Usually, a combination of salt and ethanol are added to a solution in order to allow the DNA to precipitate or come out of solution. Polar molecules are those with uneven distribution of charges in their structure, which gives them partial positive and partial negative parts in their structure. In general, the rule in solubility is "like dissolves like," which means that polar or charged solutes can dissolve in a polar solvent. Ionic and polar solutes which are "attracted" to and dissolve in water are called "hydrophilic" (water-loving), while nonpolar solutes, which do not dissolve in water are called "hydrophobic" (water-fearing or hating).
DNA has a sugar-phosphate backbone in its structure. The phosphate (PO3-) groups of the backbone are negatively charged. Water, being a polar molecule (with the oxygen end being more negatively charged, and the hydrogen ends being more positive), can interact with the negatively-charged phosphate groups of the DNA and allow the DNA to dissolve in water.
When salt (usually sodium acetate) is added, the positive ions of the salt (e.g. Na+ for sodium acetate) interact with the negatively-charged ends of the phosphate groups (PO3-) in the sugar backbone. This "neutralizes" the charges of the negatively-charged phosphate groups. As a result, the amount of water molecules able to interact with the phosphate groups diminishes, and this lessens the solubility of the DNA.
However, because water has a relatively high dielectric constant (index of polarity), it would be fairly difficult for the Na+ ions to interact with the PO3- groups. Adding the ethanol, which has a lower dielectric constant than water, makes it easier for the Na+ ions to come together with the PO3- groups, and shields it charge from the water molecules. This makes the DNA molecules less hydrophilic and less soluble. As a result, the DNA molecules come out of solution (through a process called precipitation).
<span>She was measuring a rate of change is probably the correct answer once the graph is not shown.
A rate of change in this case would refer to </span><span>the speed at which the respiration</span> is happening<span> over the measured period of time. G</span>raphically, is the slope of a line and that is why is easier to gather conclusions from a line graph instead of any other type.<span> </span>
When you don't know whether an animal was once a Carnivore, Omnivore, or Herbivore, all you have to look for is the teeth. Carnivores have long canines, as well as overall sharper teeth, while omnivores and herbivores contain flat molars.
