What are the dark, squiggly structures in the center of the cell?​

mitochondrion

Explanation:

thrombocytopenia, which is a deficiency in blood platelets, can cause bleeding and bruising in the dermis similar to senile purpura. other possible causes include: exposure to ultraviolet rays and aging skin are common causes of senile purpura. senile purpura may also be a sign of collagen loss in the skin and bones.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added