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Apply Knowledge of Diffusion

In this worksheet, students will apply their knowledge of factors that affect diffusion.

Worksheet Overview

QUESTION 1 of 10

Image of a pair of socks

 

 

Why can you smell someone's stinky PE socks from all the way across the classroom? Yuk! Normally it's because sweat and other molecules are moving away from the socks and spread out in the air. This is called diffusion. 

Diffusion is the spreading out of the particles of any substance in a solution, or particles of a gas, resulting in movement from an area of higher concentration (where there's more particles in a certain solution or area) to an area of lower concentration (where there are fewer particles).  

 

Image of particles diffusing

 

Living organisms need different substances to be able to survive and function. These substances need to be transported into and out of their cells through diffusion (as well as osmosis and active transport - you will learn more about these later!). During diffusion, molecules move from an area of high concentration to an area of low concentration. They are said to move downconcentration gradient. Particles diffuse until they are evenly spaced apart. Diffusion is a passive process which means that no energy is needed and it happens naturally. 

 

 

Diffusion in organisms

 

The surface area to volume ratio of an organism means how much area an organism has in comparison to its volume. As organisms get larger, their surface area to volume ratio gets smaller, for example, an elephant has a smaller surface area to volume ratio than a mouse! Larger organisms tend to have special adaptations to overcome their smaller surface area to volume ratio, read on to find out more!

 

Image of gas exchange in alveolus

 

In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. This is to allow sufficient molecules to be transported into and out of cells for the organism’s needs. Diffusion is the main way substances move over short distances in organisms.

Breathing involves exchanging gases in the lungs, this requires diffusion. When you breathe in, oxygen in the inhaled air diffuses through the tiny alveoli (air sacs) in your lungs into your bloodstream. The oxygen is transported around your body. Carbon dioxide is the waste gas produced by respiration. Carbon dioxide diffuses from cells into the bloodstream and is exhaled by the lungs. 

The alveoli have a few adaptations that make gas exchange very efficient. They are only one cell thick making them very thin, which allows gases to pass through easily and quickly. They also have a large combined surface area, allowing large amounts of gases to be exchanged with each breath.

 

Image of villi in intestine

 

Another example of diffusion is in the small intestine. Digested food is broken down into small molecules such as glucose and amino acids. These important molecules need to be transported around the body via the blood. The small intestine is lined with many finger-like projections called villi. The molecules diffuse through the villi of the small intestine into the blood to be transported around the body. The villi are well adapted for this function, being very thin and having finger-like projections that increase the surface area. Villi also have partially permeable membranes. This means that the membrane has pores that allow smaller molecules through but not larger molecules.

 

Image of plant photosynthesising Image of leaf anatomy

 

Diffusion also occurs in plants. Plants take in carbon dioxide for photosynthesis and produce oxygen. These enter and leave the plant through the process of diffusion. The structure of the leaf is adapted for gas exchange. There are tiny pores, called stomata, in the surface of the leaf. There are usually more stomata on the underside of a leaf than on the topside. The stomata allow carbon dioxide to enter the leaf for photosynthesis. Molecules of carbon dioxide diffuse from a region of higher concentration (the atmosphere) to a lower concentrated area (leaf). The stomata also allow oxygen to diffuse out.  

 

In single-cellular producers like prokaryotes, carbon dioxide and oxygen molecules move by diffusion through cell membranes and don't need a specialised gas exchange structure like leaves in plants.

 

 

Factors affecting diffusion

 

Different factors can affect diffusion and how quickly it happens. Some of these factors are:

 

The difference in concentrations (concentration gradient) - having a large difference in concentrations means that diffusion can occur at a quicker rate as particles will naturally move from a high to low concentration. 

The temperature - the higher the temperature, the more energy the particles will have to move and spread out.

The surface area of the membrane - the larger the surface area, the faster the rate of diffusion. This is because more particles can pass through the membrane as there is more area, as in the alveoli in the lungs.

A thin membrane - to provide a short diffusion path.

 

In the following activity, you will apply your knowledge of  the factors that affect the process of diffusion.

 

The rate of diffusion is affected by different factors. 

 

Match up the sentences describing how these factors affect the rate of diffusion.

Column A

Column B

The greater the difference in concentration...
...The faster the rate of diffusion because more p...
The greater the temperature...
...The more space for particles to move through, r...
The greater the surface area...
...The greater the movement of particles, resultin...

Alveoli have several adaptations that help to make gas exchange very efficient.

 

Select the adaptations below. 

 

Image of gas exchange in alveolus

The wall of the small intestine is lined with many projections called villi. 

 

What special features do villi have that increases the speed of diffusion? 

 

Image of villi in intestine

Very thick membranes

Finger-like projections

Continuous membrane

Very thin

10% Carbon Dioxide

Cell A 

2% Carbon Dioxide

Cell B

5% Carbon Dioxide

Cell C

 

The diagram above shows three cells. Cell A has a carbon dioxide concentration of 10%, Cell B of 2% and Cell C of 5%. 


In which directions will the carbon dioxide diffuse? 

From Cell A to Cell B and C

From Cell B to Cell A

From Cell C to Cell B

From Cell C to Cell A

Surface area to volume ratios play an important role in living organisms. Bacteria, a mouse and an elephant all have different surface areas and volumes.

 

Which has the biggest surface area to volume ratio?   

 

Image of bacteriaimage of a mouseimage of an elephant

Bacteria

Mouse

Elephant

A scientist knows that the surface area is important at gas exchange surfaces. She is modelling shapes using  1 cm³ blocks.

She makes two models A, a six-sided cuboid, and B where each block is separate. Each model contains six 1 cm³ blocks.

 

Model A: Image of six cubes together  Model B: Image of cubeImage of cubeImage of cubeImage of cubeImage of cubeImage of cube

 

 

She works out the surface area of each model by counting the sides and starts to put the results in a table. 

 

Model 

Surface area (cm2)   Volume (cm3) Surface area : volume ratio 
 A  22  6  
 B  36  6  

 

What are the surface area to volume ratios of each of the models?

 6 : 13.7 : 11 : 62.5 : 1
A
B

Diffusion occurs in plants allowing photosynthesis to occur.

 

Explain how diffusion allows plants to get carbon dioxide into plant cells by matching up the descriptions below.  

 

 

Image of leaf anatomy

Column A

Column B

Cells in the leaf
Carbon dioxide is used in cells for photosynthesis...
Air surrounding the leaf
There is a higher concentration of carbon dioxide ...
Result
Carbon dioxide diffuses through the stomata and in...

Diffusion happens in plants allowing photosynthesis to occur.

 

Explain how plant cells release oxygen by matching up the descriptions below.  

Column A

Column B

Cells in the leaf
Oxygen is made by photosynthesis - a higher concen...
Air surrounding the leaf
Oxygen diffuses out of the cells and through the s...
Result
There is a lower concentration of oxygen in the ai...

Cacti live in very arid conditions. They have leaves that have been reduced to spines.

 

How does this special adaptation reduce the loss of water vapour by diffusion?

 

image of a cactus

The spines protect the cactus from being eaten

The spines reduce the surface area

The spines increase the surface area

Less water vapour can pass through

Some prokaryotes also photosynthesise. These prokaryotes don't need specialised gas exchange structures like leaves.

 

Why?

The spines protect the cactus from being eaten

The spines reduce the surface area

The spines increase the surface area

Less water vapour can pass through

  • Question 1

The rate of diffusion is affected by different factors. 

 

Match up the sentences describing how these factors affect the rate of diffusion.

CORRECT ANSWER

Column A

Column B

The greater the difference in con...
...The faster the rate of diffusi...
The greater the temperature...
...The greater the movement of pa...
The greater the surface area...
...The more space for particles t...
EDDIE SAYS
If you found these long explanations tricky to follow, take a careful look at the key words in each of the statements. Once you focus on those, common sense should help you to sort these out. A change in concentration levels will change the concentration gradient; an increase in temperature will lead to more movement of particles; and a larger surface area will give more space. Take time to learn these key facts, as you are often asked about them in exams.
  • Question 2

Alveoli have several adaptations that help to make gas exchange very efficient.

 

Select the adaptations below. 

 

Image of gas exchange in alveolus

CORRECT ANSWER
EDDIE SAYS
How did you get on with matching all of these? The alveoli are moist which encourages gas molecules to easily dissolve, allowing gas exchange to happen quickly. They're also covered by a network of capillaries enabling gases to pass almost directly between the lungs and the bloodstream. Alveoli are also very thin - only one cell thick, in fact - and their combined surface area is very large. The above adaptations allow alveoli to be really good at their job.
  • Question 3

The wall of the small intestine is lined with many projections called villi. 

 

What special features do villi have that increases the speed of diffusion? 

 

Image of villi in intestine

CORRECT ANSWER
Finger-like projections
Very thin
EDDIE SAYS
Did you get both of these options? In the small intestine, villi are very thin, which allows substances to pass through really quickly. The finger-like projections increase the surface area of the small intestine, which speeds up the rate of diffusion.
  • Question 4

10% Carbon Dioxide

Cell A 

2% Carbon Dioxide

Cell B

5% Carbon Dioxide

Cell C

 

The diagram above shows three cells. Cell A has a carbon dioxide concentration of 10%, Cell B of 2% and Cell C of 5%. 


In which directions will the carbon dioxide diffuse? 

CORRECT ANSWER
From Cell A to Cell B and C
From Cell C to Cell B
EDDIE SAYS
Particles will always move from a higher concentration to a lower concentration. Cell A has more carbon dioxide particles than Cell B or Cell C, so particles will move out of Cell A and into Cell B and Cell C until there are equal numbers of particles in each cell. Cell C has a higher concentration of carbon dioxide than Cell B, so again particles will diffuse out of Cell C and into Cell B.
  • Question 5

Surface area to volume ratios play an important role in living organisms. Bacteria, a mouse and an elephant all have different surface areas and volumes.

 

Which has the biggest surface area to volume ratio?   

 

Image of bacteriaimage of a mouseimage of an elephant

CORRECT ANSWER
Bacteria
EDDIE SAYS
Did you fall into the carefully laid trap here? Although the elephant is the largest organism of the three, its surface area to volume ratio doesn’t increase at the same rate. Remember as cells get bigger the surface area to volume ratio gets smaller.
  • Question 6

A scientist knows that the surface area is important at gas exchange surfaces. She is modelling shapes using  1 cm³ blocks.

She makes two models A, a six-sided cuboid, and B where each block is separate. Each model contains six 1 cm³ blocks.

 

Model A: Image of six cubes together  Model B: Image of cubeImage of cubeImage of cubeImage of cubeImage of cubeImage of cube

 

 

She works out the surface area of each model by counting the sides and starts to put the results in a table. 

 

Model 

Surface area (cm2)   Volume (cm3) Surface area : volume ratio 
 A  22  6  
 B  36  6  

 

What are the surface area to volume ratios of each of the models?

CORRECT ANSWER
 6 : 13.7 : 11 : 62.5 : 1
A
B
EDDIE SAYS
To calculate the surface area of model A (a cuboid): (2 x 3) + ( 2 x 1) + (3 x 1) x 2 = 22 cm² To calculate the volume of the cuboid: 2 x 1 = 2 ; 2 x 3 = 6 cm³ 22 ÷ 6 = 3.7 Surface area to volume ratio = 3.7 : 1 To calculate the surface area of model B: 1 x 1 x 6 = 6 cm² There are six individual cubes so, 6 x 6 = 36 cm² To calculate the volume of model B: For one cube: 1 x 1 x 1 = 1 cm³ For six cubes: 1 x 6 = 6 cm³ 36 ÷ 6 = 6 Surface area to volume ratio = 6 : 1
  • Question 7

Diffusion occurs in plants allowing photosynthesis to occur.

 

Explain how diffusion allows plants to get carbon dioxide into plant cells by matching up the descriptions below.  

 

 

Image of leaf anatomy

CORRECT ANSWER

Column A

Column B

Cells in the leaf
Carbon dioxide is used in cells f...
Air surrounding the leaf
There is a higher concentration o...
Result
Carbon dioxide diffuses through t...
EDDIE SAYS
Did you match these three up correctly? Remember, more concentrated → less concentrated! There's more carbon dioxide in the atmosphere than the cells in the leaf, so carbon dioxide naturally moves down a concentration gradient into the cells.
  • Question 8

Diffusion happens in plants allowing photosynthesis to occur.

 

Explain how plant cells release oxygen by matching up the descriptions below.  

CORRECT ANSWER

Column A

Column B

Cells in the leaf
Oxygen is made by photosynthesis ...
Air surrounding the leaf
There is a lower concentration of...
Result
Oxygen diffuses out of the cells ...
EDDIE SAYS
Did you think you'd already done this question!! It is very similar to the previous one, but this time it is about the diffusion of oxygen! Oxygen follows the opposite pathway to carbon dioxide, so there's more oxygen in the cells in the leaf compared to the atmosphere, so oxygen diffuses out of the cells.
  • Question 9

Cacti live in very arid conditions. They have leaves that have been reduced to spines.

 

How does this special adaptation reduce the loss of water vapour by diffusion?

 

image of a cactus

CORRECT ANSWER
The spines reduce the surface area
Less water vapour can pass through
EDDIE SAYS
This required a bit of thought, didn't it? Did you opt for the first answer? If so, you are quite right that the spines do offer protection to the cactus from the attentions of plant eaters, but this has nothing to do with the loss of water vapour. Think of a cactus spine as a very finely rolled leaf. The surface area of the spine is much lower than if it would be for a typical leaf. This is advantageous to the cactus as less water vapour is lost to the environment through diffusion. This is especially important as cacti are found in very hot and dry environments where water is precious!
  • Question 10

Some prokaryotes also photosynthesise. These prokaryotes don't need specialised gas exchange structures like leaves.

 

Why?

CORRECT ANSWER
EDDIE SAYS
Don't be put off by this tricky name - just think back to what you know about diffusion. Prokaryotes are single-celled organisms, making them very small. They also have partially permeable membranes which allows gases to diffuse directly into the cell. Multicellular organisms are a little more complex and so they need different adaptations to allow diffusion to occur, like having stomata in leaves. Well done for reaching the end of another activity!
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