Question
Differentiate between arteries and veins with respect to their structure, function, and the type of blood they carry.
(NCERT Class 7, Chapter 11 — Transportation in Animals and Plants)
Solution — Step by Step
| Feature | Arteries | Veins |
|---|---|---|
| Direction of blood flow | Away from the heart | Towards the heart |
| Type of blood | Usually oxygenated (except pulmonary artery) | Usually deoxygenated (except pulmonary vein) |
| Wall thickness | Thick, muscular, elastic | Thin, less muscular |
| Lumen (inner space) | Narrow | Wide |
| Valves | No valves | Have valves to prevent backflow |
| Blood pressure | High pressure | Low pressure |
| Pulse | Can be felt (wrist, neck) | Cannot be felt |
| If cut | Blood spurts out | Blood flows out steadily |
Arteries carry blood pumped directly from the heart at high pressure. Their thick, elastic walls can stretch and recoil with each heartbeat — that’s what you feel as your pulse.
Veins carry blood back at low pressure. Since the pumping force has weakened by this point, veins have valves — small flaps that prevent blood from flowing backwards due to gravity. This is especially important in the legs, where blood must travel upward.
- Pulmonary artery — carries deoxygenated blood from the heart to the lungs
- Pulmonary vein — carries oxygenated blood from the lungs to the heart
So arteries and veins are defined by direction (away from / towards heart), NOT by the type of blood they carry.
Why This Works
The circulatory system is a closed loop. The heart pumps blood out through arteries, it reaches the organs through tiny capillaries (where exchange of gases and nutrients happens), and then returns through veins. Each vessel type is designed for its specific job.
The key insight is that “artery” and “vein” refer to the direction of flow relative to the heart, not the oxygen content. Once you understand this, the pulmonary exceptions make perfect sense — the pulmonary artery goes away from the heart (so it’s an artery), even though it carries deoxygenated blood.
Alternative Method — Remember with a trick
A for Artery = Away from heart. V for Vein = Valves present. For the exceptions, remember: pulmonary circuit is “opposite land” — arteries carry deoxygenated blood, veins carry oxygenated blood.
Common Mistake
The most common error in exams: writing “arteries carry oxygenated blood and veins carry deoxygenated blood” as a universal rule. This earns partial marks at best, because the examiner expects you to mention the pulmonary exceptions. Always add “except pulmonary artery/vein” to score full marks on this question.