Required Practical: Osmosis Flashcards

All 8 cards in this deck

What are the steps of the required practical investigating the effect of salt or sugar solution concentration on plant tissue?

e.g. potato cylinders in a range of sugar solutions

1. Cut equal-sized potato cylinders, blot dry and record the starting mass of each.
2. Place one in each concentration of solution for the same set time.
3. Remove, dry the surface with a paper towel, reweigh and calculate the percentage change in mass.

In the osmosis required practical with potato in salt solution, what is the independent variable?

The concentration of the salt solution.

Why are potato pieces dried with a paper towel before being reweighed in the osmosis practical?

So that only the mass of the potato is measured, as surface liquid would make the mass higher.

Name two variables that must be controlled in the osmosis required practical.

Any two of: volume of solution, time left in solution, temperature, size/shape of the potato pieces.

On a graph of percentage change in mass against solution concentration, what does the point where the line crosses zero tell you?

The concentration of the solution equal to the concentration inside the plant cells, where there is no net movement of water.

What are the steps to calculate the percentage change in mass of plant tissue?

e.g. starting mass $2.5$ g, final mass $2.7$ g

1. Find the change in mass: $2.7-2.5=0.2$ g
2. Divide by the starting mass: $0.2\div2.5=0.08$
3. Multiply by 100: $8\%$ increase

Why is percentage change in mass used rather than change in mass in the osmosis practical?

The pieces may have slightly different starting masses, so percentages allow a fair comparison.

True or false? In the osmosis required practical, a potato piece that gained mass must have been in a solution more concentrated than its cell contents.

False. Mass is gained when the solution is more dilute than the cell contents, so water moves into the cells by osmosis.