Starch Hydrolysis
Summary
TLDRThe lab experiment investigates starch hydrolysis by bacteria, focusing on the production of an exoenzyme called diastasis. Starch agar plates streaked with two bacterial samples were incubated and then tested with iodine, a starch indicator. A clear zone around one bacterium indicates starch hydrolysis due to diastasis, as the iodine does not turn dark, whereas the other shows no hydrolysis with a brown coloration. This visual differentiation highlights the presence or absence of the enzyme's activity in breaking down starch into glucose.
Takeaways
- đ§Ș The lab is conducting a test on starch hydrolysis to determine if a bacterium can produce an exoenzyme called diastasis.
- đż The bacteria are streaked on a starch agar plate and incubated to observe their effect on starch.
- đ§ Iodine is used as an indicator to test for the presence of starch; it turns a dark color when it binds with starch.
- đ A clear zone around bacterial growth indicates starch has been hydrolyzed by the exoenzyme diastasis, as there is no longer any starch to react with the iodine.
- đŠ The iodine is added to the Petri plate just enough to cover the surface of the agar to avoid excess spillage.
- â± After adding iodine, the plate is left for about 30 seconds to a minute to allow for the reaction to occur.
- đ« Care must be taken not to tip or pick up the plate to prevent the liquid iodine from spilling.
- đ Excess iodine is poured into a disposal container to maintain safety and cleanliness in the lab.
- đŹ A white background is used to enhance visibility of the clear zone, making it easier to assess the results of the hydrolysis.
- đ The results show that the bacterium on the left did not hydrolyze starch as the agar turned brown, while the one on the right did, indicated by a clear zone.
- đ The presence or absence of a clear zone is the key observation for determining whether starch has been hydrolyzed by the bacterium.
Q & A
What is the purpose of the starch hydrolysis test in the lab?
-The purpose of the starch hydrolysis test is to determine whether a bacterium can produce an exoenzyme called diastasis that can break down starch into glucose.
What is the role of diastasis in this experiment?
-Diastasis is an exoenzyme that, if produced by the bacterium, can hydrolyze starch into glucose.
What type of medium was used for the bacteria in the experiment?
-A starch agar plate was used for the bacteria in the experiment.
How were the bacteria applied to the starch agar plate?
-The bacteria were applied to the starch agar plate by making single streaks using an auger.
What is the function of iodine in the starch hydrolysis test?
-Iodine is used as a starch indicator in the test. It reacts with starch, turning it a dark brown to black color, which indicates the presence of unhydrolyzed starch.
What does a clear zone around bacterial growth indicate after iodine is added?
-A clear zone around bacterial growth indicates that the starch has been hydrolyzed by the exoenzyme diastasis, as there is no longer any starch to react with the iodine.
How long should iodine be left on the plate after being added?
-Iodine should be left on the plate for about 30 seconds to a minute to allow for the reaction with the starch.
Why is it important to be careful with the iodine after it has been added to the plate?
-It is important to be careful with the iodine because it is a liquid and can run off the plate if it is tipped or picked up, potentially staining clothes or skin.
What was the method used to remove excess iodine from the plate?
-The excess iodine was poured into a disposal container to prevent it from running off the plate.
How can the results of the starch hydrolysis test be more easily observed?
-The results can be more easily observed by placing a white background behind the plate, which helps to contrast the clear zone against the dark iodine-stained agar.
What was the outcome for the two organisms tested in the script?
-The organism on the left did not hydrolyze the starch, as indicated by the brown color where the starch reacted with iodine. The organism on the right produced a clear zone, indicating that it hydrolyzed the starch.
Outlines
đŹ Starch Hydrolysis Test Overview
This paragraph introduces a lab experiment focused on starch hydrolysis, where the goal is to determine if a bacterium can produce an exoenzyme called diastasis capable of breaking down starch into glucose. The experiment involves streaking two types of bacteria on a starch agar plate and incubating it. The presence of hydrolyzed starch is indicated by a clear zone around bacterial growth after iodine is added to the plate, which would otherwise turn dark in the presence of starch.
đ Iodine Application for Starch Detection
The procedure for adding iodine to the Petri plate is described, which is a crucial step in the starch hydrolysis test. Iodine acts as a starch indicator, turning a dark brown to black color when it binds with starch. The correct amount of iodine is applied to cover the agar surface without excess, and the plate is allowed to sit for a minute to develop the results. Care is taken to avoid spilling the iodine, which could affect the outcome or cause safety issues.
đ Observing the Hydrolysis Results
After the iodine has been added and given time to react, the results of the starch hydrolysis test are observed. The process involves removing excess iodine and examining the plate for clear zones around the bacterial growth. A white background is used to enhance visibility of these clear zones. The results indicate that the bacterium on the right has successfully hydrolyzed the starch, creating a clear zone, while the one on the left has not, as evidenced by the brown coloration where starch is still present.
Mindmap
Keywords
đĄStarch Hydrolysis
đĄExoenzyme
đĄDiastasis
đĄAgar
đĄIncubation
đĄIodine
đĄStarch Indicator
đĄClear Zone
đĄPetri Plate
đĄBacterial Growth
đĄColor Change
Highlights
The lab test involves starch hydrolysis to determine if a bacterium can produce the exoenzyme diastasis.
Diastasis enzyme is capable of breaking down starch into glucose.
Starch agar plates were prepared with single streaks of bacteria for testing.
Incubation of the plate is necessary after streaking the bacteria.
Iodine is used as a starch indicator in the test.
Iodine reacts with starch, turning it a dark brown to black color.
A clear zone around bacterial growth indicates starch hydrolysis by diastasis.
Adding iodine to the Petri plate is the method to test for starch presence.
The iodine solution should just cover the agar surface without excess.
A waiting period of about a minute is required after adding iodine.
Excess iodine should be carefully disposed of to avoid contamination.
A white background helps in observing the clear zone resulting from starch hydrolysis.
The left bacterium did not hydrolyze starch as indicated by the brown color.
The right bacterium produced diastasis, evidenced by the clear zone around its growth.
The presence or absence of starch can be visually confirmed after iodine addition.
The test demonstrates the practical application of enzymatic activity in bacteria.
The lab procedure highlights the importance of careful handling and observation in microbiology.
Transcripts
another test we're doing in today's lab
is starch hydrolysis we're looking for
the ability of a bacterium to produce an
EXO enzyme called diastasis that can
hydrolyze or break down starch into
glucose so we took a plate of starch
agar and we made single streaks of the
two bacteria we're testing on the auger
and we incubated the plate now to find
out if the starch has been hydrolyzed
we're going to be adding iodine to the
plates and grams iodine iodine is a
starch indicator iodine combines with
starch and turns the starch a dark brown
to black color so the iodine reacts with
the starch and turns dark we know that
starch is still present and it has not
been hydrolyzed but if we see a clear
zone around the growth where the auger
doesn't turn dark after adding the
iodine we know there's no longer any
starch there indicating that has been
hydrolyzed by an XO enzyme diastasis so
the first thing we have to do is add the
iodine to the Petri plate now what we're
going to do is add enough iodine to just
cover the surface of the auger so we
squirt some iodine on the plate we're
going to swirl it around a little bit
make sure that it covers that plate we
don't want to add any more than we
really need to just cover the auger
surface
and then we're going to let that sit for
about 30 seconds or a minute
and then we'll take a look and see if
starch has been hydrolyzed by the
bacterium or not now that approximately
minutes gone by we're going to look at
the results of the starch auger now we
have to be very careful because we did
add liquid iodine to the plate and if we
tip the plate or pick it up that iodine
is going to run out and that could run
on you or get on your skin your face if
you hold it up to the light or something
like that so we have to be very careful
not to pick up or tip the plate to help
provide any excess iodine from running
off what we're going to do is take the
excess iodine and pour it in the
disposal container that we'll be sitting
out when we do this lab
and now we're ready to take a look at
the results now to help us see the
results better I put a white background
up on the lab bench so that we can see
the clear zone a little bit more clearly
I've already poured as we saw the excess
iodine into our disposal beaker and I
make sure I get off the excess iodine
off because I am going to have to pick
up the plate so you can see the results
although you can see it pretty well on
the lab bench so if we take a look at
the results here we'll notice that the
bacterium on the left the agar has
turned a brown color where the starch is
still present and has reacted with the
iodine so we notice right up to the
bacterial growth it all appears brown so
the organism on the Left did not
hydrolyze the starch on the other hand
if we look at the organism on the right
we see a clear zone extending out from
beyond the growth and it's clear because
there's no longer any starch present
there to react with the iodine so that
bacterium produced an EXO enzyme that
hydrolyzes the starch so the organism on
the right hydrolyzed starch the one on
the Left did not hydrolyze starch
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