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Explain Diffusion

In this worksheet, students will explain the process of 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? Yuck! 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 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 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 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

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! 

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. 

 

Image of gas exchange in alveolus

 

The alveoli have a few adaptations that make gas exchange very efficient. They are only one cell thick making them very thin allowing 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 adapted by being very thin and having finger-like projections that increase the surface area. Villi also have partially-permeable membranes. This means it has pores that allow smaller molecules through but not larger molecules.

 

Image of plant photosynthesising 

 

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.  

 

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, like in the alveoli in the lungs.
- a thin membrane- to provide a short diffusion path

 

In the following activity, you will explain the process of diffusion.

 

Diffusion is the main way in which substances move over short distances in organisms. What type of substances needs to move?

Waste Products

Oxygen

Cells

Food

Describe the process of diffusion.

Waste Products

Oxygen

Cells

Food

In which of the following does diffusion not occur?

Solids

Liquids

Gases

Water vapour

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 heart

Carbon dioxide entering the leaf of a plant for photosynthesis

Glucose entering the blood from the small intestine

 O O O O O O O O O

Cell A 

 O O O

Cell B

 

 

The diagram above shows two cells. Cell A has nine particles and Cell B has three particles. Which direction will the particles diffuse? 

From Cell A to Cell B

From Cell B to Cell A

No movement

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 greater the movement of particles, resultin...
The greater the surface area...
...the faster the rate of diffusion because more p...

Diffusion of carbon dioxide, oxygen and water vapour into or out of the leaf is greatest when the stomata are...

Can you finish this sentence off?

Closed

Partially opened

Opened

Plants have special adaptations that control the exchange of gases. These are called stomata and are mainly found on the underside of leaves. Why might they be found on the underside?

Closed

Partially opened

Opened

Plants need carbon dioxide for photosynthesis. Surrounding the leaf the air has a higher concentration of carbon dioxide in comparison to inside the leaf. Explain what happens next. 

 

Carbon dioxide diffuses from the leaf through the stomata into the air

Carbon dioxide diffuses from the air through the stomata into the leaf

Oxygen diffuses through the stomata and into cells in the leaf to supply photosynthesis

Cacti are found in desert areas where conditions are often dry and hot. Cacti have spines instead of leaves. This reduces the surface area. Why does having spines with a small surface area an important adaptation for a cactus?

More water vapour diffuses out of the cactus

Less photosynthesis can occur

Less water vapour diffuses out of the cactus

  • Question 1

Diffusion is the main way in which substances move over short distances in organisms. What type of substances needs to move?

CORRECT ANSWER
Waste Products
Oxygen
Food
EDDIE SAYS
The main substances like oxygen, food substances and waste products are crucial for survival so diffusion is an ideal way to obtain these (or get rid of for waste). These substances are also important to plants!
  • Question 2

Describe the process of diffusion.

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

In which of the following does diffusion not occur?

CORRECT ANSWER
Solids
EDDIE SAYS
In order for diffusion to occur particles need to be able to move. In solids, particles are vibrating around a fixed position but are not free to move like in liquids and gases.
  • Question 4

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 leaf of a plant for photosynthesis
Glucose entering the blood from the small intestine
EDDIE SAYS
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. In the small intestine, glucose and other important molecules diffuse into the blood to be transported around the body to where it's needed. Carbon dioxide, oxygen and water vapour also diffuse into and out of the leaves of a plant.
  • Question 5

 O O O O O O O O O

Cell A 

 O O O

Cell B

 

 

The diagram above shows two cells. Cell A has nine particles and Cell B has three particles. Which direction will the particles diffuse? 

CORRECT ANSWER
From Cell A to Cell B
EDDIE SAYS
Particles will move from a higher concentration to a lower concentration. Cell A has more particles than Cell B so particles will move out of Cell A and into Cell B until there are equal numbers of particles in each cell.
  • Question 6

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
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 7

Diffusion of carbon dioxide, oxygen and water vapour into or out of the leaf is greatest when the stomata are...

Can you finish this sentence off?

CORRECT ANSWER
Opened
EDDIE SAYS
In order for gases to diffuse in or out of the plant, the stomata have to be open.
  • Question 8

Plants have special adaptations that control the exchange of gases. These are called stomata and are mainly found on the underside of leaves. Why might they be found on the underside?

CORRECT ANSWER
EDDIE SAYS
Having stomata on the underside of the leaf is a clever adaptation that plants have to decrease the loss of water vapour by diffusion. If there were more stomata on the top part of the leaf, more water vapour would diffuse out of the plant as the leaf would be more exposed to the suns heat.
  • Question 9

Plants need carbon dioxide for photosynthesis. Surrounding the leaf the air has a higher concentration of carbon dioxide in comparison to inside the leaf. Explain what happens next. 

 

CORRECT ANSWER
Carbon dioxide diffuses from the air through the stomata into the leaf
EDDIE SAYS
Don't forget that gases move from a higher concentration to a lower concentration so apply what you know to the given situation. In this case, the carbon dioxide will diffuse into the plant.
  • Question 10

Cacti are found in desert areas where conditions are often dry and hot. Cacti have spines instead of leaves. This reduces the surface area. Why does having spines with a small surface area an important adaptation for a cactus?

CORRECT ANSWER
Less water vapour diffuses out of the cactus
EDDIE SAYS
A small surface area means that there is less space for the water molecules to be in contact with and pass out of. This means that the water can be conserved for photosynthesis.
---- OR ----

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