Give evidence that leaves are external structures

Woody plants have a tough, waterproof outer layer of cork cells commonly known as bark, They provide structural support, mainly to the stem and leaves.

They are external structures because their veins are on the outside.

Explanation:

you can see the Leaf's vains because it's an external structure. if you can't see the Leaf's vains it means its internal

osteogenesis imperfecta (oi) refers to a congenital ailment of bones. in the condition, the bones become brittle or fragile. this ailment is a general result of the defect or mutations in the genes (colia1 or colia2). this mutation results in imperfect collagen formation either in quantity or quality wise.  

there are eight kinds of oi defects, and each kind varies with certain distinctions in symptoms. the usual symptoms include frequent bone fractures, loss of hearing in infants, protruding eyes, discoloration of the white in the eyes, respiratory issues, loosening of the joints, short stature, and other symptoms.