The nucleus of an animal cell is made up of long chains of chromosomes bundled together to form quite a dense part of the cell. These chromosomes in the nucleus contain genetic information in order for the cell to reproduce and survive. Inside the nucleus is the nucleolus, this can be recognised within the nucleus as a denser object. The nucleolus, also made up of chromosomes, functions in RNA and ribosome synthesis. The nucleus is linked to the rest of the cell by the endoplasmic reticulum. The nuclear envelope, a double membrane, links with the ER in order to transport the manufactured proteins out of the cell.
The endoplasmic reticulum is an internal transport system within the cell. There are two types of ER, rough and smooth. The smooth endoplasmic reticulum is used in the synthesis of lipids and membrane proteins. It has a smooth texture because it is not continuous with the rough ER and it is made up of tubes rather than flattened sacs. The rough endoplasmic reticulum is rough because it is covered with ribosomes, which are used in the synthesis of proteins.
The Golgi apparatus is made up of stacks of flattened cavities lined with smooth endoplasmic reticulum. These cavities are formed by the fusion of vesicles, which have been taken from the smooth endoplasmic reticulum. It is linked to secretary vesicle used in the exocytosis of proteins.
The mitochondria are situated in the cytoplasm and are known as the powerhouses of the cell. They are the site of the synthesis of ATP which is the energy used in aerobic respiration. The wall of the mitochondria consists of two membranes, separated by fluid. The inner membrane is folded, creating partitions within the organelle known as cristae. The folding of the inner membrane increases the surface area of the organelle, allowing a greater area for the synthesis of ATP.
The new organelles in the cytoplasm possibly formed from endocytosis are known as vacuoles and act as storage bubbles. They can store molecules that need to be digested, and also waste products that need to be secreted from the cell. This process of secretion is known as exocytosis. These sacks have membranes formed from cell surface membrane known as the tonoplast.
The Structure of a typical Plant Cell
Plant cells and animal cells are comparable in that some of their organelles inside the cell are alike and some differ. For example plant cells also possess a nucleus, which contain genetic information to reproduce. The cell also contains a cell membrane, which has a similar structure in order to allow substances to pass in and out of the cell. However, where the membrane solely surrounds the animal cell, the plant cell has a cell wall.
In the cell wall, long chains of cellulose link together to form ribbon-like microfibrils. The cellulose microfibrils are set in a gel like matrix containing polysaccharides. There are two inner layer made from this cellulose. The outer layer of the cell wall is called the middle lamella and is made from calcium pectate. This layer is used to cement neighbouring cell walls together. The complex structure of the cell wall, means that as well as being strong it is also able to give a little to the withstand high pressures within the cell. The cell wall is fully permeable to water and solutes and the gel like matrix is hydrophilic, meaning that the cell walls normal state is saturated like a sponge. Cell walls also contain plasmodesmata, communication channels between two cells, linked by the cytoplasm.
A plant cell vacuole is different to the animal cell membrane. It is much larger compared to the rest of the cell and has a different function. A plant cell vacuole, which takes up the centre of the cell, is filled with cell sap. Cell sap is a solution salts and sugars as well as waste products and pigment stored in the cell for growth, secretion or use in a particular synthesis. The cell sap is held in place by a tonoplast, this tonoplast controls the exchange of solutions between the vacuole and cytoplasm.
The structure of the plant cell’s cytoplasm is very similar to that of the animal cell, however, one of the fundamental differences is that they have different organelles suspended in it and different reactions occur within the different cytoplasm. One of the predominant features of the plant cell cytoplasm is the chloroplast suspended within it. These chloroplasts are the site of photosynthesis. The chloroplasts contain the green pigment, chlorophyll, which gives the plants their green colour. Also suspended in the cell are tiny grana, which are responsible for taking in the light in order to carry out photosynthesis. Chloroplasts are similar to the mitochondria, in that they supply energy to the cell. The differences, where the mitochondria supply the energy for respiration, the chloroplasts supply the energy for photosynthesis. Chloroplasts also contain DNA to produce energy for photosynthesis to occur.
Plant cells, however also need to carry out respiration so they contain mitochondrion. They also contain Golgi apparatus for import and export of the cell. In fact the only organelle, which the animal cell contains and the plant cell doesn’t, is the centriole. In the animal cell, the centriole is used in nuclear division and is situated near the nucleus. This difference occurs due to the different reproductive systems of plant and animal cell.
So, in conclusion, I have noticed that the plant cell contains a number of organelles that an animal cell does not have and in looking into the functions of these cell parts then we can understand why these fundamental differences occur.
The chloroplasts mostly found in cells in the leaf or in areas where the light is most likely to enter the cell, are a vital part of photosynthesis. This is a prime example of the structure of the cell being vital to the function. Animal cells do not have chloroplasts because they do not carry out photosynthesis.
The vacuole in a plant cell is different to that of an animal cell in that it is one large object in the centre of the cell, rather that smaller storage sacs suspended in the animal cell cytoplasm. The reason for this is that animal cell vacuoles form if and when they are needed. Substances needed to be stored in the vacuole of an animal, such as waste products or energy stored will either be digested by enzymes and/or secreted from the cell individually. Whereas in the plant cell, all the substances are stored in the same vacuole.
The cell wall, with its strong structure gives support to the cell and ensures that it maintains a constant shape. This role is not only vital to the individual cell in maintaining their shape, but is also vital in the overall structure of the plant as an organism. On the other hand, animal cell do not have cell wall. This is due to the fact that generally the overall structure of animals as organisms does not rely on the cells individual make up for cell. The different types of structural cells for example bone cells, work together to form bone tissue, which then makes up the skeleton.
So, the differences between plant and animal cells are due to their individual function in order to contribute to the overall function of the organism. Although in this essay, I have only discussed the structure of a typical animal cell and plant cell. However, as I mentioned earlier, through evolution, the structure of some cell have developed in order to better carry out their individual roles more successfully.