Photosynthesis is important to living organisms because it is

the foundation of most food chains.

the source of nitrogen gas in the air.

how animals get carbon dioxide to breathe.

the process that occurs in most ecosystems.

Option A

Explanation: Photosynthesis can be defined as the process by which plants make food by the help of the necessary elements like carbon dioxide, water, sunlight with the help of chlorophyll.

This process is the basis for food chain to start as plants lie in the category of producers. Every food chain starts with producers.

So, it is the foundation of most of the food chains.

regulation of gene expression. gene expression can be regulated by various cellular processes with the aim to control the amount and nature of the expressed genes. these regulatory proteins bind to dna and send signals that indirectly control the rate of gene expression

explanation: