exhausted – adj. completely used up
biological clock – n. a system that controls natural processes such as waking, sleeping and aging
yield – n. the amount of something that is produced by a plant or farm
manipulate – v. to use or change for a particular purpose
in tune with – (idiom; figurative) to be in agreement with someone or something
How would improved crop yields affect your country? We want to hear from you. Write your thoughts in the comments section.