In a muscle cell, Ca2+ enters the cytoplasm through a channel in the sarcoplasmic reticulum (SR) and is removed back into the SR from the cytoplasm by a pump. The graph shows the number of Ca2+ ions in the cytoplasm of muscle cells over time in three different birds. Initially, there are very few Ca2+ ions in the cytoplasm of the cells (i.e., “steady state”). When a stimulus occurs, Ca2+ is released into the cytoplasm at the rate of 100 units/ms for each bird (i.e., “stimulus”). After several milliseconds (time point X), the number of Ca2+ ions in the cytoplasm is different for each bird despite having the same rate of Ca2+ ions entering the cytoplasm. a) Explain how Bird 1 has more Ca2+ ions in the cytoplasm of its muscle cells compared to Birds 2 and 3 given that Ca2+ ions entered the muscle cells of all three birds at the same rate. b) Explain how Bird 3 has no change in Ca2+ ions in its muscle cells while Birds 1 and 2 both show increased Ca2+ ions in their muscle cells given that Ca2+ ions entered the muscle cells of all three birds at the same rate.