Excitation-contraction coupling refers to the series of events that begins with the excitation of the sarcolemma in response to stimulation by a neurotransmitter, and results in the release of calcium ions from the sarcoplasmic reticulum.
Hence, option D is the 1st process that starts the excitation-contraction coupling.
The most appropriate microscope for studying the internal parts of the cell is ELECTRON MICROSCOPE. The correct option is B.
Electron microscope, which is a compound microscope is usually used to study the internal environment of the cell because of the easiness with which one can easily distinguish the cell organelles from one another. Electron microscope gives great clarification of the cellular components and allow scientists to observe minute details about cellular structures. Electron microscope usually magnify specimens to one million times of their real sizes.
A species<span> is a way to </span>classify<span> an </span>organism by its distinct characteristics that match others in a population<span> - </span>organisms<span> within a </span>species<span> have the ability to produce offspring with one another.</span>
Biodiversity generally refers to the variety and variability of life on Earth. According to the United Nations Environment Programme(UNEP), biodiversity typically measures variation at the genetic, species, and ecosystem level.[1] Terrestrial biodiversity tends to be greater near the equator,[2] which seems to be the result of the warm climateand high primary productivity.[3] Biodiversity is not distributed evenly on Earth, and is richest in the tropics. These tropical forest ecosystems cover less than 10 percent of earth's surface, and contain about 90 percent of the world's species.[4] Marine biodiversitytends to be highest along coasts in the Western Pacific, where sea surface temperature is highest, and in the mid-latitudinal band in all oceans. There are latitudinal gradients in species diversity.[5]Biodiversity generally tends to cluster in hotspots,[6] and has been increasing through time,[7][8] but will be likely to slow in the future.[9]
Rapid environmental changes typically cause mass extinctions.[10][11][12] More than 99.9 percent of all species that ever lived on Earth, amounting to over five billion species,[13] are estimated to be extinct.lstimates on the number of Earth's current species range from 10 million to 14 million,[f which about 1.2 million have been documented and over 86 percent have not yet been described] More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described.[18]The total amount of related DNA base pairson Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes.[19] In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon).[20] In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor (LUCA) of all organisms living on Earth.[21]
The age of the Earth is about 4.54 billion years.[22][23][24] The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago,[25][26][27] during the Eoarchean Era after a geological crust started to solidify following the earlier molten HadeanEon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.[28][29][30] Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old meta-sedimentary rocks discovered in Western Greenland.More recently, in 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia.[32][33] According to one of the researchers, "If life arose relatively quickly on Earth .. then it could be common in the universe.
decreased and then increased after major waves of mass extinctions
Answer is.
The right answer is 34.78%
The interphase is the period of the cell cycle that the cell transcribes its genes and the chromosomes are duplicated. It can be subdivided into several phases:
* phase G1
* phase S: during which the chromosomal material is doubled by DNA replication. This is called chromosome duplication.
* phase G2.
Phase G1 is the longest phase of the interphase (its duration depends on the type of cell), followed by phase S, then phase G2.
To calculate the proportion of phase S in the interphase simply make the division:
phase duration S / interphase duration = 8/23 = 0.3478 (in percentage that is 34.78% (0.3478*100)).
