Any GCSE Bilogy Teachers out there?

[Milliways]

DD is doing triple Science, and having a prob with new Biology teacher. They are doing coursework on Osmosis. Teacher looked at her graph and said was wrong but "can't say what it should look like". Told another group that data (for graph) was wrong so wold loose marks, but if they make data up will loose marks etc etc.

Now, if DD can find out if her data (from experiment) is wrong, should she produce a graph from THAT data and then explain why she thinks data is wrong & what results/graph should have been? How can she find out WHAT is wrong with either graph or data? TO be told something is wrong but can't tell you what or why & can't change results anyway seems stupid.

Ant advice (before I get mad at parents evening next week).

TIA

[Jimjamskeepingoffvaxthreads]

Most standard text books will have the "correct" graph. What did she do? Potato chips or something?

She should produce a graph from her results and then explain why it is wrong.

[Blandmum]

OK

There could be something wrong about the graph that does not include the data itself.

The thing you change (normaly the concentration of the solution) should be along the x axis.

The thing that changes as a result (the mass or lenth of the potato) should be along the y axis.

It should have an informative title, axis should be labeled. Data points plotted correctly.

THeir data are their data, and shouldn't be fudged. You do lose a mark if the repeats are not close together.

Don't go mad with the teacher though, we are very limited in the help we can give during c/w

The point at while the line crosses the x axis shows the point where thereis no change in mass, and no net movement of water. The concentration of solute at that point is equivalent to the concentration within the potato chip....the isotonic point.

Just don't tell anyone I told you!

Have they been given a guide? Has your dd checked that she has done everything that she should....you'd be amazed at what they can forget to do!

[Blandmum]

and agree with JJ, polt the graph and explain the errors plausibly...in fact there are marks for this.

Just make sure there are no errors with the graph as opposed to the data.

[Whizzz]

was just about to post - you need martianbishop !!

[Milliways]

Thanks everyone - will go & show her your comments

[Milliways]

OK, she says Thanks - but already had all those points, thinks it's a problem with the shape of graph (It was Potato Chips btw).

Apparently hers looks like a wonky Xsquared graph that goes from positive to negative.

[Blandmum]

has she plotted the x axis from zero added salt (or sugar) to saturated solution, or the other way round?

[Milliways]

X axis starts at 0 and goes up in steps of 0.2 Molars of sugar solution where 0.2 is the amount of sugar and the 0.8 remaining would be water. The axis finishes at 1 Mol.