Lesson B4: Osmosis, Diffusion, Active Transport

Key Ideas   Unit Checklist

  Video Lesson

How does food from photosynthesis get to all parts of a plant? Watch this video to learn about how substances move into plant cells.

  Lesson B4: Osmosis, Diffusion, Active Transport

Figure B.1.4.1 – The scent from the flowers on a lilac tree can spread throughout a neighbourhood in the spring.
Figure B.1.4.2 – Lily flowers have a strong scent.


Scented Flowers

Many flowers smell pleasant to humans. Flowers smell because they make tiny scented particles that are highly concentrated inside the flower. The particles spread away from the flower to an area of lower concentration, which is why we can smell them. This is an example of diffusion.

Flowers smell pleasant to insects such as bees. The scent of flowers attracts pollinating insects to the plant.
Reading and Materials for This Lesson

Science in Action 7
Reading: Pages 106-107

Materials:
2 clear glass or plastic cups, tall glass cup, tablespoon measuring spoon, paring knife, plate, spoon, fork, wooden spoon, shallow glass pan, small Ziplocâ„¢ bag, water, hot water, cornstarch, iodine, raw potato, salt, paper coffee filter, scissors, pencil, tape, rubbing alcohol (isopropyl alcohol), green leaves
Figure B.1.4.3 – The scent of lavender (left) attracts pollinating bees. Humans enjoy the scent of lavender flowers in soaps, creams, and perfumes.Many other flowers also attract insects.

Stinky Flower

Not all flowers smell pleasant. The corpse flower is a giant flower from Indonesia that blooms for only one or two days. It smells like rotting meat. The diffusion of the rotting meat scent attracts flies and beetles instead of bees to pollinate the plant. The Muttart Conservatory in Edmonton has a corpse flower that blooms every few years.
Figure B.1.4.4 – Corpse flowers grow taller than humans do.

 Watch More

Corpse Flower

Watch this video to see how people react to the stench of a blooming corpse flower.

  Try It!

Iodine Diffusion

Try this simple experiment to observe the diffusion of iodine particles. Iodine turns a dark blue colour when it is mixed with starch.

Materials:

  • clear glass or plastic cup
  • tablespoon measuring spoon
  • small Ziplocâ„¢ bag
  • water
  • cornstarch
  • iodine (an antiseptic you can find at a drugstore)
Iodine stains skin, clothing, and any materials it comes into contact with.
Instructions:

    1. Put 4 tablespoons of cornstarch and water into the clear cup.

    2. Fill the Ziploc bag half full of water.

    3. Add several drops of iodine to the Ziploc bag until the water turns a dark yellow colour.

    4. Seal the Ziploc bag. Turn it upside down over a sink to be sure it has no leaks.

    5. Put the sealed Ziploc bag into the cup of cornstarch. Leave the bag in the cup for 30 minutes.

    6. After 30 minutes, pull the bag from the cup. What do you observe?


Questions:

Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.

The starch turned blue because it came into contact with iodine. Iodine turns starch a blue colour.
Iodine moved out of the plastic bag by the process of diffusion. The iodine particles were small enough to fit through little pores in the plastic bag. This caused the iodine to move from an area of high concentration inside the bag to an area of low concentration outside the bag.
The plastic Ziploc bag has tiny pores that an iodine particle was small enough to fit through. Plant cell membranes have tiny pores that let very small particles diffuse into the cell.

  Try It!

Potato Osmosis

Try this simple experiment to observe the process of osmosis in potato slices.

Materials:

  • raw potato
  • paring knife
  • 2 plastic or glass cups
  • plate
  • spoon
  • fork
  • water
  • salt

Take care with the sharp knife; don't cut yourself or anyone else!
Instructions:

    1. Fill both cups half full of water. To one cup, add 5 tablespoons of salt; then, stir to dissolve the salt.

    2. Cut three circular slices of potato. Each slice should be about 1 cm wide.

    3. Put one potato slice in the cup of pure water. Put one potato slice in the cup of salt water. Leave one potato slice on the plate.
    4. Leave the potato slices for 45 minutes.

    5. After 45 minutes, use the fork to take the potato slices from the cups. Put all three potato slices on the plate. Compare the three potato slices. Bend the potato slices. What do you observe?

Questions:

Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.

The potato slice in pure water became crisper and stiffer than the original potato slice. If you tried bending the pure water potato slice, it may have snapped easily in half. The pure water potato slice changed because of osmosis. A higher concentration of water particles was available outside the potato than inside the potato. This caused water from the cup to move into the potato cells. More water in the potato cells made the potato more crisp.
The potato slice in salt water became soft and wilted compared to the original potato slice. If you tried to bend the salt water potato slice, you would know that it became very flexible. The salt water potato slice changed because of osmosis. Putting salt in the water resulted in a lower concentration of water in the cup compared to a higher concentration of water in the potato cells. This caused water from the potato cells to move from the potato cells and into the cup. Less water in the potato cells made the potato shrivel and become less stiff.



Figure B.1.4.5 – The leaves of deciduous trees change colour and fall from the trees during autumn.

Figure B.1.4.6 – Maple leaves can turn orange and yellow as well as red.


Colour Changing Leaves

In summer, leaves on trees and plants are green. The green colour comes from tiny green particles in the chloroplasts of plant cells. Tiny particles with a colour are called pigments. The green pigment in plants is called chlorophyll.

Leaves have hidden colours. Leaves have orange and yellow coloured pigments that the green chlorophyll pigment covers during summer. In the fall, when the days become shorter, plants stop making chlorophyll. The green colour disappears from leaves, allowing the yellow and orange pigments to show.

Figure B.1.4.7 – The leaves of most deciduous trees in Alberta turn yellow in colour.

 Watch More

Leaf Pigments

Watch this video to see green chloroplasts through a microscope.

Sunny days and cool nights in the fall help some types of leaves turn a bright red colour. Watch this video to learn more about why leaves change colour.

  Try It!

Leaf Pigments

Try this activity to separate the various coloured pigments from a leaf.

Materials:

  • tall glass cup
  • wooden spoon
  • hot water
  • shallow glass pan
  • paper coffee filter
  • scissors
  • pencil
  • tape
  • rubbing alcohol (isopropyl alcohol)
  • green leaves of one type (You can use outdoor leaves, houseplant leaves, or spinach leaves.)
Take care with the hot water and the rubbing alcohol.
Hot water can cause severe burns, and rubbing alcohol is flammable and is a skin irritant.
Instructions:

    1. Cut the green leaves into small pieces and put them into the tall glass cup.

    2. Pour a small amount of rubbing alcohol over the leaves. Use enough to cover them -- about 1 to 2 cm of rubbing alcohol in the glass.

    3. Use the wooden spoon to mash the leaves against the side of the glass. The rubbing alcohol should start to turn a green colour.

    4. Put this tall glass of rubbing alcohol into a shallow glass pan of hot water for 20 minutes while you prepare the other parts of the experiment.

    5. Cut a strip of coffee filter 15 cm long by 2 cm wide.

    6. Tape one end of the coffee filter to the middle of a pencil.

    7. Place the pencil on the top of the glass so the other end of coffee filter hangs down and touches the green rubbing alcohol.

    8. Let the end of the coffee filter sit in the rubbing alcohol for 2 hours.

    9. After 2 hours, take the filter paper out of the rubbing alcohol. What do you observe?

Questions:

Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.

You should observe various coloured stripes on the filter paper. Depending on the type of leaf you used, you should have a green stripe, a yellow stripe, and maybe an orange stripe.
Plants contain more than one colour of pigment. Green chlorophyll pigment hides the yellow and orange pigments in a plant. In this experiment, you used rubbing alcohol to separate these pigments in a plant leaf.



  Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.

Unit B Lesson 4 Self-Check

Instructions


Complete the following 6 steps. Don't skip steps – if you do them in order, you will confirm your understanding of this lesson and create a study bank for the future.

  1. DOWNLOAD the self-check quiz by clicking here.

  2. ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.

  3. COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.

  4. REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.

  5. SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.

  6. CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!


Self-Check Time!
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Self-Check Quiz Answers

Click each of the suggested answers below, and carefully compare your answers to the suggested answers.

If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.

Saltwater in the soil around a plant creates a lower concentration of water outside the plant compared to a higher concentration of water inside the plant. During osmosis, water moves from the higher concentration to the lower concentration. In this case, water moves from inside the plant to outside the plant. Water leaving the plant cells causes the plant to wilt.
Diffusion is the process that causes nitrogen fertilizer to move inside the garden plants. When the gardener put nitrogen fertilizer on the soil, there was a high concentration of fertilizer outside the plant, compared to a low concentration of fertilizer inside the plant. The fertilizer diffused from the high concentration outside the plant to the lower concentration inside the plant.
Osmosis and diffusion are similar because they both involve the movement of substances from high concentration to low concentration, across a cell membrane. Osmosis and diffusion are different because osmosis involves water, and diffusion involves substances other than water.
The cell membrane allows some substances to enter a plant cell, while keeping other substances out of the plant cell. The cell membrane makes sure the plant cell only gets the particular substances that it needs to live.
Tree trunk cells need thick cell walls to make the trunk rigid, so it can support the weight of the tree. Grass blade cells need flexible cell walls, so that the grass is able to move and bend in the wind.