Final answer:
A substance that causes harm to an organism when ingested is identified as a poison, which is a broad term encompassing harmful substances including toxins and venoms. The correct answer is option: a. poison
Step-by-step explanation:
The substance that causes harm to an organism through ingestion is a poison. Poisons can cause death, injury, or harm to organs when introduced to the body in sufficient quantities. The field of toxicology studies the adverse effects of chemical, physical, or biological agents on living organisms, including poisons.
Toxins are a specific type of poison produced naturally by organisms, while venoms are toxins that are injected through bites or stings. Vitamins, on the other hand, are essential nutrients the body needs in small amounts to function properly but they are not considered poisons when ingested at recommended levels.