Figure 1.1 the structure of a plant cell
Chloroplasts
Chloroplasts are members of a family of organelles called . Chloroplasts are large, double membrane-bound structures (about 5 micrometers across) that contain , which absorbs sunlight. Additional membranes within the chloroplast contain the structures that actually carry out photosynthesis. Cells use sunlight as their energy source; the sunlight must be converted into energy inside the cell in a process called . Chloroplasts are the structures that perform this function.
Chloroplasts carry out energy conversion through a complex set of reactions similar to those performed by mitochondria in animals. The double membrane structure of chloroplasts is also reminiscent of mitochondria. The inner membrane encloses an area called the stoma, which is analogous to the matrix in mitochondria and houses DNA, RNA, ribosomes, and different enzymes. Chloroplasts, however, contain a third membrane and are generally larger than mitochondria.
The plant cell wall
The cell wall is a complex matrix which surrounds a plant cell. It is a rigid structure rigid cell wall surrounding the cell membrane that helps to support the plant and which protects individual cells. . This wall can range from 0.1 to 10 micrometers thick and is composed of fats and sugars. The tough wall gives added stability and protection to the plant cell.
Vacuoles
Vacuoles are the most visible compartment of a plant cell which is large, liquid-filled organelles found only in plant cells. 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. This division is based on internal complexity.
Prokaryotic cells are highly organised cells, and do not have a nucleus. These cells are simple in structure, with no recognizable organelles. They have an outer cell wall that gives them shape. Right under the rigid cell wall is the more fluid membrane. The cytoplasm does not exhibit much structure when viewed by electron microscopy. Figure 1.3 shows the structure of a prokaryotic cell.
Figure 1.3 shows the structure of a prokaryotic cell.
Eukaryotic are animal plant cells. These cells tend to be larger than the cells of bacteria, and have developed specialized packaging and transport mechanisms that may be necessary to support their larger side. Figure 1.4 below shows the structure of a plant and animal cell.
Figure 1.4 showing the structure of a plant and animal cell.
Advantages of using optical and electron microscopes in studying the structure of cells
The electron microscope has a greater resolution than a light microscope. It uses an electron beam instead of light, and electromagnets instead of glass lenses. It has a shorter wavelength greater resolution, but the disadvantages are that specimen must be dead and dehydrated; its image also has to be viewed in black and white on screen, therefore a false colour is used. Because electron microscopes use a vacuum, and living organisms can not survive in a vacuum because they need oxygen for respiration; living organisms would not survive the complex staining and preparation procedures.
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.
Bibliography:
The information was gathered from various resources; by using the internet and text books.
The websites which were used were:
www.cellsalive.com
www.plantcell.org
AS for the text books:
AQA biology As
AQA biology A2
