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Microorganisms, or microbes, span all three domains of life – bacteria, archaea, and many unicellular eukaryotes including some fungi and protists.Typically defined as unicellular life forms that can only be observed with a microscope, microorganisms were the first cellular life forms, and were critical for creating the conditions for the evolution of more complex multicellular forms.
Quorum sensing induced by small molecules allows bacteria to control cooperative activities and adapts their phenotypes to the biotic environment, resulting, e.g., in cell-cell adhesion or biofilm formation. All animals and plants form associations with microorganisms, including protists, bacteria, archaea, fungi, and viruses.
A holobiont is a collection of closely associated species that have complex interactions, such as a plant species and the members of its microbiome. [2] [9] Each species present in a holobiont is a biont, and the genomes of all bionts taken together are the hologenome, or the "comprehensive gene system" of the holobiont. [10]
Human interactions with microbes include both practical and symbolic uses of microbes, and negative interactions in the form of human, domestic animal, and crop diseases. Practical use of microbes began in ancient times with fermentation in food processing ; bread , beer and wine have been produced by yeasts from the dawn of civilisation, such ...
There are five main modes of seed dispersal: gravity, wind, ballistic, water, and by animals. Some plants are serotinous and only disperse their seeds in response to an environmental stimulus. Dispersal involves the letting go or detachment of a diaspore from the main parent plant.
The organisms that constitute the microbial world are characterized as either prokaryotes or eukaryotes; Eukaryotic microorganisms possess membrane-bound organelles and include fungi and protists, whereas prokaryotic organisms are conventionally classified as lacking membrane-bound organelles and include Bacteria and Archaea.
The human gut contains approximately thirty-eight trillion microbes. [13] The gut is a dynamic ecosystem as it is composed of both constant and transient components, meaning some bacteria establishes itself and remains throughout the human’s lifetime and other bacteria is ingested and later leaves in feces. [14]
Like all animals, humans carry vast numbers (approximately 10 13 to 10 14) of bacteria. [3] Most are in the gut, though there are many on the skin. Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial, [4] particularly the ones in the gut.