Monday, February 14, 2011

Movements of Substances Across the Plasma Membrane

Passive Diffusion
Simple diffusion is the movement of a substance from a region of high concentration to a region of low concentration. This is known as moving down the concentration gradient. For example; a pinch of table sugar placed at the bottom of a glass containing water will dissolve in water completely to form a solution of uniform concentration. The sugar is referred to as the solute and water as the solvent. Compounds in a tea bag placed in a cup of hot water diffuse uniformly throughout the water until the colour of the water is brown. You can also use potassium permanganate instead of tea leaves.
Diffusion is faster at high temperatures. It is also faster in gases than in liquids and is slowest in solids.

Passive diffudion

Osmosis
Osmosis is defined as the movement of water molecules from a region of higher concentration of water to a region of lower concentration of water through a semi-permeable membrane.
The plasma membrane is selectively permeable to molecules. Smaller molecules cross the cell membrane more easily than large molecules. Water, carbon dioxide and oxygen cross the membrane easily. Glucose and other large compounds are too large to cross easily.


In osmosis water moves from a region of low solute concentration to a region of high solute concentration. In the diagram above water moves from A to B through the semi-permeable membrane(SP). The glucose molecules in B are too large to pass across the semi-permeable membrane, SP and enter A. Incoming water molecules cause the level of the glucose solution in B to rise while the level of water in A drops.

Osmosis can also be demonstrated using a peeled potato. A hollow is made in a potato; the potato is placed on a petri dish containing distilled water. Sugar crystals are placed in the hollow. Twenty four hours later, it is found that the sugar crystals have formed a solution and that the water level in the petri dish has decreased because water has moved to the hollow by osmosis.
 
Types of Solutions
Most animal cells are isotonic with their environment. This means that the concentrations of the salts inside the cells are equal to the concentrations of the salts in the blood so that there is no net flow of water in either direction. A solution whose osmotic concentration is lower than the salt concentration of the blood or that of the body fluids is referred to as hypotonic. On the other hand, a hypertonic solution has a higher osmotic concentration than that of the body.

If red blood cells are placed in a hypotonic solution, water will diffuse into the red blood cells by osmosis . This water will accumulate in the cells and the cells  will expand in size and finally the cells will burst. On the other hand, if the red blood cells are put in a hypertonic solution, water will diffuse out from the cells to the hypertonic solution, causing the cells to shrink.







 
Facilitated Diffusion
Some molecules are too big to pass through the plasma membrane. In order to cross the membrane, they attach themselves to carrier proteins on the plasma membrane, which will carry them across the membrane, just as a river ferry does when it carries people with their properties across a river. Such carrier proteins transport their substances from a region of high concentration to a region of low concentration. Facilitated diffusion does not require energy.




 





 Active Transport
A cell will sometimes accumulate a certain compound at higher concentration than it is in the surrounding medium. A liver cell, for example, will continue to pick up glucose from the blood even when the concentration of glucose in the liver far exceeds that present in the blood. For human, the sodium- 
    potassium pump is a very good example to explain the active transport. Sodium ions(Na+) are pumped  
    out of te cell and the potassium ions(K+) are pumped into the cell. Energy is needed for this process in  
    the form of ATP.




The movement of charged molecules(ion) in active transport uses both a carrier protein and the energy provided by ATP to pump the molecules against the concentration gradient. Active transport is also important in nerve action, muscle contraction and kidney function. Active transport requires energy.

37 comments:

  1. In order for the cell cytoplasm to communicate with the external environment, materials must be able to move through the plasma membrane. This movement ...

    ReplyDelete
  2. http://www.youtube.com/watch?v=tK4lzxQuxTM

    ReplyDelete
  3. Hi there. I'm
    sorry to bother you but I happened to run across your blog site and noticed you're using the exact same theme
    as me. The only issue is on my website, I'm
    unable to get the page layout looking
    like yours. Would you mind emailing me at: dougdupre@gmail.com so I can
    get this figured out. By the way I've bookmarked your web
    site: http://www.blogger.com/comment.g?blogID=6357960651849162877&postID=6266223548718031955 and will certainly be visiting
    frequently. Thanks alot :)!
    Also visit my webpage :: Child Custody attorneys

    ReplyDelete
  4. It may be an additional to help you it's unlikely that any affordable overcoats brand name. Those fault lines not only pointed at Nick, but they also pointed at various sets of parents, friends, neighbors. The brand has sustained the time testing any brand goes through over the decades thanks to mouth-publicity it receives.

    My blog post: jual sweater

    ReplyDelete
  5. Xbox Live comes in two flavors, Silver and Gold, but regardless of which you choose, you
    can integrate it with Windows Live Messenger. Before you log onto Facebook to change your status to something about how you
    got reamed by Microsoft on Christmas, you need to visit and give our Godsend of
    a generator a click and get your free xbox live codes.
    One and only thing superior to System is almost certainly Console Take up residence, given it grants the opportunity to relax and play along contacts -and complete unknown
    people to from the globally.

    ReplyDelete
  6. Hello everybody....

    Thanks for your support... Really appreciate it...

    ReplyDelete
  7. Hiya. I
    was thinking about adding a website link back to your website since
    both of our websites are based around the same topic.
    Would you prefer I link to you using your site address:
    http://www.blogger.com/comment.g?blogID=6357960651849162877&postID=6266223548718031955 or website title: Blogger:
    PANITIA BIOLOGI SMKASR.
    Please make sure to let me know at your earliest convenience.
    Thanks

    my web site; View here

    ReplyDelete
  8. It's a shame you don't have a
    donate button! I'd without a doubt donate to this
    outstanding blog! I suppose for now i'll settle
    for book-marking and adding your RSS feed to my Google account.
    I
    look forward to fresh updates and will share this blog
    with my Facebook group. Chat soon!

    My homepage View Here
    My site > View my web page

    ReplyDelete
  9. In the final stages, the dimpling is obvious both when lying down and standing up.
    There are cellulite creams made with natural ingredients that
    stimulate the skin and reduce water retention beneath the skin.
    Finding a way to prevent it in the first place remains an impossibility until science can tell us where
    it comes from.

    My weblog stretch marks on biceps fast

    ReplyDelete
  10. Smartlipo laser assisted liposuction melts those stubborn pockets of fat and tightens the skin.
    It contains natural ingredients like olive oil, jojoba oil,
    and other essential oils. Many articles report eating healthy foods low in fat, but high
    in fruits, vegetables and fiber.

    Also visit my website ... how to get rid of cellulite using coffee grounds

    ReplyDelete
  11. SEM has changed into a crucial part with the public relations
    effort. The most popular backlinking approach will be to distribute content to article publication sites similar to
    Ezine - Articles. Each search engine has its own algorithms which can be rules that determine how websites
    are placed in their internet search engine rank.

    Also visit my web-site :: article builder software

    ReplyDelete
  12. I've been exploring for a bit for any high-quality articles or blog posts on this sort of space . Exploring in Yahoo I ultimately stumbled upon this web site. Studying this info So i am satisfied to show that I've a very
    just right uncanny feeling I discovered just what I needed.

    I such a lot indisputably will make sure to do not disregard this web site and
    provides it a look on a relentless basis.

    my webpage mederma stretch mark therapy reviews

    ReplyDelete
  13. Why users still make use of to read news papers when in this
    technological globe the whole thing is existing on net?


    My blog ... buy large solar panels

    ReplyDelete
  14. Definitely believe that which you said. Your favorite justification seemed to be on the web the
    easiest thing to be aware of. I say to you, I definitely get irked while people think about worries that they plainly do not know
    about. You managed to hit the nail upon the top and defined out the whole
    thing without having side effect , people could take a signal.
    Will probably be back to get more. Thanks

    Visit my website - family survival kit list

    ReplyDelete
  15. I'm amazed, I have to admit. Rarely do I encounter a blog that's both educative and
    entertaining, and without a doubt, you've hit the nail on the head. The issue is something not enough people are speaking intelligently about. I'm very happy that I
    found this in my search for something concerning this.


    Also visit my website family survival kit video

    ReplyDelete
  16. You're so awesome! I don't suppose I have read through anything like this before.

    So nice to discover somebody with genuine thoughts on this
    subject. Seriously.. many thanks for starting this up.
    This website is something that is required on the internet,
    someone with a little originality!

    Also visit my website; http://onthank.info

    ReplyDelete
  17. I believe that it would be beneficial to you if the agent had prior experiences in finding, listing, and selling properties
    in your area of interest. Indications are growing that
    investors will bring a rebirth of interest in property this
    spring. The activity can occur immediately before or after the
    meeting.

    Feel free to visit my website: vuokra-asunto lahti

    ReplyDelete
  18. This paste will be applied directly to the skin tag 3 times a
    day until the skin tag falls off. Small and soft skin growths
    acquired on the skin are called skin tags. There are a wide range of self tanners
    to choose from at department stores, but why not treat yourself to a spray tan at your nearest tanning salon.


    my blog: how to get rid of warts around fingernails

    ReplyDelete
  19. Wow that was odd. I just wrote an extremely long comment but after I clicked submit my comment didn't appear. Grrrr... well I'm not
    writing all that over again. Anyhow, just wanted to say great
    blog!

    my weblog - How to get rid of stretch marks

    ReplyDelete
  20. After I originally left a comment I seem to have clicked the -Notify me when
    new comments are added- checkbox and now whenever a comment is
    added I receive 4 emails with the exact same comment.
    There has to be a way you are able to remove me from that service?
    Kudos!

    Feel free to surf to my web page; wiki.poly.net.nz

    ReplyDelete
  21. Hi there! Do you know if they make any plugins to safeguard against
    hackers? I'm kinda paranoid about losing everything I've worked hard on.
    Any tips?

    Feel free to visit my web site; ford ranger forum

    ReplyDelete
  22. You can visit it for watching, boxing, wrestling, basketball and hockey

    my webpage - click reference

    ReplyDelete
  23. In most cases, a bad comment in your blog or post
    to their social outlets has been read by many people
    to leave. Posting an ad in the classifieds
    section would have been much cheaper for them, but no where near as effective.
    Even if you're not getting shares on Google, don't stop
    generating brand engagement and participating in conversations.


    Also visit my weblog :: http://buyfacebooklikesnow.webs.com

    ReplyDelete
  24. Hey There. I discovered your blog using msn. This is a
    really smartly written article. I will be sure to bookmark it and return
    to learn more of your helpful info. Thanks for the post. I
    will certainly comeback.

    my blog post - diet plan for women

    ReplyDelete
  25. It's enormous that you are getting ideas from this piece of writing as well as from our argument made at this place.

    My blog: www.malekith.net

    ReplyDelete
  26. Thanks for ones marvelous posting! I definitely enjoyed reading it, you will
    be a great author.I will be sure to bookmark your blog and definitely will come back down the road.
    I want to encourage one to continue your great posts, have
    a nice holiday weekend!

    My blog - getting pregnant

    ReplyDelete
  27. Yeah obviously.... That really important to use a? ipad schooling
    in primary school, secondary school and university...

    Feel free to visit my webpage - can surgery cure premature ejaculation

    ReplyDelete
  28. First off, different vaginal infections tend to have very similar symptoms, so if a woman is experiencing one
    for the first time, or is unsure about a proper
    course of treatment, she should definitely see her doctor in order to get a proper diagnosis.
    While tea tree oil is safe, as long as not used internally.
    But of course, this is not necessarily the reflect the opinion of the other people.


    My web site best yeast infection treatment

    ReplyDelete
  29. Does anyone know about Pumpkin Seed Oil benefits?
    Is it a good Primal oil?

    Also visit my webpage health cooking classes nyc

    ReplyDelete
  30. Hey there! This post couldn't be written any better! Reading through this post reminds me of my old room mate! He always kept talking about this. I will forward this article to him. Pretty sure he will have a good read. Thanks for sharing!

    Feel free to visit my homepage; viagra

    ReplyDelete
  31. You've made some decent points there. I checked on the net for more information about the issue and found most individuals will go along with your views on this web site.

    Feel free to visit my webpage :: InternetRead

    ReplyDelete
  32. Al-Mu'akh-khir (The Delayer) He Has the Power to Delay any affair that He desires. These individuals or organizations emerged from the original Brotherhood and benefited from the Saudi’s outpouring of funds. Who has created death and life that He may test you which of you is best in deed.

    Here is my web site - islamic finder seattle

    ReplyDelete
  33. Very same here, sauces have always been a mystery to me, Richard discussed it within a way even a caveman could recognize.


    Here is my blog post - why should we eat healthy food

    ReplyDelete
  34. I got this web page from my friend who informed me regarding this website
    and now this time I am browsing this web site and reading very informative
    posts here.

    Also visit my web site :: mp3 player neu

    ReplyDelete
  35. Having reаd this I thought it wаs extremelу infогmative.
    I appreciate you finԁing the time and effort to put this informative
    article tοgether. I οnce again fіnd myself ρersonally
    sρending waу too much time both reading and posting commеnts.

    Вut so ωhat, it was still worth іt!

    Look into mу pаgе - Click More

    ReplyDelete
  36. Using such power chord can help build up strength of the finger and dexterity as
    well as one's familiarity with the instrument. The new trend today in learning to play guitar is by online. This is caused by several things, most commonly because you may not be pressing hard enough.

    My site :: how to play guitar

    ReplyDelete