When a plant is not strong enough to support its own weight, the problem is the plant is not producing enough cellulose.
Option D
<h3><u>
Explanation:</u></h3>
A plant is unable to support itself when it is not producing enough cellulose.
Cellulose is a biochemical present in all living beings.
In the case of plants, cellulose is a critical component that is required by plants for their strength. Cells of a plant are surrounded by cell walls which are made tough due to the presence of cellulose in them.
Hence, the different parts of a plant such as a stem, branches, leaves, etc, are strong in nature.
When the amount of cellulose in a plant is less than it should be, the plant fails to support itself and starts bending.