Ib Biology Topic Notes

Topics: Cell membrane, Cell, Membrane biology Pages: 3 (822 words) Published: January 27, 2013
2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.

Phospholipid molecules make up the cell membrane and are hydrophilic (attracted to water) as well as hydrophobic (not attracted to water but are attracted to other hydrophobic tails). They have a hydrophilic phosphate head and two hydrophobic hydrocarbon tails. Cell membranes are made up of a double layer of these phospholipid molecules. This is because in water the hydrophilic heads will face the water while the hydrophobic tails will be in the center because they face away from the water. The phospholipid bilayer makes the membrane very stable but also allows flexibility. The phospholipid in the membrane are in a fluid state which allows the cell to change it’s shape easily.

2.4.3 List the functions of membrane proteins.

Membrane proteins can act as hormone binding sites, electron carriers, pumps for active transport, channels for passive transport and also enzymes. In addition they can be used for cell to cell communication as well as cell adhesion.

2.4.4 Define diffusion and osmosis.

Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.

2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion.

Membranes are semi-permeable which means that they allow certain molecules through but not others. The molecules can move in and out through passive transport which is a method that does not require any input of outside energy. It can either be done by simple diffusion or facilitated diffusion. Molecules will go from a region of high concentration to a region of low concentration as they move randomly and eventually become evenly...
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