In plants, collenchyma is a tissue that supports living elongated cells with irregular cell walls that have thick deposits of cellulose in their cell walls and appear polygonal.
Collenchyma has living cells.
Hence it is not a dead tissue
The tissue is primarily found in the cortex of stems and leaves, and it serves as the primary support tissue for many herbaceous plants.
The thickened cell walls and longitudinal interlocking of the cells give the tissue its strength.