Eucharist is a sacrament of Initiation. The action of Eucharist is doing as Jesus did at the last supper using bread and wine and his words and actions.
Bible References
Luke 9. 10-17 Feeding The Five Thousand John 6. 1-13 Feeding The Five Thousand
The bread is the body of Jesus and was ate at the last supper.
Wine signifies blood, and blood signifies life. It means Jesus surrendered His natural human life.
The chalice symbolizes the glass from which Jesus Christ drank with his disciples during the Last Supper.
Grape is the wine they used at the last supper.
because it's unleavened bread so it's made from wheat.