Carbohydrates - Welsh Government



Cell Membranes and Transport

This PowerPoint presentation coincides with the following section of the BY1 specification for the Biology and Human Biology AS courses. The relevant section of the Teacher’s Guidance material follows, together with some explanatory notes.

Specification:

The principal components of the plasma membrane and the fluid mosaic model. Factors affecting permeability of the membrane.

Teacher’s Guidance Notes:

▪ The principal biochemical constituents of the cell membrane are protein and phospholipid.

▪ The phospholipid molecules are arranged as a bilayer with hydrophilic heads and hydrophobic tails.

Explanatory Notes

This PowerPoint presentation may at first seem abstract. It is meant as a tool for the teacher to illustrate the nature of the phospholipid molecule and how it behaves around water.

|Slide |Notes |

|[pic] |The green sphere represents the phosphate and is the ‘head’ |

| |component of the phospholipid. The yellow rods represent two fatty |

| |acid molecules and constitute the ‘tail’ component. This is the |

| |format used throughout the presentation. |

|[pic] |A diving board scenario is used to introduce the student to the |

| |concept of hydrophilic and hydrophobic. The molecule is seen diving |

| |head first into water and this merits 10 marks. The subsequent slide|

| |shows a feet first dive which gets 0 marks. The diver turns head |

| |down in the water to get the 10 marks again. |

|[pic] |This slide sees many molecules diving off the board in turn, to form|

| |a monolayer with hydrophobic tails pointing up and the hydrophilic |

| |heads pointing down into the water One click is sufficient to see |

| |the whole slide develop. |

|[pic] |This next slide demonstrates what happens when this type of molecule|

| |is added to water, the non-polar tails of the molecules clump into |

| |the centre of a ball like structure, called a micelle, because they |

| |are hydrophobic or "water hating". The polar head of the molecule |

| |faces the water molecules on the outside of the micelle. |

|[pic] |This final slide shows the arrangement of two layers, two molecules |

| |thick, forming a bilayer, with their hydrophobic tails pointing |

| |inwards away from the water both inside and outside the cell. |

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