What does "keystone" mean?

The scientists studied as many as 1,130 ____ - from bacteria to primates - to understand how evolution built life forms that survived in the face of natural adversities.

A groundbreaking new study suggests that the future of drug making might lie with _________ chickens whose eggs have been engineered to produce human proteins.

Bacteria can become _______ to antibiotics.

In "prevalent" where does the stress fall?

Females have two X ___________. Males have one X and one Y.

_______ break down the food we eat so it can be converted into energy.

In "parasite", the last syllable rhymes with SEAT or SIGHT?