Introduction to Biology

Domains of Life

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

• Bacteria: Prokaryotic, unicellular organisms lacking a nucleus.

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

• Eukarya: Eukaryotic organisms with cells containing a nucleus; 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: Organization, metabolism, responsiveness, growth, development, reproduction, homeostasis.

• Nonliving things: May have structure but lack metabolism, growth, and reproduction.

Scientific Method

The scientific method is a systematic approach to investigation.

1. Observation

2. Question

3. Hypothesis

4. Experiment

5. Data Collection

6. Analysis

7. 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.

• 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: Transfer of electrons between atoms; forms charged ions.

• Covalent Bonds: Sharing of electrons between atoms; strong and stable.

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

Polarity of Molecules

• Polar molecules: Unequal sharing of electrons; have 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).

Element vs. Molecule

• 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

Cell organelles perform specialized functions essential for cell survival.

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.

• Formula: (for a cube),

Microscopy Types

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

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

• Fluorescence Microscopy: Used to visualize specific molecules with fluorescent tags.

Plasma Membrane Structure

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

• Selective permeability allows certain substances to pass.

What Can and Can't Pass Through the Plasma Membrane

• Can pass: Small, nonpolar molecules (e.g., O2, CO2), water (via aquaporins).

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

Types of Junctions

• Tight Junctions: Seal cells together, prevent leakage.

• Desmosomes: Anchor cells, provide mechanical strength.

• Gap Junctions: Allow communication between cells.

Cellular Processes

Diffusion

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

• Occurs across cell membranes.

• Example: Oxygen diffusing into cells.

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 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.

• Produces 2 ATP and 2 NADH per glucose.

Electron Transport Chain (ETC)

• Most ATP is produced in the ETC, located in the inner mitochondrial membrane.

• Protein complexes transfer electrons and pump protons to generate ATP.

Citric Acid Cycle Electron Carriers

• NADH and FADH2 are electron carriers.

• They receive electrons from metabolic reactions and donate them to the ETC.

Tissues & Organ Systems

Types of Connective Tissues

Types of Tissues and Their Functions

Location of Each Tissue Type

• Epithelial: Skin, lining of digestive tract.

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

• Muscle: Skeletal muscles, heart (cardiac), stomach (smooth).

• Nervous: Brain, spinal cord, peripheral nerves.

Type of Muscle in the Stomach

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

Types of Junctions (Summary Table)