Hemoglobin is a molecule with a central iron atom responsible for carrying oxygen in your blood cells, as a result, when an oxygen atom bonds to the iron atom, hemoglobin causes the blood to appear bright red (think of it like iron rusting due to exposure to oxygen).
Veins appear blue due to how light reflects off of the various tissues but our blood is NOT blue when it isn't exposed to oxygen.
Arteries have oxygen-rich blood and veins have oxygen-poor blood. Veins carry blood toward the heart and arteries carry blood away from the heart. You can remember this easily because our cells need oxygen and, because arteries carry oxygen-rich blood, they are responsible for carrying blood away from the heart to the different parts of our bodies.
Veins carry the oxygen-depleted blood back toward the heart so it can become oxygen-rich again.
It's the coordinated/directed movement towards the direction of light. Light is the stimulus
Answer: the nucleus
Because it contains protons and neutrons whose mass is too much when compared to electrons.
Hope this helps ʕ•ᴥ•ʔ
