Step 1: Biology is the broad science that studies living organisms, and it is divided into branches based on which living things are studied.
Step 2: The branch of biology that deals with plants, their structure, growth, reproduction and classification, is called botany.
Step 3: Zoology, by contrast, is the branch of biology that studies animals, not plants. Physics is the study of matter, energy and forces, and chemistry is the study of substances and how they react, neither of which is specific to living plants.
Step 4: Since the question asks specifically about plants, physics and chemistry are ruled out because they are not life sciences, and zoology is ruled out because it covers animals, not plants.
Answer: Biology, specifically botany, option D.