Learning objectives / Learning outcomes / Specification link-up / Kerboodle
Students should learn:
·  that water often moves across boundaries by osmosis and why it is important
·  that osmosis is the diffusion of water through a partially-permeable membrane from a dilute to a more concentrated solution
·  that differences in concentrations of solutes inside and outside cells cause water to move by osmosis. / Most students should be able to:
·  define osmosis
·  distinguish between diffusion and osmosis
·  carry out an experiment to find out about the process of osmosis
·  explain the results of experiments in terms of osmotic movement of water.
Some students should also be able to:
·  explain the importance of osmosis in plants and animals. / Dissolved substances move by diffusion and by active transport. [B3.1.1 a)]
Water often moves across boundaries by osmosis. Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules. [B3.1.1 b)]
Differences in the concentrations of the solutions inside and outside a cell cause water to move into or out of the cell by osmosis. [B3.1.1 c)]
Controlled Assessment: B4.5 Analyse and interpret primary and secondary data. [B4.5.4 a)] / Chapter map: Exchange of materials
Data handling skills: Osmosis in potatoes
Practical: Investigating osmosis in beetroot
How science works: Investigating osmosis in beetroot
Support: Which way does the flow go?
Bump up your grade: Which way does the flow go?
Lesson structure / Support, Extend and Practical notes
Starters
Bouncy Castle – Show a picture of a Bouncy Castle. Has anyone got younger brothers or sisters who love these? How do they stay upright? Why don’t they burst? What would happen if they were made out of elastic rubber like a thicker version of balloons? Draw out the idea of a balance of air going in, air coming out and pressure on a non-elastic skin providing support. Link with osmosis in plants providing support for plant tissues. (5 minutes)
What happens to the chips – Show the students a bag of chips. Ask who is going to the chip shop tonight. At what time? Explain that there is always a rush on at about six o’clock, so the owners prepare the chips in advance and keep them in water. Ask, ‘What effect does the water have on the chips?’ Support students by giving them some suggestions from which to choose. Draw out some ideas from the class. Extend students by asking them to suggest ways of testing these ideas. (10 minutes)
Main
·  Modelling osmosis in cells (see ‘Practical support’). The results from the model cells can be used to illustrate the principles of osmosis. Ask students to interpret each one in terms of the diffusion of water and sucrose molecules and the effect of the partially-permeable membrane. Students may find it easier to understand osmosis if it is explained in terms of the diffusion of water molecules from where they are in high concentration (i.e. in a dilute solution) to where there is a lower concentration (i.e. a more concentrated solution). Diagrams help.
·  Investigating osmosis in potato tissue (see ‘Practical support’).
·  There are variations on the above which can be tried. Some students could measure changes in dimensions (i.e. length or volume) and others could measure changes in mass. Are the results similar? Which do they consider to be the most accurate?
·  Setting up an osmometer – A simple osmometer can be made using a length of Visking tubing, tied securely at one end, filled with a concentrated sugar solution. (For quick results use syrup or treacle only slightly diluted) and then a capillary tube tied securely in the top. The whole apparatus is held in place by a clamp and stand and lowered into a beaker of water. The level of sucrose in the capillary tube is measured at the start and then again at regular intervals (5 minutes). A graph can be plotted of the distance moved by the sucrose against time.
Plenaries
Follow up to ‘What happens to the chips?’ – If the demonstrations were set up at the beginning of the experiment, they can be looked at. What has happened to the chips? They can be measured, their texture assessed and the results discussed. Support students by asking them whether their chosen suggestions were correct. Students can be extended by asking them to calculate percentage change in dimensions. (5 minutes)
Bank account osmosis – who is most in the red? – Select three students. Tell one they are overdrawn by £10. Tell another they are overdrawn by £20 and the third by £30. Give them each 2p. Tell them that they have to give it to anyone who has less money than they have (i.e. is more overdrawn than them). The money should go from the £10 overdrawn to the £20 overdrawn and finish up with the £30 overdrawn. Explain that it is the same with osmosis. The coins represent water, which always goes to the most negative of any pair of cells in contact. (10 minutes) / Support
Carry out a stop motion of a plant wilting and being re-hydrated using Intel play microscopes (the kit pot plastic ones). Explain using a football and a pump.
Extend
Get students to investigate the effect of partial drowning. What effect would it have on the water balance in the body?
Practical support
Investigating osmosis
Equipment and materials required
Lengths of dialysis (Visking) tubing for each group of students,
Molar sucrose solution which can be diluted to the concentrations required, beakers, string, small measuring cylinders or pipettes to fill the tubes, glass tubes.
Details
Use the dialysis (Visking) tubing to make model cells. Lengths of tubing, about 10 cm long, should be wetted thoroughly and one end of each tied firmly with string. Fill the tubing bags with a concentrated sugar solution (molar sucrose) and tie the open ends firmly with string. These Visking tubing bags represent cells and can be immersed in beakers of water, less concentrated and more concentrated sugar solutions.
Investigating osmosis in potato tissue
Equipment and materials required
Fairly large potatoes, cork borers to make cylinders of tissue, knives and tiles to cut chips, molar sucrose, boiling tubes and racks, rulers and balances, tissues or paper towels to dry potato discs or slices.
Details
Chips or discs of potato tissue can be immersed in different concentrations of salt or sugar solutions, left for a period of time and then their change in mass or dimensions measured. Such experiments offer opportunities for the introduction of ‘How Science Works’ concepts and can be used as whole investigations. The change in mass or length can be plotted against the concentration of the solution and the solution which results in the least change is considered to be equivalent to the concentration of the cell sap of the potato.
Safety: Take care with sharp implements.
Course / Subject / Topic / Pages
Biology / Biology / B3 1.1 Osmosis / Pages 214-215
Learning objectives / Learning outcomes / Specification link-up / Kerboodle
Students should learn:
·  that active transport is the absorption of substances against a concentration gradient
·  that energy from respiration is needed to carry out active transport
·  that active transport enables cells to take up ions from very dilute solutions
·  that sugars and ions can pass through cell membranes. / Most students should be able to:
·  describe how active transport occurs
·  state examples of active transport in plants and animals
·  explain the importance of active transport to plants and animals.
Some students should also be able to:
·  explain in detail how active transport across a cell membrane takes place. / Substances are sometimes absorbed against a concentration gradient. This requires the use of energy from respiration. The process is called active transport. Active transport enables cells to absorb ions from very dilute solutions. [B3.1.1 g)] / Animation: Active transport
Lesson structure / Support, Extend and Practical notes
Starters
‘Hungry hippos’ game – Remind students of this game, where they have to grab marbles from a central arena using hippo-shaped scoops. The marbles caught end up in the traps. Use this as an analogy to describe taking molecules from an area of low concentration to an area of high concentration. (5 minutes)
Quick quiz – Give the students ten short questions on slips of paper, on osmosis and diffusion to recap work done so far. Support students by supplying them with the answers and getting them to match the answer to the correct question. Extend students by giving them the answers and getting them to write the questions. (10 minutes)
Main
·  If easily available, show some animations on active transport. Note: It is very difficult to explain how active transport works without referring to carrier proteins and pumps in the membranes.
·  Prepare a PowerPoint presentation on the need for certain mineral ions for healthy growth, (nitrate, magnesium and phosphate) the presence of these ions in the soil solution and the cell sap, and the way that plants accumulate ions against the concentration gradient.
·  A useful example of the need for energy in respiration is to describe a hydroponics system, where solutions are aerated to provide oxygen for the respiration of the roots.
·  Show photographs of marine vertebrates and discuss the problems of the salt in their diets and how they get rid of it. There is some information on the internet, especially from the RSPB web site. www.rspb.org.uk
·  To get across the idea of energy being needed, use a revolving door analogy. If something valuable is on the far side (students to decide what it is!), then it is worthwhile keeping on giving the door a good hard shove, even if you have got plenty inside already.
Plenaries
‘Where in the body? – Give the students a blank body diagram each and get them to draw on where active transport will take place. Support students by providing them with strips of paper or labels with the names of body parts on them. Get them to place the labels for body parts where active transport takes place on to their blank diagrams. Extend students by getting them to explain why active transport occurs and what is being actively transported. Annotate with reasons. Examine in pairs. (10 minutes) / Support
Use a short piece of hose-pipe with a perforated section where it passes a large card labelled ‘kidney’. Pour a mixture of salt and sugar into the tube. Catch the salt and sugar as it comes out and put it back into another hole in the hose pipe that comes after the perforations. Explain that we need to reabsorb some substances even when there are more of them on the inside than on the outside and that this takes energy.
Extend
Get students to do internet research on the number of ATP molecules produced during respiration of a glucose molecule. Relate this to the energy required to take in a molecule of glucose by active transport. If needed, set up a ‘Scavenger Hunt’ style series of URLs with the data needed on them.
Course / Subject / Topic / Pages
Biology / Biology / B3 1.2 Active transport / Pages 216-217
Learning objectives / Learning outcomes / Specification link-up / Kerboodle
Students should learn:
·  that sweat containing water and mineral ions is lost during exercise and can affect the concentration of the body fluids
·  that water and mineral ions need to be replaced to avoid dehydration
·  that sports drinks are claimed by the manufacturers to help the body replace used energy and replace water and mineral ions lost during sweating
·  there are cheaper and equally effective alternatives to branded sports drinks. / Most students should be able to:
·  explain that the water and mineral ions lost by sweating during exercise need to be replaced to avoid dehydration
·  describe the composition of sports drinks
·  describe how sports drinks restore the concentration of the body fluids
·  evaluate the claims made by the manufacturers of sports drinks.
Some students should also be able to:
·  assess the value of using sports drinks or alternatives after different levels of exercise. / Most soft drinks contain water, sugar and ions. [B3.1.1 d)]
Sports drinks contain sugars to replace the sugar used in energy release during the activity. They also contain water and ions to replace the water and ions lost during sweating. [B3.1.1 e)]
If water and ions are not replaced, the ion / water balance of the body is disturbed and the cells do not work as efficiently. [B3.1.1 f)]
Evaluate the claims of manufacturers about sports drinks. [B3.1] / WebQuest: Sports drinks
Lesson structure / Support, Extend and Practical notes
Starters
Sweating it out – Show a picture of a very sweaty face. Ask if students can remember the last time they were so hot that sweat was running down their face. Take examples. Ask if anyone has had sweat running into their eyes and what this feels like. Draw out that it is irritating because of the salt in your sweat. Ask where the salt has come from and draw out any consequences of losing salt from the body. (5 minutes)
Half time! – Show photographs or video of footballers or rugby players at half time taking drinks. Get the students to discuss with a friend what they would recommend the coach to put in the drinks bottles and why. Support students by handing out some clue cards to assist in forming and recording their opinions. Extend students by asking them how they would go about finding out the correct quantities of ingredients to put into the drinks. (10 minutes)