Cell differentiation: when a stem cell changes to a specialized one.
        
             
        
        
        
Answer: Base pairs occur when nitrogenous bases make hydrogen bonds with each other. 
Explanation: Each base has a specific partner: guanine with cytosine, adenine with thymine (in DNA), The hydrogen bonds are weak allowing it to "unzip"
 
        
             
        
        
        
Explanation:
The liver does many important things including: Makes bile, which helps carry away waste and break down fats in the small intestine during digestion. Makes certain proteins for blood plasma. Makes cholesterol and special proteins to help carry fats through the body.
 
        
             
        
        
        
It is hard to understand this question but ill give you my best answer. The hearts level of organisation to cells is immense, the heart pumps blood to every cell in the body (so they can respire) through a system of Arteries, veins and capillaries. The blood is pushed by the force of the heart through the arteries, the main (and largest) tubes for transportation to segments of the body further away from the heart. This goes into a smaller system of veins that brake off into a tree kind of pattern to reach every cell. These later brake off into the capillaries that have walls only 1 cell thick. This is how blood is transported to each cell that requires energy and oxygen to respire.
        
             
        
        
        
Answer: Meth
Explanation:
Meth is a stimulant that affects the "Pleasure Reward Pathway" by altering the reuptake of the neurotransmitter dopamine, consequently leaving an excess dopamine in the synapse. It also increases the activity of the dopamine synthesizing enzyme Tyrosine Hydrolase, thus ensuring continuous release.