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In this chapter of IBDP Biology, we will learn the structure and functions of cell membrane.
Structure and functions of cell membrane
- When it comes to IBDP Biology, the cell membrane consists of phospholipids bilayer with proteins floating in it.
- Their hydrophilic heads are in contact with watery exterior or water interior.
- The hydrophobic tail regions in the centre of the membrane, away from water.
- Channel protein has pores and allows ions to pass through.
- Carrier proteins change their shape to carry specific molecules across the membrane.
Other proteins may be attached to the carrier proteins and function as enzymes, antigens or receptors sites for complementary-shaped signalling chemicals such as hormones.
- Eukaryotic cell membrane contains cholesterol; it regulates the fluidity of the membrane, maintains mechanical stability and resists the effects of temp changes on the structure of the membrane.
Diffusion
- When it comes to IBDP Biology, Simple Diffusion: small, hydrophobic and non-polar.
- Facilitated diffusion: large, charged, hydrophilic and polar. This is the transport of substances across a membrane by a trans-membrane protein molecule. This is a passive process and moves down the concentration gradient.
- Osmosis: diffusion of water molecules through a partially permeable membrane.
Osmosis is the diffusion of water through a partially permeable membrane. It is a special case of diffusion in that the concentrations of solutes in the water can effect how it occurs.
Active Transport
- Active Transport involves the movement of molecules across a membrane using proteins in the phospholipids bilayer similar to carrier proteins. These use energy in the form of ATP to 'pump' molecules in one direction across a membrane
- Active Transport means that a substance can move against the concentration gradient and at a much faster rate than Diffusion alone.
Factors that affect the rate of simple diffusion
When it comes to IBDP Biology, factors are
- Temperature: as it increases, molecules get more kenetic energy so the rate of diffusion increases
- Diffusion distance: the thicker the membrane the slower the rate of diffusion
- Surface area: more diffusion happens in larger surface area, cells specialised for absorption has micro villi
- Size of diffusion molecule: smaller ions/molecules diffuse more rapidly than larger molecules
- Concentration gradient: the steeper this gradient, the faster the diffusion to the side where there are fewer molecules, down the gradient.
This is the end of the topic
