National 5 Biology Unit 1 – Cell Biology Section 2 – Transport across the Membrane

We will be learning how to: Name and describe the components of a cell membrane in terms of the fluid mosaic model. Carry out experiments on the effect of ethanol and temperature on beetroot cells. Describe diffusion as a method of passive transport down a concentration gradient for substances such as glucose, carbon dioxide and oxygen. Describe osmosis as a method of passive transport down a concentration gradient for the movement of water through a selectively permeable membrane. Describe the movement of water into and out of animal cells when they shrink or burst. Describe the movement of water into and out of plant cells when they become turgid or plasmolysed. Describe the relationship the relationship between different concentrations of solutions and their effect on cells. State that active transport requires energy for membrane proteins to move molecules and ions against the concentration gradient.

Cell Membrane Structure

The Fluid Mosaic Model The current accepted theory for the structure of the cell membrane is the Fluid mosaic model This consists of a double layer (bilayer) of phospholipids And a mosaic of proteins

Phospholipids Phospholipids are the main structural components of membranes Phospholipids form a bilayer (2 layers) They each have a hydrophilic (water-loving) head And two hydrophobic (water-hating) tails Hydrophilic head Head Symbol HydrophobicTails

The Phospholipid Bilayer The phospholipids line up with the hydrophobic tails pointing inwards, away from the fluids inside and outside the cells This forms the bilayer

How do things get in and out of the cell through the membrane? The Proteins How do things get in and out of the cell through the membrane? There must be holes… The proteins can be: Partially embedded in the phospholipid layer Spanning the phospholipid layer from one side to the other Have channels forming pores Are attached to the surface Made of proteins

The proteins have various functions within the cell membrane

The Functions of the Proteins Provide structural support Contain channels allowing transport of small molecules through the membrane Act as facilitators for diffusion Act as carriers for active transport Act as receptors for hormones Act as receptors for enzymes which act on the membrane Serve as antigenic markers (tissue type)

Fluid Mosaic Model of the Plasma Membrane proteins Pore (surrounded by proteins) Hydrophilic head Hydrophobic tail Phospholipid bilayer

Selectively Permeable Membrane All cells are enclosed with a cell membrane. A selectively permeable cell membrane is one that allows certain molecules or ions to pass through it by means of active or passive transport. Some substances cross the membrane freely, some cross with assistance, and others do not cross at all

Diffusion and Cell Membrane Structure You’re going to watch a video about the cell membrane. The answer to each question can be found in the video. What is the outer layer of an animal cell called? The lipid molecules have one side that attracts water and one side that repels it – true or false? What do the proteins in the membranes do? Give one example. How many layers of lipids does our cell membrane have? Do the proteins stay still or change positions?

Membrane Investigation – Red Cabbage Cells Cytoplasm Nucleus Cell Wall Vacuole Cell Membrane Plant and Animal cells

Method Aim – To predict what will happen when cells are added to acid, alcohol, hot water and cold water. You will need: A test tube rack 4 test tubes A piece of red cabbage A corer Alcohol Acid Things to think about – Where is the red pigment concentrated? Where will the pigment go if the membrane is damaged?

Method Measure 6ml of water in tube A Measure 6ml of alcohol in tube B Label the boiling tubes 1, 2, 3 and 4 Measure 6ml of water in tube A Measure 6ml of alcohol in tube B Measure 6ml of acid in tube C Measure 6ml of water in tube D Use the corer to get 4 pieces of red cabbage. Put one in each test tube Put tube 4 in the water bath

Investigation A B C D water water alcohol acid 70⁰C 30⁰C

Results! This is what you should have seen 1 2 3 4

Results A B C D water water alcohol acid 70⁰C 30⁰C

Results Conclusion In which tubes did bleeding occur? B (alcohol), C (acid) and D (high temperature) Explain why bleeding has occurred in these tubes. Acid , and high temperature (70˚C) destroys proteins in membrane Alcohol destroys lipid part of membrane Conclusion

Evaluation What was the purpose of tube A List what variables you kept constant How could you make your experiment more reliable?

Diffusion (Passive Transport)

Start Timer Think, Pair, Share 4 When the membrane broke down the red cell sap moved into the acid/alcohol/water Why do think this happened? Can you describe how the sap moved in terms of concentration? 2

Diffusion As the ammonium hydroxide (an alkali) moves through it turns the pH paper blue. This demonstrates that the gas is spreading out from a region of high to low concentration.

Particles move in the spaces between other particles

Diffusion This is the movement of a substance from an area of high concentration to a low concentration down a concentration gradient DOES NOT REQUIRE ENERGY High concentration Low concentration

Diffusion Diffusion

Selectively Permeable – what do you think? Substances that can pass through the membrane Substances that cannot pass through the membrane Starch amino acids proteins cells glucose

Model Cell experiment You will need to set up: Method a length of visking tubing a boiling tube a test tube rack a filter funnel a paper towel a plastic syringe, a dropper a dimple tray stopclock starch and glucose solution Iodine solution Benedict’s solution water bath Method 1. Fill tubing with starch and glucose solution 2. Wash and dry bag 3. Place in boiling tube 4. Immediately test sample of water for glucose and starch 5. Test every 4 minutes

Collect sucrose and starch solution A boiling tube Some visking tubing Boiling tube rack Filter funnel Dimple tray Stopclock Iodine Benedicts solution Goggles Pippette/droppper Collect

Instructions: Open your visking tubing and tie a knot in one end Funnel in some sucrose/starch solution Tie off the other end Put the visking tubing in your boiling tube Add water to the boiling tube and pipette some water out immediately to test for starch or sugar Test every four minutes

Selectively Permeable Substances that can pass through the membrane Substances that cannot pass through the membrane Starch Amino Acids Proteins Glucose Cells Starch amino acids proteins cells glucose

Diffusion and Cell Membrane Structure The channels in the proteins will let molecules like sugar/glucose through, but not larger things like starch. Because of this we say the membrane is selectively permeable. Plant and Animal cells

Sites of Diffusion Where do you think diffusion happens in your body? What way does each substance move?

Diffusion Glucose Carbon dioxide Oxygen Why is diffusion important to cells? To gain raw materials for respiration and photosynthesis. To remove waste products

Importance of Diffusion in the Body Where do you think diffusion happens in your body? What way does each substance move?

Importance of Diffusion glucose oxygen nucleus cell membrane cytoplasm carbon dioxide Human cheek cell

lung cells High O2 conc O2 Low CO2 conc O2 O2 Low O2 conc CO2 High CO2 conc cells CO2

Water molecules are also free to move in and out of the cell. So what’s next? Water molecules are also free to move in and out of the cell. However a cell needs to have some control which substances can enter and leave the cell. If not, then it could gain substances it doesn’t need or even lose substances it does need due to diffusion.

Diffusion: true or false? Boardworks Science for Scotland: S1 and S2 Competition Diffusion: true or false?

Diffusion in Multicellular Animals Blood returning to the lungs from cells has a higher CO2 concentration and lower oxygen concentration than the air in the lungs. CO2 diffuses from the _____ into the ________ and oxygen diffuses from the ________ into the ________. Diffusion is also essential for dissolved food (e.g. ___________ and __________ _______ ) moving from the blood to respiring cell. Urea also moves in the opposite direction by diffusion. blood lungs blood lungs glucose amino acids

Diffusion in Green Plants Green plants need diffusion to get the raw materials needed for photosynthesis ( ___________ ________ and _________) CO2 diffuses from the air, through the stomata and into the air spaces in the leaf. Water moves from the soil into the roots, then enters the xylem and then enters the leaf cells. carbon dioxide water

Osmosis

Osmosis

Osmosis in Potato Samples Draw a diagram of your apparatus before and after the experiment Label all parts e.g. solutions, samples & mass Write an explanation for your results: - Pure water - Salt solution

Explain why the sucrose molecules do not diffuse across the membrane. In what direction do the water molecules diffuse? Explain how a selectively permeable membrane works.

High water concentration Low water concentration Selectively permeable membrane Sucrose molecules High water concentration Low water concentration Water molecules Inside the cell Outside the cell

Selectively permeable membrane Sucrose molecules Water molecules are small enough to pass across the selectively permeable membrane Water molecules Inside the cell Outside the cell

Water molecules passing into the cell Selectively permeable membrane Water molecules passing into the cell Inside the cell Outside the cell

Selectively permeable membrane Sucrose molecules Osmosis continues until the water molecules are evenly spread inside and outside of the cell Water molecules Inside the cell Outside the cell

Osmosis Osmosis

Osmosis Expt: potato cylinder Osmosis

Three bits of potato are put into different concentrations of solution Three bits of potato are put into different concentrations of solution. Inside the potato cells there is a concentration of around 2%. What happens to each? Discuss with class variables, why did you blot the cylinders before weighed them Distilled water 2% salt solution 10% salt solution

High and low concentrations Boardworks Science for Scotland: S1 and S2 Competition High and low concentrations During osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions. Dilute solutions have a high concentration of water molecules. Concentrated solutions have a low concentration of water molecules. pure water dilute solution concentrated solution

Boardworks Science for Scotland: S1 and S2 Competition Predicting osmosis

Model Cell – Gummy Bears! Collect 2 gummy bears and two beakers Put a few centimetres of water in one beaker Put a few centimetres of salt solution in the other beaker Put a gummy bear in each Label your beakers with your intials and the solution used

Direction of Osmosis? 1 High water concentration Low water concentration (100% water) 2 10% sucrose solution (90% water) distilled water (90% water) (80% water) 3 10% sucrose solution 20% sucrose solution (90% water) (99% water) 4 10% starch solution 1% starch solution (100% water) (99.5% water) 5 distilled water 0.5% sucrose solution (100% water) 6 animal cell distilled water

Boardworks Science for Scotland: S1 and S2 Competition Osmosis and cells Plant and animal cells are surrounded by a partially-permeable plasma membrane. This allows water and other small molecules to diffuse across. Plant cells additionally have a strong cell wall surrounding the membrane which offers support and protection. plasma membrane cell wall red blood cell plant cell

Animal cells in water

Osmosis and animal cells Boardworks Science for Scotland: S1 and S2 Competition Osmosis and animal cells

Plant cells in water turgid plasmolysed

Osmosis and plant cells Boardworks Science for Scotland: S1 and S2 Competition Osmosis and plant cells

Animal Cells Plant Cells In distilled water, an animal cell will gain water & burst In strong salt/sugar solution, an animal cell will lose water & shrink Animal Cells In distilled water, plant cells gain water & become swollen (turgid) Plant Cells In strong salt/sugar solution, plant cells lose water, the cytoplasm & vacuole shrink in from the cell wall – cell becomes plasmolysed

The animal cell does not. Why does the animal cell burst in distilled water when the plant cell does not? The plant cell has a rigid cell wall that helps the plant cell keep its shape. The animal cell does not.

Unicellular Animals Contractile vacuole with canals to collect water When water passes in, vacuole expands then bursts when full When one vacuole is emptying, the other is filling This is osmoregulation

Now I can….. Define diffusion. Describe examples of substances which enter and leave the cell by diffusion. Discuss the importance of diffusion to cells. State that osmosis is a ‘special case’ of diffusion of water Explain osmotic effects in plant and animal cells Explain the meaning of the terms plasmolysed and turgid.

Active Transport

We will be learning… To state what is meant by active transport To describe the process of active transport To give examples of substances which move by active transport To state what factors limit the rate of active transport

What is a Concentration Gradient? The difference in concentration between two areas Which is the steepest gradient? Which particles move up a gradient (to an area of high concentration)?

Diffusion Which way will the particles move?

Moving against a concentration gradient ENERGY What do think is required to move the molecules against the concentration gradient? This is active transport

Active Transport The movement of molecules from a region of low concentration to a region of high concentration against a concentration gradient

Active Transport Inside of cell Outside of cell ATP ADP P

Active Transport molecules ow igh oncentration Low conc. High conc.

Protein molecules act as carrier molecules.                              These proteins recognise specific substances and transfer them across the plasma membrane.

Sodium Potassium Pump Sodium moves out of the cell. So where must the sodium ion concentration be higher?

An example of active transport Sodium and potassium ion movement in nerve cells. Potassium ions move into the cell. So where must the potassium ion concentration be higher?

Active transport carriers are often called ‘pumps’ . They often work by swapping one substance for another.

Factors affecting active transport Can you think of any? Remember! Active transport needs energy from respiration (the burning of food in the presence of oxygen inside a cell). Glucose concentration Oxygen concentration Temperature

Factors affecting active transport Describe and explain the results shown

Summary Make a list or table of similarities and differences between active transport and diffusion.

Now I can….. State what is meant by active transport Describe the process of active transport Give examples of substances which move by active transport State what factors limit the rate of active transport

Passive Transport

Active Transport - Sodium pump