organisms vs species or populations;
adaptation vs acclimation;
cause vs purpose

NEVER say that organisms adapt to their environment, OR evolution is when organisms adapt to their environment, OR that organisms adapt to their environment in order to survive.

Here's why:
1. Only groups of organisms can evolve (populations or species); individual organisms never evolve.

2. Biological adaptations (as a noun. referring to structures that help survival), in the evolutionary sense, and as properly used in class and text, can only "develop" as characteristics of a species or population, generally over a long period of time, involving many generations. These must not be confused with the "acclimations" or "adjustments" an individual organism might make, consciously or otherwise, enabling it to survive better (such as "developing resistance to a disease" or "adapting to higher altitudes", etc.)

In a similar sense, the word "adaptation," when used as a verb, for the process by which biological adaptations "develop," usually refers to natural selection, a major mechanism of evolution. To further avoid confusion, when a feature that is typical of a species (or population), and helps it to survive and/or reproduce, that group simply evolved that feature (or that adaptation).

3. Therefore, because "organisms" generally refers to individual living creatures (or plants, etc.), not to groups of the same species, the word "organisms is an ambiguous term (has more than one meaning), and can reflect poor understanding of evolution, the word should be avoided. Instead of "organisms," refer to "species" or "populations" adapting (by natural selection) to avoid confusion. Never refer to "organisms" OR individuals adapting.

4. The change that an individual can make during its lifetime (e.g., making more red blood cells at higher altitudes) is NOT biological adaptation. Changes that an individual organism makes within its lifetime, adjusting itself to a different environment, should be called "acclimation" or an "adjustment," NOT an adaptation. The ability to do that probably evolved in its species (over many generations), but the actual process of an individual changing that results in better survival (of that individual) is best called "acclimation."

5. Purpose vs Cause: Many people automatically assume that changes happen for some particular purpose, when in reality, there is no tangible evidence that biological changes happen for a purpose. Changes that happen are clearly the result of events that happened before causing that change, with no intention or ultimate goal. The mechanism for what causes those changes (mostly natural selection) should be studied in MS and HS. The thinking here is a bit tricky, and it's very hard for children to understand this, until about the ages of 10-11. In any case, at all grade levels, try to use phrases that reflect the process of natural selection (without giving it that name), and mainly avoid the use of phrases suggesting that changes happen for some ultimate purpose. Unfortunately, lots of literature (and even science textbooks, and parents, and teachers) persist in the "ultimate purpose" idea, saying things like "monkeys have long tails so they can move easily in trees," or that "birds have wings in order to fly," etc. Instead, we should say things like "we have teeth (for example) because of changes over many generations gradually produced teeth, and those teeth helped them to survive better." Or birds have wings because long ago, their arms changed over many generations in several ways that enabled "pre-birds" or "early-birds" to move from tree to tree faster and more safely.