Introduction to Biology

Domains of Life

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

• Bacteria: Prokaryotic, unicellular organisms with simple cell structure.

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

• Eukarya: Eukaryotic organisms, including plants, animals, fungi, and protists; cells contain membrane-bound organelles.

Hierarchy of Living Organisms

Biological organization follows a hierarchical structure from smallest to largest.

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

Shared Characteristics of Living and Nonliving Things

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

• Nonliving things: May have structure and mass, but lack the above characteristics.

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 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.

• Helps in analyzing biological processes at molecular and cellular levels.

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 of electrons.

• 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 substances: pH < 7

• Basic substances: 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).

Structure & Function of Cells

Cell Organelles: Names, Functions, and Shapes

Cell organelles perform specialized functions within eukaryotic cells.

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.

Diffusion

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

• Important for gas exchange and nutrient 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

• Can pass: Small, nonpolar molecules (e.g., O2, CO2), some small polar molecules (e.g., H2O).

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

Active Transport

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

• Example: Sodium-potassium pump.

Isotonic Solutions

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

• Cells retain their normal shape in isotonic solutions.

Glycolysis

Glycolysis is the first step of cellular respiration, breaking down glucose to produce ATP.

• Occurs in the cytoplasm.

• Produces pyruvate, ATP, and NADH.

Electron Transport Chain and ATP Production

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

Electron Carriers in Citric Acid Cycle

• NADH and FADH2 are electron carriers, receiving electrons from metabolic reactions.

Tissues & Organ Systems

Types of Connective Tissues

Types of Tissues and Their Functions

• Epithelial Tissue: Covers surfaces, lines cavities, protection, absorption.

• Connective Tissue: Supports, binds, protects organs.

• Muscle Tissue: Movement, contraction.

• Nervous Tissue: Communication, control.

Location of Each Tissue Type

• Epithelial: Skin, lining of digestive tract.

• Connective: Tendons, ligaments, fat, bone, blood.

• Muscle: Skeletal muscles, heart, stomach.

• Nervous: Brain, spinal cord, nerves.

Type of Muscle in the Stomach

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

Types of Junctions

• Tight Junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap Junctions: Allow communication between cells.

Example: Gap junctions in cardiac muscle allow coordinated contraction.