Eukaryotic Cell
Prokaryotic Cell
Fig 1 (Darling, ND)
Eukaryotes usually contain mitochondria, which are the site of aerobic respiration and absorb glucose and oxygen and provide energy, which is transferred in cells. However these are not present in prokaryotes. Ribosomes are found in both prokaryotes and eukaryotes, two types in eukaryotes. One is in the cytoplasm and the other, smaller type is found in the mitochondria. The prokaryotic cells only contain one type of ribosome of one size.
Flagella if present in eukaryotes, have a complex structure, both structurally and bio chemically. On the other hand if they are present in prokaryotes then they have a much simpler structure. The size of these two types of cells is different, prokaryotes are generally less that 5µm whilst eukaryotes are 10µm or larger and have up to one thousand times more volume than a prokaryotic cell.
The type of cell found in animals and plants are eukaryotic. Although they are very similar there are a few important differences. Below is a diagram of an animal and a plant cell showing the organelles that are contained within them.
Fig 2. (Armstrong, ND)
Plant and animal cells are both eukaryotes as they both have a nucleus. The nucleus is the largest most visible organelle which is enclosed by a nuclear envelope made up of up to two membranes, perforated with pores. These allow selected molecules to pass in and out when needed and helps the nucleus to function correctly. The nucleus contains the chromatin (DNA) of the cell and chromatin which is the cytoplasm that is found in the nucleus. The densest part of the nucleus is called the nucleolus and this contains the chromosomes.
Both cells contain lysosomes. These small bubbles of liquid within a membrane contain enzymes that (lysozymes) that digest protein and unwanted material (Indge et al, 2000, p.13). Lysosomes are manufactured in the Golgi apparatus which are in both animal and plant cells. It is a stack of membrane bound vesicles which modifies and packages proteins.
Only plant cells have a cell wall which is made of cellulose, and is freely permeable. It provides rigidity and strength to the cell but both animal and plant cells have cell surface membranes. Along with cell identification and cell adhesion, the cell surface membrane allows the exchange and transport of materials into and out of the cell. The cell surface membrane is made up of two layers of phospholipids (fluid mosaic model) and this structure is important for the function of diffusion.
To keep the shape of the cell membrane, animal and plant cells both have cytoplasm, which is made up of 90% water. This is where all the other organelles are held, but are free to move around. Within this, both cells have Mitochondria. Mitochondria are needed for respiration, to create energy for movement, division etc. The folded membrane (crista) inside the mitochondria increases surface area for surface bound membrane reactions.
Other similarities are rough endoplasmic reticulum (ER) and smooth ER, the membrane of which joins with the nuclear envelope (Boyle, Senior, 2002, p.11). The ER is a system of flat sacs (cisternae), the structure of which enables it to be a transport network for molecules. The Rough E R is covered in ribosomes, which are packets of RNA and protein and are the site of protein synthesis. Some ribosomes are free to move around in the cytoplasm. The rough ER makes proteins and sends them to the Golgi apparatus to be packaged. The ER plays different functions depending on the cell type for example detoxifies chemicals in liver cells.
Plant cells have large vacuoles which can occupy up to 90% of the cell. They are filled with sugars and salts and help provide structural support for the cell. Although animal cells may have vacuoles, they are ‘smaller and more numerous’ (Boyle, Senior, 2002, p.6) and are used for intracellular digestion and release of cellular waste products. Plant cells also have chloroplast to absorb sunlight, and combine it with carbon dioxide and water. This then photosynthesises so that they can produce starch for the rest of the plant, for it to use as energy.
Each organelle within cells has specific tasks and the structure of organelles is relevant in allowing them to perform these tasks in the best way possible. Animal cells carry out many functions such as respiration, cell division and the ability to kill bacteria. A plant cell also needs to respire and kill infections, but it needs to be able to photosynthesise and keep turgor pressure as well. Comparing the two it is clear to see that prokaryotes and eukaryotes have many differences. Eukaryotic cells also differ depending on the type of cell that it is. Take plant and animal cells for example, these may look different and have varied organelles to enable them to perform a specific function. The main difference between plant cells and animal cells is that plant cells have a cell wall, chloroplasts and large vacuoles.
References
Armstrong, W.D. (ND) Comparison of Plant and Animal Cells, [online]. Available from [Accessed 28 November 2011]
Boyle, M. and Senior, K. (2002) Human Biology. 2nd ed. London: HarperCollinsPublishers Limited, pp 3, 6, 11.
Darling, D. (ND) The Encyclopedia of Science, [online]. Available from [Accessed 28 November 2011]
Indge, B., Rowland, M. and Baker, M. (2000) A new introduction to Human Biology. London: Hodder and Stroughton, p 13.
