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Topic Review

Bilaminar Blastocyst

Bilaminar blastocyst or bilaminar disc refers to the epiblast and the hypoblast, evolved from the embryoblast. These two layers are sandwiched between two balloons: the primitive yolk sac and the amniotic cavity. The inner cell mass, the embryoblast, begins to transform into two distinct epithelial layers just before implantation occurs. The epiblast is the outer layer that consists of columnar cells. The inner layer is called the hypoblast, or primitive endoderm, which is composed of cuboidal cells. As the two layers become evident, a basement membrane presents itself between the layers. The final two layers of the embryoblast are known collectively as the bilaminar embryonic disc as well as the bilaminar blastocyst or bilaminar blastoderm. This bilaminar blastocyst also defines the primitive dorsal ventral axis. Blastocyst implantation will occur during the second week of fetal development in the endometrium of the uterus; the epiblast is dorsal and the hypoblast is ventral.

7.0K
19 May 2023

Topic Review

African Golden Wolf

The African golden wolf (Canis lupaster) or African wolf is a canine native to North Africa, West Africa, the Sahel, northern East Africa, and the Horn of Africa. It is the descendant of a genetically admixed canid of 72% gray wolf (Canis lupus) and 28% Ethiopian wolf (Canis simensis) ancestry. It is listed as least concern on the IUCN Red List. In the Atlas Mountains, it was sighted in elevations as high as 1,800 m (5,900 ft). It is primarily a predator, targeting invertebrates and mammals as large as gazelle fawns, though larger animals are sometimes taken. Its diet also includes animal carcasses, human refuse, and fruit. The African golden wolf is a monogamous and territorial species; offspring remain with the family to assist in raising their parents' younger pups. It was previously classified as an African variant of the golden jackal (Canis aureus), with at that time at least one subspecies (C. a. lupaster) having been classified as a wolf. In 2015, a series of analyses on the species' mitochondrial DNA and nuclear genome demonstrated that it was, in fact, distinct from the golden jackal, and more closely related to the gray wolf and the coyote (Canis latrans). It is nonetheless still close enough to the golden jackal to produce hybrid offspring, as indicated through genetic tests on jackals in Israel, and a 19th-century captive crossbreeding experiment. It plays a prominent role in some African cultures; in North African folklore, it is viewed as an untrustworthy animal whose body parts can be used for medicinal or ritualistic purposes, while it is held in high esteem in Senegal's Serer religion as being the first creature to be created by the god Roog.

7.0K
23 Nov 2022

Topic Review

In biology, taxonomy (from grc τάξις (taxis) 'arrangement', and -νομία (-nomia) 'method') is the scientific study of naming, defining (circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a more inclusive group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain, kingdom, phylum (division is sometimes used in botany in place of phylum), class, order, family, genus, and species. The Swedish botanist Carl Linnaeus is regarded as the founder of the current system of taxonomy, as he developed a ranked system known as Linnaean taxonomy for categorizing organisms and binomial nomenclature for naming organisms. With advances in the theory, data and analytical technology of biological systematics, the Linnaean system has transformed into a system of modern biological classification intended to reflect the evolutionary relationships among organisms, both living and extinct.

6.9K
05 Dec 2022

Topic Review

Light-independent Reactions

The light-independent reactions, or dark reactions, of photosynthesis are chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled area of a chloroplast outside the thylakoid membranes. These reactions take the products (ATP and NADPH) of light-dependent reactions and perform further chemical processes on them.

6.7K
09 Nov 2022

Topic Review

Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are an informal grouping within the proboscidean family Elephantidae. Elephantidae is the only surviving family of proboscideans; extinct members include the mastodons. Elephantidae also contains several extinct groups, including the mammoths and straight-tusked elephants. African elephants have larger ears and concave backs, whereas Asian elephants have smaller ears, and convex or level backs. The distinctive features of all elephants include a long proboscis called a trunk, tusks, large ear flaps, massive legs, and tough but sensitive skin. The trunk is used for breathing, bringing food and water to the mouth, and grasping objects. Tusks, which are derived from the incisor teeth, serve both as weapons and as tools for moving objects and digging. The large ear flaps assist in maintaining a constant body temperature as well as in communication. The pillar-like legs carry their great weight. Elephants are scattered throughout sub-Saharan Africa, South Asia, and Southeast Asia and are found in different habitats, including savannahs, forests, deserts, and marshes. They are herbivorous, and they stay near water when it is accessible. They are considered to be keystone species, due to their impact on their environments. Elephants have a fission–fusion society, in which multiple family groups come together to socialise. Females (cows) tend to live in family groups, which can consist of one female with her calves or several related females with offspring. The groups, which do not include bulls, are usually led by the oldest cow, known as the matriarch. Males (bulls) leave their family groups when they reach puberty and may live alone or with other males. Adult bulls mostly interact with family groups when looking for a mate. They enter a state of increased testosterone and aggression known as musth, which helps them gain dominance over other males as well as reproductive success. Calves are the centre of attention in their family groups and rely on their mothers for as long as three years. Elephants can live up to 70 years in the wild. They communicate by touch, sight, smell, and sound; elephants use infrasound, and seismic communication over long distances. Elephant intelligence has been compared with that of primates and cetaceans. They appear to have self-awareness, and appear to show empathy for dying and dead family members. African bush elephants and Asian elephants are listed as endangered and African forest elephants as critically endangered by the International Union for Conservation of Nature (IUCN). One of the biggest threats to elephant populations is the ivory trade, as the animals are poached for their ivory tusks. Other threats to wild elephants include habitat destruction and conflicts with local people. Elephants are used as working animals in Asia. In the past, they were used in war; today, they are often controversially put on display in zoos, or exploited for entertainment in circuses. Elephants are highly recognisable and have been featured in art, folklore, religion, literature, and popular culture.

6.7K
09 Nov 2022

Topic Review

Muesli (/ˈmjuːzli/ MEWZ-lee; Template:Lang-gsw Template:IPA-gsw, non-Swiss Standard German: Müsli [ˈmyːsli] (listen)) is a cold oatmeal dish based on rolled oats and ingredients like grains, nuts, seeds and fresh or dried fruits. This mix may be combined with one or more liquids like milk, almond milk, other plant milks, yogurt, or fruit juice and left for a time to soften the oats before being consumed. Developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital, it is now eaten as a standard breakfast dish, and also in Switzerland as a supper called Birchermüesli complet: muesli with Café complet (milk coffee, accompanied with bread, butter, and jam. (Butterbrot)).

6.6K
15 Nov 2022

Topic Review

Arthropods (/ˈɑːrθrəpɒd/, from grc ἄρθρον (arthron) 'joint', and πούς (pous) 'foot' (gen. ποδός)) are invertebrate animals having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. Arthropods are bilaterally symmetrical and their body possesses an external skeleton. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. Some species have wings. They are an extremely diverse group, with up to 10 million species. The haemocoel, an arthropod's internal cavity, through which its haemolymph – analogue of blood – circulates, accommodates its interior organs; it has an open circulatory system. Like their exteriors, the internal organs of arthropods are generally built of repeated segments. Their nervous system is "ladder-like", with paired ventral nerve cords running through all segments and forming paired ganglia in each segment. Their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong. Arthropods use combinations of compound eyes and pigment-pit ocelli for vision. In most species, the ocelli can only detect the direction from which light is coming, and the compound eyes are the main source of information, but the main eyes of spiders are ocelli that can form images and, in a few cases, can swivel to track prey. Arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many bristles known as setae that project through their cuticles. Similarly, their reproduction and development are varied; all terrestrial species use internal fertilization, but this is sometimes by indirect transfer of the sperm via an appendage or the ground, rather than by direct injection. Aquatic species use either internal or external fertilization. Almost all arthropods lay eggs, but many species give birth to live young after the eggs have hatched inside the mother, and a few are genuinely viviparous, such as aphids. Arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form. The level of maternal care for hatchlings varies from nonexistent to the prolonged care provided by social insects. The evolutionary ancestry of arthropods dates back to the Cambrian period. The group is generally regarded as monophyletic, and many analyses support the placement of arthropods with cycloneuralians (or their constituent clades) in a superphylum Ecdysozoa. Overall, however, the basal relationships of animals are not yet well resolved. Likewise, the relationships between various arthropod groups are still actively debated. Today, Arthropods contribute to the human food supply both directly as food, and more importantly, indirectly as pollinators of crops. Some species are known to spread severe disease to humans, livestock, and crops.

6.6K
06 May 2023

Topic Review

Sea urchins (/ˈɜːrtʃɪnz/) are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone — from the intertidal seashore down to 5,000 metres (16,000 ft; 2,700 fathoms). The spherical, hard shells (tests) of sea urchins are round and spiny, ranging in diameter from 3 to 10 cm (1 to 4 in). Sea urchins move slowly, crawling with tube feet, and also propel themselves with their spines. Although algae are the primary diet, sea urchins also eat slow-moving (sessile) animals. In the food chain, the predators who eat sea urchins are the sea otter and the starfish, the wolf eel, the triggerfish, and human beings. Adult sea urchins have fivefold symmetry, but their pluteus larvae feature bilateral (mirror) symmetry, indicating that the sea urchin belongs to the Bilateria group of animal phyla, which also comprises the chordates and the arthropods, the annelids and the molluscs, and are found in every ocean and in every climate, from the tropics to the polar regions, and inhabit marine benthic (sea bed) habitats, from rocky shores to hadal zone depths. The fossil record of the Echinoids dates from the Ordovician period, some 450 million years ago; the closest echinoderm relatives of the sea urchin are the sea cucumbers (Holothuroidea); both are deuterostomes, a clade that includes the chordates. The animals have been studied since the 19th century as model organisms in developmental biology, as their embryos were easy to observe; this has continued with studies of their genomes because of their unusual fivefold symmetry and relationship to chordates. Species such as the slate pencil urchin are popular in aquariums, where they are useful for controlling algae. Fossil urchins have been used as protective amulets.

6.5K
19 Oct 2022

Topic Review

Mathematical Modeling and Computational Tools in Drug Design

The conventional drug discovery approach is an expensive and time-consuming process, but its limitations have been overcome with the help of mathematical modeling and computational drug design approaches. Previously, finding a small molecular candidate as a drug against a disease was very costly and required a long time to screen a compound against a specific target. The development of novel targets and small molecular candidates against different diseases including emerging and reemerging diseases remains a major concern and necessitates the development of novel therapeutic targets as well as drug candidates as early as possible. In this regard, computational and mathematical modeling approaches for drug development are advantageous due to their fastest predictive ability and cost-effectiveness features. Computer-aided drug design (CADD) techniques utilize different computer programs as well as mathematics formulas to comprehend the interaction of a target and drugs. Traditional methods to determine small-molecule candidates as a drug have several limitations, but CADD utilizes novel methods that require little time and accurately predict a compound against a specific disease with minimal cost.

6.5K
01 Aug 2022

Topic Review

Artificial Flower

Artificial flowers are imitations of natural flowering plants used for commercial or residential decoration. They are sometimes made for scientific purposes (the collection of glass flowers at Harvard University, for example, illustrates the flora of the United States). Artificial plants vary widely from mass-produced varieties that are distinguishable from real plants by casual observation to highly detailed botanical or artistic specimens. Materials used in their manufacture have included painted linen and shavings of stained horn in ancient Egypt, gold and silver in ancient Rome, rice-paper in China , silkworm cocoons in Italy, colored feathers in South America, and wax and tinted shells. Modern techniques involve carved or formed soap, nylon netting stretched over wire frames, ground clay, and mass-produced injection plastic mouldings. Polyester has been the main material for manufacturing artificial flowers since the 1970s. Most artificial flowers in the market nowadays are made of polyester fabric.

6.4K
05 Sep 2025

Biography

Gurū Nānak (15 April 1469 – 22 September 1539), also referred to as Bābā Nānak ('father Nānak'),[1] was the founder of Sikhism and is the first of the ten Sikh Gurus. His birth is celebrated worldwide as Guru Nanak Gurpurab on Katak Pooranmashi ('full-moon of Kattak'), i.e. October–November. Nanak is said to have travelled far and wide across Asia teaching people the message of ik onk

6.4K
09 Dec 2022

Topic Review

Short-Faced Bear

The short-faced bear (Arctodus sp.) is an extinct bear genus that inhabited North America during the Pleistocene epoch from about 1.8 Mya until 11,000 years ago. It was the most common tremarctine bear in North America and many of its fossils have been found in the La Brea tar pits in southern California . There are two recognized species: the lesser short-faced bear (Arctodus pristinus) and the giant short-faced bear (Arctodus simus), with the latter considered to be one of the largest known terrestrial mammalian carnivores that has ever existed. It has been hypothesized that their extinction coincides with the Younger Dryas period of global cooling commencing around 10,900 BC.

6.4K
05 Nov 2022

Topic Review

The sex ratio is the ratio of males to females in a population. In most sexually reproducing species, the ratio tends to be 1:1. This tendency is explained by Fisher's principle. For various reasons, however, many species deviate from anything like an even sex ratio, either periodically or permanently. Examples include parthenogenic species, periodically mating organisms such as aphids, some eusocial wasps such as Polistes fuscatus and Polistes exclamans, bees, ants, and termites. The human sex ratio is of particular interest to anthropologists and demographers. In human societies, however, sex ratios at birth may be considerably skewed by factors such as the age of mother at birth, and by sex-selective abortion and infanticide. Exposure to pesticides and other environmental contaminants may be a significant contributing factor as well. As of 2014, the global sex ratio at birth is estimated at 107 boys to 100 girls (1,000 boys per 934 girls).

6.3K
19 Oct 2022

Topic Review

A biorhythm (from Greek βίος – bios, "life" and ῥυθμός – rhuthmos, "any regular recurring motion, rhythm") is an attempt to predict various aspects of a person's life through simple mathematical cycles. The theory was developed by Wilhelm Fliess in the late 19th century, and was popularized in the United States in late 1970s. Scientific analysis shows that biorhythms have no more predictive power than chance, providing no evidence for their existence. "The theory of biorhythms is a theory that claims our daily lives are significantly affected by rhythmic cycles."

6.2K
01 Dec 2022

Biography

François Truffaut

François Roland Truffaut (French: [fʁɑ̃.swa ʁɔ.lɑ̃ tʁyfo]; 6 February 1932 – 21 October 1984) was a French film director, screenwriter, producer, actor, and film critic. He is widely regarded as one of the founders of the French New Wave.[1] In a film career lasting over a quarter of a century, he remains an icon of the French film industry, having worked on over 25 films. Truffaut's

6.2K
23 Nov 2022

Biography

John David McAfee (/ˈmækəfiː/ MAK-ə-fee;[1][2] 18 September 1945 – 23 June 2021)[3][4] was a British-American computer programmer, businessman, and two-time presidential candidate who unsuccessfully sought the Libertarian Party nomination for president of the United States in 2016 and 2020. In 1987, he wrote the first commercial anti-virus software, founding McAfee Associates to sell his

6.2K
05 Dec 2022

Topic Review

Flocculus (Cerebellar)

The flocculus (Latin: tuft of wool, diminutive) is a small lobe of the cerebellum at the posterior border of the middle cerebellar peduncle anterior to the biventer lobule. Like other parts of the cerebellum, the flocculus is involved in motor control. It is an essential part of the vestibulo-ocular reflex, and aids in the learning of basic motor skills in the brain. It is associated with the nodulus of the vermis; together, these two structures compose the vestibular part of the cerebellum. At its base, the flocculus receives input from the inner ear's vestibular system and regulates balance. Many floccular projections connect to the motor nuclei involved in control of eye movement.

6.1K
02 Nov 2022

Topic Review

Porridge (historically also spelled porage, porrige, or parritch) is a food commonly eaten as a breakfast cereal dish, made by boiling ground, crushed or chopped starchy plants—typically grain—in water or milk. It is often cooked or served with added flavorings such as sugar, honey, (dried) fruit or syrup to make a sweet cereal, or it can be mixed with spices or vegetables to make a savoury dish. It is usually served hot in a bowl, depending on its consistency. Oat porridge, or oatmeal, is one of the most common types of porridge. Gruel is a thinner version of porridge.

6.1K
02 Nov 2022

Topic Review

Electrocommunication

Electrocommunication is the communication method used by weakly-electric fish. Weakly-electric fish are a group of animals that utilize a communicating channel that is "invisible" to most other animals: electric signaling. Electric fish communicate by generating an electric field that a second individual receives with its electroreceptors. The fish interprets the message using the signal's frequencies, waveforms, delay, etc. The best studied species are two freshwater lineages- the African Mormyridae and the South American Gymnotiformes. While weakly-electric fish are the only group that have been identified to carry out both generation and reception of electric fields, other species either generate signals or receive them, but not both. Animals that either generate or receive electric fields are found only in wet or aquatic environments due to water's relatively low electrical resistance, compared to other substances (e.g. air). So far, communication between electric fish has been identified mainly to serve the purpose of conveying information such as: species courtship and biological sex motivational status (e.g. attack warning, submission, etc.) environmental conditions

6.1K
31 Oct 2022

Topic Review

Evolution of Dinosaurs

Dinosaurs evolved within a single lineage of archosaurs 243-233 Ma (million years ago) from the Anisian to the Carnian ages, the latter part of the middle Triassic. Dinosauria is a well-supported clade, present in 98% of bootstraps. It is diagnosed by many features including loss of the postfrontal on the skull and an elongate deltopectoral crest on the humerus. In March 2017, scientists reported a new way of classifying the dinosaur family tree, based on newer and more evidence than available earlier. According to the new classification, the original dinosaurs, arising 200 million years ago, were small, two-footed omnivorous animals with large grasping hands. Descendants (for the non-avian dinosaurs) lasted until 66 million years ago.

6.1K
14 Oct 2022

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