Practicals Flashcards
(16 cards)
Investigating enzyme activity - how fast a product appears
- The enzyme catalyses the breakdown of hydrogen peroxide into water and oxygen
- Collect the oxygen and measure how much is produced in a set time
- Use a pipette to add a set amount of hydrogen peroxide to a boiling tube
- Set up rest of apparatus - add a source of catalyst (potato) to the hydrogen peroxide and quickly attach the bung
- Record how much oxygen is produced in first minute
- Repeat over a range of temperatures
Control variables: pH, potato used, size of potato pieces
Investigating enzyme activity - how fast a substrate disappears
- Enzyme amylase breaks down starch into maltose
- Detect starch with iodine solution - if present the iodine will go from brown/orange to blue/black
- Put a drop of iodine solution to each spotting tile well
- Every 10 seconds add mixture using a pipette
- When iodine remains brown/orange record time taken
- Repeat with a range of temperatures
What helps to keep constant temperature
Water bath
Diffusion experiments
- Make agar jelly with phenolphthalein (pH indicator) and dilute sodium hydroxide - will be pink
- Put dilute HCl into a beaker
- Cut a few cubes from the jelly and put them into a beaker with the acid
- If you leave them for long enough, they will turn colourless as the acid diffuses into the agar jelly and neutralises the sodium hydroxide
To investigate the rate of diffusion use different sized cubes - cube with largest SA:V will lose its colour fastest
Osmosis experiment - living
Potato cylinders
1. Cut potato into identical cylinders and add to beakers with different sugar solutions (one pure water and other very concentrated sugar solution, some in between)
2. Measure the length of the cylinders
3. Leave each in a beaker for around 30 mins
4. Re measure their lengths
5. If they have drawn in water due to osmosis they will be longer
Osmosis experiment - non living
- Fix some visking tubing over the end of a thistle funnel
- Pour in some sugar solution
- Put the thistle funnel into a beaker of pure water - measure where solution comes up to on glass tube
- Leave apparatus over night - then measure where solution is - water should have been drawn in via osmosis, forcing the solution up the glass tube
Testing a leaf for starch
- Dunk the leaf in boiling water to stop chemical reactions in the leaf
- Put leaf in boiling tube with ethanol and heat in a water bath until it boils - this gets rid of any chlorophyll and makes the leaf a white-ish colour
- Rinse the leaf with cold water and add iodine - if starch is present it will then turn blue-black
What does the starch test show
Whether photosynthesis is taking place - if a plant can’t photosynthesise, it can’t make starch
Test to show that chlorophyll is needed for photosynthesis
Use green and white leaves - only the green ones contain chlorophyll
1. Take a variegated leaf from a plant that has been exposed to light - record which parts are green
2. Test leaf for starch - only the bits that green will turn blue black
Suggests that only the parts of the leaf that contained chlorophyll could photosynthesise and produce starch
Test to show that CO2 is needed for photosynthesis
Use a sealed bell jar, light, soda lime and plant
1. The soda lime will absorb the CO2 out of the air in the jar
2. If you leave the plant in the jar for a while and then test a leaf for starch, it won’t turn blue-black
This shows no starch has been made so no photosynthesis could occur without the CO2
Test to show that light is needed for photosynthesis
Use a plant that has been grown in the dark for 48 hours - will have used up its starch stores
Cut a leaf from the plant and test it for starch - leaf won’t turn blue-black
Light is needed for photosynthesis so no starch is made
Test to show the rate of photosynthesis
Use a light source a set distance from a test tube with pondweed and water, attached to a gas syringe with an oxygen bubble
1. Gas syringe should be empty to start with
2. Sodium hydrogencarbonate can be added to the water to make sure plant has enough CO2
3. A source of light is placed at a specific distance from the pondweed
4. Pondweed is left to photosynthesise for a set time - as it photosynthesises the oxygen will collect in the gas syringe
5. Measure length of gas bubble - proportional to the volume of O2 produced
6. Repeat with different distances from the light
Control temperature and time
Testing carbon dioxide production
Hydrogencarbonate indicator
Usually orange but turns yellow with CO2
1. Use germinating beans and boiling beans (the control)
2. Same amount of hydrogencarbonate indicator in each test tube and seal with a bung
3. Leave for a set period of time
4. Germinating seeds - indicator will turn yellow
Investigating effect of exercise on breathing rate
- Sit still for five minutes then count for one minute the number of breaths you take
- Do four mins of exercise then stop and count breaths for a minute
- Repeats and work out mean results - use multiple people to do the same and compare results
Investigating the release of carbon dioxide in a breath
Set up two boiling tubes each with the same amount of lime water
Put mouth around mouthpiece and breathe in and out several times
As you breathe in air from the room is drawn through test tube A - contains little CO2 - remains colourless
When you breathe out the exhaled air bubbles through the limewater in boiling tube B - air contains CO2 - limewater turns cloudy
Investigate conditions needed for germination
- Take four boiling tubes and put some cotton wool at the bottom of each one
Tube 1 - water, oxygen, room temp - control
Tube 2 - no water, oxygen, room temp
Tube 3 - water, oxygen, low temperature
Tube 4 - water, no oxygen, room temp - Put 10 seeds on each cotton wool
- Leave for a few days and observe what happened
- Germination will only happen in Tube 1 - all conditions are needed to germinate
