DNA structure. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C).
Dichotomous key is a tool <span> - a series of questions and choices </span>that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. The first step is observing the whole specimen you want to identify. Observing the habitat in which it is growing,its size and overall shape and some<span> distinguishing features. It is very important to make carefully these observations in order to use the key.</span>
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