英語聽力文摘682 昆蟲血為何是綠色或黃色
You’ve probably heard someone use the phrase “blood red,” but have you ever wondered if all blood really is red? For example, think about the bugs you’ve seen splatter against your car’s windshield, leaving behind a clear, yellowish, or greenish liquid. That liquid, is hemolymph, or insect blood.
Insect Blood
The blood of an insect functions differently than the blood of a human. In humans, blood gets its red color from hemoglobin, which travels through blood vessels carrying oxygen from the lungs to the rest of the body. Insect blood, however, does not carry gasses and has no hemoglobin. Instead, bugs have a system of tubes that transport gasses directly between their cells and the outside air.
In fact, insects don’t even have blood vessels. Instead there is a hollow space inside their external skeleton in which their blood oozes around. This cavity extends to the antennas, legs, and wing veins. The bug’s heart, a long tube that stretches the length of its body, pushes the blood from the rear end of the insect on forward. The bug may also have little hearts at the ends of its extremities to help move the blood along.
Pigment
Pumping blood is a slow process: it takes about eight minutes for an insect’s blood to circulate completely. Like human blood, bug blood carries nutrients and hormones to the insect’s cells. The greenish or yellowish color of insect blood comes from the pigments of the plants the bug eats.
