1. 2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion (3).

2. Some molecules are so small that they pass through the membrane with little resistance This includes Oxygen and Carbon Dioxide Lipid molecules (even though very large) pass through membranes with very little resistance also.

4. Larger molecules (red) move passively through the membrane via channel proteins These proteins(grey) have large globular structures and complex 3d-shapes The shapes provide a channel through the middle of the protein, the 'pore' The channel 'shields' the diffusing molecule from the non-charged/ hydrophobic/ non- polar regions of the membrane.

5. 2.4.6 Explain the role of protein pumps and ATP in active transport across membranes(3).

6. Explain means to give a detailed account of causes, reasons or mechanisms. Molecules are moved against the concentration gradient from a region of their low concentration to a region of their high concentration. Active mean that the membrane protein 'pump' requires energy (ATP) to function The source of energy is ATP is produced in cell respiration Transported molecules enter the carrier protein in the membrane. The energy causes a shape change in the protein that allows it to move the molecule to the other side of the membrane.

7. Sodium and potassium pumps

8. The sodium-potassium, pump that creates electro-chemical gradient across the cell membrane of all cells. Cells are -ve charged on the inside relative to the outside. This pump is modified in the nerve cell to create some of the electrochemical phenomena seen in nerve cells

9. 2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane(3).

10. Cells will manufacture molecules for secretion outside of the cell. Some of these secretion molecules are complex combinations of proteins, carbohydrates and lipids. The base protein is coded for by a gene whose expression begins the process.

11. Protein is already synthesised and present in the rER. The protein is moved through the rER and modified. A spherical vesicle is formed form the end of the rER with the protein inside. The vesicle migrates to the golgi apparatus. Vesicle and golgi membranes fuse. The protein is released into the lumen of the golgi apparatus. The golgi modifies the protein further by adding lipid or polysaccharides to the protein. A new vesicle is formed from golgi membrane which then breaks away. The vesicles migrates to the plasma membrane. The vesicle migrates to the plasma membrane fuses and secretes content its contents out of the cell. A process called exocytosis.

12. Exocytosis and endocytosis animation http://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535:: 535::/sites/dl/free/0072437316/120068/bio02.s wf::Endocytosis%20and%20Exocytosis http://www.youtube.com/watch?feature=player _detailpage&v=K7yku3sa4Y8

13. Homework Samples of 5 plant tissue discs were incubated in dilute sodium chloride solutions at different temperatures. After 24 hours, it was found that the uptake of ions from the solutions was as follows.(arbitrary units). Comment on how absorption of sodium chloride occurs, giving your reasons. Sodium ionsChloride ions Tissue at 5 o C8040 Tissue at 25 o C16080