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http://community.boredofstudies.org/21/business-studies/273158/interdependence-other-key-functions.html
Katsumi gives an example how he'd approach the question in the link above.
Could your biology teacher been talking about a neuron?
See: https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2011exams/pdf_doc/2011-hsc-exam-biology.pdf 32A (Communications)
and the sample answer given...
1. Get enough Sleep
2. Hand in practice questions from past exams/papers to teachers to mark.
3. Eat healthily and exercise.
4. Put aside time for hobbies/relaxing.