Question: Why are blood cells red


  1. Hi @choclava, interestingly, not all blood cells are red! There are white and red blood cells.

    The red ones (also known as erythrocytes) are the most common and really important for transporting oxygen around our bodies. The are red because they contain haemoglobin, an iron-containing biomolecule that can bind oxygen. The iron component gives them their colour (we have farms near me that have iron-rich earth and it’s bright orange-red in colour – as is rust – for the same reason!).

    The white blood cells (leukocytes) are cells of the immune system involved in defending the body against both infectious disease and foreign materials.


  2. Hey @choclava,

    Mia’s got that one covered. But here’s something a little different.
    Not all animals have red blood.

    There are a family of fish called ‘Channichthyidae’ also known as white blooded fish that live in reaaaaly deep cold waters around Antarctica. Their blood contains no haemoglobin (which makes everyones blood red). They can absorb oxygen straight into their body, which isn’t very efficient but seems to work for them.

    Some animals can have blue blood as well (scorpions, crabs, butterflies, and the octopus). Instead of using haemoglobin which is red, they use haemocyanins which is clear when empty and blue when it carries oxygen. Haemoglobin is red because of the iron, and haemocyanin is blue because of 2 copper atoms.