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ob·li·gate 'äb-li-gət, -lə-.gāt adj
1) restricted to one particularly characteristic mode of life or way of functioning <the infant is an \obligate nose breather (Jour. Amer. Med. Assoc.)> <an \obligate parasite>
2) biologically essential for survival <\obligate parasitism>
ob·li·gate·ly adv
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adj.
describing an organism that is restricted to one particular way of life; for example, an obligate parasite cannot exist without a host. Compare facultative.
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ob·li·gate (obґlĭ-gāt) [L. obligatus] not facultative; necessary; compulsory; capable of survival only under particular conditions, as an obligate aerobe.Medical dictionary. 2011.