In primary succession, newly exposed or newly formed rock is colonized by living things for the first time. In secondary succession, an area that was previously occupied by living things is disturbed, then re-colonized following the disturbance.
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). The order of these bases is what determines DNA's instructions, or genetic code.
Answer:B
Explanation: Pernicious anemia is a condition caused by too little vitamin B12 in the body. It is one form of vitamin B12 deficiency anemia. Vitamin B12 helps the body make healthy red blood cells and helps keep nerve cells healthy. ... The most common cause of pernicious anemia is the loss of stomach cells that make intrinsic factor.
