Asei

ASEI/PDSI LESSON PLAN TOPIC: Nutrition and transport in plants SUBTOPIC: Osmosis LESSON TOPIC: Effect of salt concentration on the mass and length of Irish potatoes DURATION: 40 min. FORM: 3 PARTICIPANTS: 40 DATE: 06/01/10 RATIONALE: Osmosis is a special type of diffusion. It is defined as the movement of water (solvent) molecules from an area of low concentration (low solute concentration) to an area of high solute concentration through the semi permeable membrane. The membrane is selectively permeable and only allows the water and very small molecules to pass through freely. Large solute molecules e.g. sucrose molecules cannot pass through it. It is imperative therefore for the learners to have knowledge of this process which would be used in the understanding of how the digested food molecules in their bodies move from the gut into the body cells. OBJECTIVES: By the end of the lesson learners should be able to: a) Identify different variable in the given data b) Slice well measured pieces of Irish potato. c) Graphically present information of length against concentration. TEACHING/LEARNING MATERIALS 4-different concentrations of salt /sugar (5%,10%, 15%, and 20%), beakers(tins), razor blades, Irish potatoes rulers and distilled water, threads,(strings), and (straight)30 cm dry sticks. REFERENCES, Medi I. K. & Meredith H. M. (1989). The Senior Certificate Biology, Dzuka Publishing Co. Ltd, Blantyre, Malawi. Pages 97-99. LESSSON PROCEDURE |Lesson Sequence |Teaching/Learning Activities |Learning Points | |Introduction |Ask learners to: | | |(5 min) |define osmosis |Recap of the prior knowledge and making | | |Explain the difference between osmotic pressure and osmotic potential. |hypotheses. | | |Predict what would happen to the size and mass of a peeled potato tuber |Osmotic pressure describes the pull with | | |stayed in the 30%salt solution for one day |which a solution draws water into itself | | | |Osmotic potential refers to the ability of | | |Bridge students’ answers to the current lesson topic. |a cell or solution to take in water by | | | |osmosis. | |Lesson Development |Step 1 | | |( 25 min ) |Ask learners to be in groups of four provide them with all the required |Carrying out investigations, collecting | | |materials. |data, and analyzing the results. | | |Step 2: | | | |Ask learners to do the activities of the day by following the procedures | | | |as outlined in the work sheet provided | | | |Step 3: | | | |Ask the learner to draw table and graph of results for the activities 1 | | | |and 2 respectively | | |Conclusion |Discuss the factors that affect the rate of diffusion in general. Discuss|Summary of all concepts learned and | |(5 min) |the identified variables in the conducted experiments |extension of ideas. | |Evaluation |Ask learners to orally answer the following question: |Formative assessment | |(5 min) |Why is it detrimental to ones healthy to drink half a litter of undiluted| | | |orange squash (sobo) at a go' | | | |Assign student to find out other situations that demonstrate osmosis. | | WORK SHEET ACTIVITY 1. EFFECT OF SALT CONCENTRATION ON MASS OF IRISH POTATO Materials: (Distilled) water, 5% salt solution, beakers (tins), razor blades, Irish potato, rulers, threads (strings), and (straight) 30cm dry stick. Procedure 1. Cut two slices of Irish potato with the following measurements: 40mm length, 10mm height and 10mm width. (Make sure that the measurements are accurate as possible so that they have the same volumes, hence equal masses.) 2. Using the string (thread) tie each block of Irish potato carefully. 3. Tie the strings to which the blocks of Irish potato on the opposite sides of the dry stick. 4. Put another string at the centre of the stick so that the two blocks of Irish potato balance as shown in the diagram below. 5. Immerse one block in water and the other in dilute salt solution carefully. 6. Ensure that the strings are not immersed in the solutions by sticking them to the container while the blocks only are fully immersed in the solution. 7. Wait for 20 minutes and slowly remove the blocks from the two solutions and observe. String Irish potato block Water Dilute salt solution - Identify the variables in this experiment' - Is there any relationship between the variables' If yes, state the relationship. This is an example of inverse relationship. ACTIVITY 1: EFFECT OF SALT CONCENTRATION ON LENGTH OF IRISH POTATO SLICES In Biology, the concentration of solutions used is in percentage form and not molarity. Therefore to prepare the correct concentrations always follow this simple procedure. If you want to make a 1% concentration of sugar solution, measure 1 gram of sugar and dissolve in 100ml of water. MATERIALS: - 4 different concentrations of salt/sugar (5%, 10%, 15% and 20%), beakers (tins), razor blades, Irish potatoes, rulers, and (distilled) water. PROCEDURE 1. Cut four slices of Irish potato with the following measurements: - 40 mm length, 5 mm height and 5 mm width. 2. Label five tins using the concentrations of sugar/salt. 3. Pour about 10cm3 of the solution according to the label each tin has. 4. Put one slice in each solution. 5. Wait for 15 minutes and measure each slice, record the results in the table below. |SUGAR/SALT CONCENTRATION (%) |LENGTH OF POTATO SLICE (mm) | | | | | | | | | | | | | | | | a. State the Independent, control and Dependent variables. b. Plot a graph showing length against concentration. c. What is the relationship between length and concentration' d. At what concentration is there no change in length'