The above statement is true.
Heme iron is found only in meat, poultry, seafood, and fish, so heme iron is the type of iron that comes from animal proteins in our diet. While the non-heme iron, by contrast, is found in plant based foods like grains, beans, vegetables, fruits, nuts, and seeds. However, it is also found in animal products such as eggs or milk/dairy and it also comprises more than half the iron contained in animal meat.
The phenomenon is tolerance.
Tolerance can be found in many aspects of physiology,
For example, when you feel a pain somewhere due to touching something sharp, the feel will be less intense when you feel it the next times.
When you eat a lot of sweets, you tung will temporarily lose its ability to feel sugars
Another example in pharmacology, when you drug in a chronic way, its effect will decrease.
Expendable can mean having little to no value when compared to the big picture or something that's designed to only be used once and then destroyed. Since I don't have any context, I can't decipher which one it would be.
