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Photokinesis
Photokinesis is a change in the velocity of movement of an organism as a result of changes in light intensity. The alteration in speed is independent of the direction from which the light is shining. Photokinesis is described as positive if the velocity of travel is greater with an increase in light intensity and negative if the velocity is slower. If a group of organisms with a positive photokinetic response is swimming in a partially shaded environment, there will be fewer organisms per unit of volume in the sunlit portion than in the shaded parts. This may be beneficial for the organisms if it is unfavourable to their predators, or it may be propitious to them in their quest for prey. In photosynthetic prokaryotes, the mechanism for photokinesis appears to be an energetic process. In cyanobacteria, for example, an increase in illumination results in an increase of photophosphorylation which enables an increase in metabolic activity. However the behaviour is also found among euk ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phototaxis
Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis. Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite. Two types of positive phototaxis are observed in prokaryotes. The first is called scotophobotaxis (from the word " scotophobia"), which is observed only under a microscope. This occurs when a bacterium swims by chance out of the area illuminated by the microscope. Entering darkness signals the cell to reverse flagella rotation direction and reenter the light. The second type of phototaxis is true phototaxis, which is a directed movement up a gradient to an increasing amount of light. This is analogous to positive chemotaxis except that the attractant is light rather than a chem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kinesis (biology)
Kinesis, like a taxis or tropism, is a movement or activity of a cell or an organism in response to a stimulus (such as gas exposure, light intensity or ambient temperature). Unlike taxis, the response to the stimulus provided is non-directional. The animal does not move toward or away from the stimulus but moves at either a slow or fast rate depending on its "comfort zone." In this case, a fast movement (non-random) means that the animal is searching for its comfort zone while a slow movement indicates that it has found it. Types There are two main types of kineses, both resulting in aggregations. However, the stimulus does not act to attract or repel individuals. Orthokinesis: in which the speed of movement of the individual is dependent upon the stimulus intensity. For example, the locomotion of the collembola, ''Orchesella cincta'', in relation to water. With increased water saturation in the soil there is an increase in the direction of its movement towards the aimed place. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fungi; or unicellular microorganisms such as protists, bacteria, and archaea. All types of organisms are capable of reproduction, growth and development, maintenance, and some degree of response to stimuli. Beetles, squids, tetrapods, mushrooms, and vascular plants are examples of multicellular organisms that differentiate specialized tissues and organs during development. A unicellular organism may be either a prokaryote or a eukaryote. Prokaryotes are represented by two separate domains – bacteria and archaea. Eukaryotic organisms are characterized by the presence of a membrane-bound cell nucleus and contain additional membrane-bound compartments called organelles (such as mitochondria in animals and plants ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Predation
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the host) and parasitoidism (which always does, eventually). It is distinct from scavenging on dead prey, though many predators also scavenge; it overlaps with herbivory, as seed predators and destructive frugivores are predators. Predators may actively search for or pursue prey or wait for it, often concealed. When prey is detected, the predator assesses whether to attack it. This may involve ambush or pursuit predation, sometimes after stalking the prey. If the attack is successful, the predator kills the prey, removes any inedible parts like the shell or spines, and eats it. Predators are adapted and often highly specialized for hunting, with acute senses such as vision, hearing, or smell. Many predatory animals, both vertebrate and inv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in carbohydrate molecules, such as sugars and starches, which are synthesized from carbon dioxide and water – hence the name ''photosynthesis'', from the Greek ''phōs'' (), "light", and ''synthesis'' (), "putting together". Most plants, algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the energy necessary for life on Earth. Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centers that contain green chlorophyll (and other colored) pigments/chromoph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connections". Pearson Education. San Francisco: 2003. In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: ''Bacteria'' (formerly Eubacteria) and ''Archaea'' (formerly Archaebacteria). Organisms with nuclei are placed in a third domain, Eukaryota. In the study of the origins of life, prokaryotes are thought to have arisen before eukaryotes. Besides the absence of a nucleus, prokaryotes also lack mitochondria, or most of the other membrane-bound organelles that characterize the eukaryotic cell. It was once thought that prokaryotic cellular components within the cytop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue-green algae, although they are not usually scientifically classified as algae. They appear to have originated in a freshwater or terrestrial environment. Sericytochromatia, the proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria. Cyanobacteria use photosynthetic pigments, such as carotenoids, phycobilins, and various forms of chlorophyll, which absorb energy from light. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes. These are flattened sacs called thylakoids where photosynthesis is performed. Phototrophic eukaryotes such as green plants perform photosynthesis in plast ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eukaryote
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacteria and Archaea (both prokaryotes) make up the other two domains. The eukaryotes are usually now regarded as having emerged in the Archaea or as a sister of the Asgard archaea. This implies that there are only two domains of life, Bacteria and Archaea, with eukaryotes incorporated among archaea. Eukaryotes represent a small minority of the number of organisms, but, due to their generally much larger size, their collective global biomass is estimated to be about equal to that of prokaryotes. Eukaryotes emerged approximately 2.3–1.8 billion years ago, during the Proterozoic eon, likely as flagellated phagotrophs. Their name comes from the Greek εὖ (''eu'', "well" or "good") and κάρυον (''karyon'', "nut" or "kernel"). Euka ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astasia Longa
Astasis is a lack of motor coordination marked by an inability to stand, walk or even sit without assistance due to disruption of muscle coordination. The term ''astasia'' is interchangeable with ''astasis'' and is most commonly referred to as ''astasia'' in the literature describing it. Astasis is the inability to stand or sit up without assistance in the absence of motor weakness or sensory loss (although the inclusion of 'the lack of motor weakness' has been debated by some physicians). It is categorized more as a symptom than an actual disease, as it describes a disruption of muscle coordination resulting in this deficit. The disturbance differs from cerebellar ataxia in that with astasis the gait can be relatively normal, with balance significantly impaired during transition from a seated to standing position. This balance impairment is similar to patients with vestibulocerebellar syndrome, which is a progressive neurological disease with many symptoms and effects. Astasis ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Euglena Gracilis
''Euglena gracilis'' is a freshwater species of single-celled alga in the genus ''Euglena''. It has secondary chloroplasts, and is a mixotroph able to feed by photosynthesis or phagocytosis. It has a highly flexible cell surface, allowing it to change shape from a thin cell up to 100 µm long, to a sphere of approximately 20 µm. Each cell has two flagella, only one of which emerges from the flagellar pocket (reservoir) in the anterior of the cell, and can move by swimming, or by so-called "euglenoid" movement across surfaces. ''E. gracilis'' has been used extensively in the laboratory as a model organism, particularly for studying cell biology and biochemistry. Taxonomy A morphological and molecular study of the Euglenozoa put ''E. gracilis'' in close kinship with the species ''Khawkinea quartana'', with ''Peranema trichophorum'' basal to both, although a later molecular analysis showed that ''E. gracilis'' was, in fact, more closely related to ''Astasia longa'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Discodoris Boholiensis
''Discodoris boholiensis'', known commonly as the Bohol discodoris,Le Bris, S., Müller, Y., Pean, M. in: DORIS, 25/10/2014 ''Discodoris boholiensis'' Bergh, 1877 Données d'Observations pour la Reconnaissance et l'Identification de la faune et la flore Subaquatiques. is a species of sea slug in the family Discodorididae.Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005''Classification and nomenclator of gastropod families''.Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. . ISSN 0076-2997. 397 pp. It gets its name from the island of Bohol in the Philippines. ''Discodoris boholiensis'' has a distinctive pattern of chocolate brown and cream-white all over its flattened body and wavy-edged mantle. It reaches a length of . Description The body of ''Discodoris boholiensis'' is roughly oval-shaped, with a wavy margin, broad and rather flattened, up to long and wide. The head is not clearly demarc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tunicate
A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time called Urochordata, and the term urochordates is still sometimes used for these animals. They are the only chordates that have lost their myomeric segmentation, with the possible exception of the 'seriation of the gill slits'. Some tunicates live as solitary individuals, but others replicate by budding and become colonies, each unit being known as a zooid. They are marine filter feeders with a water-filled, sac-like body structure and two tubular openings, known as siphons, through which they draw in and expel water. During their respiration and feeding, they take in water through the incurrent (or inhalant) siphon and expel the filtered water through the excurrent (or exhalant) siphon. Most adult tunicates are sessile, immobile and perman ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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