JAMB Exam  >  JAMB Notes  >  Biology for JAMB  >  Facilitated Diffusion

Facilitated Diffusion | Biology for JAMB PDF Download

Facilitated Diffusion

As pointed out earlier, a gradient must already be present for diffusion to occur. The diffusion rate depends on the size of the substances; obviously smaller substances diffuse faster. The diffusion of any substance across a membrane also depends on its solubility in lipids, the major constituent of the membrane. Substances soluble in lipids diffuse through the membrane faster. Substances that have a hydrophilic moiety, find it difficult to pass through the membrane; their movement has to be facilitated. Membrane proteins provide sites at which such molecules cross the membrane. They do not set up a concentration gradient: a concentration gradient must already be present for molecules to diffuse even if facilitated by the proteins. This process is called facilitated diffusion.

In facilitated diffusion special proteins help move substances across membranes without expenditure of ATP energy. Facilitated diffusion cannot cause net transport of molecules from a low to a high concentration – this would require input of energy. Transport rate reaches a maximum when all of the protein transporters are being used (saturation).                  


Facilitated Diffusion | Biology for JAMBFacilitated Diffusion | Biology for JAMB


               Figure. Facilitated diffusion


Facilitated diffusion is very specific: it allows cell to select substances for uptake. It is sensitive to inhibitors which react with protein side chains. The proteins form channels in the membrane for molecules to pass through. Some channels are always open; others can be controlled. Some are large, allowing a variety of molecules to cross. The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allowing molecules up to the size of small proteins to pass through. Figure shows an extracellular molecule bound to the transport protein; the transport protein then rotates and releases the molecule inside the cell, e.g., water channels – made up of eight different types of aquaporins.


Passive symports and antiports

Some carrier or transport proteins allow diffusion only if two types of molecules move together. In a symport, both molecules cross the membrane in the same direction; in an antiport, they move in opposite directions (Figure ). When a molecule moves across a membrane independent of other molecules, the process is called uniport.


Facilitated Diffusion | Biology for JAMB

The document Facilitated Diffusion | Biology for JAMB is a part of the JAMB Course Biology for JAMB.
All you need of JAMB at this link: JAMB
224 videos|175 docs|151 tests

Top Courses for JAMB

FAQs on Facilitated Diffusion - Biology for JAMB

1. What is facilitated diffusion?
Ans. Facilitated diffusion is a process in which substances, such as ions or polar molecules, are transported across cell membranes with the help of specific transport proteins. Unlike simple diffusion, facilitated diffusion requires the assistance of these specialized proteins to move substances across the membrane.
2. How does facilitated diffusion differ from simple diffusion?
Ans. Facilitated diffusion differs from simple diffusion in that it requires the presence of specific transport proteins to assist the movement of substances across the cell membrane. Simple diffusion, on the other hand, does not require any proteins and relies solely on the concentration gradient for the movement of substances.
3. What are the transport proteins involved in facilitated diffusion?
Ans. There are two main types of transport proteins involved in facilitated diffusion: channel proteins and carrier proteins. Channel proteins form pores or channels in the cell membrane, allowing specific substances to pass through. Carrier proteins, on the other hand, bind to specific substances and undergo a conformational change to transport them across the membrane.
4. Can facilitated diffusion transport substances against their concentration gradient?
Ans. No, facilitated diffusion can only transport substances along their concentration gradient, from an area of higher concentration to an area of lower concentration. Since it does not require energy, it cannot transport substances against their concentration gradient, which would require the input of energy.
5. What factors can affect the rate of facilitated diffusion?
Ans. Several factors can affect the rate of facilitated diffusion. These include the concentration gradient of the substance, the number of available transport proteins, the affinity of the transport proteins for the substance, and the temperature. A steeper concentration gradient, a higher number of transport proteins, a stronger affinity, and an optimal temperature typically result in a faster rate of facilitated diffusion.
224 videos|175 docs|151 tests
Download as PDF
Explore Courses for JAMB exam

Top Courses for JAMB

Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

Previous Year Questions with Solutions

,

mock tests for examination

,

Facilitated Diffusion | Biology for JAMB

,

past year papers

,

pdf

,

MCQs

,

Objective type Questions

,

Exam

,

study material

,

Sample Paper

,

shortcuts and tricks

,

ppt

,

practice quizzes

,

Facilitated Diffusion | Biology for JAMB

,

Important questions

,

Semester Notes

,

Summary

,

Viva Questions

,

Extra Questions

,

Facilitated Diffusion | Biology for JAMB

,

video lectures

,

Free

;