Answer:
The correct answer is B. the two strands of DNA must separate.
Explanation:
DNA is a double-stranded structure. The two strands are joined together by the formation of hydrogen bonds between complementary nucleotides. So before the replication takes place these two strands must be separated.
The separation of DNA strand is accomplished by the action of a helicase enzyme which breaks the hydrogen bond between complementary nucleotides and separated the two DNA strands.  
After separation, the DNA polymerase binds to separated DNA and replicating the DNA. So the right answer is B.
 
        
             
        
        
        
After the macrophage fails the Helper T Cell stimulates the B cells if pathogen is extracellular and Cytotoxic T Cells if the pathogen is intracellular. Once the pathogen is killed the B Cells create Memory B Cells and the Killer T Cells create memory T Cells.
        
             
        
        
        
Answer:
E. Gene is amplified by multiplication of cloning host
Explanation:
PCR is a very powerful technique that can help us to amplify exponentially one gene from a very small sample of DNA.
As seen in the attached image, the process begins with a single DNA molecule, for the first cycle, that DNA molecule denaturalizes into two strands, the primers bind to their complementary sides and then the DNA polymerase builds the new DNA strands. The number of copies of the gene that can be obtained with each cycle are 2ⁿ copies, where n is the cycle number. 
 
        
             
        
        
        
Answer:
Rocks can be divided into three basic classifications: igneous, sedimentary, and metamorphic. The following tests are used by experts to classify rocks: Hardness Test Minerals are scaled in range from 1 to 10, with 1 being softest and 10 hardest. The method of determining hardness is the scratch test.
 
        
             
        
        
        
Answer:
The pathway of oxygen from lungs to the body tissues is alveoli → red blood cells → blood vessels → tissues (option b).
Explanation:
The oxygen (O₂) required by the tissues comes from the air inspired by the respiratory system. The pathway of entry of O₂ to the body and tissues is:
- O₂ from the air reaches the lungs.
- In the pulmonary alveoli, gas exchange occurs, that is, O₂ passes into the blood capillaries and is captured by the red blood cells, while CO₂ is released and passes into the alveoli to be eliminated.
- O₂ in the red blood cells travels through the blood vessels.
- The tissues receive the O₂ and a second gaseous exchange occurs at the tissue level, as they release CO₂ that will be carried to the alveoli.
Tissue oxygenation depends on the integrity of the respiratory and circulatory systems.
<em>     The other options do not show the correct order in which the oxygen travels from the alveoli to the tissues.</em>