First Unit 3 SAC?

[Irving4Prez]

The movement of water molecules across the semi-permeable plasma membrane from an area of low solute concentration to an area of high solute concentration is called osmosis. However, this is not the completely ONLY means by which water travels across the membrane. Some protein channels called aquaporins allow the facilitated diffusion/channel-mediated transport of water molecules across the plasma membrane.

Mainly however, osmosis is the path taken by water molecules, that want to fit in with the cool solutes and ditch the poor, innocent cell cool analogy hey?

Watch your definition, not all water molecules can move across the semi-permeable membrane. It's just 'free water molecules', hydrated water molecules will be unable to cross the semi-permeable membrane due to their size.

[Yacoubb]

Watch your definition, not all water molecules can move across the semi-permeable membrane. It's just 'free water molecules', hydrated water molecules will be unable to cross the semi-permeable membrane due to their size.

But mentioning the partially-permeable membrane is enough to imply that not all water molecules enter and they selectively cross the membrane. However, I see your point; maybe mentioning the movement of free water molecules across the partially-permeable membrane...so on, and so forth!

[Snorlax]

First SAC was ridiculous. Report write up+application question for 50 marks...
Isn't it suppose to be out of 25? FUUUUUUUUUUUUUUUUU

[Daenerys Targaryen]

First SAC was ridiculous. Report write up+application question for 50 marks...
Isn't it suppose to be out of 25? FUUUUUUUUUUUUUUUUU

At least if you lose a few marks the total percentage isn't raped.
Mine were generally out of 25..

[Snorlax]

At least if you lose a few marks the total percentage isn't raped.
Mine were generally out of 25..

50 mins for the whole SAC...Found it absolutely impossible to write in-depth with quality..
Just hope other SACs aren't gonna be like this..

[Daenerys Targaryen]

Dont all the bio sacs need to be out of 25?

[pi]

Schools can do whatever they want for SACs, mine were all 25 marks back in the day but other schools had other numbers.

As for not being able to write enough detail in 50mins, that's a good move by your school. You can't regurgitate the textbook in the exam either and this is good prep for the long run imo.

[Stick]

My first SAC was literally just on osmosis… somebody went into a little bit too much detail in their revision... XD Anyway, I thought I did pretty well but I couldn't think of a second variable that needed to be controlled in my experiment so I put something that probably won't get me that second mark. Other than that, there was a pretty tricky question involving a plant stem cut into quarters longitudinally with the rigid, dead epithelial layer and a softer, more flexible interal layer labelled (the diagram was like a C, where the soft, flexible layer was on the outside of the C). Three of these pieces were then placed in three different types of solutions and they bent in different ways. To give you a taste of what I answered with, there was one quarter where the soft flexible layer expanded such that it then become the outside of the C. I said it was a hypotonic solution since these soft flexible cells increased in size and took up more space, but others said it was hypertonic and that the epithelial layer lost water. My friend who is very competent in Biology said the latter wasn't true since these cells are impervious to water so I'm hoping that's the case. It seems the question effectively polarised the class. It was also a difficult SAC to complete on time and many didn't finish, but I still managed to get it done fairly comfortably.

[Snorlax]

Schools can do whatever they want for SACs, mine were all 25 marks back in the day but other schools had other numbers.

As for not being able to write enough detail in 50mins, that's a good move by your school. You can't regurgitate the textbook in the exam either and this is good prep for the long run imo.

Yeah one of our biol teachers acknowledged it was a difficult SAC time-wise...guess it's better in the long run...
Hope i don't loose any motivation once i get the results back..

[sabii]

Hi, I am also going to be doing a Prac Report on Osmosis in Potato- the materials we are using are fresh potato, sucrose solution and distilled water. What do you guys think the aim/hypothesis is?
Will it involve putting a patato slice in sucrose solution and then in water and observing the difference? For the water solution, there is less water inside the cell (hypotonic) so the water will move inside the cell and make it more turgent. In the sucrose solution there is more water molecule inside the cell in comparison to the surrounding so the water will move out of the cell making in flaccid (hypertonic).
Is that right? 

[Yacoubb]

Aim: the aim of the experiment was to observe the osmotic activity of water molecules in a potato cells when placed in solutions with differentbsolute concentrations.

Hypothesis: If potato cells are placed in the hypertonic solution, then the potato cell would plasmolyse. If the potato cell is placed in the hypotonic solution, the potato cell will become turgid. If the potato cell is placed in the isotonic solution, the potato cell will become flaccid.

[sabii]

Doesn't flaccid mean it goes floppy? If it is an isotonic solution it means there is an equilibrium on both sides of the membrane therefore water will not come in or go out thus the mass remains the same and the structure would also not be affected? Isn't a hypertonic solution flaccid because water moves out of the cell???

[Fantasia94]

Doesn't flaccid mean it goes floppy? If it is an isotonic solution it means there is an equilibrium on both sides of the membrane therefore water will not come in or go out thus the mass remains the same and the structure would also not be affected? Isn't a hypertonic solution flaccid because water moves out of the cell???

Yeah, you are correct. Water will not move in or out of the cell because conc. of solutes is the same in both the cell and the external environment in an isotonic solution. If the solution is hypertonic you would expect water to move out of the cell into the external environment which therefore results in the cell shrinking and becoming flaccid.

[Yacoubb]

Plant cells are normally turgid; hence, they remain turgid in an isotonic solution because no water molecule movement occurs

[sabii]

Ok thanks guys!!! How about the mosaic model? I have a dot point on my Osmosis potato SAC revision sheet that says we should know the mosaic noedel of the cell membrane including the functions of all its components? what would I say?

Do you simply have to state the cell membrane is made up a phopholipid bilayar; where the heads (phosphate) are hydropllic and face outwards and the tails are hydrophobic which means they repel with water hence face inwards. There are also protein channels embedded in the membrane that assist large non-soluble substances to pass the membrane. What about the glycolipid? what do they do?