On Earth, there are creatures with red, blue, green, and yellow blood

Blood, the life-sustaining fluid that circulates through the bodies of animals, is commonly associated with the color red. However, the natural world is full of surprises, and blood can appear in a variety of colors depending on its chemical components.

On Earth, there are creatures with red, blue, green, yellow, and even purple blood, each color revealing fascinating insights into the diversity of life and the biochemical adaptations that different species have evolved.

Red Blood: The Iron Connection

The most familiar color of blood, red, is found in most vertebrates, including humans. This coloration is due to the presence of hemoglobin, a protein that contains iron and is responsible for oxygen transport. Hemoglobin binds with oxygen in the lungs and carries it to tissues throughout the body, turning bright red when oxygenated and a darker red when deoxygenated.

Blue Blood: The Copper Connection

In contrast, many invertebrates, such as octopuses, squids, crustaceans, and spiders, have blue blood. This is due to the presence of hemocyanin, a copper-containing protein that also serves as an oxygen carrier. When hemocyanin binds with oxygen, it turns blue, providing these animals with a means to transport oxygen efficiently in their often cold and low-oxygen aquatic environments.

Green Blood: The Chlorocruorin Connection

Some worms and leeches possess green blood, thanks to a different oxygen-carrying molecule known as chlorocruorin. This iron-based protein is chemically similar to hemoglobin but imparts a green color to the blood when it binds with oxygen. Chlorocruorin is particularly effective in the low-oxygen environments where these creatures often live.

Yellow Blood: The Vanabin Connection

Yellow blood is found in certain insects, ascidians (sea squirts), and sea cucumbers. This coloration comes from vanabin, a protein that binds vanadium. While the exact function of vanabin in these animals is still not fully understood, it highlights the remarkable biochemical diversity that exists in nature.

Purple Blood: The Hemerythrin Connection

A few species of marine worms have purple blood, colored by hemerythrin. Unlike hemoglobin and hemocyanin, hemerythrin does not contain heme groups but instead relies on iron to bind oxygen. This protein turns a striking purple when oxygenated, adding to the spectrum of blood colors found in the animal kingdom.

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