Timeline of evolution and Evolutionary history of life The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea. Later, some eukaryotes that already contained mitochondria also engulfed cyanobacteria -like organisms, leading to the formation of chloroplasts in algae and plants.
Bacteria Cell Structure They are as unrelated to human beings as living things can be, but bacteria are essential to human life and life on planet Earth. Although they are notorious for their role in causing human diseases, from tooth decay to the Black Plague, there are beneficial species that are essential to good health.
For example, one species that lives symbiotically in the large intestine manufactures vitamin K, an essential blood clotting factor. Other species are beneficial indirectly.
Bacteria give yogurt its tangy flavor and sourdough bread its sour taste. They make it possible for ruminant animals cows, sheep, goats to digest plant cellulose and for some plants, soybean, peas, alfalfa to convert nitrogen to a more usable form.
Bacteria are prokaryotes, lacking well-defined nuclei and membrane-bound organelles, and with chromosomes composed of a single closed DNA circle.
They come in many shapes and sizes, from minute spheres, cylinders and spiral threads, to flagellated rods, and filamentous chains. They are found practically everywhere on Earth and live in some of the most unusual and seemingly inhospitable places.
Evidence shows that bacteria were in existence as long as 3. Even older than the bacteria are the archeans also called archaebacteria tiny prokaryotic organisms that live only in extreme environments: Many scientists now believe that the archaea and bacteria developed separately from a common ancestor nearly four billion years ago.
Millions of years later, the ancestors of today's eukaryotes split off from the archaea. Despite the superficial resemblance to bacteria, biochemically and genetically, the archea are as different from bacteria as bacteria are from humans.
In the late s, Antoni van Leeuwenhoek became the first to study bacteria under the microscope. During the nineteenth century, the French scientist Louis Pasteur and the German physician Robert Koch demonstrated the role of bacteria as pathogens causing disease.
The twentieth century saw numerous advances in bacteriology, indicating their diversity, ancient lineage, and general importance. Most notably, a number of scientists around the world made contributions to the field of microbial ecology, showing that bacteria were essential to food webs and for the overall health of the Earth's ecosystems.
The discovery that some bacteria produced compounds lethal to other bacteria led to the development of antibiotics, which revolutionized the field of medicine. There are two different ways of grouping bacteria.
They can be divided into three types based on their response to gaseous oxygen. Aerobic bacteria require oxygen for their health and existence and will die without it.
Anerobic bacteria can't tolerate gaseous oxygen at all and die when exposed to it. Facultative aneraobes prefer oxygen, but can live without it.
The second way of grouping them is by how they obtain their energy. Bacteria that have to consume and break down complex organic compounds are heterotrophs. This includes species that are found in decaying material as well as those that utilize fermentation or respiration.
Bacteria that create their own energy, fueled by light or through chemical reactions, are autotrophs. Capsule - Some species of bacteria have a third protective covering, a capsule made up of polysaccharides complex carbohydrates.
Capsules play a number of roles, but the most important are to keep the bacterium from drying out and to protect it from phagocytosis engulfing by larger microorganisms. The capsule is a major virulence factor in the major disease-causing bacteria, such as Escherichia coli and Streptococcus pneumoniae.
Nonencapsulated mutants of these organisms are avirulent, i. Cell Envelope - The cell envelope is made up of two to three layers: Cell Wall - Each bacterium is enclosed by a rigid cell wall composed of peptidoglycan, a protein-sugar polysaccharide molecule.
The wall gives the cell its shape and surrounds the cytoplasmic membrane, protecting it from the environment. It also helps to anchor appendages like the pili and flagella, which originate in the cytoplasm membrane and protrude through the wall to the outside.
The strength of the wall is responsible for keeping the cell from bursting when there are large differences in osmotic pressure between the cytoplasm and the environment. Cell wall composition varies widely amongst bacteria and is one of the most important factors in bacterial species analysis and differentiation.
For example, a relatively thick, meshlike structure that makes it possible to distinguish two basic types of bacteria.
A technique devised by Danish physician Hans Christian Gram inuses a staining and washing technique to differentiate between the two forms. When exposed to a gram stain, gram-positive bacteria retain the purple color of the stain because the structure of their cell walls traps the dye.
In gram-negative bacteria, the cell wall is thin and releases the dye readily when washed with an alcohol or acetone solution. Cytoplasm - The cytoplasm, or protoplasm, of bacterial cells is where the functions for cell growth, metabolism, and replication are carried out.
It is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as ribosomes, a chromosome, and plasmids.
The cell envelope encases the cytoplasm and all its components.Mar 02, · Bacterial cells are prokaryotic while the human cells are eukaryotic.
Bacterial cells have a cell wall composed of peptidoglycan while human cells are devoid of . ADVERTISEMENTS: In this article we will discuss about the structure and components of bacterial cell.
Structure of Bacterial Cell: Bacterial cells (prokaryotic cells) are structurally much simpler than eukaryotic cells and the two cell types are compared in Table They consists of various cell surface structures, cell wall, plasma membrane, many .
The bacterial cell wall is seen as the light staining region between the fibrils and the dark staining cell interior. Cell division in progress is indicated by the new septum formed between the two cells and by the indentation of the cell wall near the cell equator.
Bacteria Cell Structure. They are as unrelated to human beings as living things can be, but bacteria are essential to human life and life on planet Earth.
Mar 04, · Bacterial cells are prokaryotic while the human cells are eukaryotic. Bacterial cells have a cell wall composed of peptidoglycan while human cells are devoid of cell walls.
Cytoplasm - The cytoplasm, or protoplasm, of bacterial cells is where the functions for cell growth, metabolism, and replication are carried out. It is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as ribosomes, a chromosome, and plasmids.