What makes the shell of a coconut tough?
collenchyma
Coconut shell is composed of sclerenchyma tissues. Sclerenchyma tissues are composed of long, narrow and thick cells, which are dead. These cells develop very thick walls due to the deposition of lignin. Lignin makes the tissue tough.
Parenchyma is present in the soft tissues and help in photosynthesis and food storage. Collenchyma provides flexibility and support to plant parts. Xylem is a vascular tissue that helps in conduction.