Question

Thorns, spines and prickles are
A. Defensive organs
B. Respiratory organs
C. Both (A) and (B)
D. None of the above

Answer 1

Although thorns, spines and prickles are often used interchangeably, they are different things. Thorns, spines and prickles are organs that protect them from their predators.

Complete answer: Thorns, spines and prickles are hard, rigid extensions of leaves, roots, stems or buds that have sharp and stiff ends. The major function of all these is to physically deter herbivorous animals from eating the plant and plant parts. Though all these perform a similar function, these sharp projections differ depending on their origin and the presence of vascular tissue. Thorns and spines are modified stems and leaves respectively and have vascular bundles inside. Prickles come from a plant’s epidermis (the outermost cell layer) and they do not have vascular bundles inside. As a result, prickles can be removed more easily than thorns and spines. A sharp-pointed structure that is a modified branch often arises from the main stem at leaf axils. For example, firethorn and hawthorns.
a) Spine: It is a sharp projection developed from a leaf part. For example, honey locust is the most notorious woody plant that bears spines. Moreover, in cacti, the entire leaf of the plant transformed into spines. It not only reduces the water loss by restricting leaf surface area but protects the plant from the animals as well.
b) Prickles: Prickles arise from stem tissue and are the extensions of its cortex and epidermis. For example, rose stems.
Therefore, option A is the correct answer.

Note: Some animals and plants, for example, the Acacia tree and giraffe have evolved in response to each other. The plants grow very long spines and animals develop very long tongues to reach past the spines and feed on the leaves of the plant.