The cell was placed in a hypertonic solution. Glucose is a monosaccharide while starch is a polysaccharide. The concentration on the outside is higher compared to that on the inside. The cells have cell membrane that is semi-permeable.
Movement of molecules is dependent on the concentation gradient. However, the size of molecules determine the diffusion rate. Small and light molecules diffuse faster than large and heavy molecules thus glucose diffused faster than starch.
The cell membrane being permeable suggested that it allows molecules of small sizes to pass but not large ones.
