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1. Describe the various ways by which seeds are dispersed. Explain any one event. (3)
2. What will happen if there are no red blood cells and platelets in the blood? Explain.
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Answer:
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1. Red blood cells take seven days to develop from stem cells called hemocytoblasts.
Hemocytoblasts, or multipotent hematopoietic stem cells, give rise to myeloid stem cells, which differentiate into myeloblasts, megakaryocytes, and red blood cells (erythrocytes). Red blood cell production is regulated by the hormone erythropoietin, which is produced by cells in the kidneys and liver.
Mature red blood cells are flexible, oval or round biconcave discs that move easily through the blood vessels. Certain pathologies, such as sickle-cell anemia, alter the shape and flexibility of red blood cells, making it difficult for them to move smoothly through blood vessels.
Unlike most other eukaryotic cells, mature red blood cells don’t have nuclei. When they enter the bloodstream for the first time, they eject their nuclei and organelles, so they can carry more hemoglobin, and thus, more oxygen.
Each red blood cell has a life span of around 100–120 days. Old, dead, or damaged red blood cells are engulfed by phagocytic cells in the liver, spleen, and lymph nodes. The iron from these cells is subsequently recycled to produce new hemoglobin.