To restrict one content type to only one organic group,you can:-

1. You may create a vocabulary term with any name. For eg:organicgroups.

2. You may add lists(terms) to that Vocabulary.

3. Then while creating a content,Associate a vocabulary term with each content as per the organic group for which you are creating the content.

To restrict one content type to only one organic group,you can:

1. You may create a vocabulary with any name. For example: organicgroups.
2. You may add lists (terms) to that vocabulary.
3. Then while creating a content, associate a vocabulary term with each content node as per the organic group for which you are creating the content.