Investigating Water Potential Flashcards

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1
Q

What is the purpose of calibration curves?

A

They are used to determine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations.

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2
Q

How is a calibration curve used to find the concentration of plant tissue?

A

Plot a calibration curve of percentage change in mass against concentration. Find the x-intercept where the plant tissue is isotonic to the sucrose solution.

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3
Q

What occurs when plant tissue is placed in a hypotonic solution?

A

Water moves into the plant tissue by osmosis, plant tissue increases in mass.

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4
Q

What occurs when plant tissue is placed in a hypertonic solution?

A

Water moves out of the plant tissue by osmosis, plant tissue decreases in mass.

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5
Q

Why are the potato discs left in solution for 20 minutes?

A

To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution.

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6
Q

What is water potential determined by?

A

The concentration of solutes.
The higher the solute concentration then the lower the water potential.

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7
Q

Outline the procedure of investigating osmosis using potato tissue.

A
  1. Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5 cm3 to 5 different test tubes.
  2. Cut a potato into equal sized chips and weigh.
  3. Place a chip in each test tube and leave for 20 minutes.
  4. Take out, dab the excess water and weigh them again.
  5. Calculate the percentage change in mass.
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8
Q

Why is the percentage change used rather than the actual change in mass?

A

Potato chips may not all have same starting mass.
Percentage change allows comparison.

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9
Q

What is indicated by the x-intercept of the calibration curve?

A

The concentration that is isotonic to the solution tested.

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10
Q

Explain the change in mass in the potato chips.

A

The potato chips with concentration lower than the sucrose solution (higher water potential) lose mass as there is a net movement of water out of the cells.
The potato chips with concentration higher than the sucrose solution (lower water potential) gain mass as there is a net movement of water into the cells.

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11
Q

Why are the potato chips dabbed dry after removing from the sucrose solution?

A

To remove any excess water clinging to its surface.

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12
Q

What are the controlled variables of this practical?

A

Volume of sucrose solution Size of potato chips
Length of time left in solution
Dab each potato disc with paper towels

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