destroyer bio #127

[baedero1]

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#127. I know what the answer is, but i do not understand the a), b).

a) differenciation occur when a cell has become specialized.
b) differenciation will arise as a result of selective gene expression.

can any1 explain these two?

#132. Does mollusks have a closed circulatory system?

thanks.

 

[mddang]

a) differenciation occur when a cell has become specialized.
Specialized means certain cells perform certain tasks.

For example, if undergrad students were stem cells, doctors, dentists, lawyers, and vets would be the specialized cells.

Intestinal cells are specialized for absorption, neurons are specialized for receiving, processing, and sending information, alpha cells in the pancreas are specialized for the secreted of glucagon, etc...

b) differenciation will arise as a result of selective gene expression.
Certain cells will only synthesize certain proteins. This is done by selective gene expression, which means only certain genes are transcribed into mRNA, and this mRNA is exported out of the nucleus and translated into the protein that it codes for.

For example, only the beta cells of the pancreas will express the gene that codes for the peptide hormone insulin. This is why it is only these cells in our body that produce insulin.

can any1 explain these two?

#132. Does mollusks have a closed circulatory system?
No, if you mean slugs, snails clams, and all those other guys.
Circulatory system (open circulatory system - except cephalopods which have a closed system)

http://en.wikipedia.org/wiki/Mollusk