1. The membranes of all organelles, including the cell surface membrane, consist mainly of one type of lipid. Name this lipid.
Answer
Phospholipid.
2. Name five ways that molecules can move across a membrane.
Answer
Simple diffusion, facilitated diffusion, osmosis, active transport,
3. Give four factors that affect the rate of diffusion.
Answer
Temperature, surface area, concentration gradient, thickness of exchange surface.
4. What properties would a molecule have that would make it able to cross the phospholipid bilayer by facilitated diffusion ?
Answer
Polar, large, water soluble.
5. The figure below shows the movement of two different molecules, A and B, across the cell surface membrane. Name the process by which the molecules are moving across the membrane in each line.
Answer
A = facilitated diffusion,
6. Describe and explain the shape of line A.
Answer
As the concentration of surrounding molecules increases, the rate of movement across the membrane also increases, up until a point where it remains constant. This because all the transport proteins are being used and have become the limiting factor.
7. Describe and explain the shape of line B.
Answer
As the concentration of surrounding molecules increases, the rate of movement across the membrane also increases. Does not reach a maximum as does not involve transport proteins, so is not limited by this.
8. Explain which line would represent the movement of amino acids, ions and carbon dioxide.
Answer
Line A represents the movement of amino acids and ions because they require transport proteins to cross the membrane. Line B represents the movement of carbon dioxide because gases are small and lipid‑soluble, allowing them to move across by simple diffusion.