Introduction to Biology

Domains of Life

The domain system classifies all living organisms into three major groups based on cellular structure 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: Exhibit organization, metabolism, responsiveness, growth, development, reproduction, and 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. 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.

• Example: Studying cell organelles to understand cell function.

Atoms, Elements, and Molecules

• Element: A pure substance consisting of only one type of atom.

• Molecule: Two or more atoms bonded together.

Radioisotope Technology

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

• Example: PET scans use radioisotopes to visualize metabolic activity.

Types of Bonds

• Ionic Bonds: Formed when electrons are transferred between atoms.

• Covalent Bonds: Formed when atoms share electrons.

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

Polarity

• Polar Molecules: Have uneven distribution of charge (e.g., water).

• Nonpolar Molecules: Have even distribution of charge (e.g., methane).

Acids, Bases, and pH

• Acidic: pH < 7

• Basic (Alkaline): pH > 7

• Neutral: pH = 7

Changing Atomic Charges

• Atoms gain or lose electrons to become 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 a higher surface area-to-volume ratio, allowing efficient exchange.

• 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 proteins or structures using fluorescent dyes.

Diffusion

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

• Example: Oxygen diffusing into cells.

Plasma Membrane Structure

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

• Selective permeability allows certain substances to pass while blocking others.

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 Solution

An isotonic solution has equal solute concentration inside and outside the cell, resulting in no net water movement.

• Cells retain their normal shape in isotonic solutions.

Chemical Processes in Cells

Glycolysis

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

• Occurs in the cytoplasm.

• Produces 2 ATP molecules per glucose.

Electron Transport Chain and ATP Production

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

• Location: Inner mitochondrial membrane.

Electron Carriers in Citric Acid Cycle

• NAD+ and FAD are electron carriers.

• They gain electrons from metabolic reactions and transfer them to the electron transport chain.

Tissues & Organ Systems

Types of Tissues and Their Functions

There are four main types of tissues 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 Each Tissue Type

• Epithelial: Skin, lining of digestive tract.

• Connective: Bone, blood, cartilage, tendons.

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

• Nervous: Brain, spinal cord, peripheral nerves.

Type of Muscle in the Stomach

• Smooth muscle is found in the stomach and other internal organs.

Types of Junctions

• Tight junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap junctions: Allow communication between cells.