Transport Across Membranes

Can you remember the role of the cell membrane?

The Cell Membrane

• Controls what enters and leaves the cell.

• Watch the following video clip and see if you can name 2 new parts of the membrane at the end.

The Cell Membrane

• The cell membrane is made of proteins and phospholipids.

• Label these on your diagram.

• Proteins can either pass through the membrane or float on the surface.

• Phospholipids have a phosphate head and lipid tails.

The Cell Membrane

Fluid Mosaic Model

• Phospholipids provide the membrane with fluidity.

• The combination of large proteins and small phospholipids make the membrane look like a mosaic.

Model Cell Membrane

• Now try building a model cell membrane with your partner.

• You should be prepared to present your model to your table in 10mins.

• Remember to use the terminology we have learned in describing your model.

Question Time!

1. What is the role of the cell membrane?

2. Name the two structures which make up the cell membrane?

3. Why is the cell membrane shown using a “fluid mosaic model”?

Transport Across the Membrane - Diffusion

What is diffusion?

Diffusion Experiment

Equipment:

Petri Dish20ml waterFood colouringLaminated circleTimer

Diffusion Experiment

• Place the laminated circle under the Petri dish.

• Add 20ml of water to the Petri dish.

• Add one drop of food colouring to the Petri dish.

• Immediately, start the timer.

• At 1 minute, 3 minutes, 5 minutes and 8 minutes colour in the Petri dish to show how far the colour had spread.

Diffusion Experiment

Diffusion

• Watch the video clip.

• http://www.bbc.co.uk/learningzone/clips/the-cell-membrane/10644.html

• Can you pick out a definition of diffusion which matches the result of your experiment?

• the movement of a substance from an area of high concentration to an area of low concentration.

• Diffusion is a form of passive transport.

It does not require energy.

Diffusion

• During diffusion substances move down a concentration gradient.

Diffusion

High

Low

Why is it important?

• Diffusion is important in animals to allow the raw materials needed for respiration to enter, e.g. Oxygen and Glucose.

• It also allows the products of respiration to leave the cell, e.g. Carbon dioxide and Water.

Why is it important?

• Diffusion is important in plants to allow the raw materials needed for photosynthesis to enter, e.g. Water and Carbon Dioxide.

• It also allows the products of photosynthesis to leave the cell, e.g. Oxygen and Glucose.

Question Time!

1. What is the definition of diffusion?2. Why is diffusion an example of passive transport?3. During diffusion substances move down a concentration

gradient, what does this mean?4. Which substances will move in and out of an animal cell

by diffusion?5. Which substances will move in and out of an plant cell

by diffusion?6. What effect will a uniform concentration have on

diffusion?7. Glucose is constantly used up in the cell. Why does this

help diffusion to continue?8. Why is diffusion important in animal cells?

Visking Tubing 1

Equipment:

BeakerWaterVisking Tubing15ml Starch Solution15ml Glucose

SolutionClips

• Test the liquid inside and outside the visking tubing for starch.

• Test the liquid inside and outside the visking tubing for glucose.

• Draw a diagram and make a note of your results.

Visking Tubing 1

• Test the liquid inside and outside the visking tubing for starch.

• Test the liquid inside and outside the visking tubing for glucose.

• Draw a diagram and make a note of your results.

• What does this show about the cell membrane?

Visking Tubing 2

The membrane is selectively permeable to small molecules (e.g. oxygen, carbon dioxide and water).

Larger molecules such as dissolved food pass through more slowly.

Even larger molecules cannot pass through at all. All this is due to the tiny pores (holes) in the membrane.

Diffusion in Multicellular Organisms

• Diffusion is very important in the lungs.

• When you breath in, the concentration of oxygen is higher in the lungs than in the blood.

• Therefore oxygen diffuses from the

to the and CO2 diffuses from the to the .

Questions

1. What is the definition of diffusion?2. Why is diffusion an example of passive

transport?3. Why is the cell membrane called selectively

permeable?4. What effect will a uniform concentration have

on diffusion?5. Glucose is constantly used up in the cell. Why

does this help diffusion to continue?6. Why is diffusion important in multicellular

organisms?

What molecules move by diffusion?

Oxygen

Carbon Dioxide

Glucose

Water

Odd one out?

Osmosis

• The movement of water from an area of high concentration to an area of low concentration through a selectively permeable membrane.

Drowning Gummies

The drowning gummies expt

You will be adding gummy sweets to different solutions and observing what happens to the sweets.

Before starting we need the vital statistics of your new gummy friends

The measurements

You will have 3 gummy friends to ‘play’ with.

You need measurements for each one (so 3 tables)

The MethodSet up the experiment as shown below using your chosen

gummies

Tap water 40% salt water

The Results

When instructed remove your gummies on to a paper towel and complete the ‘After’ measurements.

Use the ‘mass’ measurements to calculate and % change in mass

% change in mass = change in mass x 100 initial mass

Use the information about change in mass to graph your results

• Analysis: In your own words explain the difference between the three gummies and what you think was happening.

• Evaluation: Is there anything could be done to improve the experiment?