sodium-potassium pump. n. The enzyme-based mechanism that maintains correct cellular concentrations of sodium and potassium ions by removing excess ions from inside a cell and replacing them with ions from outside the cell.
Algae and nitrogen-fixing bacteria are photosynthetic organisms.
C. Permafrost
Permafrost is the layer beneath the "active layer". The active layer consists of soil that freezes and thaws every year. However, the requirement for permafrost is that it be frozen for two or more years consecutively. This is why permafrost exists in cold environments such as tundras.
The correct answer to your question is Guanine, so D on plato.
