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Answer: (b) Cholesterol</h2>
Explanation:
As the name suggests, cholesterol is a sterol (a modified steroid). It is biosynthesized by animal cells.
The four important characteristics of respiratory surface are:
1. Thin walls
2. Moisture
3. Large surface area
4. Blood supply
Respiratory system or respiratory tract is divided into upper and lower tract. Upper respiratory tract includes nose and its cavities, sinuses, pharynx and the part of the larynx. Lower respiratory tract consists of the trachea, bronchi, bronchioles and the alveoli.
Alveoli are the ends of the respiratory tract the smallest units in it. Alveoli are small folded air sacs that are branching off from alveolar ducts and providing an extremely large surface area for the gas exchange. Gas exchange occurs thanks to small blood vessels – capillaries that surround alveoli and it occurs via the process of diffusion.
So, respiratory surface is thin membrane also known as the blood–air barrier that consists of the alveolar epithelial cells, their basement membranes and the endothelial cells of the alveolar capillaries.
Answer:
because they have thicker walls
Explanation:
blood is punped our of the heart very fast which means it would need a blood vessel witch thick walls to withstand the pressure. thin walls would cause the blood vessle damage and may evwn break as it wouldn't be able to withstans the pressure.
