▁simple ▁ad hes ion ▁to ▁complex ▁cell ular ▁different iation . ▁ ▁Like ▁other ▁cell ular ▁functions , ▁cell - cell ▁recognition ▁is ▁impact ed ▁by ▁det r iment al ▁mut ations ▁in ▁the ▁gen es ▁and ▁prote ins ▁involved ▁and ▁is ▁subject ▁to ▁error . ▁ ▁The ▁bi ological ▁events ▁that ▁unfold ▁due ▁to ▁cell - cell ▁recognition ▁are ▁important ▁for ▁animal ▁development , ▁micro bi om es , ▁and ▁human ▁medicine . ▁ ▁Fund ament als ▁ ▁Cell – cell ▁recognition ▁occurs ▁when ▁two ▁mole cules ▁restricted ▁to ▁the ▁pl asma ▁memb ran es ▁of ▁different ▁cells ▁bind ▁to ▁each ▁other , ▁trigger ing ▁a ▁response ▁for ▁communication , ▁co operation , ▁transport , ▁defense , ▁and / or ▁growth . ▁ ▁R ather ▁than ▁indu ce ▁a ▁dist al ▁response , ▁like ▁secret ed ▁h orm ones ▁may ▁do , ▁this ▁type ▁of ▁binding ▁requires ▁the ▁cells ▁with ▁the ▁sign alling ▁mole cules ▁to ▁be ▁in ▁close ▁proxim ity ▁with ▁each ▁other . ▁ ▁These ▁events ▁can ▁be ▁grouped ▁into ▁two ▁main ▁categories : ▁In tr insic ▁Rec ogn ition ▁and ▁Ext r insic ▁Rec ogn ition . ▁ ▁In tr insic ▁Rec ogn ition ▁is ▁when ▁cells ▁that ▁are ▁part ▁of ▁the ▁same ▁organ ism ▁associate . ▁ ▁Ext r insic ▁Rec ogn ition ▁is ▁when ▁the ▁cell ▁of ▁one ▁organ ism ▁recogn izes ▁a ▁cell ▁from ▁another ▁organ ism , ▁like ▁when ▁a ▁m amm al ian ▁cell ▁detect s ▁a ▁micro organ ism ▁in ▁the ▁body .