Biology (cells)
A cell is a basic building block for a living organism (Sherwood 5). The human body is composed of trillions of cells which perform basic and essential functions in the body. Such functions include taking in nutrients from the body, converting nutrients into energy and carrying out other specialized functions (Davey and Michael 79).
Prokaryotic and Eukaryotic cells
Prokaryotic cells are found in organisms that lack a cell nucleus and other membrane bound organelles (Kutschera and Karl 16). Most of these organisms are usually unicellular. Eukaryotic cells are the opposite of prokaryotic as prokaryotes are defined by cells which are organized into complex structures and internal membranes and a cytoskeleton (Kutschera and Karl 16). Organisms with this type of cells have a characteristic nucleus bound membrane.
How are Prokaryotic and Eukaryotic cells similar?
One of the similarities between these two cells is that they both have cell walls. However, the cell walls differ as each is made of different types of materials. Cytoplasm, which is a fluid like matrix is found in both prokaryotic and eukaryotic cells. Another similarity between these two types of cells is that both have a supportive cytoskeleton within them (Kutschera and Karl 18).
DNA is found in both cells as is RNA. In both cells, an extension of the plasma membrane which is supported by elements of cytoskeleton is present (Kutschera and Karl 17). The extensions have similar functions in both cells as they are used to help cells adhere to surfaces and motility. However, there is a distinct difference between these extensions as their moving mechanisms differ (Lodish 58). Plasma membrane, a bi-layer surrounding in the cells which differentiates between the inside and the outside of the cell, is also present in both prokaryotic and eukaryotic cells.
Ribosomes are present in both these cell types. They are found to float freely in both cell types but in eukaryotic cells, they adhere to the rough endoplasmic reticulum. In their basic chemical structure, these two types of cells are both made up of vitamins, fats, minerals, carbohydrates, proteins and nucleic acid (Kutschera and Karl 16). Photosynthesis, reproduction and other processes are carried out in both cell types.
‘Chemical noses’ are present in these two types of cells (Sherwood 60). The noses are responsible for updating and making the cells aware of all the reactions occurring within them and their surroundings. Both prokaryotic and eukaryotic cells need energy supplies to survive and this is a significant similarity.
Differences between prokaryotic and eukaryotic cells
The most significant difference between prokaryotic and eukaryotic cells is that eukaryotic cells have “true” DNA containing nuclei while in prokaryotic cells, DNA is not bound on the membrane (Sherwood 65). Prokaryotic cells have a larger surface area compared to volume ratio as compared to eukaryotic cells. This feature qualifies them to have a higher metabolic rate and a higher growth rate thus a shorter generation time as compared to eukaryotic cells. The structure of the genetic material ‘DNA’ is different in these two types of cells. In prokaryotic cells, the contained DNA is a single and stable chromosome which is stored in the nucleoid (Sherwood 72). The DNA present in eukaryotic cells is a tightly bound and organized chromosome.
Prokaryotic cells and eukaryotic cells differ in their sizes. It is significant to note that prokaryotic cells are much smaller in size as compared to eukaryotic cells as they are ten times the size of prokaryotic cells (Davey and Michael 66). Another difference between these two types of cells is that the mitochondria and chloroplast in eukaryotic cells which are responsible for various metabolic processes are believed to have been derived from endosymbiotic bacteria. These metabolic processes in prokaryotic cells occur across the membrane as endosymbiots are rare (Davey and Michael 69).
The cell walls of prokaryotic cells are formed of peptidoglycan as a constituent molecule whereas the molecule which forms the cell walls of eukaryotic cells is different. However, most eukaryotic cells do not have a cell wall (Kutschera and Karl 14). One of the structural differences between these cell types is that eukaryotic cells have a nucleus but it is not present in prokaryotic cells. In cell reproduction, eukaryotic cells undergo mitosis whereas prokaryotic cells divide by cell division (Kutschera and Karl 11).
Plant and animal cells
Plant and animal cells exhibit structural differences and similarities as both are unique to their organism types.
Similarities between plant and animal cells
The similarities which exist between plant and animal cells basically exist due the common cellular organelles which are present in both of them. Plant and animal cells both have a cell surface membrane that surrounds the cell (Lodish 24). This membrane encompasses all the cell contents and is formed from proteins and lipids which distinguish the inner and outer sides of a cell. These two types of cells also have mitochondria as a common feature and similarity.
A nucleus is present in both animal and plant cells (Lodish 25). Ribosomes, Golgi body, cytoplasm and the endoplasmic reticulum are all found in both plant and animal cells. These organelles perform similar specialized functions in animal cells as in plant cells.
Differences between plant and animal cells
The main differences between plant and animal cells are due to their structures (Lodish 20). A cell wall is not present in animal cells but in plant cells it is present and formed from cellulose. Another difference between animal and plant cells is that animal cells have an irregular round shape whereas plant cells are rectangular and regular shaped. Plastids are also absent in animal cells but are present in plant cells (Lodish 33).
The plasma membrane in animal cells is only composed of only the cell membrane but in plants, there is a cell wall and a cell membrane as a difference between these two cell types (Lodish 30). Lysosomes occur in the cytoplasm of animal cells but in plant cells, they are not present. Cilia are also very rare in plant cells but present in animal cells. In plant cells, the vacuole is one and large, occupying about 90% of the cell volume but in animal cells, there are number of small vacuoles (Lodish 26). Centrioles are present in animal cells but only present in lower plant forms while chloroplast does not exist in animal cells but is present in plant cells as plants make their own food (Lodish 24).
Functions of major cell organelles
The Nucleus is cell’s command centre responsible for sending directions to the cell and also houses DNA. The Nuclear membrane is a double envelope containing nuclear pores. The Nuclear pores contain proteins that control the exit of substances such as ribosomes from the nucleus. Chromosomes control all the activities of a living cell while the Rough endoplasmic reticulum processes proteins needed by ribosomes (Davey and Michael 33 – 36).
The Smooth endoplasmic reticulum transports materials mainly lipids and glycoproteins which are needed by the cell. Chloroplasts are the site for photosynthesis which is responsible for making food in plants while mitochondria are the places where aerobic respiration takes place. Ribosomes process the cell’s genetic instructions to create proteins. The Golgi apparatus packs molecules processed by the endoplasmic reticulum to be transported out of the cell. Vesicles are responsible for breaking down molecules into smaller substances whereas Lysosomes form the cell’s recycling centre (Davey and Michael 39 – 39).
The Cytoskeleton forms a network of fibers forming the cell’s structural framework while the Cellular membrane surrounds the cytoplasm of a cell. The Cytoplasm contains all the enzymes needed for all the metabolic reactions such as glycosis. Flagella are long flexible tails used for movement and Cilia are shorter than flagella and also used for movement and contain proteins (Davey and Michael 36 – 37).
Works cited
Davey, John, and J. Michael Lord, eds. Essential cell biology. 2. Cell function. Vol. 2. Oxford
University Press, 2003.
Kutschera, Ulrich, and Karl J. Niklas. “Endosymbiosis, cell evolution, and speciation.”
Theory in Biosciences 124.1 (2005): 1-24.
Lodish, Harvey. Molecular cell biology. Macmillan, 2008.
Sherwood, Lauralee. “Human physiology: from cells to systems.” (2004): 1.
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