Microscope Types and Parts

Types of Microscopes

• A simple microscope utilizes a single lens.
• Anton van Leeuwenhoek made the first simple microscope in 1672, achieving 200x-300x magnification.
• A simple compound microscope uses two sets of lenses.
• The magnification of a simple compound microscope is 100x-200x.
• The first compound microscope was made in 1590 by Zaccharias Janssen and his son, Hans Janssen.
• Robert Hooke developed the laboratory compound microscope in 1665.
• Oil lamps and condensing lenses were used for illumination in Hooke's microscope.
• Modern compound microscopes have more than one lens.
• Modern compound microscopes include two sets of lenses: eyepiece and objectives.
• Modern compound microscopes usually include 3 to 5 objective lenses.

Main Parts of a Microscope

• Compound microscopes have three main component types: mechanical, illuminating and optical.
• Mechanical parts are the metal parts of the microscope.
• Illuminating parts are responsible for supplying light.
• Optical parts are used for magnification.

Mechanical Parts of a Microscope

• The arm connects the upper and lower parts of the microscope and is designed to safely hold the microscope.
• The base serves as the "foot" of the microscope.
• The stage is a platform where the slide with the specimen is placed.
• Stage clips hold the slide in place on the stage.
• The draw tube holds the eyepiece.
• The body tube allows a considerable distance between the eyepiece and objective lens.
• The dust shield avoids the accumulation of dust in the objective lenses.
• The revolving nosepiece holds and allows the shifting of the objective lenses.
• The coarse adjustment knob brings the objective into focus through a large adjustment.
• The fine adjustment knob brings the image into focus through a small adjustment.

Illuminating Parts of a Microscope

• The mirror (or lamp) gathers (or provides) light.
• The diaphragm regulates the amount of light.
• The condenser concentrates light to the specimen.

Optical Parts of a Microscope

• The eyepiece (or ocular) is a lens on top of the microscope where the user looks to see the specimen.
• The eyepiece magnifies the secondary image of the specimen.
• The magnification of the eyepiece is usually 10x.
• Objective lenses are mounted into the revolving nosepiece above the stage.
• Objective lenses magnify the primary image of the specimen.
• There are three main types of objective lenses: Low Power, High Power and Oil Immersion.

Objective Lenses

• Low Power Objective (LPO) has a 10x magnification, is used for initial focusing, and shows a general image.
• High Power Objective (HPO) has a 40x magnification and shows a specific/detailed part of the specimen.
• Oil Immersion Objective (OIO) has a 100x magnification, is for the study of microorganisms, and used with cedarwood oil.
• Scanning Power Objective (SPO) provides a 4x magnification for scanning the whole slide.

Discovery of the Cell

• Anton van Leeuwenhoek made a simple, single-lens microscope.
• Leeuwenhoek's microscope had a magnification of about 275x.
• Robert Hooke discovered the cell and coined the name "cell".
• Hooke used cork from a plant to observe tiny boxes that looked like rooms in a monastery.

Components of the Cell Theory

• All organisms are composed of cells, demonstrated by Theodore Schwann and Matthias Schleiden.
• The cell is the basic unit of life.
• All cells come from pre-existing cells, demonstrated by Rudolf Virchow.

Basic Cell Types

• Eukaryotic cells have a "true" nucleus.
• Eukaryotic cells contain membrane-bound organelles.
• Eukaryotic organisms are multicellular, including plants and animals.
• Prokaryotic cells have a "false" nucleus.
• Prokaryotic cells have non-membrane bound organelles.
• Prokaryotic organisms are unicellular, including bacteria.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic organisms are bacteria, while eukaryotic organisms include animals, plants, algae, fungi and protists.
• Prokaryotic cells have no definite nucleus ("false nucleus"), while eukaryotic cells have a definite nucleus ("true nucleus").
• Prokaryotic cells have few structures, while eukaryotic cells have structures that are highly structured by membranes.
• Prokaryotic cells have no mitochondria, while eukaryotic cells have 1-100 mitochondria (except red blood cells).
• Prokaryotic cells have 70S ribosomes, while eukaryotic cells have 80S ribosomes.
• Prokaryotic cells have no chloroplasts, while eukaryotic cells in plants and algae do.
• Prokaryotic cells undergo binary fission for cell division, while eukaryotic cells undergo mitosis and meiosis.
• Prokaryotic organisms are unicellular, while eukaryotic organisms are multicellular.

Cell Membrane

• The cell membrane, also called the plasma membrane, separates the cell from its external environment.
• The envelope covers and protects the cell and gives it shape.
• The cell membrane is semi-permeable, selecting materials that pass through and regulating the movement of materials.
• The bilayer phospholipid consists of phosphate layers with polar heads (hydrophilic) and lipid layers with non-polar tails (hydrophobic).
• The fluid mosaic model contains proteins and other molecules.

Nucleus

• The nucleus is normally the largest organelle.
• The nuclear envelope is a double membrane with many pores.
• The nuclear envelope controls material movement in and out of the nucleus.
• Chromosomes house the genes (DNA).
• Chromosomes contain hereditary material with instructions for traits and characteristics.
• The nucleolus is a spherical body in the nucleus for protein synthesis.

Cytoplasm

• Cytoplasm, also called protoplasm, is the inside of the cell.
• The living substance contains the organelles that perform the physiological properties of the cell.
• The gel-like material can be in a sol (semi-liquid) or gel (semi-solid) state.
• The cytosol makes up 70% of the cytoplasm.
• Cytosol is a mixture of cytoskeleton filaments, dissolved materials and water.

Organelles

• Organelles are basic cell parts that perform the physiological activities of the cell.

Endoplasmic Reticulum

• The endoplasmic reticulum is a system of membranous tubules and sacs.
• The endoplasmic reticulum is the "circulatory system of the cell".
• It is an internal transport system that allows molecules in the cell to move from one part to another.
• Rough ER (rER) is lined with ribosomes and involved in protein synthesis and transport.
• Smooth ER (sER) has no ribosomes and transports other materials besides protein.

Ribosomes

• Ribosomes are the most common organelles and are in almost all cells.
• They are not surrounded by a membrane.
• Ribosomes are protein micro-machines and the sites for protein synthesis.
• Free ribosomes float in the cytoplasm, are 70S in size, and found in prokaryotes.
• Polysomes/polyribosomes are groups of 80S ribosomes working together, translating mRNA to polypeptides.
• Attached ribosomes line the membranes of the endoplasmic reticulum, are 80S in size, and found in eukaryotes.

Mitochondria

• Mitochondria are the "powerhouse of the cell".
• Mitochondria are large organelles, second only to the nucleus and chloroplasts in size.
• They manufacture energy in the form of ATP.
• They metabolize carbohydrate and fatty acid to generate energy.
• Mitochondria act like a digestive system to breakdown nutrients to produce energy rich molecules, accomplishing aerobic respiration.
• Mitochondria are semi-autonomous organelles with their own DNA, allowing them to produce by itself by dividing.
• Mitochondria are double-membrane organelles with a smooth outer membrane, folded inner membrane and cristae (in foldings).

Golgi Apparatus

• The Golgi apparatus, also called the Golgi complex or Golgi body, acts as a processing and packaging plant, creating secretory vesicles.
• Cisternae are fused flattened sacs or folds and also referred to as dictyosomes.
• The Golgi apparatus acts as a transport agent involved in the distribution of lipids around the cell.
• The Golgi apparatus acts as a protein collector and dispatcher, with proteins synthesized in the ER packed into vesicles and fused with the Golgi body for secretion via exocytosis.
• It acts as a lysosome builder, forming lysosomes are vesicles with protein enzymes pinched off by the Golgi body to the cytoplasm.

Vacuole

• Vacuoles are storage bubbles found in cells, and are membrane-bound fluid sacs.
• Vacuoles can act a storage sac that stores large amounts of various materials, like organic and inorganic molecules.
• Vacuoles can be a transporting agent: transports needed materials into the cell via endocytosis and waste materials out of the cell via exocytosis.
• Vacuoles play a subordinate role, assisting in exocytosis and endocytosis.

Lysosome

• A lysosome is a tiny sac produced by the Golgi body.
• Lysosomes are digestive plants and contain digestive enzymes to help in the process of digestion.
• Lysosomes keep the cell clean by digesting excess and worn out organelles and engulfed bacteria or viruses.
• As a "suicide sac" when the cell is damaged, the lysosome bursts, releases enzymes and digests its own cell.

Cytoskeleton

• The cytoskeleton is a complex network of interlinking filaments or tubules and a cell skeleton.
• There are three structures to the cytoskeleton.
• Microfilaments which are contractile, made of actin, and used for cell movement and cytokinesis.
• Microtubules are rigid, hollow tubes made of tubulin, and maintain cell shape and form the centrioles (spindle fibers).
• Intermediate filaments provide strength and support.

Centrioles

• Centrioles are organizing centers for microtubules.
• Centrioles contain two bundles of microtubules at right angles to each other.
• During cell division, they form the spindle fibers for the separation of chromosomes.
• Centrosomes house the centrioles.

Flagella and Cilia

• Flagella and cilia are used for cell movement.
• Cilia are short, hair-like and numerous in number.
• Flagella are long, thread-like and fewer in number.

Cytokinesis and Interphase

• Cytokinesis is the division of the rest of the cell (cytoplasm and organelles) after the nucleus divides.
• In animal cells, the cytoplasm pinches in during cytokinesis.
• In plant cells, a cell plate forms during cytokinesis.
• After mitosis and cytokinesis, the cell returns to Interphase to continue to grow and perform regular cell activities.