5. A certain seaweed plant is found in estuaries. At high tide, the plant is exposed to sea water; at low tide, the plant is exposed to brackish water (less salty water). The concentrations of some dissolved materials remain virtually constant in the cells of the seaweed.
The concentrations of various substances inside the cells of a certain seaweed in sea water and in brackish water were determined. \( \underline{\text { Note: }} \) the cell maintains the concentration shown, in both sea water and brackish water.
Use the following key to answer the next four questions. (I, 4)
A) calcium
B) sodium
C) potassium
D) chloride
a) Which substance is actively transported into the cell from both sea water and brackish water?
b) Which substance enters by active transport in brackish water and requires no energy input to maintain it in salt water?
c) Which substance is actively transported out of the cell in sea water and actively transported into the cell in brackish water?
d) Which substance requires the cell to expend energy to maintain its concentration in sea water but not in brackish water?
