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Evolutionary computation
Published in Richard E. Neapolitan, Xia Jiang, Artificial Intelligence, 2018
Richard E. Neapolitan, Xia Jiang
In diploid organisms, each adult produces a gamete, the two gametes combine to form a zygote, and the zygote grows to become a new adult. This process is called sexual reproduction. Unicellular haploid organisms commonly reproduce asexually by a process called binary fission. The organism simply splits into two new organisms. So, each new organism has the exact same genetic content as the original organism. Some unicellular haploid organisms reproduce sexually by a process called fusion. Two adult cells first combine to form what is called a transient diploid meiocyte. The transient diploid meiocyte contains a homologous pair of chromosomes, one from each parent. A child can obtain a given homolog from each parent. So the children are not genetic copies of the parents. For example, if the genome size is 3, there are 23 = 8 different chromosome combinations that a child could have.
The Premise of Tissue Engineering: Molecular Recognition
Published in Claudio Migliaresi, Antonella Motta, Scaffolds for Tissue Engineering, 2014
Christopher J. Pateman, John W. Haycock
Unicellular organisms are the simplest known forms of life and are the most prolific living organisms due to their inherent ability to inhabit a diverse range of environments. However, in order for a more complex multicellular organism to evolve, the communicative processes between discrete cellular units and their environmental interpretation must be such that a constructive unison of purpose can take place. In this situation, individual cells typically perform highly specialized roles within the organism to perform specific tasks. This is clearly evident when considering the number of different cell types present within a large multicellular organism; the diverse range of functions they adopt; and the careful interplay between cells, tissues, and organs. The increased size and greater complexity of external environmental response provides an organism with a powerful evolutionary advantage that has driven this process to take place.
Bacterial Chemotaxis, Current Knowledge and Future Need for Application in Hydrocarbon Remediation Technologies
Published in Wael Ahmed Ismail, Jonathan Van Hamme, Hydrocarbon Biotechnology, 2023
Nisenbaum Melina, Georgina Corti-Monzón, Silvia E. Murialdo
Responding to changes in the environment is especially important for unicellular organisms, which directly interact with it (Pandey et al., 2002a). Motile bacteria have well-established sensing mechanisms to convert chemical stimuli to mechanical energy, which allows them to approach attractants and avoid repellents (Celani et al., 2010). This essential behavior is called chemotaxis. Bacterial chemotaxis allows microorganisms to locate to more advantageous niches for growth and survival (Pandey et al., 2002a; Parales et al., 2002; Ford et al., 2007). In many cases, positive chemotaxis serves to bring them closer to favorable attractive substances (chemoattractants), while negative chemotaxis moves them away from compounds that are toxic to bacteria (chemo-repellents) (Pandey et al., 2002a). Chemotaxis generally occurs against metabolizable compounds, which generates a concentration gradient of the carbon source. In some cases, chemotaxis towards non-metabolizable compounds has been observed. The ability of bacteria to modulate movement direction is the outcome of either controlled changes in the direction of flagellar rotation (Lacal et al., 2010), or by stopping and starting the flagellar motor at intervals. It is mediated by chemoreceptors expressed on the cell surface that can sense chemical species and their concentrations through specific receptor-ligand interactions, that in turn activates intracellular signaling cascades (Bray et al. 1998; Gestwicki and Kiessling, 2002). Some studies have shown that increased number of chemo-receptors in many free-living bacteria enables them to respond to a wider range of compounds, suggesting their potential to detect and move toward a wide variety of different pollutants (Sampedro et al., 2015). Although our current knowledge of chemoreceptor specificities is limited, recent research of receptor ligands promises a better understanding of the relation between the chemoeffect and bacterial habitats (Bi et al., 2018).
Gyrotactic microorganisms suspended in MHD nanofluid with activation energy and binary chemical reaction over a non-Darcian porous medium
Published in Waves in Random and Complex Media, 2022
Bioconvection describes pattern formation that occurs due to the movement of micro-organisms. This phenomenon gathers unicellular organisms (bacteria, algae) at the surface of the fluid resulting from unstable density stratification. The micro-organisms, suspended at a constant temperature, are self-propelled, have the tendency to swim in an upward direction, enhance the density of the base fluid, improve mixing, and prevent the clustering of nanoparticles. The movement of micro-organisms is categorized based on their responses to light, gravity, the combination of viscous and gravitational torques, chemicals and oxygen as phototaxis, gravitaxis, gyrotactic, chemotaxis, and oxytaxis or aerotaxis, respectively. Bioconvection phenomenon has many industrial applications, such as enzyme biosensors and bio-fuel cells, for evaluating nanoparticle toxicity with chip size micro-devices, etc., and also in a new biological technology process called (MEOR) microbial-enhanced oil recovery, which is a process for recovering oil entrapped in a porous medium by injecting preferred micro-organisms to form bioconvection. Begum et al. [11] considered a vertical cone to study variable thermo-physical properties of the bioconvective nanofluid flow. Khan et al. [12] investigate water-based nanofluid with gyrotatic micro-organisms. Bioconvection flow with oxytactic micro-organisms was considered by Balla et al. [13]. Shafiq et al. [14] took interest in second-grade bioconvective nanofluid flow. Ferdows et al. [15] investigated MHD nanofluid flow with gyrotactic micro-organisms. Tlili et al. [16] analyzed the influence of bioconvection MHD nanomicropolar fluid with gyrotactic micro-organisms. Haq et al. [17] considered steady 2-D Williamson nanofluid with suspensions of gyrotactic micro-organisms to examine slip mechanisms.