Antigens is the correct answer
Answer: Septum: Prevents oxygen rich blood mixing with oxygen poor blood in the heart.
Valves: Prevent backflow.
Explanation:
What your cells have to help overcome a problem of high activation energy are called enzymes. Enzymes are proteins that lower the activation energy of a reaction. In doing this, enzymes increase the rate of a reaction, helping it to occur faster. However, enzymes are not consumed in a reaction; they simply help it to occur.
Enzymes make things easier for your cells to work properly and help chemical reactions occur. There are hundreds of different kinds of enzymes in your cells, which all participate in different types of reactions. Enzymes can break molecules apart, build or add molecules, and even rearrange them.
In lowering the activation energy of a reaction, enzymes decrease the barrier to starting a reaction. It's important to note, however, that the change in energy remains the same between the start and end of a chemical reaction.
Reflections and absorption by the atmosphere prevent some radiation from reaching Earth's surface.
