Cells of the immune system are able to respond
to the presence of invading organisms because
they recognize the
(1) antigens present on the invaders
(2) antibodies present in invading pathogens
(3) dna pattern in the nuclei of viruses
(4) antibiotics released from microbes

1.  antigens present on the invaders

Through the antigens present to the invaders the Cells of the immune system can easily able to respond and recognize.  During an infection, chemical signals attract phagocytes to places where the pathogen has invaded the body. 

The soviet union beat the us to the first successful launch, with the october 4, 1957, orbiting of sputnik 1, and later beat the us to have the first human in earth orbit, yuri gagarin, on april 12, 1961. the "race" peaked with the july 20, 1969, us landing of the first humans on the moon with apollo 11