• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Describe the difference between prokaryotic and eukaryotic cells. Describe the theory of endosymbiosis and the evidence for and against this theory.

Extracts from this document...


Describe the difference between prokaryotic and eukaryotic cells. Describe the theory of endosymbiosis and the evidence for and against this theory. All living organisms are made up of cells. The cells can be divided into two groups: prokaryotic and eukaryotic. Prokaryotes date back to 3,500 million years ago, whilst eukaryotes are only as old as 1,500 million years. As prokaryotes come before eukaryotes, they are much simpler. Eukaryotes have become more developed and complex since prokaryotes. The two types of cells have similarities as well as differences. The similarities are that they both have a cell surface membrane, cytoplasm, DNA and ribosomes. However, even these similarities are in their own way, slightly different. For example, both cells contain DNA, but the structure of the DNA differs (explained later in more detail). As you will read below, eukaryotes are much more complex and contain many more organelles than the prokaryotes. Size Prokaryotes are usually much smaller than eukaryotes. Its average size ranges from 1 to 10 �m, whilst the eukaryotic cell is typically 10 to 150 �m. This actually gives prokaryotes a large surface-to-volume ratio, making it a simple, but efficient organism (absorbed nutrients have to travel only a small distance to diffuse completely throughout the inside of the cell). ...read more.


Animal cells are spherical in shape as they lack the cell wall. Bacteria cells come in three common shapes: coccus (round), bacillus (rod) and spirilum (helical); as well as two different types of cell walls: gram-positive and gram-negative. Cytoskeleton Eukaryotic cells have a number of protein fibres that help give the cell its shape and support. These include microtubules and filaments for inner cell movement. Prokaryotes are lacking in cytoskeletons. Flagella / Cilia / Pili The flagella (and cilia in eukaryotes) aids in cell movement. In eukaryotic cells, they have a distinct arrangement of 9+2 microtubules. In a prokaryote, the flagella (if present) consist of a singe fibril (a cylinder of protein subunits, about 20 nm thick and several �m long). Flagella can be found in prokaryotes all over the cell, or in a group at one or both ends, or as a single tail. Flagella rotate around a 'bearing' anchored in the cell wall, producing a corkscrew motion that can propel it through a fluid medium. Prokaryotic cells also have pili (filamentous structures projecting out of the cell wall). These are involved in transferring plasmids between two prokaryotic cells during mating and attaching the cell to potential hosts. Ribosomes The ribosomes of prokaryotes are smaller and float around freely in the cytoplasm. ...read more.


It seems likely that mitochondria and chloroplasts were once prokaryotes as they possess many features similar to that of prokaryotic cells: * Outer membrane is similar to plasma membrane (could have been pinched off to protect prokaryote during early stages of ingestion). * Inner membrane is similar to bacterial membrane (could have been the original prokaryotic cell membrane, retained even as it becomes the organelle of the eukaryote). * Own DNA strands are circular like that in prokaryotes, instead of linear in eukaryotes. * Own ribosomes are smaller than eukaryote's ribosomes, but similar sized to prokaryotes'. They are also able to self-replicate independently from the eukaryotic cell because they have their own sets of genes (more similar to prokaryotic genes than eukaryotic genes). It is also highly possible that this theory occurred as eukaryotes are able extremely able with the process of endocytosis. Evidence against the theory The mitochondria and chloroplasts could be made from invaginations of the plasma membrane. If the plasma membrane is able to develop into the Golgi apparatus and ER, then it could be possible that mitochondria and chloroplasts are even more highly developed invaginations of the plasma membrane. By relieving the cell of some of its functions, more energy can be directed to evolving highly specialized organelles. 7 November 2002 Nicole Lai 12.4 Unit 1: Molecules and Cells - - Topic 1.3 Cellular Organization - 1 - ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Molecules & Cells section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Molecules & Cells essays

  1. An Essay on the Differences between Prokaryote & Eukaryote cells.

    In addition, eukaryotes have a great number and diversity of organelles bounded by single membranes for example Golgi apparatus or lysosomes. When it comes to respiration, prokaryotes like bacteria use mesosomes, the exceptions being cytoplasmic membranes in blue-green bacteria. While eukaryotes use the organelle- mitochondria, which combines glucose and oxygen in the process of aerobic respiration to give energy.

  2. Comparing Eukaryotic and Prokaryotic cells.

    a prokaryotic cell there are no microtubules found where as in a eukaryotic cell they can be found towards the inside edge of the plasma membrane.

  1. Eukaryotes and Prokaryotes

    Plant Cells Animal Cells Cell walls Almost present No cell walls present outside Plastids occur in cytoplasm No plastids are found Lysosomes not usually not evident Lysosomes occur in cytoplasm Centrioles present only in cells of lower plant forms Centrioles always present Large vacuoles filled with cell sap Vacuoles, if

  2. The Structure of Prokaryotic and Eukaryotic cells.

    The eukaryotic ribosomes measure 80S (svedberg units) where as the prokaryotic ribosomes measure 70S. The development of the ER is linked with the development of the nucleus in the eukaryotic cell.

  1. Discuss how Prokaryotes are the same as Eukaryotes.

    Often these prokaryotes are found in deep volcanic vents at the bottom of the ocean, and are thought to be one of the first organisms to be created. There are two groups of prokaryotes: the bacteria and the archaea (or archaebacteria).

  2. The differences and similarities of Eukaryotic and Prokaryotic Cells.

    The cell membrane in a Prokaryotic cell also consists of a fluid phospholipid bilayer without carbohydrates and usually lacking sterols. However many bacteria do contain sterol-like molecules called hopanoids. The Prokaryotic cell is incapable of endocytosis or exocytosis unlike the Eukaryotic cell.

  1. Structure and function of membrane systems in Eukaryotic cells.

    The cell membrane has many different functions. Here is a list of functions, which I shall explain in due course: * The cell membrane is a selectively permeable barrier regulating the movement of substances, which enter and leave the cell by various different processes.

  2. Distinguish between prokaryotic and eukaryotic cells. Compare and contrast the structures of a plant ...

    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 5�m whilst eukaryotes are 10�m or larger and have up to one thousand times more volume than a prokaryotic cell.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work