Short answers, pulled from the story.
Jesus Christ commanded his disciples to share bread and wine in memory of him while referring to the bread as his body and the cup of wine as the blood of his covenant. Passages in the New Testament state that he instructed them to perform this act during a Passover meal.
Paul the Apostle wrote the earliest recorded description of the Last Supper in the First Epistle to the Corinthians during the early 50s of the 1st century. This account includes the words This is my body which is for you and Do this in remembrance of me.
The Catholic Church states that the substances of the bread and wine actually become the substances of the body and blood of Christ during consecration. The appearances or species such as colour taste feel and smell remain unaltered until the Eucharistic species subsist.
The Council of Trent definitively declared this change in 1551 stating it takes place a change of the whole substance of the bread into the substance of the body of Christ. This declaration affirmed that his body and blood are truly contained under the forms of bread and wine by God's power.
Jehovah's Witnesses commemorate Jesus' death annually on the evening corresponding to Nisan 14 according to the ancient Jewish calendar. They generally refer to the observance as the Lord's Evening Meal or the Memorial of Christ's Death.
The Congregation for the Doctrine of the Faith issued a letter dated the 24th of July 2003 from the Congregation for the Doctrine of the Faith regarding gluten issues. It allows low-gluten bread for celiacs but holds that if gluten has been entirely removed the result is not true wheaten bread.