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Cells Essay.

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Introduction

Contents Introduction 2 Differences between plants and animals cells 2 Differences between prokaryotic and eukaryotic cells 6 Advantages of using optical and electron microscopes in studying the structure of cells 8 Bibliography 9 Introduction Cells were first described in 1665 by Robert Hooke. A cell is the smallest independent unit of life; they carry out the essential processes that make the organism a living thing. Cells share certain structural and functional unit of an organism. Living cells are divided into two types prokaryotic and eukaryotic. This division is based on internal complexity. Differences between plants and animals cells Animals and plant cells are quite similar when you study them. They both contain: * Protoplasm. * A cell membrane * Cell membrane * Nucleus controlling the vital functions of the cells Few differences that exist between plant and animals are very significant and reflect a difference in the functions of each cell. The main structural difference between plant and animal cells is that plant cells have chloroplasts, a cell wall and a vacuole, whereas animal cells do not. ...read more.

Middle

A vacuole usually takes up about 50% of the cell volume, although the range in all plant cells is somewhere between 5% and 95% and have a single membrane -the tonoplast. Vacuoles are used to transport and store nutrients, waste products and other molecules. The presence of a vacuole enables plant cells to grow larger than animal cells - the expansion of a fluid filled space is a lot less costly in terms of energy expenditure than expansion of a cell full of organelle-containing cytoplasm. Vacuoles are also used for storage of substances which the plant needs, but which may be toxic to the rest of the cell. Animal cell Figure 1.2 shows the ultra structure of an animal cell. The whole cell has a diameter of about one fiftieth of a millimeter (20 um). The cell is bounded by a thin plasma membrane that encloses the cytoplasm which surrounds the nucleus. Figure 1.2 showing the structure of an animal cell. Differences between prokaryotic and eukaryotic cells Living cells are divided into two types prokaryotic and eukaryotic. ...read more.

Conclusion

In an optical microscope light rays from a light source beneath the stage are transmitted through two glass lenses in series, the objective and ocular (eye piece) lenses. The two lenses together routinely provide magnifications of up to 400 times. Some areas seem darker than others; this is because light can pass through certain parts of the specimen. It has a longer wave length therefore there is a limit to the amount of detail which an optical microscope can show, the resolving power is the minimum distance by which two point must be separated in order for them to be perceived as two separate points rather than as a single fused image. Little can be gained by magnifying an object more than 1500 times this puts a limit on the amount of structural detail that can be detected within a cell. Higher magnifications with good resolution can be achieved by using a special objective lens with a fluid situated between the lens and the objective (oil immersion). But even then it is not possible to achieve effective magnifications of more than 2000 times. ...read more.

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