"were kept together, to pair up with and were made up of"

[Odessa Dawn]

"A memory study by Daniel Wegner of Harvard University provides a neat example of this effect. Couples were asked to come into the lab to take a memorisation test. Half the couples were kept together, and half were reassigned to pair up with someone they didn't know. Both groups then studied a list of words in silence, and were then tested individually. The pairs that were made up of a couple in a relationship could remember more items, both overall and as individuals."
More: http://www.bbc.com/future/story/2012...us-intelligent

pair up
Kept Synonyms
Is made up of

Are the underlined parts synonyms for each other? Do we have an antonym for the underlined parts from the given context? I ask these questions because I want to enrich my vocabularies.

[Grumpy]

They each mean something quite different.

"were kept together" means that already established pairs were not split up. The antonym would be "were split up".
"to pair up" means that individuals were asked to find different partners to form new pairs. There's no specific antonym.
"were made up of" refers to the common attributes or qualities of each individual in a pair. In this case it was people in a relationship, but it might have been, for example, people with red hair. Again, there's no specific antonym.