Lobsters have a different respiratory pigment from humans; what is the typical color of lobster blood when it is oxygenated?

Introduction / Context:
Different animals use different respiratory pigments to transport oxygen in their body fluids, and these pigments give the blood or hemolymph characteristic colors. Humans are familiar with red blood due to hemoglobin, but many invertebrates use other pigments. This question focuses on the color of lobster blood and tests your knowledge of comparative physiology and respiratory pigments.

Given Data / Assumptions:

• The organism of interest is the lobster, a marine crustacean.
• The question asks about the color of lobster blood when oxygenated.
• Options include blue, red, white, colourless, and green.
• We assume normal, healthy lobsters with typical respiratory pigments.

Concept / Approach:
In humans and many vertebrates, the respiratory pigment is hemoglobin, an iron containing protein that gives blood a red color when oxygenated. In many arthropods and molluscs, including lobsters, the respiratory pigment is hemocyanin, which contains copper instead of iron. When hemocyanin is oxygenated, it gives the hemolymph a blue color. In deoxygenated form, it can appear more colorless or pale. This difference in metal ion and pigment structure explains why lobster blood is typically described as blue rather than red.

Step-by-Step Solution:
Step 1: Recognise that lobsters are crustaceans, not vertebrates like humans. Step 2: Recall that many crustaceans use hemocyanin as their respiratory pigment instead of hemoglobin. Step 3: Understand that hemocyanin contains copper ions that bind oxygen. Step 4: Note that when hemocyanin is oxygenated, the copper oxygen complex appears blue in color. Step 5: Contrast this with hemoglobin, where iron oxygen complexes give blood a bright red color when oxygenated. Step 6: Conclude that the best description of lobster blood color is blue.

Verification / Alternative check:
Marine biology references state that lobsters and many other crustaceans have blue blood due to the presence of hemocyanin in their hemolymph. Photographs and descriptions from scientific sources and aquaculture texts refer to the blue tinted fluid seen when these animals are injured. This contrasts with the red blood of fish and mammals, confirming that blue is the correct answer for lobsters.

Why Other Options Are Wrong:
Red: Typical of vertebrates that use hemoglobin, not of lobsters that use hemocyanin. White: Not a standard description for lobster blood and does not match the known pigment color. Colourless: While deoxygenated hemocyanin can look pale, the characteristic oxygenated color is blue. Green: Green blood is associated with some annelids or other pigmented fluids but not with lobster hemolymph.

Common Pitfalls:
Students may assume that all animals have red blood because that is what they are most familiar with in humans and many vertebrates. Another confusion arises from images of cooked lobster meat, which is red due to heat stable pigments in the shell, not due to blood color. To avoid error, remember that lobsters and many other arthropods rely on copper based hemocyanin, which gives a blue color when oxygenated.

Final Answer:
Oxygenated lobster blood is typically blue because it contains the copper based pigment hemocyanin.