ALAIN POL / CNRI / SCIENCE PHOTO LIBRARY ALAIN POL / CNRI / SCIENCE PHOTO LIBRARY
Blood cells. Light micrograph of red blood cells (erythrocytes, red) and white blood cells (leucocytes, nuclei stained purple). Red blood cells contain haemoglobin and carry oxygen and carbon dioxide to and from body tissues. White blood cells are part of the body's immune system, helping to defend against microbes and other pathogens (disease-causing organisms).
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