Systemic effects happen when a pesticide is absorbed into the body and travels through the bloodstream to organs beyond the entry point. If the chemical reaches the reproductive system, it can disrupt hormones, affect ovulation or sperm production, and even impact fetal development. That’s why reproductive problems are a classic example of systemic toxicity. Vision or hearing problems tend to come from neurotoxic or sensory-specific damage, and a skin rash is a local skin reaction; systemic exposure is more likely to involve body-wide effects, including the reproductive system. So the reproductive problems option best reflects what can happen when a chemical acts systemically.

The term being tested is how “synthetic” is used for synthetic organic insecticides. Synthetic means manufactured or man-made in a lab or factory, not something that occurs naturally. In pest control, synthetic organic insecticides are carbon-containing compounds that are produced by chemical synthesis rather than being directly sourced from nature. That’s why they’re described as synthetic: they originate from human-made chemical processes, not naturally occurring substances. The other options describe things that come from nature or natural sources (naturally occurring, plant-derived, found in soil), which is not what the word indicates here.

Systemic herbicides are absorbed by the plant and moved through its vascular system, so they reach tissues beyond the sprayed leaves. Perennial weeds survive by underground structures such as rhizomes, tubers, bulbs, or crowns that can store energy and resprout after the top growth is removed. To prevent regrowth, you need a chemical that travels to those underground parts and kills them, not just the visible shoots. That translocation to the root and storage tissues is why systemic herbicides are used for perennials. In contrast, products that stay on the leaf surface would be contact herbicides and often fail to eliminate underground propagules. Cost isn't the primary reason, and systemic products are not limited to annuals—they are chosen specifically to control perennials by reaching and destroying their underground structures.

Sunlight makes pyrethroids photolyze. When these molecules absorb UV energy, their bonds break, converting the active ingredient into different, less active or inactive compounds. This causes a rapid loss of insecticidal activity, so pyrethroids are unstable and break down quickly in sunlight. They don’t rely on volatilizing into the air as the main fate under sun, and they don’t remain stable when exposed to sunlight.