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# As biology question on water potential watch

1. You could use a graph to find the concentration of sucrose that had the same water potential as the daffodil strips. Describe how. (1 mark)

The mark scheme: Read off value where initial length divided by final length = 1

My question is what does initial length/final length actually calculate? So if it 1, it is in isotonic solution and if it is below 1, there is a decrease in length, conversely, if its above 1, there is an increase in length?

Students investigated the effect of sucrose concentration on the lengths of strips cut from daffodil flowers. They measured the strips and put them in different sucrose solutions. After two hours they measured the strips again. The table shows their results.

8 (c) There was no further change in the ratio of initial length to final length in solutions above a concentration of 0.6 moldm–3. Explain why.

Mark scheme: Strip does not shrink any more; Because of cell walls;

Can someone explain c?
2. (Original post by Mina_)
You could use a graph to find the concentration of sucrose that had the same water potential as the daffodil strips. Describe how. (1 mark)

The mark scheme: Read off value where initial length divided by final length = 1

My question is what does initial length/final length actually calculate? So if it 1, it is in isotonic solution and if it is below 1, there is a decrease in length, conversely, if its above 1, there is an increase in length?

Students investigated the effect of sucrose concentration on the lengths of strips cut from daffodil flowers. They measured the strips and put them in different sucrose solutions. After two hours they measured the strips again. The table shows their results.
It's just working out the ratio between the initial and final length. In an isotonic solution, there is no change in length so you'd expect the ratio to be 1:1.

8 (c) There was no further change in the ratio of initial length to final length in solutions above a concentration of 0.6 moldm–3. Explain why.

Mark scheme: Strip does not shrink any more; Because of cell walls;

Can someone explain c?
The initial length/final length is getting bigger with increased sucrose concentration because the final length is getting smaller. This is as water is moving out via osmosis. Plant cells have a strong rigid cell wall which prevents too much water from exiting the cell.
3. (Original post by Kvothe the arcane)
It's just working out the ratio between the initial and final length. In an isotonic solution, there is no change in length so you'd expect the ratio to be 1:1.

The initial length/final length is getting bigger with increased sucrose concentration because the final length is getting smaller. This is as water is moving out via osmosis. Plant cells have a strong rigid cell wall which prevents too much water from exiting the cell.

Thank you!

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