Besides a high voltage shock, what is another method to make e. coli competent to take up "naked" dna?
a. high concentrations of calcium ions followed by high temperature
b. high concentrations of calcium ions and several hours on ice
c. large amounts of dna added directly to a bacterial culture growing at 37c
d. high concentrations of minerals followed by high temperature
e. a high voltage shock is the only way to make e. coli competent

The correct answer is a. high concentrations of calcium ions followed by high temperature.

Explanation:

Apart from high voltage shock, calcium chloride heat shock method can be used to make E. coli competent to take up naked DNA. As both DNA and lipids contain phosphorus and phosphorus contains negative charge, therefore, ice-chilled CaCl₂ makes cation bridge between phosphorylated lipid of cell membrane and phosphorus present in the DNA.

This allows the naked DNA to attach to the cell surface of bacteria. Then cells are given heat shock which creates gaps(holes) in the membrane and makes the cells competent to take up the naked DNA by these holes.

Then the transformed cells can be selected by screening methods like growing transformed cells on media containing a suitable antibiotics.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.