Plant growth caused by external stimulus is
a. tropism
b. homeostasis
c. gibberllin
d. hormone

The correct answer for the blank is-

A. tropism.

Tropism is a biological process that indicates growth of a plant in a particular direction in response to any external stimuli (any change in the environment that induces a specific response in a biological system).

For example - Phototropism in plants is a type of tropism process in which plants tend to grow towards the direction of sunlight.

Thus, option A) is the right answer.

they may bind directly to special “promoter” regions of dna, which lie upstream of the coding region in a gene, or directly to the rna polymerase molecule.

poor water quality affects most estuarine organisms, including commercially important fish and shellfish. the pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.