Exchange of materials p.214 Osmosis Exchange of materials p.214

Requirements 24 boiling tubes 12 cork borer 12 tiles 12 pens 12 racks Cling film Potatoes Demo osmometer No worksheets

Objectives 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.

Outcomes 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.

Specification 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)]

Workbook P.101-2

Which way does the flow go? Aims In this activity you will think about the flow of money. This can help you to understand osmosis.   Task Imagine that there are three friends, all of whom have overdrafts at the bank. They meet up and compare their finances. They decide that whoever is the most overdrawn should get money from anyone who is less in debt than they are. This means that money will move from an account where there is more money, to an account where there is less money.

In the same way, water will move across a partially permeable membrane from where there is more water to where there is less water. This is called osmosis. On the diagram below, draw an arrow to show the direction in which the water will move.

In the same way, water will move across a partially permeable membrane from where there is more water to where there is less water. This is called osmosis. On the diagram below, draw an arrow to show the direction in which the water will move.

define osmosis osmosis is the … of water through a … membrane from a … to a … solution Missing words partially-permeable, more concentrated, dilute, diffusion

define osmosis osmosis is the diffusion of water through a partially permeable membrane from a dilute to a more concentrated solution Missing words partially-permeable, more concentrated, dilute, diffusion

comparing diffusion and osmosis

Comparing osmosis and diffusion Movement of any very small particle From a high to low concentration Doesn’t have to pass through a barrier Kinetic energy from particles Osmosis Movement of water molecules only From a dilute to a concentrated solution Passes through a partially permeable membrane Kinetic energy from particles

experiment to find out about the process of osmosis

Partially permeable (more concentrated solution) (dilute solution)

explain the results of experiments in terms of osmotic movement of water.

The osmometer The water is a ……. Solution, the sugar solution is more ……….. The visking tubing is a ............... ............ membrane Water moves into the visking tubing by........... The bag fills out and the contents press out on the walls. The bag is firm or ........... Water continues to move into the bag, The pressure created forces the liquid up the capillary tube.

The osmometer The water is a dilute Solution, the sugar solution is more concentrated solution The visking tubing is a partially permeable membrane Water moves into the visking tubing by osmosis The bag fills out and the contents press out on the walls. The bag is firm or turgid Water continues to move into the bag, The pressure created forces the liquid up the capillary tube.

explain the importance of osmosis in plants and animals. Read p.215

The effect of osmosis on animal and plant cells Animal cells In a concentrated solution lose water by osmosis and shrink In a dilute solution take in water by osmosis and burst as the cell membrane is weak Plant cells In a concentrated solution the cytoplasm and cell membrane shrink away from the cell wall = plasmolysed cell/flaccid In a dilute solution take in water and the cytoplasm pushes out on the cell wall = turgid/firm cell Plasmolysis video lettuce video

Slugmosis video Make a script for the video using these words Osmosis Partially permeable Diffusion of water molecules Dilute solution More concentrated solution

Osmosis in potato tissue Have you ever wondered why they store the cut chips in slightly salty water in the chip shop before they fry?

Method Each group will need: 2 x boiling tubes 1 x tube rack 1 x marker pen (?) 2 x potato chips (fair testing???) 1 x 20 cm3 syringe (for?) Some Cling film (?) Repeats / reliability (?) 1.0 M SCC 0.0 M DBB Draw a blank results table (?) Label the boiling tubes with the treatment and your initials. Using the syringe, add 20 cm3 of the sugar solution to each tube. Cut the potato chips to exactly 30 mm. Record initial length in mm on your results table. Put the chips into the boiling tubes (one per tube) and cover with cling film. Place tubes into your group’s tube rack and put carefully onto the side bench.

Table of results for osmosis in potato chips Tube Length of chip Before expt /mm Length of chip after expt /mm Change in length Percentage change in length A B Formula for percentage change = change/original x100