Here's why:

* Tissue: A group of similar cells that work together to perform a specific function. Examples include muscle tissue, nervous tissue, and epithelial tissue.

* Organ: A structure made up of different tissues that work together to perform a complex function.

Leaves are made up of multiple tissues, including:

* Epidermis: The outer layer of the leaf, protecting it and controlling water loss.

* Mesophyll: The inner layer of the leaf, containing chloroplasts for photosynthesis.

* Vascular tissue: The network of xylem and phloem that transports water and nutrients.

These tissues work together to carry out the leaf's primary function: photosynthesis.