help me please about biology?

[alkan]

1) when can we use cell counting?
2) which macromolecule or cell compartment does hoechts stain dyes?
3) why is it more feasable to look human cells under inverted microscope?

I have been seacrhing these 3 questions for hours but I havent found any logical answer from websites. pls help me..

[lordwinalot]

1) i'm not sure when we can use cell counting but...
Hemacytometers were developed for counting blood cells, but can also be used to count spermatozoa. A hemacytometer has two chambers and each chamber has a microscopic grid etched on the glass surface. The chambers are overlaid with a glass coverslip that rests on pillars exactly 0.1 mm above the chamber floor. Thus, the volume of fluid above each square of the grid is known with precision. (http://www.vivo.colostate.edu/hbooks/pathphys/reprod/semeneval/hemacytometer.html)
2)The Hoechst stains are part of a family of fluorescent stains for labelling DNA in fluorescence microscopy. Because these fluorescent stains label DNA, they are also commonly used to visualize nuclei and mitochondria. Two of these closely related bis-benzimides are commonly used: Hoechst 33258 and Hoechst 33342.
Both dyes are excited by ultraviolet light at around 350 nm, and both emit blue/cyan fluorescence light around an emission maximum at 461 nm. The Hoechst stains may be used on live or fixed cells, and are often used as a substitute for another nucleic acid stain, DAPI. The key difference between them is that the additional ethyl group of Hoechst 33342 renders it more lipophilic, and thus more able to cross intact cell membranes. In some applications, Hoechst 33258 is significantly less permeant.
These dyes can also be used to detect the contents of a sample DNA by plotting a standard emission-to-content curve.
Because the Hoechst stains bind to DNA, they can disrupt DNA replication during cell division. Consequently they are potentially mutagenic and carcinogenic. Care should be taken in their handling and disposal. (WIKI)
3)When Leonard Hayflick began his cell culture work at the Wistar Institute in the 1950s, the field was facing a nagging problem. Culture flasks were so big, that microscope objective lenses couldn't come reasonably close to the subject. Hayflick told his Leitz sales representative about the problem, and the sales rep returned with an inverted chemist's microscope popular among crystallographers. With slight modification, it became a workhorse for cell culture work.(http://www.the-scientist.com/article/home/52900/)