Practical work in Biology Things to remember when designing an experiment: C-what you change, what are you investigating O-what organism are you using R-repeat M-what you measure, how you measure S-thing you keep the same to make a fair test Key ideas about Working Scientifically: Independent variable: the thing you change Dependent variable: the thing you measure Control variables: things you keep constant You need a sensible range of independent variables

Movement into and out of cells Measuring diffusion Use scalpel to cut out agar cubes (containing phenolphthalein indicator and sodium hydroxide) Acid will diffuse into cubes and turn them colourless Repeat with different sized cubes Measuring osmosis (living) Cut up potato into cylinders Put some in sugar solution and some in pure water Measure length of cylinders before and after Distilled water potato swells up Concentrated sugar potato solution shrinks Measuring osmosis (non-living) Tie wire around one end of viscous tubing, put a glass tube in other end and tie Put sugar solution down glass tube Measure where liquid is up to Put pure water into beaker and leave overnight Water will be drawn in and liquid will move up tube Re-measure where liquid is

Demonstrating CO2 production Respiration Heat produced in respiration Prepare a set of boiled dried beans (control) and one set of germinated ones Add each set to vacuum flask, but make sure there is some air so beans can respire aerobically Put thermometer in each and seal with cotton wool Record the temp of each flask for a month thermometer Cotton wool Vacuum flask Dead boiled beans Soaked germinated beans Demonstrating CO2 production Use hydrogen carbonate solution to show that living organisms produce CO2 as they respire Boiled beans Germinated beans CO2 present (respiration) Soak some dried beans in water for 2 days until the start to germinate (and respire!) Boil a second bunch so that they die Put hydrogen carbonate indicator into 2 test tubes and put a platform made of gauze into each Seal with rubber bung and leave for set time period

Respiration Respiration rate of yeast with enzymes Measure rate of CO2 production when changing variables such as temperature, concentration of sugar solution… Mix together sugar, yeast and distilled water Attach bung with a tube leading to second test tube of water Count how many bubbles are produced in a given period of time Repeat with water bath at different temperatures (or change another variable) Respiration is controlled by enzymes so as temp increases, so should rate of respiration

Enzymes

Photosynthesis Testing a leaf for starch Photosynthesis experiments Kill leaf by dunking in boiling water to stop any chemical reactions happening Heat in water bath with ethanol to get rid of chlorophyll Rinse leaf in cold water Add iodine solution If starch is present leaf will turn blue/black. Starch will be present if leaf is photosynthesising Photosynthesis experiments Chlorophyll, CO2 and light are all needed for photosynthesis The chlorophyll test Use variegated leaves (only the green parts contain chlorophyll) Expose the leaf to sunlight Test for starch using iodine solution Only the green bit that contained chlorophyll will turn blue/back Soda lime absorbsCO2 out of the air in the jar The carbon dioxide test Leave plant in sealed bell jar with soda lime and sunlight Test plant for starch Will not change colour as CO2 is needed for photosynthesis The light test Put a plant in a cupboard to grow without light Take leaf from plant and test for starch Will no change colour as no starch can be made as light is needed for photosynthesis

Photosynthesis Measuring light intensity and photosynthesis The rate at which pondweed produces oxygen corresponds to the rate of photosynthesis. Adjust length away of light from pondweed. Measuring light intensity and photosynthesis Leave pondweed to photosynthesise for a set amount of time, oxygen will collect in capillary tube Use syringe to draw gas bubble up to ruler and measure

Exchange in plants balance Measuring transpiration (potometer) Measure distance moved by air bubble- transpiration means water is lost through the leaves so water is pulled upwards Making it more accurate: Cut stem at a slant to increase water uptake Use a bung to prevent water evaporation Measuring transpiration (using a balance) Measure the change in weight Use a layer of oil to stop evaporation balance Measuring transpiration (potometer) Changing variables: Light- use a lamp or put in cupboard Temperature- use a heater Humidity- spray water into air Wind speed- use a fan No photosynthesis Respiration and photosynthesis More photosynthesis than respiration control 2. Use hydrogen carbonate indicator to measure change in CO2 concentration 1. Set up tubes with no leaf, leaf and foil (no sunlight), leaf in gauze (a little light) and a leaf in sunlight (lots of light) Gas exchange in plants