Most cells share features such as having a nucleus, a cell membrane, cytoplasm and mitochondria.
There are differences between cells, too. Each type of cell, has its own job to do. These cells have special features that allow them to perform their functions effectively.
Red blood cells
Red blood cells carry oxygen around the body. They are well suited to this function because:
They contain haemoglobin, which carries oxygen molecules.
They don't have a nucleus, allowing more space to carry oxygen.
They are a flat disc shape (bi-concave) which gives them a large surface area, and the best chance of absorbing as much oxygen as they can.