Core Practicals Flashcards
Investigation into the effect of light on gas exchange by a leaf.
1) Put hydrogencarbonate solution into 4 boiling tubes and add leaves to three of them
2) Put bungs on all of them (the one without a leaf is the control)
3) cover one in foil, one in translucent material and leave the other two
4) put them all under bright light for a few hours
5) record the final colours of the indicator and repeat twice
Results:
untouched boiling tube should be PURPLE
- meaning low levels of carbon dioxide
- photosynthesis has taken place
Leaf with foil should be YELLOW
- carbon dioxide present
- respiration has taken place
leaf with translucent material should be MAGENTA
- some carbon dioxide present
- photosynthesis and respiration took place
control just ensures indicator is functioning
An investigation to measure the rate of photosynthesis using pondweed
1) place a piece of pondweed (elodea) in a test tube upside down
2) cut the end to make it easier for oxygen to escape
3) Put it in a beaker full of water to keep the temp of the test tube constant
4) Place a light at different distances from the test tube (5cm, 10cm, 15cm 20 cm) and record the amount of bubbles produced in 5 minutes
5) Repeat twice for reliability
results:
stronger the light the more amount of oxygen produced because light is one of the limiting factors affecting photoynthesis
An investigation into the effects of osmosis on a potato tuber tissue
(a potato tuber is a plant storage organ)
1) fill a boiling tube with water, a second with concentrated sucrose solution and a third empty
2) cut up 3 peeled potato chips 3x1x1
3) place one in each boiling tube
4) after 30 mins remove, blot and weigh the chips
5) calculate change in mass
6) repeat twice
result
water potato will GAIN mass
- water has moved from outside to inside the potato osmosis.
sucrose potato will initially gain mass, but as the concentration of the sucrose decreases mass decreases. because potato has a higher concentration of water than highly concentrated sucrose solution.
Testing leaves for starch
1) place a plant in the sun and a plant in the dark for 24 hours
2) Take leaves from the plant and put it in boiling water for 30 seconds
3) place the leaf in a tube of ethanol with boiling water and put in a water bath for 10 mins approx.
4) remove and wash with cold water then place on a white tile
5) add iodine solution if it turns blue/black it contains starch
result
plant in the dark = NO STARCH had to use it for respiration
plant in the light = has been photosynthesising so has lots of excess glucose converted into starch
Tests for starch and glucose
starch:
place sample in a dropping tile
iodine solution: turns from orange/brown to blue/black
glucose:
place sample in a test tube
benedicts solution: from blue to yellow/orange/green/finally brick red
An investigation to demonstrate that heat is produced by respiration
1) soak peas in water for 24 hours so they start germinating
2) boil a second batch to kill them
3) put both in bleach to remove bacteria then put in distilled water to remove bleac
4) place both seperately into a vacuum flask and close leaving some air in
5) provides insulation and temp changes can be measured
6) place cotton wool at the bottom so carbon dioxide can escape
7) measure the temps of the flasks
8) repeat twice for relability
results
the lives peas should have INCREASED in temp, this is because they are respiring and producing energy. heat energy given off
dead peas don’t respire, no increase of temp (if there is they aren’t all dead)
An investigation into factors that effect the rate of transpiration
4 main factors affecting: light intensity, temp, humidity, wind speed
appartus needed: rubber tubing, capillilary tube, leafy shoot, resevoir to refill capilliary tube, screw clip and a scale.
1) place the whole apparatus into a sink of water and any air in the tubing removed,
2) take a shoot and cut the stem at an angle
3) push the stem into the rubber tubing
4) remove from the water and use vaseline to seal any joints
5) place a lamp 5cm away from it
6) time the movement of water in the capillary tube
7) repeat twice
8) repeat again with lights at different points
results
if transpiration occurs the water bubble will move along the tube
if the rate of transpiration is higher the bubble will be further and move faster
this indicates the transpiration stream; (water evaporated from leaves and more moving up the stem into leaves to replace it)
Investigation to demonstrate the products of anaerobic respiration in yeast
when yeast anaerobically respires it produces ethanol and carbon dioxide useful in fermentation and for making beer
1) add 100ml of glucose solution (sugar and water) to a boiling tube then add yeast solution. put it in a water bath
2) put a bung with a delivery tube on it and put the tube in another boiling tube full of limewater
3) leave for a couple of hours
4) repeat twice
5) you can repeat again with different temps or different concentrations of sugar
results
the lime water will turn cloudy because of the carbon dioxide produced.
If the temp is increased then the co2 production will too until it reaches the optium temp, then rate will decrease as yeast denatures.
As the concentration increases the rate of c02 will and then will plateau
yeast can only deal with a certain amount of glucose at a certain rate
investigation into the effect of temp on the activity of amylase
( amylase - the digestive enzyme - breaks down starch into maltose)
1) Put 5cm3 of starch into a boiling tube and the same for amylase in a different boiling tube (using a pipette)
2) put in a water bath at room temp for 5 mins
3) pour the amylase into the starch
4) small sample of it is put immediately into a dropping tray then put iodine in
5) continue until the iodine stops turning black
6) repeat with water baths at different temps (20-60)
7) repeat twice for reliability
results
over time iodine should not change colour remaining brown. So starch has been broken down by amylase. The rate to break down the starch should increase until 40 degrees then it will slow. amylase becomes denatured after 40
investigation to demonstrate diffusion in a jelly
(agars consistency is similar to a cytoplasm high water content) it demonstrates how substances diffuse into a cell
1) die some agar jelly with potassium permanganate
2) 3 cubes of different sizes are cut out of jelly, with side lengths of 2x1x0.5
3) get a beaker of dilute hydrochloric acid and drop the jelly into it
4) time how long it takes for the cubes to go colourless
results
hcl diffuses into smallest cube fastest breaking down the pottassium permanganate. this is due to the smaller cubes having a smaller surfac aread to volume ratio.
effect of exercise on breathing rate
breathing rate changes during exercise due to the need for more chemical energy from respiration
1) subject sits still to relax for 5 mins
2) count number of breaths per min
3) do 100 starjumps
4) count number of breaths per min
5) continue to count breathing until it returns to normal
more execrise more breathing
need to get oxygen around the body, to muscles for respiration
measuring energy content in food
1) get some food that burns easily like a peanut or pasta
2) weigh it and put it on a needle
3) prepare a boiling tube with water 20cm3 and measure temp
4) burn the food and put under the water until it burns out and keep relighting until it burns no more
5) immediately measure the temp after
6) repeat
results
more energy the food has higher the temp of water
chemical energy of food converted to heat
what is the independent variable?
The factor that affects the dependent variable. The factor you change.
What is the dependant variable?
The factor that is affected by theindependent variable. The factor youmeasure
What is the control variable?
A factor that is kept constant so that itseffects on the dependent variable areconsistent throughout all experiments
6 steps to writing an experiment
Dependant variable Independent variable Method / equipment Control Repeat C
How long do you keep the potato in the sucrose solution/water/nothing?
30 mins
Why does the sucrose solution potato decrease in weight?
sucrose potato will initially gain mass, but as the concentration of the sucrose decreases mass decreases. because potato has a higher concentration of water than highly concentrated sucrose solution.
results in experiment for affecting transpiration
If transpiration occurse the water bubble will move along the tube
the higher the light intensity the faster and further away the bubble will go
it indicates the trasnpiration stream
How much yeats and sucrose solution do you use when testing the products of anaerobic respiraition in yeast?
100 cm3
Results of yeast products
Temp increases = co2 production
until optimum temp when yeast denatures
How much amylase and starch do you use
5cm3 and put into water bath for 5mins
what indicator do you use when testinng the effects of light on the gas exchange of a leaf?
HYDROGEN CARBONATE
Results of agar jelly test
hcl diffuses in breaking down pottasium permanganate
heat produced by respiration remember to wash the peas in….?
BLEACH (to remove bacteria) then distilled water (to remove bleach)
