1. Unit 2 2.1 Metabolic Pathways & their Control
Higher Biology
Unit 2
2.1 Metabolic Pathways & their Control

2. National 5 Revision
Think! With your group, write down everything you remember on the structure and function of the cell (plasma) membrane. Now “carousel”. Try to find additional information from the other groups to take back to your group.

3. National 5 Revision
Now watch a short video clip on cell membranes. How much did you remember?

4. National 5 Revision
The cell membrane controls the entry and exit of substances into and out of the cell.
It is composed of a double layer of phospholipids, with proteins embedded within it or attached to it.
Phospholipid
bilayer
Protein

5. National 5 Revision
The phospholipid bi-layer keeps the membrane fluid and flexible.
The cell membrane is selectively permeable.
This means that small molecules such as glucose can pass through the membrane freely whilst large, insoluble molecules e.g. starch cannot.
Proteins in the membrane are involved in transport.

6. National 5 Revision
The three methods of transporting molecules through the membrane are;
Diffusion – molecules move down a concentration gradient (from high to low concentration). No energy required.
Osmosis – diffusion of water molecules.
Active transport - molecules move up a concentration gradient (from low to high concentration).

7. Membranes
The cell membrane forms a boundary between the cell and its external environment.
It has the function of transporting materials into and out of the cell.
Membranes help to regulate metabolism in a cell.

8. Membranes Organelles within the cell are bound by membranes
This keeps metabolites;
close together for reactions
separated (digestive enzymes would damage the cell)

9. Membranes Some organelles have folds in their inner membranes.
These provide a large surface area for reactions.
They also form small compartments that localise metabolic pathways.

10. Membranes & Reaction Rates
These small compartments create a high surface area : volume.
This allows high concentrations of enzymes and substrates to be kept close together, resulting in faster reaction rates.

11. Membrane Proteins
Different proteins in the membrane have different functions.
For metabolism, there are proteins for;
Pores
Enzymes
Pumps

12. Pores
Protein pores allow ions and molecules to move passively across the membrane.
These channel-forming proteins allow the transport of specific substances, making the membrane selectively permeable.

13. Enzymes Some membrane proteins act as enzymes to catalyse reactions.
An example of this is the enzyme ATP synthase, which is used to produce ATP.

14. Pumps Protein pumps in the membrane are involved in active transport.
This is the movement of molecules and ions against a concentration gradient.
Protein pumps require energy from ATP for this.
This means factors that affect the rate of respiration will also affect the rate of active transport.

15. “What do you mean, I need ATP? I thought you said a tepee.”
Pumps
Limiting factors of respiration include;
temperature
concentration of oxygen
concentration of glucose
“What do you mean, I need ATP? I thought you said a tepee.”

16. Sodium-potassium Pump
An example of a protein involved in active transport is the sodium- potassium pump.
Sodium ions are actively pumped out of the cell.
Potassium ions are actively pumped in.
Sodium
Potassium

17. Key Points Membranes form compartments to localise metabolism.
Compartments allow high concentrations of metabolites and high reaction rates.
Proteins embedded in phospholipid bilayers have functions such as pores, pumps and enzymes.

18. Questions Give two examples of organelles bounded by membranes.
Explain the advantage of membrane-bound compartments in cells.
Give two roles of proteins embedded in phospholipid membranes.

19. Describe how temperature & oxygen concentration affect the rate of sodium ion transport across the membrane.
Explain why transport of sodium ions is associated with a decrease in glucose concentration.

20. Extended Answer Question
Write notes on each of the following;
metabolic pathways 4 marks
the functions of membranes 5 marks