Answer:

The cell walls of collenchyma tissues are unevenly thickened due to both cellulose and pectin.

Cellulose:
- Cellulose is the main component of plant cell walls and provides structural support and rigidity to the cells.
- It is a complex carbohydrate made up of long chains of glucose molecules that are tightly packed together.
- Cellulose molecules form microfibrils, which are arranged in a crisscross pattern to form a strong and rigid network.

Pectin:
- Pectin is a complex polysaccharide that is found in the primary cell walls of plants.
- It is made up of chains of galacturonic acid and is responsible for the gel-like consistency of plant tissues.
- Pectin acts as a cementing material, binding the cellulose fibers together and providing flexibility to the cell walls.

Uneven Thickening:
- The cell walls of collenchyma tissues are unevenly thickened due to the deposition of cellulose and pectin in specific areas.
- This uneven thickening gives the collenchyma cells their characteristic irregular shape and provides mechanical support to the plant.
- The thickening occurs in the corners and edges of the cells, where the cell walls are subjected to the most stress and strain.
- The uneven thickening allows the collenchyma cells to stretch and expand, providing flexibility to the plant as it grows.

Significance:
- The uneven thickening of collenchyma cell walls allows them to provide support to growing plant parts.
- It helps in maintaining the shape and structure of leaves, stems, and other plant organs.
- The flexibility provided by the unevenly thickened cell walls allows the plant to withstand mechanical stress and bending without breaking.
- The presence of both cellulose and pectin in the cell walls of collenchyma tissues enhances their strength and ability to withstand external forces.

In conclusion, the cell walls of collenchyma tissues are unevenly thickened due to the deposition of both cellulose and pectin. This uneven thickening provides structural support, flexibility, and strength to the plant.