1. 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

2. 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

3. 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

4. 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

5. Enzymes

6. 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

7. 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

8. 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