Answer:
I believe the awnsner is medicine. ((Not completely sure))
Explanation:
I think so because medicine is usually used to help defeat a sickness and not as much as repairing something that's wrong.
They have different types of cell walls and cell membranes.
Answer:
they need a high ‘surface to volume’ ratio, which is good for exchanging materials between the inside and outside of cells. But this is probably not really the size-limiting reason, since cells vary enormously in size and surface area to volume ratios.
Explanation:
The right answer is vein (it contains blood and has valves).
The infra-cardiac veins of small and medium caliber possess this system of fight against gravity. The valves consist of a dense connective tissue, surmounted by endothelial cells, corresponding to a fold of the intima. They allow blood circulation in the sense organ / heart but prevent venous reflux.
