Junctions

• Tight junctions: Seal cells together, prevent leakage.

• Desmosomes: Provide mechanical strength.

• Gap junctions: Allow communication between cells.

Table: Types of Tissues and Their Functions

Table: Types of Cell Junctions

Table: Cell Organelles

Equation: Surface Area to Volume Ratio

The surface area to volume ratio for a sphere is:

Equation: ATP Production in Cellular Respiration

Overall equation for cellular respiration:

Additional info: Expanded explanations and tables were added for completeness and clarity based on standard human biology curriculum.