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.
The Cell Membrane • Proteins can either pass through the membrane or float on the surface. • Phospholipids have a phosphate head and lipid tails.
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! • What is the role of the cell membrane? • Name the two structures which make up the cell membrane? • Why is the cell membrane shown using a “fluid mosaic model”?
Transport Across the Membrane - Diffusion What is diffusion?
Diffusion Experiment Equipment: Petri Dish 20ml water Food colouring Laminated circle Timer
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.
Diffusion Experiment • At 1 minute, 3 minutes, 5 minutes and 8 minutes colour in the Petri dish to show how far the colour had spread.
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?
Diffusion • 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. 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! • What is the definition of diffusion? • Why is diffusion an example of passive transport? • During diffusion substances move down a concentration gradient, what does this mean? • Which substances will move in and out of an animal cell by diffusion? • Which substances will move in and out of an plant cell by diffusion? • What effect will a uniform concentration have on diffusion? • Glucose is constantly used up in the cell. Why does this help diffusion to continue? • Why is diffusion important in animal cells?
Visking Tubing 1 Equipment: Beaker Water Visking Tubing 15ml Starch Solution 15ml Glucose Solution Clips
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.
Visking Tubing 2 • 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?
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 • What is the definition of diffusion? • Why is diffusion an example of passive transport? • Why is the cell membrane called selectively permeable? • What effect will a uniform concentration have on diffusion? • Glucose is constantly used up in the cell. Why does this help diffusion to continue? • 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.
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 Method Set 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?