What is the difference between red blood cells and white blood cells?

Both are fundamentally different.

Red blood cells are involved in carrying oxygen around the body. They are packed full of a molecule called haemoglobin which oxygen binds to to be transported to cells which need to respire. Red blood cells have a biconcave shape and no nucleus - this is so they can carry as much oxygen as possible

White blood cells are involved in your immune system. They help fight infection when a pathogen enters your body. There are two main types - phagocytes which engulf pathogens and destroy them a lymphocytes which are involved in co-ordinated immune responses and produce antibodies to fight infections

Red blood cells are red and carry the oxygen inside the whole body. White blood cells are not red and are part of the immune system. White blood cells help fight infection.

Red blood cells are concave in shape and carry oxygen around the body to respiring cells. White blood cells are involved in the body's natural defence to fight off and defend against pathogens.

Red blood cells are involved in carrying oxygen around the body to enable respiration of cells. White blood cells are part of the immune system and involved in defence against non-self material for example, pathogens, transplanted organs and cancer cells.