Short answers, pulled from the story.
A human red blood cell lives for about 100 to 120 days in circulation. In full-term infants the lifespan is shorter, around 80 to 90 days. At the end of their lifespan, aging cells are recognized by macrophages in the spleen, liver, and lymph nodes and removed through a process called eryptosis.
Adult humans have roughly 20 to 30 trillion red blood cells at any given time. They make up approximately 84% of all cells in the human body by number and account for between 40% and 45% of the blood's total volume.
Mature mammalian red blood cells eject their nucleus during development to make room for more hemoglobin. The organelles, including mitochondria and the Golgi apparatus, are also eliminated. This stripping down allows the cell to carry more oxygen and to squeeze through capillaries less than half its own diameter.
The Dutch biologist Jan Swammerdam was the first to describe red blood cells, examining frog blood under an early microscope in 1658. Anton van Leeuwenhoek independently described them in 1674 with greater precision, estimating they were about 25,000 times smaller than a fine grain of sand.
The red color comes from hemoglobin, specifically from the iron ions in its heme groups. When hemoglobin is bound to oxygen it forms oxyhemoglobin, which is scarlet; when oxygen is released it becomes deoxyhemoglobin, which is a dark red burgundy.
Diseases of the red blood cell include iron deficiency anemia, sickle-cell disease, thalassemia, hereditary spherocytosis, aplastic anemia, and polycythemia vera. The malaria parasite spends part of its life cycle inside red blood cells, feeding on hemoglobin and rupturing the cells. Both sickle-cell disease and thalassemia are more common in malaria-endemic regions because the mutations offer some protection against the parasite.