Let's look at the original hypotheses arising from the original question: "Does the size of the
substance affect its ability to diffuse across cell membranes?"
Small substances: If the size of a substance is important in its ability to
diffuse across a cell membrane, then small substances should be able to
freely diffuse across cell membranes.
?
Large substances: If the size of a substance is important in its ability to
diffuse across a cell membrane, then large substances should not be able
to freely diffuse across cell membranes.
?
Do the observations of H+?glucose and cortisol support the
hypotheses?
Explain your answer

The cell membrane is comprised of a phospholipid bilayer, proteins, and cholesterol. These components help the membrane to maintain its selective permeability and concentration of solutes and water.

The lipid molecules have polar hydrophilic heads and hydrophobic tails. These only readily allow for the movement of small non polar molecules. Other substances, like charged ions and large molecules require transport proteins to move in and out of the cell. Hypothesis: H+ is small and should be able to move freely through the membrane, While glucose is large and cannot move freely

Observing H+, despite being very small these cannot easily pass through the membrane. They require transport proteins called channels for their free movement or passive movement across the membrane.

For glucose, these molecules pass through specialized channels in facilitated diffusion. They move down their concentration gradient into the cell. To move out of the cell against its concentration gradient glucose requires ATP for active transport.
Cortisol, is a large steroid hormone, taken into the cell by simple diffusion across the lipid membrane, down its concentration gradient.