Chapter 7 (cont) - A tour of the cells. This chapter presents the following content: Microscopy; facts about cells; nucleus & ribosomes; endomembrane system; mitochondria, chloroplasts, and peroxisomes; the cytoskeleton; cell surfaces and junctions. | A Tour of the Cells Microscopy The discovery and early study of cells improved with the invention of microscopes in the 17th century. In a light microscope (LM) visible light passes through the specimen and then through glass lenses. The lenses refract light such that the image is magnified into the eye Microscopes Magnification is the ratio of an object’s image to its real size. Resolving power is a measure of image clarity. It is the minimum distance two points can be separated by and still be viewed as two separate points. Microscopes Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen. At higher magnifications, the image blurs Microscopes While a light microscope can resolve individual cells, it cannot resolve organelles. To resolve smaller structures we use an electron microscope (EM), which focuses a beam of electrons through the specimen or onto its surface. Microscopes Transmission electron microscopes (TEMs) are used mainly to study the internal ultrastructure of cells. A TEM aims an electron beam through a thin section of the specimen. The image is focused and magnified by electromagnets. To enhance contrast, the thin sections are stained with atoms of heavy metals. TEM Scanning electron microscopes (SEMs) are useful for studying surface structures. The sample surface is covered with a thin film of gold. The beam excites electrons on the surface. These secondary electrons are collected and focused on a screen. The SEM has great depth of field, resulting in an image that seems three-dimensional. SEM Electron microscopes reveal organelles, but they can only be used on dead cells Light microscopes do not have as high a resolution, but they can be used to study live cells. Microscopes are a major tool in cytology, the study of cell structures. Cytology coupled with biochemistry, the study of molecules and chemical processes in metabolism, developed into modern cell biology. Electron Microscopes The goal | A Tour of the Cells Microscopy The discovery and early study of cells improved with the invention of microscopes in the 17th century. In a light microscope (LM) visible light passes through the specimen and then through glass lenses. The lenses refract light such that the image is magnified into the eye Microscopes Magnification is the ratio of an object’s image to its real size. Resolving power is a measure of image clarity. It is the minimum distance two points can be separated by and still be viewed as two separate points. Microscopes Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen. At higher magnifications, the image blurs Microscopes While a light microscope can resolve individual cells, it cannot resolve organelles. To resolve smaller structures we use an electron microscope (EM), which focuses a beam of electrons through the specimen or onto its surface. Microscopes Transmission electron microscopes (TEMs) are used mainly to .
