Xavier listed the steps involved when sponges take in food and oxygen. 1. water is drawn in through pores and enters the central cavity. 2. food is filtered and digested. 3. water leaves through an opening at the top of the body. which describes the missing step? oxygen is removed from the water before step 3. oxygen is removed from the water after step 3. tentacles sting and paralyze prey after step 1. tentacles sting and paralyze prey before step 1.