biology p2 experiments Flashcards
effects of temperature on enzyme activity- measure how fast a product appears
1- enzyme catalase catalyses the breakdown of hydrogen peroxide into water and oxygen
2- collect oxygen produced and measure how much is given off in a set period of time e.g. every minute
3- put hydrogen peroxide solution and a source of catalase(potato) into a test tube with a bung with a delivery tube to a measuring cylinder upside down in water. the test tube is placed in a water bath at a constant temperature
4- run a series of experiments each with the water bath at different temperatures to see how it affects the enzyme catalase
5- CONTROL : enzyme conc,pH, vol of solution
effects of temperature on enzyme activity- measure how fast a substrate disappear
1- enzyme amylase catalyses the breakdown of starch to maltose- can detect starch using iodine solution which will go from orange-brown to blue-black
2- put a test tube of starch solution and amylase enzyme in a water bath at constant temp
3- use a pipette to drop mixture into iodine solution into a spotting tile
4- time how long it takes for the starch to disappear by regularly sampling the starch solution and use the different times to compare rates between different tests- time when iodine solution no longer turns blue-black as all starch has been broken down
5- by adjusting the water bath temperature, you can see how temp affects the activity of amylase
6- keep controls- enzyme conc, pH, vol of solution
investigate diffusion in a non-living system
1- make up some agar jelly with phenolphthalein and dilute sodium hydroxide which is alkaline so they will be pink
2- fill a beaker with some dilute HCl acid, and put cubes pf jelly into the beaker
3- leave the cubes for a while until eventually colourless as the acid diffuses into the agar jelly and neutralises the sodium hydroxide
4- you can investigate the rate of diffusion by using diff sized cubes of jelly and timing how long it takes for each cube to go colourless- largest surface area to vol ration will lose colour quickest
investigate osmosis in living systems
1- cut up potato into identical cylinders and get beakers with diff sugar solutions. one pure water and another very concentrated sugar solution and a few in between.
2- measure the lengths of the cylinders and leave in the beakers for half an hour-an hour
3- take them out and measure their lengths.
4- in sugary solution should have shrunk as drawn out water by osmosis to low conc of water in solution
5- in pure water, will have grown as water is drawn in through osmosis into potato
6- keep vol of solution and time constant
investigate osmosis in non-living system
1- tie a piece of wire around one end of some Visking tubing and put a glass tube at the other end- fixing with wire.
2- pour some sugar solution down the glass tube into the Visking tubing
3- out the VT in a beaker of pure water- measure where the sugar solution comes up to on the glass tube
4- leave it overnight, then measure where the liquid is in the glass tube, water should be drawn into the VT by osmosis (VT has a partially permeable membrane) and this will force the liquid up the glass tube
what’s the test for glucose?
benedict’s reagent:
add blue BR to sample and heat it but don’t boil.
-if test is positive then a coloured precipate will form
-it will change colour form blue->green->yellow->organ-> brick red
-the higher the conc of glucose, the further the colour change goes
what’s the test for starch?
Iodine solution
- starch present turns from browny-orange to blue-black
- if no starch, it stays browny-orange
how do you test a leaf for starch?
1- put the leaf in boiling water to stop chemical reactions happening inside the leaf
2- put the leaf in a boiling tube with some ethanol and heat inside a water bath- gets rid of any chlorophyll in the leaf- pale, white-ish colour
3- rinse the leaf in cold water and add iodine solution
how do you show that chlorophyll is needed for photosynthesis?
- use a variegated leaf- green parts contain chlorophyll
1) take leaf that’s been exposed to light for a bit and record which bits are green and which aren’t
2) test the leaf for starch and the green bits should turn black
3) shows that the bits that contained chlorophyll were the only bits able to photosynthesise and produce stach
how do you show that CO2 is needed for photosynthesis?
1- put a plant and soda line in a sealed bell jar with a light outside
2- the soda lime will absorb CO2 out of the air in the jar
3- leave the plant in the jar for a while and test a leaf for starch
4- it won’t turn blue-black as no starch has been made by the leaf showing CO2 is needed for photosynthesis
how do you show that light is needed for photosynthesis?
1- grow a plant in a cupboard without light but with plenty CO2 and warm enough
2- test a leaf for starch-won’t turn blue-clack as no starch has been made and so hasn’t photosynthesised- light is needed
how do you estimate transpiration rate?
use a potometer
- cut shoot underwater to prevent air entering the xylem and at a slant to increase SA
- assemble potometer in water and insert shoot under water so no air can get in
- check its watertight and airtight
- dry the leaves to allow shoot to acclimatise
- measure how long it takes for one air bubble to move across the scale per time
- keep conditions constant:temperature and air humidity
investigate the effect of exercise on breathing rate
1- firstly, sit still for 5 minutes. then for 1 minute count the number of breaths you take
2- do 4 minutes of exercise and as soon as you stop count your breaths for a minute
3- results should show that exercise increases breathing rate because muscles repire more during exercise- they need to be supplied with more O2 and have more CO2 removed so breathing rate increases.
4- control variables: time spent exercising using a stopwatch and the temperature of the room sing air conditioning or a thermostat
how do you investigate the respiration of yeast?
1- mix together sugar, yeast and distilled water, then add the mixture to a test tube
2- attach a bung with a tube leading to a second test tube of water
3- place the tube containing the yeast mixture in a water bath at a certain temperature
4- leave the tube to warm up a bit and then count how many bubbles are produced period time-1 minute
indication of respiration rate
5- repeat experiment with water bath at different temperature
6- respiration is controlled by enzymes- so as temp increases so should respiration rate up til optimum temp
- make more accurate using a gas syringe to measure volume instead of bubbles
how do you work out how much energy food has?
1- get food that burns easily - something dry like peanuts or pasta
2- weigh a small amount of food and then skewer it onto a mounted needle
3- add 25 cm^3 of water to a boiling tube- held with a clamp- this will be used to measure the amount of heat energy that’s released when the food is burnt
4- measure the temperature of the water, then set fire to the food using a Bunsen burner flame.
5- immediately hold the burning food under the boiling tube until it goes out. relight the food and hold it under the tube and keep doing this until the food won’t catch fire any more
6- measure the temperature of the water again
