Final answer:
The toxic dose is not the same for every living thing; it varies among species and individuals within those species. The lethal dose-50% (LD-50) measures toxicity but does not translate universally across all organisms. Environmental factors and the method of administration also affect toxicity levels.
Step-by-step explanation:
False. The toxic dose is not the same for every living thing. The toxicity of a substance can vary greatly among different species and even within the same species due to genetic differences, size, and metabolic rates. The lethal dose (LD-50), which is the dose lethal to 50% of a test population, is commonly used to measure the toxicity of a substance. However, LD-50 values for one species do not necessarily translate directly to another species, and can also vary based on the method of administration, such as ingestion or injection.
Moreover, factors such as environmental conditions can influence an organism's response to a toxin. An example that illustrates this is selenium; essential in small amounts for biological function, but harmful in excess. As for experiments, it is true that direct toxicological testing on humans is generally not conducted for ethical reasons. In scientific research, larger sample sizes are preferred because they can provide more reliable data and reduce the impact of anomalies.
When considering the toxicity of substances like those found in tobacco smoke, it is clear that different chemicals, such as nicotine, can have varying levels of addictiveness and toxicity. This exemplifies the principle that 'the dose makes the poison', indicating that the harmfulness of a substance is related to its concentration or amount consumed.