Final answer:
Chlorophyll is not secreted by the plant's secretory cells, but is contained within the chloroplasts and used in photosynthesis, unlike starch, resin, or nectar which are secreted.
Step-by-step explanation:
The substance among the options given that is not secreted by a plant's secretory cells or tissues is chlorophyll. Plants do produce chlorophyll within their cells, specifically in the chloroplasts found in the mesophyll cells of the leaves, where photosynthesis occurs, as described in figure 8.1. However, chlorophyll itself is not secreted but rather remains contained within the chloroplasts as part of the photosynthetic apparatus. On the other hand, substances like starch, resin, and nectar are indeed secreted either for storage, protection, or interaction with pollinators.