- Science, Chapter 3, Transportation, Form 3 - Red Blood Cells Human Blood is quite a challenging topic for me. So, "Human Blood" is in Chapter 3 under the topic of Transportation, Form 3, Science. What is Red Blood Cells? Red blood cells are round with a flattish, indented center, like doughnuts without a hole. Your healthcare provider can check on the size, shape, and health of your red blood cells using tests, such as the complete blood count screening. Red blood cells play an important role in your health by carrying fresh oxygen throughout the body. Most people don't think about their red blood cells unless they have a disease that affects these cells. Problems with red blood cells can be caused by illnesses or a lack of iron or vitamins in your diet. Some diseases of the red blood cells are inherited. Diseases of the red blood cells include many types of anemia, a condition in which there are too few red blood cell...