Microscopy and Cell Observation

Types of Microscopes

Microscopes are essential tools for studying cells and their structures. Different types of microscopes offer varying levels of magnification and resolution.

• Light Microscope (LM): Uses visible light to pass through a specimen, then through glass lenses to bend the light. Max. Mag. ×1000.

• Magnification: Increase in an object's image size compared to the original.

• Resolution: Ability to distinguish two nearby objects as separate.

• Cell Theory: All living things are composed of cells, and all cells come from other cells.

• Electron Microscope (EM): Uses a beam of electrons for higher magnification and resolution. Max. Mag. ×100,000.

  • Scanning Electron Microscope (SEM): Produces 3D images of specimen surfaces coated in metal.

  • Transmission Electron Microscope (TEM): Reveals internal cell structures.

Cell Structure and Function

Plasma Membrane

The plasma membrane is a thin, flexible boundary that separates the cell from its surroundings and regulates the passage of materials in and out.

• Surface-to-volume ratio: Cells are small to maximize this ratio, facilitating efficient exchange of materials.

• Structure: Composed of a phospholipid bilayer with embedded proteins.

Universal Cell Features

• Plasma Membrane

• Ribosomes

• DNA

• Cytosol

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure and complexity.

Cellular Components and Organelles

Genetic Control

• Nucleus: DNA replication, RNA synthesis, assembly of ribosomal subunits.

• Ribosomes: Protein synthesis.

Manufacturing, Distribution, and Breakdown

• Rough ER: Synthesis of membrane lipids and proteins, secretory proteins.

• Smooth ER: Lipid synthesis, detoxification, calcium ion storage.

• Golgi Apparatus: Modification and sorting of ER products, formation of lysosomes and transport vesicles.

• Lysosomes: Digestion and recycling (animal cells).

• Vacuoles: Storage, water balance, waste disposal (plant cells).

• Peroxisomes: Breakdown of toxic hydrogen peroxide.

Energy Processing

• Mitochondria: Cellular respiration, conversion of chemical energy in food to ATP.

• Chloroplasts: Photosynthesis (plants and algae).

Support, Movement, and Communication

• Cytoskeleton: Network of fibers for structural support.

• Cell Junctions: Regulate traffic and communication between cells.

• Plasma Membrane: Regulates entry and exit of substances.

Specialized Structures in Plant and Animal Cells

Plant Cell Structures

• Cell Wall: Made of cellulose, provides structure.

• Chloroplast: Site of photosynthesis.

• Large Central Vacuole: Stores water and nutrients.

• Plasmodesmata: Channels connecting adjacent cells.

Animal Cell Structures

• Lysosomes: Contain digestive enzymes.

• Centrosomes: Organize cell division.

• Flagella/Cilia: Movement.

Cell Junctions in Animal Cells

• Tight Junctions: Leakproof, prevent fluid passage.

• Anchoring Junctions: Fasten cells into strong sheets.

• Gap Junctions: Allow ions and molecules to flow between cells.

Membrane Structure and Function

Fluid Mosaic Model

The cell membrane is a mosaic of phospholipids and proteins, making it fluid and dynamic.

• Cholesterol: Maintains membrane fluidity and stability.

• Membrane Proteins: Serve as anchors, signals, enzymes, recognition sites, and transporters.

Bioluminescence

• Production and emission of light by living organisms via chemical reactions.

Membrane Transport Mechanisms

Passive Transport

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Selective Permeability: Membrane allows water to pass but restricts solutes.

• Concentration Gradient: Water moves from more to less free water molecules.

Osmotic Solutions

Facilitated Diffusion

• Charged substances cross the membrane via transport proteins.

• Aquaporins: Dedicated water channels.

Active Transport

• Requires energy (usually ATP) to move substances against their concentration gradient.

Bulk Transport

• Exocytosis: Export of large molecules from the cell.

• Endocytosis: Import of large molecules or fluids.

  • Phagocytosis: "Cell eating"; cell engulfs a molecule.

  • Pinocytosis: "Cell drinking"; cell takes in extracellular fluid.

  • Receptor-mediated Endocytosis: Specific molecules bind to receptors for uptake.

Cellular Energy

Types of Energy

• Kinetic Energy: Energy of motion.

• Potential Energy: Stored energy based on position/structure.

• Heat: Energy transfer from one object to another.

Endomembrane System and Endosymbiotic Theory

Endomembrane System

A complex network in eukaryotic cells for synthesis, distribution, storage, and export of molecules.

• Nuclear envelope

• Endoplasmic reticulum

• Golgi apparatus

• Lysosomes

• Vesicles and vacuoles

• Plasma membrane

Endosymbiotic Theory

Mitochondria and chloroplasts originated as small prokaryotic cells engulfed by ancestral eukaryotes.

• Evidence: Circular DNA, prokaryote-like ribosomes, reproduction by binary fission, evolutionary benefits.

Cytoskeleton

Types of Fibers

• Microfilaments: Support cell shape, involved in movement.

• Intermediate Filaments: Reinforce cell shape, anchor organelles.

• Microtubules: Shape and support the cell, serve as tracks for organelle movement.

Summary Table: Cell Junctions

Key Equations

• Surface-to-Volume Ratio:

Additional info:

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