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Define Diffusion

Worksheet Overview

QUESTION 1 of 10

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

Image of a pair of socks

 

Diffusion is the spreading out of the particles of any substance in 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 survive and function. These substances need to be transported in 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 down a concentration 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

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 air sacks (alveoli) in your lungs into your bloodstream and is transported around your body. Carbon dioxide is the waste gas produced by respiration - it diffuses from cells into the bloodstream and is exhaled by the lungs.

Image of gas exchange in alveolus

 

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.

Image of villi in intestine

 

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.

Image of plant photosynthesising

 

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 space, like in the alveoli in the lungs.

 

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

Image of noseImage of a pair of socks

 

Stuart can smell someone's smelly socks in class. How can he smell socks from a distance? Choose one answer.

Stuart has a really good sense of smell

The socks are REALLY smelly

The sweat particles diffuse into the air from the socks and spread out

Describe the process of diffusion by filling in the blanks below.

Image of particles diffusing

Stuart has a really good sense of smell

The socks are REALLY smelly

The sweat particles diffuse into the air from the socks and spread out

Image of plant photosynthesisingImage of gas exchange in alveoli

Diffusion allows many important processes to occur in different organisms. Select three examples below.

Oxygen entering the blood from the lungs

Carbon dioxide entering the lungs from the blood

Carbon dioxide entering the leaf of a plant for photosynthesis

Water entering the lungs

Why is diffusion important? Fill in the blanks below to answer this question.

Oxygen entering the blood from the lungs

Carbon dioxide entering the lungs from the blood

Carbon dioxide entering the leaf of a plant for photosynthesis

Water entering the lungs

Diffusion is a process that doesn't need energy. What is another name for not needing energy? Type one word below.

 O O O O O

Cell A 

 O O O O O O O O O O O

Cell B

The diagram above shows two cells. Cell A has five particles and Cell B has eleven particles.

 

Which direction will the particles diffuse? Select one answer below.

From Cell A to Cell B

From Cell B to Cell A

No movement

Image of a red blood cell

Red blood cells are small, really thin and have a biconcave shape. They have a large surface area.

 

Why is this useful? Select one answer.

More space for water to pass through

Less space for oxygen to move through, resulting in a slower rate of diffusion

More space for oxygen to move through, resulting in a faster rate 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 more space for particles to move through, r...
The greater the temperature...
...the faster the rate of diffusion, because more ...
The greater the surface area...
...the greater the movement of particles, resultin...

Test your knowledge of diffusion by answering true or false below.

 TrueFalse
Particles move from low concentration to high concentration
Temperature affects the rate of diffusion
Small surface area increases rate of diffusion
Oxygen and carbon dioxide are exchanged by diffusion in the lungs

Image of noseImage of a pair of socks

 

Stuart can smell someone's smelly socks in class. Where is the smell strongest? Choose one answer.

The smell is strongest at the sock

The smell is strongest away from the sock

The smell is strongest everywhere

  • Question 1

Image of noseImage of a pair of socks

 

Stuart can smell someone's smelly socks in class. How can he smell socks from a distance? Choose one answer.

CORRECT ANSWER
The sweat particles diffuse into the air from the socks and spread out
EDDIE SAYS
Good start! The socks can be smelt because sweat and other molecules are moving away from it and spreading out in the air. This is called diffusion.
  • Question 2

Describe the process of diffusion by filling in the blanks below.

Image of particles diffusing

CORRECT ANSWER
EDDIE SAYS
In diffusion, particles will move from more concentrated areas to low concentrated areas down a concentration gradient. This is a pretty standard answer when describing diffusion, so it's worth remembering for your exams.
  • Question 3

Image of plant photosynthesisingImage of gas exchange in alveoli

Diffusion allows many important processes to occur in different organisms. Select three examples below.

CORRECT ANSWER
Oxygen entering the blood from the lungs
Carbon dioxide entering the lungs from the blood
Carbon dioxide entering the leaf of a plant for photosynthesis
EDDIE SAYS
How did you do? Diffusion allows gas exchange to occur in the lungs of humans. There is a higher concentration of oxygen in the lungs compared to the blood, so oxygen moves into the blood. Carbon dioxide does the opposite and moves from the blood to the lungs to be exhaled. Carbon dioxide, oxygen and water vapour also diffuse into and out of the leaves of a plant.
  • Question 4

Why is diffusion important? Fill in the blanks below to answer this question.

CORRECT ANSWER
EDDIE SAYS
Diffusion is really important for cells to get the things they need for different processes, like respiration or photosynthesis. At the same time, diffusion allows cells to get rid of waste products too.
  • Question 5

Diffusion is a process that doesn't need energy. What is another name for not needing energy? Type one word below.

CORRECT ANSWER
passive
EDDIE SAYS
Good job if you went with 'passive'. Particles move from a high concentration to a low concentration - this process doesn't need energy. You can imagine it as a ball rolling down a hill, compared to trying to roll a ball uphill. Rolling downhill won't require your energy, whereas trying to roll a ball uphill would!
  • Question 6

 O O O O O

Cell A 

 O O O O O O O O O O O

Cell B

The diagram above shows two cells. Cell A has five particles and Cell B has eleven particles.

 

Which direction will the particles diffuse? Select one answer below.

CORRECT ANSWER
From Cell B to Cell A
EDDIE SAYS
Particles will move from a higher concentration to a lower concentration. Cell B has more particles than Cell A, so particles will move out of Cell B and into Cell A until there are equal numbers of particles in each cell.
  • Question 7

Image of a red blood cell

Red blood cells are small, really thin and have a biconcave shape. They have a large surface area.

 

Why is this useful? Select one answer.

CORRECT ANSWER
More space for oxygen to move through, resulting in a faster rate of diffusion
EDDIE SAYS
Red blood cells deliver oxygen around the body. Having a large surface area means that there is more area for the oxygen particles to pass through, allowing more oxygen to diffuse into the red blood cell.
  • Question 8

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
Are you getting the hang of it? Take the time to remember these key factors, as you are often asked about them in exams. Maybe you can try this question a few times to consolidate your knowledge?
  • Question 9

Test your knowledge of diffusion by answering true or false below.

CORRECT ANSWER
 TrueFalse
Particles move from low concentration to high concentration
Temperature affects the rate of diffusion
Small surface area increases rate of diffusion
Oxygen and carbon dioxide are exchanged by diffusion in the lungs
EDDIE SAYS
A few key statements to test yourself on. Don't forget, a larger combined surface area means a faster rate of diffusion, like in the alveoli found in the lungs. Practice makes perfect! That’s another activity ticked off!
  • Question 10

Image of noseImage of a pair of socks

 

Stuart can smell someone's smelly socks in class. Where is the smell strongest? Choose one answer.

CORRECT ANSWER
The smell is strongest at the sock
EDDIE SAYS
The socks can be smelt because the sweat molecules are moving away from the socks and spreading out in the air. The smell becomes weaker further away from the sock. Maybe Stuart needs to sit further away from the person with smelly socks on!
---- OR ----

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