Two Kinds of Iron
The human body needs iron to produce hemoglobin, a substance that helps red blood cells transport oxygen. Without enough iron, a person may feel tired and weak. Dietary sources of iron include plant sources, such as vegetables and beans, and animal foods, including poultry, red meat, and fish. However, plant and animal sources are not equal. The iron in plants, called nonheme iron, is not easily absorbed by the human digestive system. For example, a half cup of cooked spinach contains a healthy dose of over three milligrams of iron. Unfortunately, only five percent of that iron can be used by the body. On the other hand, the iron in animal foods, called heme iron, is better utilized. Heme iron is contained within a ring of protein, which helps the body to absorb it easily.
What is the main, or central, idea of the passage?
Plant and animal food sources both contain iron, which helps red blood cells carry oxygen throughout the body.
Plant and animal food sources both contain iron, but the iron in animal foods is more accessible to the body.
Heme iron, found in meat and fish, is easily absorbed by the human body.
The correct answer and explanation is:
The correct answer is:
Plant and animal food sources both contain iron, but the iron in animal foods is more accessible to the body.
Explanation:
This passage focuses on two types of iron—heme iron and nonheme iron—and how the human body absorbs and uses these forms differently. The central idea is the contrast between the iron found in plant-based foods (nonheme iron) and that found in animal-based foods (heme iron). The passage explains that while both types of iron are important for producing hemoglobin, which helps transport oxygen in the body, the body absorbs heme iron more efficiently than nonheme iron. The example of spinach highlights this point, showing that although spinach contains iron, the body can only absorb a small portion of it, whereas iron from animal sources is more easily absorbed due to its chemical structure.
The passage also emphasizes the dietary implications of these differences. It suggests that while iron is found in both plant and animal sources, the type of iron found in animal foods is significantly more accessible to the body, which may be important for individuals who need to optimize their iron intake, such as those with iron deficiency or anemia. Therefore, the main idea of the passage centers on the difference in bioavailability between plant and animal iron sources, with the iron from animal sources being more readily absorbed and used by the human body.