Cell Theory and Microscopy

• The invention of the microscope enabled the discovery of cells
• Cells are the structural and functional units of life

Cell Theory Principles

• All living organisms consist of cells
• Cells are the fundamental units of structure and function in organisms
• All cells come from pre-existing cells through the passing of genetic material

Microscope Technology

• Microscopes facilitate the study of cells

Types of Microscopes:

• Compound Light Microscope: Uses visible light and glass lenses, magnifies up to ~1000x
• Transmission Electron Microscope (TEM): Uses transmitted electrons, magnification up to 500,000x, needs thinly sliced, stained, dead specimens
• Scanning Electron Microscope (SEM): Scans the surface and creates 3D images, requires dead specimens
• Scanning Tunneling Microscope (STM): Employs electron tunneling and can view live specimens
• Atomic Force Microscope (AFM): Measures forces between a probe and the cell surface, yielding detailed images

Basic Cell Types

• Prokaryotic Cells: Lacking a nucleus, simple, unicellular (e.g., bacteria)
• Eukaryotic Cells: Contain a nucleus, larger, complex, can be unicellular or multicellular

Origin of Eukaryotic Cells

• Endosymbiotic Theory: Eukaryotic cells are thought to have evolved from a symbiotic relationship between prokaryotic cells
• Complexity in cells and organisms arose over time through these relationships

Plasma Membrane

• A flexible, selectively permeable boundary that controls what enters and leaves the cell
• Selective Permeability: Allows certain substances to pass while blocking others
• Important for structure of the cell

Fluid Mosaic Model

• States the membrane is flexible with moving molecules forming a pattern

Phospholipid Bilayer

• Consists of two layers of phospholipids, featuring hydrophilic heads facing outward and hydrophobic tails facing inward

Structure of the Plasma Membrane

• Composed of phospholipids, proteins, cholesterol, and carbohydrates

Phospholipid Bilayer

• Hydrophilic (polar) heads face water, hydrophobic (nonpolar) tails face inward
• This arrangement forms a barrier separating the internal and external cell environments

Membrane Proteins

• Receptors: Transmit signals
• Support Proteins: Maintain the cell's structure
• Transport Proteins: Facilitate the movement of substances in and out of the cell

Cholesterol

• Keeps the membrane fluid and prevents fatty acid tails from sticking together and helps maintain homeostasis

Carbohydrates

• Aid in cell recognition and communication

Function of the Plasma Membrane

• Homeostasis: Maintains a stable internal balance within the cell
• Selective Permeability: Regulates the entry and exit of substances

Cellular Transport

• Substances move into or out of a cell using different processes

Cellular Transport: Active Transport

• Requires energy, ATP, for movement of substances

Cellular Transport: Diffusion

• Particles go from areas of high to low concentration

Cellular Transport: Dynamic Equilibrium

• Particles are evenly distributed but continue moving

Cellular Transport: Facilitated Diffusion

• Passive transport using transport proteins

Cellular Transport: Osmosis

• The diffusion of water across a membrane

Cellular Transport: Exocytosis

• The cell expels materials through this process

Cellular Transport: Endocytosis

• The cell engulfs materials through this process

Hypertonic Solution

• High solute concentration outside the cell causing water to move out

Hypotonic Solution

• Low solute concentration outside the cell causing water to move in

Isotonic Solution

• Equal solute concentration inside and outside the cell

Passive Transport (No Energy Required): Diffusion

• Substances move from high to low concentration

Passive Transport (No Energy Required): Facilitated Diffusion

• Transport proteins aid molecule movement

Passive Transport (No Energy Required): Osmosis

• Water relocates to balance solute concentration

Effect of Solutions on Cells

• Isotonic: No net water movement; cell remains stable
• Hypotonic: Water enters, animal cells may burst
• Hypertonic: Water exits; cell shrinks

Active Transport (Requires Energy/ATP): Sodium-Potassium Pump

• Moves 3 Na⁺ out and 2 K⁺ in against their concentration gradient, requiring ATP

Active Transport (Requires Energy/ATP): Endocytosis

• Cell engulfs materials like nutrients or bacteria

Active Transport (Requires Energy/ATP): Exocytosis

• Cell expels materials like waste or proteins

Coupled Transport

• Sugars enter cells using Na⁺ ions via coupled channels, conserving energy

Key Concepts

• Microscopes enabled the discovery of cells and Cell Theory
• Cells are either prokaryotic (simple) or eukaryotic (complex)
• Plasma Membrane regulates homeostasis and selective permeability
• Passive Transport moves substances without energy; Active Transport requires ATP
• Solutions affect cells differently depending on their concentration
• Endocytosis and Exocytosis move large materials in and out of cells

Organelles

• Structures and their functions in prokaryotic and eukaryotic cells

Vacuole

• Stores food, enzymes, or waste, predominantly in plant cells

Ribosome

• Produces proteins and is not membrane-bound

Nucleolus

• Produces ribosomes inside the nucleus

Mitochondrion

• Converts fuel into usable energy (ATP)

Golgi Apparatus

• Modifies, sorts, and packages proteins

Lysosome

• Digests worn-out organelles and invaders

Flagellum

• A long, whip-like structure used for movement

Endoplasmic Reticulum (ER)

• Site for protein and lipid synthesis, comes in rough and smooth types

Cytoplasm

• Semifluid material inside the plasma membrane

Cytoskeleton

• Provides cell structure, includes microtubules & microfilaments

Chloroplast

• Captures light for photosynthesis, found only in plants

Cilium

• Short hair-like structures used for movement

Centriole

• Aids in cell division and is made of microtubules

Cell Wall

• Protects and provides structure: cellulose in plants; peptidoglycan in prokaryotes

Functions of Organelles

• Prokaryotic Cells: Chemical processes occur directly in the cytoplasm
• Eukaryotic Cells: Processes occur within specific organelles

Cell Structures Overview

• Cytoskeleton: Supports cell structure and aids in movement
• Microtubules: Hollow tubes used for movement
• Microfilaments: Thin threads that help with shape and movement
• Centrioles: Assist in cell division

Cilia vs. Flagella

• Cilia: Short, numerous, move like oars
• Flagella: Long, fewer, move like a whip

Cell Wall

• Offers support and protection in plants & prokaryotes

Controlling Cell Activities

• Nucleus: Stores DNA, controls growth, function, and reproduction
• Nuclear Envelope: Double membrane surrounding the nucleus

Energy Conversion

• Mitochondria: Site of cellular respiration
• Chloroplasts: Perform photosynthesis and contain chlorophyll in thylakoids

Protein Production Pathway

• Nucleolus: Produces ribosomes
• Nucleus: Houses DNA and makes mRNA
• Ribosomes: Translate mRNA into proteins
• Rough ER: Processes and folds proteins
• Golgi Apparatus: Sorts and packages proteins
• Secretory Vesicles: Transport proteins
• Cell Membrane: Releases proteins via exocytosis

Comparing Plant & Animal Cells

• Plant Cells: Have chloroplasts, vacuoles, and cell walls
• Animal Cells: Usually lack these structures

Review Questions

• Cell Wall Presence: Found in plants and prokaryotic cells
• Protein Synthesis: Takes place in ribosomes
• Cytoskeleton Components: Includes microtubules, microfilaments, and centrioles
• Main Protein Synthesis Site: Ribosomes

Cell theory states all living organisms are composed of cells, and these cells arise from pre-existing cells. Microscopy is essential for studying cells. Different types of microscopes, like light, TEM, and SEM, offer varying magnification and imaging capabilities.