Why is mitochondria different in the cells of older people ?

Water changes bacteria in the soil converts this nutrient into a usable form. plants take up the usable nutrient through the soil and assimilate it into proteins, making it part of the plant. an animal eats the plants, and the nutrient becomes part of the animal. when the animal dies, it decomposes, returning the nutrient back to the soil. which cycle is being described? water cycle carbon cycle nitrogen cycle phosphorous cycle