Cell structure

• Microscopy topics cover light, UV, and electron microscopy, terminologies, resolving power, magnification, contrast, defects, and corrections of the Light Microscope
• Specific objectives on microscopy include understanding the need for improving microscope design, knowing simple microscopes, defects, corrections, magnification, and different types of light microscopes
• Units of measurements in microscopy include micrometers (µm), nanometers (nm), and Angstroms (Ǻ)
• Credit for developing cell theory is given to Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow
• Cell theory states that all living things are made up of cells, cells come from pre-existing cells, and cells are the fundamental unit of structure and function in living organisms
• Cells have a large surface area-to-volume ratio
• Cells come in a variety of sizes and shapes, with some moving rapidly and others being stationary
• The course covers the history of the cell, starting from Robert Hooke's discovery in 1665 to the development of modern cell theory by Schwann, Schleiden, and Virchow
• The broad course objectives also include tissue preparation for cellular examination, cell fractionation, homogenization, centrifugation, and instrumentation for cellular analysis
• Students should be able to summarize methods of disrupting and fractionating cells, as well as analyze cells and tissues using techniques like chromatography, autoradiography, and spectrophotometry
• The course covers the theory and application of a variety of light microscopes, advances in studying cell structure and function over the centuries, and the theory and application of electron microscopy in Biology
• Students should be able to evaluate the advantages and disadvantages of electron microscopy in Biology
• The cell is defined as the smallest unit capable of independently performing life functions
• The cell was first discovered and named by Robert Hooke in 1665, and Antony van Leeuwenhoek was the first to observe live cells under a microscope
• A timeline of cell history includes key events like the discovery of cells in cork by Hooke, Leeuwenhoek's observation of protozoa, and the proposal of cell theory by Schwann and Schleiden
• The cell theory states that all living things are made up of cells, cells come from pre-existing cells, and the cell is the fundamental unit of structure and function in living organisms
• Cells are diverse in size, shape, and function, with some organisms consisting of a single cell while others are multi-cellular
• Microorganisms and their components are measured in small units like micrometers (µm) and nanometers (nm)
• There are two types of light microscopes: simple microscopes and compound microscopes
• Simple microscopes have only one lens and are used for quick viewing of objects requiring magnification
• Defects of simple microscopes include spherical aberration and chromatic aberration, which can affect resolution and clarity of images
• Ways to reduce spherical aberration include using specialized aspherical lenses, coating lens periphery with opaque materials, and using oil immersion lenses
• Plano-convex lenses are used for focusing parallel rays of light to a single point
• Plano-convex lenses are the best choice for focusing parallel rays of light to a single point
• They can be used to focus, collect and collimate light
• The asymmetry of this lens shape minimizes spherical aberration in situations where the object and image are located at unequal distance from the lens
• The optimum case is where the object is placed at infinity with parallel rays entering the lens and the final image is a focused point
• Chromatic Aberration is a common optical problem that occurs when a lens is unable to bring all wavelengths of color to the same focal plane
• It can also occur when wavelengths of color are focused at different positions in the focal plane
• Chromatic aberration is caused by lens dispersion, with different colors of light traveling at different speeds while passing through a lens
• The image can look blurred or noticeable colored edges (red, green, blue, yellow, purple, magenta) can appear around objects, especially in high-contrast situations
• Chromatic aberration is caused by the dispersion of the lens material—the variation of its refractive index with the wavelength of light
• Light of different wavelengths is focused to different positions, resulting in fringes of color around the image
• Ways of correcting chromatic aberration include using flint glass and crown which have equal but different focal lengths, known as Achromatic Doublet
• Another way is by using more complex systems of lenses
• Chromatic aberration can be minimized by using an achromatic doublet in which two materials with differing dispersion are bonded together to form a single lens
• Light microscopy refers to the use of any kind of microscope that uses visible light to observe specimens
• This reduces the amount of chromatic aberration over a certain range of wavelengths, though it does not produce perfect correction
• The curvatures of the lens materials and their composition are designed to minimize distortion of image shapes and colors
• Light microscopes are of two different basic types: Compound Microscopes and Dissecting Microscopes