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 lacking a nucleus.

• Archaea: Prokaryotic, unicellular, 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:

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism

Shared Characteristics of Living and Nonliving Things

• Living things: Exhibit metabolism, growth, reproduction, response to stimuli, and homeostasis.

• Nonliving things: May have structure and composition but lack 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.

• Example: Regulation of body temperature.

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.

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; results in charged ions.

• Covalent Bonds: Formed by sharing electrons between atoms; strong and stable.

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

Polarity of Molecules

• Polar molecules: Unequal sharing of electrons; have partial positive and negative 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

Radioisotopes are used in medical imaging, cancer treatment, and biological research due to their radioactive properties.

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 surface area-to-volume ratio, affecting nutrient and waste exchange.

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

• Formula: for a cube

• 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 regulates transport.

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.

Diffusion

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

Active Transport

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

Isotonic Solution

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

• Cells retain their normal shape in isotonic solutions.

Chemical Processes in Cells

Glycolysis

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

Electron Transport Chain and ATP Production

• Most ATP is produced by 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

There are four main tissue types in the human body, each with specialized functions.

Types of Connective Tissues

• Loose connective tissue: Supports and binds other tissues.

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

• Cartilage: Flexible support.

• Bone: Rigid support and protection.

• Blood: Transport of nutrients and waste.

Locations of Tissue Types

• Epithelial: Skin, lining of digestive tract.

• Connective: Bone, blood, cartilage.

• Muscle: Skeletal muscles, heart, stomach.

• Nervous: Brain, nerves.

Type of Muscle in the Stomach

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

Types of Junctions

• Tight junctions: Seal cells together, preventing leakage.

• Desmosomes: Provide mechanical strength by anchoring cells.

• Gap junctions: Allow communication between cells via small molecules.

Example: Gap junctions in cardiac muscle allow synchronized contraction.