RP: Osmosis Practical

Question 1

What is the independent variable?

Answer 1

The independent variable is the one you change.

Question 2

What is the dependent variable?

Answer 2

The dependent variable is the one you measure.

Question 3

What is the control variable?

Answer 3

The control variable is the one you keep the same.

Question 4

What is the osmosis practical?

Answer 4

Osmosis practical:
What is the concentration of the salt in a potato?
Put the potato into different concentrations of salt solution until there is no change.

Question 5

What is the independent variable in the osmosis practical?

Answer 5

Independent variable:
Concentration of salt solutions

Question 6

What is the dependent variable in the osmosis practical?

Answer 6

Dependent variable:
Mass/ length of potato.

Question 7

What is the control variable in the osmosis practical?

Answer 7

Control variable:
Time vegetable is soaked in salt solution.

Question 8

What piece of equipment is used to make the potato cylinder in the osmosis practical?

Answer 8

A cork borer is used to make the potato cylinder.

Question 9

What piece of equipment is used to cut off the potato skin in the osmosis practical?

Answer 9

A scalpel is used to cut of the potato skin

Question 10

What three posibilties will occur once the potato has soaked in the salt solution?

Answer 10

• Gains mass
• Loses mass
• Mass is the same

Question 11

When does the potato gain mass?

Answer 11

• If it is in a dilute solution, it will gain mass.
• The solution is hypotonic to the solution inside the cell.

Question 12

When does the potato lose mass?

Answer 12

• If it is in a concentrated solution, it will lose mass.
• The solution is hypertonic to the solution in the cell.

Question 13

When does the potato mass stay the same?

Answer 13

• If it is in the same concentration as the potato salt solution.
• The solution is isotonic to the solution in the cell .

Question 14

What does “dilute” mean?

Answer 14

A substance that contains more solvent than dissolved solute.

Question 15

What does “concentrated” mean?

Answer 15

A substance that contains more dissolved solute than solvent.

Question 16

Give 2 factors that depend on whether a substance will diffuse through a semi- permeable membrane.

Answer 16

• Solubility of substance
• Size of molecules

Question 17

What is a turgid cell?

Answer 17

One that is swollen/ hard due to the gain of water.

Question 18

What is lysis?

Answer 18

Lysis is when an animal cell splits down a cell membrane.

Question 19

When does lysis occur to an animal cell?

Answer 19

Lysis occurs when an animal cell is placed in a hypotonic solution.

Question 20

What is the process of “crenation?”
TIP: THINK OF CREMATED BODIES

Answer 20

Crenation is the shrivelling of a cell when it is placed in a hypertonic solution.

Question 21

What are the 8 steps of the osmosis practical?

Answer 21

1.) Cut off skin using scalpel
2.) Cork borer–> 5 cyclinders
3.) Use scalpel –> make lengths equal (3cm)
4.) Measure the mass of each cylinder
5.) 10cm³ of each concentration in boiling tubes + distilled water
LEAVE
6.) Blot cyclinders with paper towel
7.) Measure mass and length again: calculate percentage change.
8.) Plot results on a graph

Question 22

Why is it good to cover the testube in this prcactical?

Answer 22

• Evaporation changes concentration of salt solutions.
• Cover to reduce evaporation

Question 23

What are 2 ways to improve the osmosis practical?

Answer 23

• Repeat experiment: mean percentage change.
• Lid on beaker

Question 24

What are 2 pieces health and safety do you need to know for this practical?

Answer 24

• Be careful when using sharp knives
• Keep water away from electronic balance.

Question 25

Why is percentage change better than just knowing change?(2)

Answer 25

• They all start at different masses
• Percentages show how much water is absorbed/ lost relative to the initial mass.

Question 26

Why do we peel the skin off the potato before cutting the potatos?

Answer 26

• Skin may affect rate of osmosis.

Question 27

Why is it important to use potato cylinders of the same length when seeing how concentration of salt solution affects osmosis? (1 mark)

Answer 27

Potato cylinders need to have the same surface area as that affects rate of osmosis.