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Module 1: Cells
1.1.2 Cell Membranes
(a) outline the roles of membranes within cells and at the surface of cells

Membranes at the SURFACE of cells (Plasma Membranes WITHIN cells
Membranes)
controls which substances enter and leave the separates organelles from the cytoplasm
cell controls which substances enter and leave…

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Module 1: Cells

(d) describe the roles of components of the cell membrane:

Molecule Structure Function
Stability Cholesterol Small, steroid molecules, Binds to the hydrophobic tails,
longer than they are wide causing them to pack more
Hydrophobic fit between closely together makes the
fatty acid tails membrane less fluid and…

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Module 1: Cells
Increasing the temperature gives the molecules more kinetic energy, so
they move faster, making the membrane 'leaky' and more permeable



Temperature above 45oC The phospholipid bilayer starts to melt (break down) and the membrane
becomes more permeable
Channel proteins and carrier proteins in the membrane denature so…

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Module 1: Cells
acting as antigens on the surface of cells. Cells of the immune system have receptors that detect the
glycoproteins and can determine whether they are 'self' or 'non self'

Many drugs work by binding to receptors in cell membranes. They either trigger a response in the cell,…

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Module 1: Cells

























Active Transport:
Protein 'Pumps' Bulk Transport
A molecule attaches to the carrier protein, the Bulk transport is possible because membranes can
protein changes shape and this moves the easily fuse , separate and 'pinch off'
molecule across the membrane releasing it on the Energy is needed in…

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Module 1: Cells






























(i) explain what is meant by osmosis, in terms of water
potential

Osmosis is the movement of water molecules by diffusion from a region of high water potential to a region of
low water potential across a partially permeable membrane

Water potential is a measure of the…

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Module 1: Cells
















In pure water, water moves into a cell by osmosis down a water potential gradient.

Animal Cell becomes haemolysed (bursts open)
Plant Cell the cell wall prevents bursting. The membrane pushes against the cell wall and the cell
becomes turgid

In a very low water potential solution…

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