Experiment - OB11. To compare the levels of Carbon Dioxide in Inhaled & Exhaled Air.
Safety googles and gloves must always be worn, when chemicals are involved.
We have 2 testubes containing limewater. Limewater is a clear solution and it turns milky when Carbon
Dioxide is present...
The testube on the left, contains a stopper which has 2 pieces of tubing.
A long piece going into the limewater and a short piece which dosn't reach the limewater.
I'm going to Exhale air from my lungs into the limewater. And it should turn milky, once there is enough Carbon Dioxide...
As you can see, After about 15 secs blowing. The limewater has gone from clear to milky...
Indicating the presence of Carbon Dioxide.
I will now switch the stopper, with the tubing. From the testube on the left, to the one on the right.
This time. Rather than breathing out on the tube going into the limewater. We will inhale air through
the short tubing. The air is being drawn in from the room. And as it contains much less Carbon Dioxide
It will take longer for the Limewater to turn milky.
I will now suck through the short tube...
The amount of air that must pass through the limewater to turn it milky, takes considerately longer than
the one on the left. So, we will keep drawing in air until it turns milky...
As you can see. The limewater in this testube has eventually turned milky. But this is after 7 mins of
drawing in air from the room, into the limewater.This experiment shows that there is far more Carbon
Dioxide in Exhaled air. Than there is in Inhaled air. That's the end of Experiment OB11...
Experiment - OB49. To show that starch is produced by a photosynthesizing leaf.
Safety goggles, again. Must be worn.
In this Experiment, We take a leaf and we will test the presence of startch using the chemical Iodine.
The leaf must first be treated under several stages...
The first stage involves placing the leaf into a beaker of boiling water. For 1 min.
This helps to remove the the waxy qudicle from the leaf. The leaf is then removed from the boiling water
and placed into a testube of alcohol...
The alcohol will disolve the chylorphyl from the leaf, But the alcohol must be first be heated.
As alcohol is extremely flammable. It cannot be heated directly and must be heated in a water bath..
The leaf is left in the alcohol in the water bath. Until all the chlorophyll has been removed...
After aprox. 10 min. The alcohol can be seen to have turn green in colour. This is because the chlorophyll
has disolved from the leaf into the alcohol. We now remove the alcohol from the water bath...
And place it on the testube rack..
Because we no longer need to use the water bath, the Bunsen Burner can be switched off or the Chimney
can be closed, giving an orange flame. Which makes it easier to see and safer to use...
We now pour the alcohol out of the testube and remove the leaf from the testube...
We now remove the leaf from the testube, and place it into warm water to soften it.
5-10 secs is long enough...
The leaf is then spread on a white tile... And tested with the chemical Iodine...
This is the end of Experiment OB49...
Experiment - OB58. to investigate the conditions necessary for germination.
There are 3 factors, which must be present for seeds to germinate...
They are: Water, Oxygen and a suitable temperature.
Here we set up 4 testubes. The testube here, the seeds are placed on moist cotten wool, in an open testube
In a warm atmosphere. This is known as our control.
These seeds are in similar conditions, i.e: moist cotten wool with the presence of oxygen.
But this will be place in a fridge at 4 oC.
The seeds in this testube are placed in water that has been boiled and then cooled, which removes the
oxygen present in water. And a layer of oil is placed on top to prevent any further oxygen entering the
water...
The seeds in the last testube are placed on dry cotten wool, in a warm enviroment, in an open testube...
The testubes are going to be left like this for one week and we will return to them to see the results..
One week has passed... And we return to look at the seeds in the testubes...
The seeds int his testube have germinated, this is because they had the 3 conditions needed: Water, Oxygen
& a suitable temperature...
The seeds in this testube did not germinate because the have been placed in a fridge at 4 oC...
Similarly. These seeds did not germinate, because they were in water that was boiled and cooled.
Hense they were not exposed to any oxygen.
And these seeds have not germinated because they were placed in dry cotten wool...
That is the end of experiment OB58...
Experiment - OB65. To investigate the presence of micro-organisms in air & in soil...
For this experiment, we used 3 petri dishes...
The first petri dish is our control. SO it remains sealed through out the experiment.
The second petri dish is going to be exposed to air. SO we remove the lid for aprox. 5 min...
The thrid dish we sprinkle a small amount of soil on the edgar inside the dish...
And put the lid back on as quickly as possible...
The 3 Petri dishes are now placed upside down in an incubator at 25 oC for aprox. 1 week...
1 week has passed. And we have removed the petri dishes from the incubator at 25 oC...
The first petri dish, which is our control, shows no growths or micro-organisms
Which means the dish itself was sterilized...
The second dish had been exposed to air for aprox. 5 min. It contains "a fluffy" or "moldy" growths.
This indicates the presence of fungi. The third dish which is exposed to small amount of soil shows
smooth, round growths. Which indicate the presence of bacteria.
And some "moldy" or "fluffy" growths, which indicate the presence of fungi...
That is the end of experiment OB65...