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Image A shows two conjoined cells forming a dumbbell shape; the fertilization envelope has been removed so that the mesh-like outer layer can be seen. Image B shows the sea urchin embryo when it has divided into 16 conjoined cells; the overall shape is rounder than in image A. Image C shows a “water melon” sea urchin which appears as a peach-colored ball covered in white protruding spines.
A sea urchin begins life as a single cell that (a) divides to form two cells, visible by scanning electron microscopy. After four rounds of cell division, (b) there are 16 cells, as seen in this SEM image. After many rounds of cell division, the individual develops into a complex, multicellular organism, as seen in this (c) mature sea urchin. (credit a: modification of work by Evelyn Spiegel, Louisa Howard; credit b: modification of work by Evelyn Spiegel, Louisa Howard; credit c: modification of work by Marco Busdraghi; scale-bar data from Matt Russell)

A human, as well as every sexually reproducing organism, begins life as a fertilized egg (embryo) or zygote. Trillions of cell divisions subsequently occur in a controlled manner to produce a complex, multicellular human. In other words, that original single cell is the ancestor of every other cell in the body. Once a being is fully grown, cell reproduction is still necessary to repair or regenerate tissues. For example, new blood and skin cells are constantly being produced. All multicellular organisms use cell division for growth and the maintenance and repair of cells and tissues. Cell division is tightly regulated, and the occasional failure of regulation can have life-threatening consequences. Single-celled organisms use cell division as their method of reproduction.

Questions & Answers

what causes demand curve shift to left
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Owusu
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Favour Reply
what causes demand curve shifted to the left?
Richard
what is demand
John Reply
demand is amount of goods and services that a consumer is willing and able to purchase at a giving price over a period of time
roy
demand is some specific thing thats needed by consumer at a certain time
Melat
demand is the willingness and ability to demand a particular product at a particular price and at a particular time
Rahul
demand is an ability and willingness of a consumer to purchase a particular commodity at a given price over a period of time
adebiyi
What does the 45-degree line show
Hassan Reply
the supply line
Neolskae
been unemployed mean s u don't have work whilst been out of labour for means you are not in age of working or you are above the working age (aged)
roy Reply
no, only the working age
roy
Please briefly explain the relationship between the scarcity, choice and opportunity costs
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What is the effect of raising in price to revenue
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yes
Saa
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nebye
price effect
Hez
when you increase price, you increase revenue
Hez
What are the types of price elasticity of supply
jamilu Reply
What's are the types of elasticity
jamilu
what is effect of riaising in price to revenue
Shiyghan Reply
consumer consumption will reduce, as well as demand will fall.
kuntu
what cause inflation
Foday Reply
expenditure on capital goods by the business is known as?
rhandzu Reply
ok
Shiyghan
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Shiyghan
capital expenditure
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fundamental of ecnomics
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Amadou
fu fundamentals of economic problems
Suzan Reply
what are the examples of price elasticity of supply
violet Reply
elastic, inelastic, unitary
joseph
Researchers demonstrated that the hippocampus functions in memory processing by creating lesions in the hippocampi of rats, which resulted in ________.
Mapo Reply
The formulation of new memories is sometimes called ________, and the process of bringing up old memories is called ________.
Mapo Reply
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Source:  OpenStax, Cellular reproduction. OpenStax CNX. Feb 26, 2014 Download for free at http://cnx.org/content/col11635/1.1
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