Bacteria
|
|
|
|
Bacteria
Bacteria (singular: bacterium) are unicellular microorganisms. Bacteria are prokaryotes and, unlike animals and other eukaryotes, bacterial cells do not contain cell nuclei or other membrane-bound organelles. Although the term bacteria has traditionally been generally applied to all prokaryotes, the scientific nomenclature changed after the discovery that prokaryotic life consists of two very different groups of organisms that evolved independently. These evolutionary domains are called Bacteria and Archaea. Bacteria are a few micrometres long and have many different shapes including spheres, rods or spirals. The study of bacteria is bacteriology, a branch of microbiology. The first bacteria were observed by Anton van Leeuwenhoek in 1674 using a single-lens microscope of his own design. His observations were published in a long series of letters to the Royal Society. The name bacterium was introduced much later, by Christian Gottfried Ehrenberg in 1828, and is derived from the Greek word βακτηριον meaning "small stick". Cellular structure Intracellular structures The bacterial cell is surrounded by a lipid membrane, or cell membrane, which encompasses the contents of the cell, or cytoplasm, and acts as a barrier to hold nutrients, proteins and other essential molecules within the cell. As they are prokaryotes, bacteria do not have membrane-bound organelles in their cytoplasm and thus contain few intracellular structures. They consequently lack mitochondria, chloroplasts and the other organelles present in eukaryotic cells, such as the golgi apparatus and endoplasmic reticulum. Many important biochemical reactions, such as energy generation, occur due to concentration gradients across membranes creating a potential difference, analogous to a battery. The absence of internal membranes in bacteria means these reactions, such as electron transport, occur across the plasma membrane, between the cytoplasm and the periplasmic space. Bacteria do not have a membrane-bound nucleus and their genetic material is typically a single circular chromosome located in the cytoplasm in an irregularly-shaped body called the nucleoid. The nucleoid contains the chromosome with associated proteins and RNA. Like all living organisms, bacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from those of eukaryotes and Archaea. The order Planctomycetes are an exception to the general absence of internal membranes in bacteria, as they have a membrane around their nucleoid and contain other membrane-bound cellular structures. Some bacteria also produce intracellular nutrient storage granules, such as glycogen, polyphosphate, sulfur or polyhydroxyalkanoates. These granules enable bacteria to store compounds for later use. Certain bacterial species, such as the photosynthetic Cyanobacteria, produce internal gas vesicles which they use to regulate their buoyancy to regulate the optimal light intensity or nutrient levels. |
Kumkum / safron - Crocus sativus
Crocuses belong to the family Iridaceae. The saffron crocus is classified as Crocus sativus, It is a shrub. Leaves are seen towards the base of the stem and are compactly arranged.Read More about safron.....
|
| |
||
