Question

Which of the following is true about pneumatophores in mangroves?

Answer 1

Mangroves are plants that live in extremely saline water. They are able to live in coastal regions that are partially underwater. Thus these plants need adaptations to help them get more oxygen. The pneumatophores are ‘breathing tubes’ that grow upwards from the roots of the mangrove and help them to get more oxygen.

Complete answer:
The roots of mangroves are usually submerged underwater. Additionally, the environment that these plants grow in is very saline. Therefore one adaptation to help these trees deal with the low oxygen is the pneumatophores. These tubes stick out from the soil and allow the trees to get more oxygen.
When we talk about aerotropic, geotropic, and hydrotropic, we are referring to the type of environment that the plant is growing towards. For example, if the roots of a plant start growing towards some water then they would be called positively hydrotropic.
Pneumatophores grow upwards out of the ground and into the air. The ground that mangroves grow in are often underwater. Therefore we can say that the pneumatophores are growing away from the ground and water and into the air.

Thus the answer to this question is D: They are positively aerotropic, negatively geotropic and negatively hydrotropic.

Note:
Pneumatophores grow towards the air therefore they can be called positively heterotrophic. These structures also grow out of the saline and wet ground that the mangroves grow in, therefore they are negatively hydrotropic and geotropic.