Plant guard cells(保卫细胞) have a higher [C1-] than the outside environment. The most likely explanation for this is( ).

单项选择题在下列组织中, 紧密连接特别重要的有( )

单项选择题钙泵的作用主要是( )。

单项选择题The hormone glucagons(胰高血糖素) stimulates the breakdown of stored glycogen in liver and muscle cells by the following enzymes. Which is the first enzyme that must be activated ( )

单项选择题Which one of the following is incorrect for the biogenesis of eukaryotic ribosomes( )