People are prevented to achieve certain goals by biological, psychological, social or cultural barriers, such as:

Such biological barriers included fastidious bacterial hosts that were unable to survive in natural environments.

In addition to biological barriers, the conference advocated the use of additional safety factors.

But until now, formidable biological barriers have prevented scientists from domesticating the thousands of other fish in the sea.

Melatonin is a small molecule, and it slips readily across biological barriers through the placenta.

Several barriers protect organisms from infection, including mechanical, chemical, and biological barriers.

For some people there are biological barriers to losing weight at all, while others aspire to unrealistically lean ideals.

This formed a biological barrier between east and west.

Infection of the brain, though serious, is rare due to the biological barriers which protect it.

Maybe there are some biological barriers we don't understand.