Concept:Plants lack muscles or skeletons, so they rely on cellular structures for mechanical support.
Explanation:Cell walls, made of cellulose, give each plant cell a rigid frame.
They help the plant keep its shape and resist pulling or compression forces.
Turgor pressure is the outward push of water inside the cell against the cell wall.
When cells are full of water, this pressure makes stems and leaves firm and upright.
Together, cell walls and turgor pressure provide the main support system in plants.
Answer:D. Cell walls and turgor pressure