Cell transport is useful because it's, essentially, the movement of cells across the blood/veins. Active transport uses energy, while passive transport does not.
I’m not sure if that’s the answer but what immediately pops up in my mind is the food chain. Primary consumers (herbivores) consume producers (plants). Secondary consumers consume primary consumers etc. At the end of the day, all kinds of animals die and decompose, providing nutrients for producers to grow, continuing the circle of life.
Lion is a top predator that hunts secondary consumers. Simba’s father died and contribute to the circle of life. I hope it gave you some pointers!
Answer:
d. cells
cardiac tissue are made up of cells.