Crossing membranes - Passive processes
- Created by: Steff06
- Created on: 04-04-16 14:40
View mindmap
- Passive processes - Diffusion
- Diffusion:
- Molecules possess KINETIC ENERGY. Processes such as diffusion only depend kinetic energy are known as PASSIVE processes.
- The movement of molecules from a region of HIGH concentration to a region of LOW concentration of that molecule DOWN a concentration gradient.
- In diffusion, molecules are distributed EVENLY. When even, the molecules continue to move around. The state where there is no overall movement is known as EQUILIBRIUM.
- In living organisms, activities + features ensure equilibrium is NOT reached. E.g CO2 in photosynthesis maintained at conc gradient.
- Molecules continue to diffuse down their conc gradient without using energy from the cell. RATE of diffusion is affected by a number of processes.
- Factors affecting diffusion:
- TEMPERATURE: INCREASING temp increases kinetic energy. Rate of RANDOM movement increases as does rate of diffusion.
- SIZE of molecule: SMALLER molecules diffuse FASTER than larger ones.
- CONC GRADIENT: More molecules on 1 side increases con gradient which increases rate of diffusion.
- STIRRING/MOVING: Stirring a liquid/movement increases movement of molecules/rate of diffusion.
- SURFACE AREA: GREATER SA = diffusion occurs more rapidly. Cells are adapted to increase SA. E.g. red blood cells are biconcave, alveoli increase SA in lungs.
- DISTANCE/THICKNESS: Diffusion is SLOWER with THICK membranes as there is a greater distance for molecules to travel.
- TEMPERATURE: INCREASING temp increases kinetic energy. Rate of RANDOM movement increases as does rate of diffusion.
- LIPID-BASED molecules:Fat-soluble molecules can pass through the bilayer, diffusing down a conc gradient. Steroid hormones are lip-based and so diffuse through membranes.
- Very SMALL molecules and ions: CO2 and O2 are small enough to pass through the bilayer. Water molecules are very small so some can pass directly through the membrane even though they are polar (charged).
- LARGER/CHARGED molecules: Small, charged molecules e.g. sodium/glucose cannot pass through the lipid bilayer. Channel proteins/carrier proteins allow these substances through the membranes. Diffusion of these molecules is known as FACILITATED DIFFUSION.
- Very SMALL molecules and ions: CO2 and O2 are small enough to pass through the bilayer. Water molecules are very small so some can pass directly through the membrane even though they are polar (charged).
- CHANNEL proteins: Form PORES in the membrane shaped to only allow 1 type of ion through. They are GATED so can be opened/closed.
- CARRIER proteins: Shaped so that a SPECIFIC molecule e..g glucose can fit into them at the membrane surface. When the specific molecule fits, the protein changes shape to allow the molecule through to the other side.
- SIMPLE diffusion: Gases e.g. CO2/O2, lipid-based like steroid hormones.
- FACILITATED diffusion using CHANNEL proteins: e.g. sodium and calcium ions.
- FACILITATED diffusion using CARRIER proteins: e.g. larger molecules like glucose and amino acids.
- Diffusion:
Similar Biology resources:
Teacher recommended
Comments
No comments have yet been made