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Apply the Process of Osmosis to Cells

Worksheet Overview

QUESTION 1 of 10

Ever wondered why your urine is often darker and more concentrated in the summer? Probably not, it's not the nicest thing to be thinking about! But often it's because we tend to sweat more in the summer months, so we lose a lot more water. Our kidneys then will try and keep a hold of more water for many of our important processes, resulting in more concentrated urine! This movement of water into and out of our cells is called osmosis.

 

Image of particles moving via osmosis

 

Osmosis is the diffusion of water molecules from a low concentration solution to a high concentration solution, across a partially permeable membrane.

A partially permeable membrane has holes or pores in it that allow water molecules through but are too small to allow larger molecules through. 

During osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions.

Dilute solutions have a high concentration of water molecules so have a high water potential. 

Concentrated solutions have a low concentration of water molecules so have a  low water potential.

 

 

Osmosis in organisms

Plant and animal cells are surrounded by a partially permeable plasma membrane. This allows water and other small molecules to diffuse across. Plant cells additionally have a strong cell wall surrounding the membrane, which offers support and protection. Animal cells don't have a cell wall. This means they respond differently to plant cells to the gain and loss of water.

 

Image of osmosis occurring in red blood cells

 

In dilute solutions, osmosis can cause animals cells, such as red blood cells, to swell up and sometimes even burst. This is because water will move from a high concentration outside the cell to a lower concentration inside the cell.  In concentrated solutions, water loss causes the cells to shrink. In order to remain healthy, animal cells need to maintain a balance. This means that the water concentration both inside and outside the cell are equal. 

 

Image of plant cells in different concentrations of water

 

 

Plants require water in order to photosynthesise. The roots of a plant contain root hair cells which are specialised cells that increase the surface area of the cells for maximum absorption of water by osmosis. In pure water, plant cells will take in water via osmosis and become firm or turgid. In a concentrated solution (not much water present), the cell loses water and starts to shrink and becomes flaccid.  

 

In humans, the concentration of water and salt in the blood is controlled by the kidneys. The kidneys ensure that we have the right concentration of water by getting rid of the excess water as urine.


 

Calculations Involving Osmosis

 

Image of weighing scales

 

Osmosis can be demonstrated using cubes of potatoes of roughly the same mass. By placing the cubes in different concentrations of sugar solutions, the cubes might gain or lose mass, or might even stay the same mass.

Scientists will be able to calculate the percentage change in mass to see how much mass was gained or lost, and converting to percentages often makes for easier comparison. Percentage mass is calculated by using the following equation:

 

(Final mass – initial mass) ÷ initial mass x 100

 

For example, a potato cube has an initial mass of 1 g. After placing it in a sugar solution for 30 minutes, its mass was 1.1 g. Its percentage change in mass is 10%. 

(1.1 g - 1 g) ÷ 1 g  x 100 = +10%

The plus sign shows there was an increase in mass. A minus sign shows a loss in mass.

 

In the following activity, you will apply the process of osmosis to cells. 

Plant and animal cells use the process of osmosis to transport water into or out of their cells.

 

Describe osmosis. 

 

Image of particles moving via osmosis

Cell membranes are partially permeable.

 

What is a partially permeable membrane? 

 

Image of particles moving via osmosis

A partially permeable membrane does not have holes in it

A partially permeable membrane has holes in it

It only allows waste products through

It allows water molecules through but the holes are too small to allow larger molecules through

Lisa is drinking orange squash. She finds it too sweet, so adds more water to her glass of squash. She is diluting it.

 

In terms of water potential, what is happening to the squash?

 

image of orange juice

The water potential increases

The water potential decreases

The water potential remains the same

What happens to red blood cells when they are placed in a concentrated salt solution? 

 

Image of osmosis occurring in red blood cells

They lose water and shrink

They gain water and swell

They stay the same

Plants take in water through their root hair cells.

 

What happens if too much water is taken into the cells?

 

Image of plant cells in different concentrations of water

Cell gains water

Cell loses water

Cell becomes turgid

Cell stays the same

 Image of water molecules Image of water moleculesImage of water molecules

Cell A 

 < Permeable membrane

 Image of water moleculesImage of water molecules

Cell B

 

The diagram above shows two cells separated by a permeable membrane. Cell A has twelve molecules of water and Cell B has eight molecules of water.

 

In which direction will the water move?

From Cell A to Cell B

From Cell B to Cell A

No movement

Osmosis can be demonstrated using cubes of potatoes of roughly the same mass. By placing the cubes in different concentrations of sugar solutions, the cubes might gain or lose mass, or might even stay the same mass.

Lara did an experiment in school on the effect of sugar solutions on potato pieces.  The potato pieces were of equal size. She measured the mass of each potato cube and placed each one in a beaker containing different concentrations of sugar solution. After two hours, each potato cube's mass was measured.

 

Beaker  1 2 3 4 5
Sugar concentration (M)  0.2 0.4 0.6 0.8 1
Initial mass (g) 2 2 2 2 2
Final mass (g) 2.20 2.15 1.96 1.80 1.73
% change in mass 10 7.5 -2 (a) -13.5

 

Calculate the percentage change in mass in beaker 4 (a). 

Lara did an experiment in school on the effect of sugar solutions on potato pieces.  The potato pieces were of equal size. She measured the mass of each potato cube and placed each one in a beaker containing different concentrations of sugar solution. After two hours, the mass of each potato cube was measured.

 

Beaker  1 2 3 4 5
Sugar concentration (M)  0.2 0.4 0.6 0.8 1
Initial mass (g) 2 2 2 2 2
Final mass (g) 2.20 2.15 1.96 1.80 1.73
% change in mass +10 +7.5 -2 -10 -13.5

 

Explain why the mass of the potatoes decreased in beakers 3, 4 and 5. 

Water entered the potato for respiration

Water left the potato cells by osmosis

The concentration of water outside the cells was higher than inside the cells

The concentration of water outside the cells was lower than inside the cells

In which of these scenarios is osmosis occurring? 

A red blood cell losing water

Oxygen entering the blood from the lungs

A plant absorbing water from the soil

Glucose moving into the bloodstream from the small intestine

 Image of water molecules Image of water moleculesImage of water molecules

Cell A 

 < Permeable membrane

 Image of water moleculesImage of water molecules

Image of water molecules

Cell B

 

The diagram above shows two cells separated by a permeable membrane. Cell A and Cell B each contain twelve molecules of water.

 

In which direction will the water move? 

From Cell A to Cell B

From Cell B to Cell A

No net movement

  • Question 1

Plant and animal cells use the process of osmosis to transport water into or out of their cells.

 

Describe osmosis. 

 

Image of particles moving via osmosis

CORRECT ANSWER
EDDIE SAYS
Well done if you remembered this definition! Osmosis is really important for cells - they're able to get the water they need for different processes like photosynthesis. Like gases in diffusion, water molecules move from a less concentrated (more water) solution to a more concentrated (less water) solution.
  • Question 2

Cell membranes are partially permeable.

 

What is a partially permeable membrane? 

 

Image of particles moving via osmosis

CORRECT ANSWER
A partially permeable membrane has holes in it
It allows water molecules through but the holes are too small to allow larger molecules through
EDDIE SAYS
Did you get the two correct options this time? A partially permeable membrane is selective and only allows water and small particles to pass through it.
  • Question 3

Lisa is drinking orange squash. She finds it too sweet, so adds more water to her glass of squash. She is diluting it.

 

In terms of water potential, what is happening to the squash?

 

image of orange juice

CORRECT ANSWER
The water potential increases
EDDIE SAYS
How did you get on with this one? Adding water to orange squash means you are increasing the number of water molecules in the solution. This increases the water potential. This means that the orange squash has more water to mix with, making it taste less sweet.
  • Question 4

What happens to red blood cells when they are placed in a concentrated salt solution? 

 

Image of osmosis occurring in red blood cells

CORRECT ANSWER
They lose water and shrink
EDDIE SAYS
Don't worry if you are finding this tricky - it is confusing when we talk about concentrations of solutions. What you need to understand is that if a solution is concentrated (as in the salt solution in this question), there is a low concentration of water molecules in it. This means that there is a higher concentration of water molecules inside the red blood cells than in the salt solution. Water will therefore move out of the red blood cells into the salt solution, which will make the red blood cells shrink and look wrinkled. Have you got this yet?
  • Question 5

Plants take in water through their root hair cells.

 

What happens if too much water is taken into the cells?

 

Image of plant cells in different concentrations of water

CORRECT ANSWER
Cell gains water
Cell becomes turgid
EDDIE SAYS
Did you remember the key fact for osmosis? Water moves from a higher concentration of water molecules to a lower concentration of water molecules. If the plant's surroundings are wet, then water enters the plant cells by osmosis making the cells firm and turgid. So it's important to water your plants, but not to overdo it!
  • Question 6

 Image of water molecules Image of water moleculesImage of water molecules

Cell A 

 < Permeable membrane

 Image of water moleculesImage of water molecules

Cell B

 

The diagram above shows two cells separated by a permeable membrane. Cell A has twelve molecules of water and Cell B has eight molecules of water.

 

In which direction will the water move?

CORRECT ANSWER
From Cell A to Cell B
EDDIE SAYS
Did you remember it?! Water will move from a higher concentration to a lower concentration. There are more water molecules in Cell A than Cell B ,so water will move from Cell A, through the partially permeable membrane, and into Cell B until there are an equal number of molecules in each cell.
  • Question 7

Osmosis can be demonstrated using cubes of potatoes of roughly the same mass. By placing the cubes in different concentrations of sugar solutions, the cubes might gain or lose mass, or might even stay the same mass.

Lara did an experiment in school on the effect of sugar solutions on potato pieces.  The potato pieces were of equal size. She measured the mass of each potato cube and placed each one in a beaker containing different concentrations of sugar solution. After two hours, each potato cube's mass was measured.

 

Beaker  1 2 3 4 5
Sugar concentration (M)  0.2 0.4 0.6 0.8 1
Initial mass (g) 2 2 2 2 2
Final mass (g) 2.20 2.15 1.96 1.80 1.73
% change in mass 10 7.5 -2 (a) -13.5

 

Calculate the percentage change in mass in beaker 4 (a). 

CORRECT ANSWER
-10
EDDIE SAYS
Don't worry that this appears to be a maths question - just think back to the formula in the Introduction and follow it through. To calculate the percentage change in mass: (Final mass – initial mass) ÷ initial mass x 100 (1.80 - 2) ÷ 2 x 100 = -10 You've got it!
  • Question 8

Lara did an experiment in school on the effect of sugar solutions on potato pieces.  The potato pieces were of equal size. She measured the mass of each potato cube and placed each one in a beaker containing different concentrations of sugar solution. After two hours, the mass of each potato cube was measured.

 

Beaker  1 2 3 4 5
Sugar concentration (M)  0.2 0.4 0.6 0.8 1
Initial mass (g) 2 2 2 2 2
Final mass (g) 2.20 2.15 1.96 1.80 1.73
% change in mass +10 +7.5 -2 -10 -13.5

 

Explain why the mass of the potatoes decreased in beakers 3, 4 and 5. 

CORRECT ANSWER
Water left the potato cells by osmosis
The concentration of water outside the cells was lower than inside the cells
EDDIE SAYS
Another tricky one but just remember the vital definition of osmosis! Water moves from where it is more concentrated to where it is less concentrated. In beakers 3, 4 and 5, the concentration of sugar is high meaning that the concentration of water will be lower in the sugar solution than in the potatoes. The water will therefore move out of the potatoes into the sugar solution, resulting in a decrease in mass. This is osmosis at work! Well done if you worked that one out.
  • Question 9

In which of these scenarios is osmosis occurring? 

CORRECT ANSWER
A red blood cell losing water
A plant absorbing water from the soil
EDDIE SAYS
Did you get the two correct options? Remember in questions like these to look for the answers that mention water - osmosis is all about the movement of water molecules. An answer that mentions gas is usually referring to diffusion.
  • Question 10

 Image of water molecules Image of water moleculesImage of water molecules

Cell A 

 < Permeable membrane

 Image of water moleculesImage of water molecules

Image of water molecules

Cell B

 

The diagram above shows two cells separated by a permeable membrane. Cell A and Cell B each contain twelve molecules of water.

 

In which direction will the water move? 

CORRECT ANSWER
No net movement
EDDIE SAYS
How did you find this final question? There are equal numbers of water molecules in Cell A and Cell B, so water will continue to move at an equal rate between the cells. Well done for completing this tricky activity. Hopefully, you are feeling more confident with this topic now.
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