Friday, August 10, 2012

REAGENTE LIMITANTE

O texto abaixo faz parte de minhas lições de Biologia do Curso de Licenciatura pela Universidade Metropolitana de Santos. (Valdemir Mota de Menezes, o Escriba)

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Reagente limitante
A razão entre os números de mols de moléculas de hidrogênio e oxigênio
na produção de água é 2:1. Essa razão é chamada razão estequiométrica
e possui valor fixo.
2 H2 + O2 2 H2O
Se, ao realizar uma reação, são escolhidas quantidades arbitrárias de
reagentes, é muito comum que um dos reagentes seja completamente
consumido antes dos outros. Isto ocorre quando existe uma quantidade
adicional (um excesso) de qualquer um dos reagentes, apresentando-se
além da razão estequiométrica. Este excesso permanecerá sem reagir.
Na reação de produção de água citada acima, se 3 mol de H2 e 1 mol de
O2 estiverem presentes no início da reação, somente 2 mol de H2 reagirão,
consumindo completamente 1 mol de O2. Depois que o O2 for consumido,
nenhuma reação posterior poderá acontecer e nenhum produto posterior
poderá ser formado. Neste caso, o oxigênio é o reagente limitante, devido
à quantidade de água formada ser limitada pela quantidade de oxigênio
presente, não pelo hidrogênio. O hidrogênio encontra-se em excesso.
Se a mesma reação fosse iniciada com 3 mol de H2 e 2 mol de O2, o hidrogênio
seria consumido totalmente, mas restaria 0,5 mol de O2 em excesso.
Nesta situação o H2 seria o reagente limitante.

SOLUTE AND SOLVENT

Solute and Solvent

It is a frequent component of a solution is present in an amount much larger than the other components. This component is called solvent and each of the other components is called solute. After dissolve one gram of sugar in one liter of water, we refer to water as the solvent and sugar as the solute. Because they are very common, solutions where the solvent is water are called aqueous solutions. (by Biologist Valdemir Mota de Menezes)

MICROSCOPE

Text read by Valdemir Mota de Menezes, the Scribe

Microscope

From Wikipedia, the free encyclopedia

This article is about microscopes in general. For light microscopes, see optical microscope.

Microscope

Uses	Small sample observation
Notable experiments	Discovery of cells
Inventor	Zacharias Janssen
Related items	Optical microscope Electron microscope

18th century microscopes from theMusée des Arts et Métiers, Paris

A microscope (from the Greek: μικρός, mikrós, "small" and σκοπεῖν, skopeîn, "to look" or "see") is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy.Microscopic means invisible to the eye unless aided by a microscope.

There are many types of microscopes, the most common and first to be invented is theoptical microscope which uses light to image the sample. Other major types of microscopes are the electron microscope (both the transmission electron microscope and the scanning electron microscope) and the various types of scanning probe microscope.

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[edit]History

Main article: Timeline of microscope technology

The first microscope to be developed was the optical microscope, although the original inventor is not easy to identify. An early microscope was made in 1590 in Middelburg,Netherlands.^[1] Two eyeglass makers are variously given credit: Hans Lippershey (who developed an early telescope) and Zacharias Janssen. Giovanni Faber coined the namemicroscope for Galileo Galilei's compound microscope in 1625 ^[2] (Galileo had called it the "occhiolino" or "little eye").

[edit]Rise of modern light microscopy

[edit]Electron microscopy

An ant as imaged using a scanning electron microscope(SEM)

[edit]Scanning probe microscopy

[edit]Fluorescence and light microscopy

The most recent developments in light microscope largely centre on the rise of fluorescence microscopy in biology. During the last decades of the 20th century, particularly in the post-genomic era, many techniques for fluorescent labeling of cellular structures were developed. The main groups of techniques are small chemical staining of cellular structures, for example DAPI to label DNA, use of antibodies conjugated to fluorescent reporters, see immunofluorescence, and fluorescent proteins, such as green fluorescent protein. These techniques use these different fluorophores for analysis of cell structure at a molecular level in both live and fixed samples.

The rise of fluorescence microscopy drove the development of a major modern microscope design, the confocal microscope. The principle was patented in 1957 by Marvin Minsky, although laser technology limited practical application of the technique. It was not until 1978 when Thomas and Christoph Cremer developed the first practical confocal laser scanning microscope and the technique rapidly gained popularity through the 1980s.

Main article: Microscopy#Sub-diffraction techniques

Much current research (in the early 21st century) on optical microscope techniques is focused on development of superresolutionanalysis of fluorescently labeled samples. Structured illumination can improve resolution by around two to four times and techniques like stimulated Emission Depletion microscopy are approaching the resolution of electron microscopes.

[edit]Types

Types of microscopes

Microscopes can be separated into several different classes. One grouping is based on what interacts with the sample to generate the image, i.e., light orphotons(optical microscopes), electrons (electron microscopes) or a probe (scanning probe microscopes). Alternatively, microscopes can be classed on whether they analyse the sample via a scanning point (confocal optical microscopes, scanning electron microscopes and scanning probe microscopes) or analyse the sample all at once (wide field optical microscope and transmission electron microscopes).

Wide field optical microscopes and transmission electron microscopes use the theory of lenses (optics for light microscopes and electromagnet lenses for electron microscopes) in order to magnify the image generated by the passage of a wave transmitted through the sample, or reflected by the sample. The waves used are electromagnetic (in optical microscopes) or electron beams (inelectron microscopes). Resolution in these microscopes is limited by the wavelength of the radiation used to image the sample, where shorter wavelengths allow for a higher resolution.

Scanning optical and electron microscopes, like the confocal microscope and scanning electron microscope, use lenses to focus a spot of light or electrons onto the sample then analyze the reflected or transmitted waves. The point is then scanned over the sample to analyze a rectangular region. Magnification of the image is achieved by displaying the data from scanning a physically small sample area on a relatively large screen. These microscopes have the same resolution limit as wide field optical and electron microscopes.

Scanning probe microscopes also analyze a single point in the sample and then scan the probe over a rectangular sample region to build up an image. As these microscopes do not use electromagnetic or electron radiation for imaging they are not subject to the same resolution limit as the optical and electron microscopes described above.

[edit]Optical

Main article: Optical microscope

The most common type of microscope (and the first invented) is the optical microscope. This is an optical instrument containing one or more lenses producing an enlarged image of a sample placed in the focal plane. Optical microscopes have refractive glass and occasionally of plastic or quartz, to focus light into the eye or another light detector. Mirror-based optical microscopes operate in the same manner. Typical magnification of a light microscope, assuming visible range light, is up to 1500x with a theoretical resolution limitof around 0.2 micrometres or 200 nanometres. Specialized techniques (e.g., scanning confocal microscopy, Vertico SMI) may exceed this magnification but the resolution is diffraction limited. The use of shorter wavelengths of light, such as the ultraviolet, is one way to improve the spatial resolution of the optical microscope, as are devices such as the near-field scanning optical microscope.
Sarfus, a recent optical technique increases the sensitivity of standard optical microscope to a point it becomes possible to directly visualize nanometric films (down to 0.3 nanometre) and isolated nano-objects (down to 2 nm-diameter). The technique is based on the use of non-reflecting substrates for cross-polarized reflected light microscopy.

CBP Office of Field Operations agent checking the authenticity of a travel document at an international airport using astereo microscope

Ultraviolet light enables the resolution of microscopic features, as well as to image samples that are transparent to the eye. Near infrared light can be used to visualize circuitry embedded in bonded silicon devices, since silicon is transparent in this region of wavelengths.

In fluorescence microscopy, many wavelengths of light, ranging from the ultraviolet to the visible can be used to cause samples to fluoresce to allow viewing by eye or with the use of specifically sensitive cameras.

Phase contrast microscopy is an optical microscopy illumination technique in which smallphase shifts in the light passing through a transparent specimen are converted intoamplitude or contrast changes in the image. The use of phase contrast does not requirestaining to view the slide. This microscope technique made it possible to study the cell cyclein live cells.

The traditional optical microscope has more recently evolved into the digital microscope. In addition to, or instead of, directly viewing the object through the eyepieces, a type of sensor similar to those used in a digital camera is used to obtain an image, which is then displayed on a computer monitor. These sensors may use CMOS or charge-coupled device (CCD) technology, depending on the application.

[edit]Electron

Main article: Electron microscope

Three major variants of electron microscopes exist:

Scanning electron microscope (SEM): looks at the surface of bulk objects by scanning the surface with a fine electron beam. See also environmental scanning electron microscope (ESEM).
Transmission electron microscope (TEM): passes electrons through the sample, analogous to basic optical microscopy. This requires careful sample preparation, since electrons are scattered so strongly by most materials.This is a scientific device that allows people to see objects that could normally not be seen by the naked or unaided eye.