Question

Which of the following parts of the plant shows negative geotropism?
A) Leaves
B) Stems
C) Roots
D) Both a and b

Answer 1

Hint: Geotropism is an integral part of plant growth that orients the plant in such a way that it gets maximum sunlight.

Complete Answer:
- Stems of the plant show negative geotropism while the roots show positive geotropism. This implies that the roots grow downwards i.e. in the direction of the gravity and stems grow upward i.e. in the direction opposite to the gravity.
- Tropism refers to the response or orientation of a plant or certain lower animals to a stimulus. This stimulus acts with greater intensity from one direction as compared to the other.
- Geotropism refers to the growth of a plant or any immovable animal in response to the force of gravity. It is also known as gravitropism. It is due to the coordinated process of differential growth by a plant or fungus in response to gravity acting on it. This gravity can be either artificial gravity or natural gravity.
- There is a variety of tropism that can be seen naturally such as Phototropism (in response to light), Geotropism (in response to gravity), Chemotropism (in response to particular substances), Thigmotropism (in response to mechanical stimulation), Traumatropism (due to the wounding lesion), and Galvanotropism or electrotropism (due to electric current), etc. Most of these tropic movements are orthotropic; i.e. they are directed in the direction of the stimulus.

So, the correct answer is Stem.

Note: Charles Darwin was one of the first scientists to report geotropism. It orient’s the position of the root and shoots and is mediated by the plant hormone called auxin. Differential sensitivity of plants to auxin helps to explain Darwin’s original observation that stems and roots respond in the opposite way to the forces of gravity. Pneumatophores (slender, upright root coming out of the soil to aid in respiration) act as an exception to geotropism.