Selectively permeable means that cells only allow certain molecules to enter or exit a cell.
In order to balance the centrifuge. If you don't then the machine will spin out of control and get damaged
The correct answer is: C) exposing the bacteria to an antibiotic that kills cells lacking the resistant plasmid
The plasmids are inserted into bacteria by the process called transformation. Bacteria need to be treated, for example with heat, in order to take up foreign DNA (recombinant plasmid). A inserted recombinant plasmid contains an antibiotic resistance gene, which allows bacteria to survive in the presence of a specific antibiotic. So, this fact is used for the selection of bacteria that are and are not transformed.
Worldwide, there are 107 boy babies born for every 100 girl babies. This skewed ratio is partly due to sex-selective abortion and "gendercide," the killing of female infants, in countries such as China and India where males are more desired. But even discounting those factors, the completely natural male-to-female sex ratio still hovers around 105:100, meaning that women are inherently more likely to give birth to boys. Why?
Several factors influence whether a sperm containing a Y sex chromosome or one containing an X chromosome will be first to fertilize an egg, including parental ages, their environmental exposure, stress, the stage in the mother's ovulation cycle and even whether she has had children previously; all these forces combine to set the average sex ratio at fertilization at 105:100.