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Biology Lessons & Terms

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Why can the Golden Ratio be found all over nature? Monophyletic, Paraphyletic, Polyphyletic defined. 17th July 2003 Question What do terms like monophyletic, paraphyletic and polyphyletic mean?

Monophyletic, Paraphyletic, Polyphyletic defined

Answer These terms are used to describe groupings of organisms, and indicate the extent to which they can be considered as ``natural groups''. They are best explained using examples, so consider the following family-tree diagram: Aves / / Crocodilia / Mammalia \ Dinosauria \ \ / \ \ / \ \ / Synapsida Reptilia \ / \ / \ / Amniota Here are examples of all three types of group: Consider the group consisting of all the animals in this diagram - that is, Amniota. So far, so straightforward. Because clades are so important, there is common notation for specifying them (taken from the Phylocode: see note 9.4.1 in Clade(A+B) is a node-based definition meaning ``the most recent common ancestor of A and B, together with all its descendents'', or equivalently, ``the least inclusive clade containing A and B''.

It's unfortunate that this notation is so clumsy. Biology: Free Stanford Course by Robert Sapolsky. Genetic drift v. Natural selection. Genetic drift or allelic drift is the change in the frequency of a gene variant (allele) in a population due to random sampling.[1] The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces.

Genetic drift v. Natural selection

A population's allele frequency is the fraction of the copies of one gene that share a particular form.[2] Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation. Homologous v Analogous Structures. Homologous structure (bones in tetrapod forelimbs) Analogous structure (wings in insects and tetrapods) Introductory Biology.

Convergent Evolution. Convergent evolution describes the independent evolution of similar features in species of different lineages.

Convergent Evolution

Convergent evolution creates analogous structures that have similar form or function, but that were not present in the last common ancestor of those groups.[1] The cladistic term for the same phenomenon is homoplasy, from Greek for same form.[2] The recurrent evolution of flight is a classic example of convergent evolution. Flying insects, birds, and bats have all evolved the capacity of flight independently. They have "converged" on this useful trait. Convergent evolution is similar to, but distinguishable from, the phenomena of parallel evolution. Parallel evolution occurs when two independent but similar species evolve in the same direction and thus independently acquire similar characteristics—for instance gliding frogs have evolved in parallel from multiple types of tree frog. Causes[edit] Significance[edit] Distinctions[edit] Cladistic definition[edit] Semelparity and iteroparity. Semelparity and iteroparity refer to the reproductive strategy of an organism.

Semelparity and iteroparity

A species is considered semelparous if it is characterized by a single reproductive episode before death, and iteroparous if it is characterized by multiple reproductive cycles over the course of its lifetime. Some plant scientists use the parallel terms monocarpy and polycarpy. (See also plietesials.) In truly semelparous species, death after reproduction is part of an overall strategy that includes putting all available resources into maximizing reproduction, at the expense of future life (see "Trade-offs", below).

In any iteroparous population there will be some individuals who die between their first and second reproductive episodes, but unless this is part of a syndrome of programmed death after reproduction, this would not be called semelparity. This distinction is also related to the difference between annual and perennial plants. Overview[edit] How do I find the number of protons, electrons and neutrons that are in an atom of...? How many protons, electrons and neutrons are in an atom of krypton, carbon, oxygen, neon, silver, gold, etc...?

How do I find the number of protons, electrons and neutrons that are in an atom of...?

To find the number of protons, electrons and neutrons in an atom, just follow these easy steps: Step 1 - Gather Information The first thing you will need to do is find some information about your element. Go to the Periodic Table of Elements and click on your element. If it makes things easier, you can select your element from an alphabetical listing. Use the Table of Elements to find your element's atomic number and atomic weight. Step 2 - The Number of Protons is... The atomic number is the number of protons in an atom of an element. The interesting thing here is that every atom of krypton contains 36 protons. Step 3 - The Number of Electrons is... By definition, atoms have no overall electrical charge. Electrons are arranged around atoms in a special way. An atom can gain or lose electrons, becoming what is known as an ion. Camoflauge in Animals.

Mimicry Some animals and plants look like other things -- they mimic them. Mimicry is another type of deceptive coloration. It can protect the mimic from predators or hide the mimic from prey. If mimicry was a play, there would be three characters. The Model - the species or object that is copied. The Mimic - looks and acts like another species or object. The Dupe- the tricked predator or prey. The poisonous coral snake and the harmless king snake look a lot alike. The viceroy butterfly and monarch butterfly were once thought to exhibit Batesian mimicry where a harmless species mimics a toxic species.