def set_namespace_root(namespace):
    """
    Stores the GO ID for the root of the selected namespace.

    Parameters
    ----------
    namespace : str
        A string containing the desired namespace. E.g. biological_process, cellular_component
        or molecular_function.

    Returns
    -------
    list
        The list of GO ID's of the root terms of the selected namespace.
    """
    if namespace == 'biological_process':
        namespace_list = ['GO:0008150']
    elif namespace == 'cellular_component':
        namespace_list = ['GO:0005575']
    elif namespace == 'molecular_function':
        namespace_list = ['GO:0003674']
    else:
        namespace_list = ['GO:0008150', 'GO:0005575', 'GO:0003674']

    return namespace_list