Question

How do spines and thorns help the plants in the desert?

Answer 1

Desert plants modified their leaves as spines to reduce the loss of water. It also prevent animals to eat the plant.

Answer 2

The spines and thorns prevent the plant to be eaten by the animals in deserts.  

Explanation:

The leaf of the plants or cactus modified into the spines or thorns to reduce the water loss from the plant body.

To reduce loss of water means they need to reduce the pores of the leaves so the desert plant changed their leaves to the spines or thorns to reduce the pores and reduce the water loss.