pH
Acidic
Neutral
Basic
Organisms and pH
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Organisms and pH
Introduction
Journals and Snapshots
The Snapshot button is used to capture the
screen.
The Journal is where snapshots are stored
and viewed.
The Share button is used to export
or print your journal to turn in your
work.
Each page of this lab that
contains the symbol
should be inserted into your
journal. After completing a
lab page with the snapshot
symbol, tap
(in the
upper right hand corner) to
insert the page into your
journal.
Note: You may want to take a
snapshot of the first page of
this lab as a cover page for
your journal.
Organisms and pH
Lab Challenge
• What effect does pH have on the health of organisms?
• What effect do man-made and biological buffers have on pH?
Organisms and pH
pH
Background
• Solutions that are acidic produce a large
number of H+ ions, which affects biological
molecules in the solution. Proteins can
become denatured (unraveled) when the pH
of the surrounding solution changes.
Higher H+
• Solutions with very low pH are highly acidic;
solutions with very high pH are highly
alkaline (basic). A pH equal to 7 is neutral.
Neutral
Higher OH-
• pH is a measure of the acidity/alkalinity of
water.
Acidic
Basic
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Battery Acid
Sulfuric Acid
Stomach Acid, Vinegar
Lemon Juice
Black Coffee
Saliva
Distilled Water
Sea Water
Baking Soda
Milk of Magnesia
Ammonia
Soapy Detergents
Bleach
Drain Cleaner
Organisms and pH
Self-Check
1. A solution with a very low pH is _______. An
example is _________.
a) basic : bleach
b) acidic : stomach acid
c) basic : orange juice
d) neutral : sea water
e) acidic : soapy water
This image is a reminder to
tap
to take a snapshot
of the page after you have
entered your response.
Organisms and pH
...Background
• An organism’s pH can be changed by adding carbon dioxide (CO2) to its
bloodstream. Mammals have an enzyme in the bloodstream called carbonic
anhydrase. This enzyme combines CO2 with H2O to form carbonic acid (H2CO3).
Carbonic acid increases the amount of CO2 the blood can hold and transport.
Some of the carbonic acid molecules break down, releasing H+ ions.
• The more an organism exerts itself, the more carbonic acid is produced,
decreasing blood pH. When CO2 is removed from the bloodstream, pH
increases. Low blood pH triggers a breathing response in the brain, causing the
lungs to expel CO2. Breathing is one way an organism controls pH.
Organisms and pH
Self-Check
2. When CO2 is added to the bloodstream, what is the
overall effect?
a) decrease in carbonic anhydrase
b) no change in pH
c) increase in pH
d) decrease in pH
e) increase in huffing and puffing
Organisms and pH
...Background
• Another way organisms control pH is through the use of buffers.
• A buffer is a compound that can combine chemically with free H+ ions in
solution. Because these extra H+ ions are neutralized, the organism’s overall pH
does not change.
• A buffer can also release H+ ions when combined with an alkaline (basic)
substance. These extra H+ ions neutralize the OH- ions produced by the base.
The overall pH does not change. If an acidic or basic substance is added to a
buffered solution, the solution’s pH will not be significantly changed – until the
buffer is used up.
• One common buffer is sodium bicarbonate, NaHCO3, more commonly known as
baking soda.
Organisms and pH
Self-Check
3. How does a buffer neutralize alkaline/basic
substances?
a) by producing H+ ions
b) by capturing H+ ions
c) by producing OH- ions
d) magic
Organisms and pH
Safety
• Use all standard laboratory safety procedures.
• Wear safety glasses and lab coats or aprons.
• Dispose of chemicals and solutions as instructed.
Organisms and pH
Materials and Equipment
Collect all of these materials before beginning the lab.
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pH sensor
Sensor extension cable
Beaker (6), 50mL
Beaker, 250mL
Erlenmeyer flask (2), 1L
Graduated cylinder, 10mL
Disposable pipettes (2)
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Detergent solution
Lemon juice
Distilled Water
White vinegar
Liver suspension
Buffer solution
Organisms and pH
Sequencing Challenge
A. Measure the
initial pH of various
solutions.
B. Set up your
equipment.
C. Record pH data as
you add detergent
to water, buffer, and
liver.
D. Clean up.
E. Analyze the data
and determine if any
biological solutions
are good buffers.
The steps to the left are part
of the procedure for this lab
activity. They are not in the
right order. Determine the
correct sequence of the
steps, then take a snapshot
of this page.
Organisms and pH
Prediction: Water + Lemon Juice
Q1:What do you predict will happen to the pH of the
water when lemon juice is added?
Organisms and pH
Collect Data: Water + Lemon Juice
1. Connect the pH sensor to the SPARK Science
Learning System.
2. Pour 25 mL of distilled water into a 50 mL beaker.
3. Rinse the pH sensor with distilled water and place
it into the beaker.
4. Wait a few seconds, then tap
collection.
to start data
5. Record the initial pH for Water + Lemon Juice in
the data table on the next page.
Organisms and pH
To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight
it in yellow.
3. Tap
to open the
Keyboard screen.
Organisms and pH
Collect Data: Water + Lemon Juice
6. Continue recording data as you add 30 drops of
lemon juice using a clean pipette. Use the glass
stirring rod to gently mix the solution in the
beaker while adding the lemon juice.
7. Wait 30 seconds following the last drop of
lemon juice and then tap to stop data
collection.
8. Record the final pH for Water + Lemon Juice in
the data table on the previous page.
Organisms and pH
Prediction: Water + Detergent
Q2:What do you predict will happen to the pH of the
water when detergent is added?
Organisms and pH
Collect Data: Water + Detergent
1. Pour 25 mL of distilled water into a clean 50 mL
beaker.
2. Rinse the pH sensor with distilled water and
place it into the beaker.
3. Wait a few seconds, then tap
collection.
to start data
4. Record the initial pH for Water + Detergent in
the data table on the next page.
Organisms and pH
To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight
it in yellow.
3. Tap
to open the
Keyboard screen.
Organisms and pH
Collect Data: Water + Detergent
5. Continue recording data as you add 30 drops of
detergent using a clean pipette. Use the glass
stirring rod to gently mix the solution in the
beaker while adding the detergent.
6. Wait 30 seconds following the last drop of
detergent and then tap
to stop data
collection.
7. Record the final pH for Water + Detergent in the
data table on the previous page.
Organisms and pH
Prediction: Buffer + Lemon Juice
Q3:What do you predict will happen to pH of the buffer solution as
lemon juice is added?
Organisms and pH
Collect Data: Buffer + Lemon Juice
1. Pour 25 mL of buffer solution into a clean 50 mL
beaker.
2. Rinse the pH sensor with distilled water and place
it into the beaker.
3. Wait a few seconds, then tap
collection.
to start data
4. Record the initial pH for Buffer + Lemon Juice in the
data table on the next page.
Organisms and pH
To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight
it in yellow.
3. Tap
to open the
Keyboard screen.
Organisms and pH
Collect Data: Buffer + Lemon Juice
6. Continue recording data as you add 30 drops of
lemon juice using a clean pipette. Use the glass
stirring rod to gently mix the solution in the beaker
while adding the lemon juice.
7. Wait 30 seconds following the last drop of lemon
juice and then tap
to stop data collection.
8. Record the final pH for Buffer + Lemon Juice in the
Data Table on the previous page.
Organisms and pH
Prediction: Buffer + Detergent
Q4:What do you predict will happen to the pH of the buffer solution
when detergent is added?
Organisms and pH
Collect Data: Buffer + Detergent
1. Pour 25 mL of buffer solution into a clean 50 mL
beaker.
2. Rinse the pH sensor with distilled water and place
it into the beaker.
3. Wait a few seconds, then tap
collection.
to start data
4. Record the initial pH for Buffer + Detergent in the
data table on the next page.
Organisms and pH
To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight
it in yellow.
3. Tap
to open the
Keyboard screen.
Organisms and pH
Collect Data: Buffer + Detergent
6. Continue recording data as you add 30 drops of
detergent using a clean pipette. Use the glass
stirring rod to gently mix the solution in the beaker
while adding the detergent.
7. Wait 30 seconds following the last drop of
detergent and then tap
to stop data collection.
8. Record the final pH for Buffer + Detergent in the
Data Table on the previous page.
Organisms and pH
Prediction: Liver + Lemon Juice
Q5:What do you predict will happen to the pH of the liver solution when
lemon juice is added?
Organisms and pH
Collect Data: Liver + Lemon Juice
1. Pour 25 mL of liver suspension into a clean 50
mL beaker.
2. Rinse the pH sensor with distilled water and
place it into the beaker.
3. Wait a few seconds, then tap
collection.
to start data
4. Record the initial pH for Liver + Lemon Juice in
the data table on the next page.
Organisms and pH
To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight
it in yellow.
3. Tap
to open the
Keyboard screen.
Organisms and pH
Collect Data: Liver + Lemon Juice
6. Continue recording data as you add 30 drops
of lemon juice using a clean pipette. Use the
glass stirring rod to gently mix the solution in
the beaker while adding the lemon juice.
7. Wait 30 seconds following the last drop of
lemon juice and then tap
to stop data
collection.
8. Record the final pH for Liver + Lemon Juice in
the data table on the previous page.
Organisms and pH
Prediction: Liver + Detergent
Q6:What do you predict will happen to the pH of the liver solution when
detergent is added?
Organisms and pH
Collect Data: Liver + Detergent
1. Pour 25 mL of liver suspension into a clean 50 mL
beaker.
2. Rinse the pH sensor with distilled water and place
it into the beaker.
3. Wait a few seconds, then tap
collection.
to start data
4. Record the initial pH for Liver + Detergent in the
data table on the next page.
Organisms and pH
To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to highlight
it in yellow.
3. Tap
to open the
Keyboard screen.
Organisms and pH
Collect Data: Liver + Detergent
6. Continue recording data as you add 30 drops of
detergent using a clean pipette. Use the glass
stirring rod to gently mix the solution in the beaker
while adding the detergent.
7. Wait 30 seconds following the last drop of
detergent and then tap
to stop data collection.
8. Record the final pH for Liver + Detergent in the
Data Table on the previous page.
Organisms and pH
Data Analysis
1. Calculate the change in
pH for each of the six
experiments. Record
your results in the data
table.
To Enter Data into a Table:
1. Tap
to open the tool
palette.
2. Tap
then tap a cell in
the data table to
highlight it in yellow.
3. Tap
to open the
Keyboard screen.
Organisms and pH
Data Analysis
2. Which solution had the
greatest increase in pH?
Which had the greatest
decrease?
Organisms and pH
Analysis
1. What is significant about the pH change in the liver suspension?
What does it tell us about biological compounds, in general?
Organisms and pH
Analysis
2. List the following common compounds in order from most acidic to
most basic: distilled water, detergent solution, lemon juice.
Organisms and pH
Analysis
3. Do organisms appear to have effective ways to avoid large changes in pH?
Give an example using experimental evidence.
Organisms and pH
Synthesis
1. There are buffers in the human blood system. Why is that important for you?
Organisms and pH
Synthesis
2. Hemoglobin in red blood cells binds to oxygen from the lungs. The hemoglobin
somehow “knows” to release this oxygen when the blood passes near oxygenstarved tissues. How is this possible?
Organisms and pH
Multiple Choice
1. Which of the following biochemical substances
located in the human body is not maintained at a
neutral pH?
a) blood
b) stomach fluids
c) internal material of living cells
d) lymph
Organisms and pH
Multiple Choice
Rate of Enzyme
Activity
2. Which choice it true for the graph shown?
Pepsin
Trypsin
A. More enzymes are
present at a higher pH.
C. Pepsin is less effective at
low pH than trypsin.
B.
D.pH affects the activity rate
of enzymes.
Pepsin is less sensitive to
pH than trypsin.
Organisms and pH
Multiple Choice
3. 5 mL of lemon juice was added to 10 mL of each of
the following substances and the results recorded.
Which substance has the best buffering capacity?
a) Milk
pH change = -3.2
b) Liver
pH change = -3.0
c) Tap water
pH change = -4.0
d) Egg whites
pH change = -2.8
Organisms and pH
Congratulations!
You have completed the lab.
Please remember to follow your teacher's instructions for cleaning-up and submitting
your lab.
Organisms and pH
References
Images are taken from PASCO documentation, public domain clip art, or Wikimedia Foundation Commons.
http://www.flickr.com/photos/moorthygounder/2228827558/ See attribution of license terms at:
http://creativecommons.org/licenses/by/2.0/deed.en
http://commons.wikimedia.org/wiki/File:Dolphins_300.jpg
http://commons.wikimedia.org/wiki/File:Fried_egg,_sunny_side_up.jpg
http://commons.wikimedia.org/wiki/File:Glass-of-water.jpg