Which structure controls the movement of substances into and out of the cell?.

the membrane

Explanation;

Every cell in the body is enclosed by a cell (Plasma) membrane. The cell membrane separates the material outside the cell, extracellular, from the material inside the cell, intracellular. It maintains the integrity of a cell and controls passage of materials into and out of the cell.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.