A researcher heats a solution of DNA and notices that as the temperature increases, the absorbance of ultraviolet light at 260 nm increases dramatically. This is because .

The question is incomplete as it does not have the options which are:

3. the double strands of DNA are separating

Explanation:

Ultraviolet light is absorbed by the DNA molecule therefore the UV light is used to find the DNA concentration of a sample.

The ultraviolet light is absorbed by the nitrogenous bases present between the sugar-phosphate backbone of the DNA molecule. The part of the base which absorbs the UV light is the presence of the heterocyclic rings.

Since these heterocyclic rings are involved in the hydrogen bond therefore when DNA exists in its double-stranded form, it absorbs less UV light.

When the DNA sample is heated then the DNA gets denatured and DNA becomes single-stranded. The heterocyclic rings absorb the UV light more easily thus increasing the absorbance.

Thus, Option-3 is correct.

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.