44 



MINERAL SALTS ABSORPTION IN PLANTS 



M^ 



H^ 



Mi 



XH-t X H 



(~) 



XM >-XIVI 



(a) 

 X-< X' 



(~) 



XM >-XIVl 



M- 



H* 



^M* 



^M'' 



^PC 



A" 



OH' 



M*- 



YOH-«— y'OH 



YA >-YA 



(b) 



Y-< y' 



(~) 



YA >-y'a 



(d) 



OH" 



-M"- 



m! 



z-<- 



-z' 



r 



ZAM->-ZAIVI 



(f) 



^A- 



Fig. 13. Interrelationships between cation and anion transport 

 a. Active cation transport involving exchange; b. active anion transport 

 involving exchange; c. Active cation transport accompanied by passive 

 anion absorption; d. Active anion transport accompanied by passive cation 

 transport; e. Active transport of cations and anions by separate carrier 

 systems; f. Active transport of cations and anions by a common carrier 



system. 



(Fig. 13c). Alternatively, active transport of anions might create 

 the necessary electrochemical gradient for passive cation accum- 

 ulation across a cation-permeable barrier (Fig. 13d). 



Active transport could equally be involved in the movement of 

 both cations and anions across an impermeable membrane. The 

 system might comprise separate carriers linked through a common 

 energy supply (Fig. 13e) or there might be an amphoteric carrier 



