un-bundling...

a port channel configured with 2 ports each side creates a bundle...

als1#sh int po1                                                                
Port-channel1 is up, line protocol is up (connected)                           
  Hardware is EtherChannel, address is 0009.b73f.ce8c (bia 0009.b73f.ce8c)     
  MTU 1500 bytes, BW 200000 Kbit, DLY 1000 usec,                               
     reliability 255/255, txload 1/255, rxload 1/255                           
  Encapsulation ARPA, loopback not set                                         
  Full-duplex, 100Mb/s, media type is unknown media type                       
  input flow-control is off, output flow-control is off                        
  Members in this channel: Fa0/11 Fa0/12   


 als2#sh int po1                                                               
Port-channel1 is up, line protocol is up (connected)                          
  Hardware is EtherChannel, address is 0009.b752.d78b (bia 0009.b752.d78b)       MTU 1500 bytes, BW 200000 Kbit, DLY 1000 usec,                              
     reliability 255/255, txload 1/255, rxload 1/255                          
  Encapsulation ARPA, loopback not set                                        
  Full-duplex, 100Mb/s, media type is unknown media type                      
  input flow-control is off, output flow-control is off                       
  Members in this channel: Fa0/11 Fa0/12                    

  note the status of int f0/11 below:

als2#sh int f0/11 trunk                                                        
                                                                               
Port        Mode         Encapsulation  Status        Native vlan              
Fa0/11      on           802.1q         trunk-inbndl  1                        
                                      (Po1)               

 mistakenly the bundle is disrupted with access mode

als2(config)#int f0/11                                                         
als2(config-if)#sw mode acc                                                    
als2(config-if)#end                                                            
als2#sh int f0/11 trunk                                                        
                                                                               
Port        Mode         Encapsulation  Status        Native vlan              
Fa0/11      off          802.1q         not-trunking  1    

it becomes unbundled, though f0/12 is yet a member

 als2#sh int po1                                                               
Port-channel1 is up, line protocol is up (connected)                          
  Hardware is EtherChannel, address is 0009.b752.d78c (bia 0009.b752.d78c)       MTU 1500 bytes, BW 100000 Kbit, DLY 1000 usec,                              
     reliability 255/255, txload 1/255, rxload 1/255                          
  Encapsulation ARPA, loopback not set                                        
  Full-duplex, 100Mb/s, media type is unknown media type                      
  input flow-control is off, output flow-control is off                       
  Members in this channel: Fa0/12                       
  

als2#sh int f0/12 trunk                                                        
                                                                               
Port        Mode         Encapsulation  Status        Native vlan              
Fa0/12      on           802.1q         trunk-inbndl  1                        
                                      (Po1)                             

als2#sh spann int f0/11                                                        
no spanning tree info available for FastEthernet0/11 

als2#config t                                                                  
Enter configuration commands, one per line.  End with CNTL/Z.                  
als2(config)#int f0/11                                                         
als2(config-if)#sw mode trunk                                                  
als2(config-if)#end                                                            
als2#sh int f0/11 trunk                                                        
                                                                               
Port        Mode         Encapsulation  Status        Native vlan              
Fa0/11      on           802.1q         trunk-inbndl  1                        
                                      (Po1)                      

als2#sh spann int f0/11                                                        
                                                                               
Vlan             Role Sts Cost      Prio.Nbr Type                              
---------------- ---- --- --------- -------- --------------------------------  
VLAN0001         Altn BLK 12        128.65   P2p                               
als2#

the port channel remained intact with one member...