# Define Osmosis

In this worksheet, students will define osmosis.

Key stage:  KS 4

GCSE Subjects:   Biology: Single Subject, Biology: Combined Science

GCSE Boards:   OCR 21st Century

Curriculum topic:   Living Together: Food and the Ecosystem

Difficulty level:

### QUESTION 1 of 10

Osmosis is the diffusion of water molecules from a low concentration solution to 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.
• Concentrated solutions have a low concentration of water molecules

Osmosis in plants

Plant cells are surrounded by a partially-permeable cell membrane. This allows water and other small molecules to diffuse across. Plant cells have a strong cell wall surrounding the membrane which offers support and protection.

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

Calculations Involving Osmosis

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

Scientists will be able to calculate the change in mass to see how much mass was gained or lost by using the following equation:

Final mass (g) – initial mass (g) = change in mass (g)

In the following activity, you will define and describe osmosis.

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

Fill in the blanks below to answer this question.

Cell membranes are partially permeable. What is a partially permeable membrane? Choose two answers from below.

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 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. What has she done to her orange squash?

Water is absorbed by root hair cells in plants. The water will move from a high concentration to a low concentration. Why do plants need water? Select one answer below.

For absorbing water

For photosynthesis

For metabolism

What is the name of the structure of the plant where water is absorbed by osmosis?  Type one answer below.

Plants take in water through their root hair cells. If too much water is taken into the cells, the cells swell up. If there is too little water, what may happen? Select two answers below.

Cell gains water

Cell loses water

Cell becomes flaccid

Cell stays the same

 Cell A < Permeable membrane   Cell B

The diagram above shows two cells separated by a permeable membrane. Cell A has four molecules of water and Cell B has eight molecules of water. Which direction will the water move? Select one answer below.

From Cell A to Cell B

From Cell B to Cell A

No movement

Sally was preparing potatoes to make some chips. She wanted to wash her raw potato chips so placed them in a bowl of pure water. What is likely to happen to the mass of the potato chips? Select one answer below.

The mass stays the same

The mass increases

The mass decreases

What do the following terms mean? Match up the key terms to the definitions.

## Column B

Turgid
The cell swells as more water is moving into the c...
Flaccid
Allows certain substances to pass through and not ...
Partially permeable
The cell shrinks as water is moving out of the cel...

Osmosis can be demonstrated using cubes of potatoes of roughly the same mass. Placing the cubes in different concentrations of sugar solutions the cubes might gain or lose mass, or may 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 it in a beaker of 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) 2.2 2.15 1.96 1.8 1.73

Calculate the change in mass in beaker 2 and beaker 3. Select two answers.

+0.16g

+0.15g

0.04

-0.04g

• Question 1

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

Fill in the blanks below to answer this question.

EDDIE SAYS
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? Choose two answers from below.

A partially-permeable membrane has holes in it
It allows water molecules through but are too small to allow larger molecules through
EDDIE SAYS
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. What has she done to her orange squash?

Diluted it
Dilute
EDDIE SAYS
Adding water to orange squash means you are diluting your drink. This means that the orange squash has more water to mix with making it taste less sweet.
• Question 4

Water is absorbed by root hair cells in plants. The water will move from a high concentration to a low concentration. Why do plants need water? Select one answer below.

For photosynthesis
EDDIE SAYS
Water, as well as carbon dioxide and oxygen, are needed for photosynthesis to occur. Without these, plants won\'t be able to respire and grow.
• Question 5

What is the name of the structure of the plant where water is absorbed by osmosis?  Type one answer below.

roots
root hair cell
EDDIE SAYS
The roots and root hair cells are really important, they are the structure where water enters for photosynthesis. Water passes into the root hair cells via osmosis.
• Question 6

Plants take in water through their root hair cells. If too much water is taken into the cells, the cells swell up. If there is too little water, what may happen? Select two answers below.

Cell loses water
Cell becomes flaccid
EDDIE SAYS
Water moves from a higher concentration to a lower concentration. If the plant\'s surroundings are dry then water leaves the plant cells making cells flaccid. A bit like if you forget to water your plants they start to wilt!
• Question 7
 Cell A < Permeable membrane   Cell B

The diagram above shows two cells separated by a permeable membrane. Cell A has four molecules of water and Cell B has eight molecules of water. Which direction will the water move? Select one answer below.

From Cell B to Cell A
EDDIE SAYS
Water will move from a higher concentration to a lower concentration. There are more water molecules in Cell B than Cell A so water will move from Cell B through the partially permeable membrane and into Cell A until there are equal numbers of molecules in each cell.
• Question 8

Sally was preparing potatoes to make some chips. She wanted to wash her raw potato chips so placed them in a bowl of pure water. What is likely to happen to the mass of the potato chips? Select one answer below.

The mass increases
EDDIE SAYS
The water is pure so the cells of the potato will have less water than its surroundings; water will move into the potato chips increasing its mass.
• Question 9

What do the following terms mean? Match up the key terms to the definitions.

## Column B

Turgid
The cell swells as more water is ...
Flaccid
The cell shrinks as water is movi...
Partially permeable
Allows certain substances to pass...
EDDIE SAYS
Take the time to remember these key terms as you are often asked about them in exams. Maybe you can try this question a few times to consolidate your knowledge.
• Question 10

Osmosis can be demonstrated using cubes of potatoes of roughly the same mass. Placing the cubes in different concentrations of sugar solutions the cubes might gain or lose mass, or may 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 it in a beaker of 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) 2.2 2.15 1.96 1.8 1.73

Calculate the change in mass in beaker 2 and beaker 3. Select two answers.

+0.15g
-0.04g
EDDIE SAYS
To calculate the change in mass: (Final mass – initial mass). For Beaker 2: 2.15 - 2 = 0.15g For Beaker 3: 1.96 - 2 = -0.04g
---- OR ----

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