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So we should now have an idea about most of the main structures of a cell. Remember our factory analogy = around the outside is the fence = controls what gets in and out. Its the same with cells the membrane controls what gets in and out - cells need supplies, - raw materials to do what they do. Plus as they exist in a liquid environment water is really important along with all the things that are dissolved in it.
You may need to go back and remind your self about the plasma membrane structure = it will help.
Step 1(a) : First thing to realise is that not everything gets across the membrane = its "choosey" about what gets across. The technical description is "Selectively Permeable". Here is a "plain English" translation of what that looks like. (Learn)
Step 1(b) : Now some things can just move happily across the membrane without any help = passive transport. While others need a push = active transport.
Here is this explained with pictures to help ..... (Learn)
Step 1(c) : What about the things that need help - active transport that requires energy. How does that happen?
These next clips show you how that can be done. (Learn)
Mission 1 : Have you passively absorbed the information or is it requiring a bit of active help? See how you get on with the introduction questions on cell transport. (Learn)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Step 2 : Time for a closer look at these processes - we'll start with the simplest - Diffusion. We have all experienced the effects of diffusion ......
Need a reminder? Have a look a what was covered back in Yr 9 (Learn)
Mission 2 : Can you define diffusion in plain non science speak English? (Learn) (Share)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Challenge 1 : Observing diffusion - you can do this in the lab at school or you can also try this at home by using a drop of food colouring in a bowl of water - what is your hypothesis about what the difference will be between hot and cold water?
If you need to remember Particle Theory - go and have a look at your Yr 11 Science work on Chemistry .... in particular the Rates of Reaction stuff .... this video might help too. (Learn) (Create) (Share)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Step 3 : So which way does diffusion go, how does it know to go in or out of the cell? Does it know?
It all depends on what we call the "concentration gradient" = think of it as the "slope" that diffusion travels down. A steep slope = a steep gradient = diffusion happens faster.
Maybe its easier to watch in action ..... (Learn)
Mission 3 : Now that your fish are healthy see how you get on with the questions on concentration gradient. (Learn)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Step 4 : What about those molecules that don't need extra energy = move by passive transport - but are too big to, or they are an ion whose charge prevents them simply diffusing across the membrane. They get a bit of help from some channels formed in the membrane by proteins = their transport is called "facilitated" diffusion.
Smell the cooking? = diffusion - but how do large molecules like sugars get into you cells - by getting some help from channel or carrier proteins. Have a look and see how this is done. (Learn)
Mission 4 : How did you get on absorbing that information? See how you did b completing the questions on facilitated diffusion. (Learn)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Step 5 : So when is diffusion not diffusion?? ...... When its Osmosis. Osmosis is the diffusion of water across the semi-permeable membrane. It always goes from an area of high water concentration to an area of low water concentration. Until it reaches equilibrium.
The tricky part is that sometimes the concentration of water is affected by what and how much is dissolved into it - for example 100ml of sugary water will have a lower water concentration than 100ml of pure water.
Its easier to watch happen ..... (Learn)
Mission 5 : Did you "Osmose" that?? Check your knowledge by completing the Osmosis questions in your workbook. (Learn)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Step 6 : Now it gets tricky - you should by now, I hope, be familiar with what a concentration gradient is. With osmosis this concentration gradient becomes called "water potential". Think of it as the potential for water to move from one side of the membrane to the other. We just have to figure out which way its going to go - or its "Tonicity"
Water will always move from an area of high water concentration (or water potential) to an area of lower water concentration (or water potential).
Bring on the terms hypertonic (or high), hypotonic (or low) and isotonic (or the same). The tricky bit is that these terms refer to what is dissolved in the water = a hypertonic solution means it has a high concentration of solute - the stuff dissolved - it actually has a low concentration of water = low water potential.
Maybe its better to see this in action .... (Learn)
Mission 6 : Soaked all that up? Brains about to under go "lysis"? Let the knowledge pressure out onto paper by reading and completing the tonicity and tonicity and cells pages in your workbooks. (Learn)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Challenge 2 : We are going to do this as part of an internal assessment - so finish off this cell transport section and then go here ..... but save these pages as they will be REALLY useful .....
https://sites.google.com/hornby.school.nz/kascience/yr-12-biology/osmosis-process-a-s-91153-bio-2-1-int-practical-investigation (Learn) (Create) (Share)
Step 7 : Now its time to get active - this is where the cells spends some energy (remember that ATP thingy) to get what it needs into,or out of the cell. Sometimes it is because the ion or molecule can't get through the membrane and facilitated diffusion won't work for the particular molecule or ion. Or the cell is moving the particles, whatever they are, against the concentration gradient - think biking up hill - it takes energy.
We've all ready bumped into how this is done - carrier molecules (but needing energy to get them to function) or one of the cytosises ( Pinocytosis, Phagocytosis etc)
Here is a reminder to activate you. (Learn)
Mission 7 : Lets see how you got on - was the information passively or actively absorbed - will it take energy to re-emerge as you answer the questions on active transport with regard to carrier proteins and cytosis. (Learn)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Challenge 3 : So why are cells small (and whales big) ??? I hope we can carry out this practical in the lab - but if not here is an example of what we are looking for - but in reverse (check the reactants used with the agar blocks)
Watch the video ..... Then
If we get to do it for real or not - have a go at the questions. (Learn) (Share)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Step 8 : What about fish in fresh water? Salt water? Or anything in water - osmosis can be both your friend and your greatest danger ..... remember lysis .....
Watch osmoregulation in action .... and when it goes wrong. (Learn)
Mission 8 : Read the information about both these unicellular organisms (don't drink the pond water) and see how you get on with the questions in your workbook on them. (Learn)
Done that? = Share with your teacher.
Yes = now its time for your next Step/Video clip/Challenge/Mission.
No = go back and complete the Step/Video clip/Challenge/Mission please.
Mission 9 : At the end of this section of your workbook you'll find (maybe) a puzzle page or two, a review planning page then a practice copy of the end of topic test. Complete these pages plus don't forget the definition page found at the start of the topic = you'll be ready for the test. (Learn)
Here is a video that sort of sums it all up.
Cell transport review questions - you should have completed these by now = we'll go over the answers together. This should give you an idea of where you are at with your understanding of cell transport = let you know what you need to do the get ready for the practice exam at the end of the whole section on cell structures and functions.
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