Biology 12 ACIDS BASES AND CELLS Name _________________ Organisms are often very sensitive to the effect of acids and bases in their environment. They need to maintain a stable internal pH in order to survive—even in the event of environmental changes. Many naturally occurring biological, geological, and man-made chemicals are capable of stabilizing the environment’s pH. This may allow organisms to better survive in diverse environments found throughout the earth. It is very important for cells to maintain the correct pH in order to survive and function properly; however, many of the metabolic reactions that occur in cells tend to shift the pH away from the ideal position. Objective of this lab: Use different methods of pH measurement. Measure the pH of some biological chemicals. To investigate the extent to which certain substances resist changes in pH. To investigate how cells maintain the correct pH in spite of metabolic activities that shift the pH towards either the acidic or basic end of the scale? In other words, how do cells maintain homeostasis with respect to pH? Prelab To be completed before starting the lab. Living cells need to maintain a fairly constant internal environment. This is called _________________________________. The cell will not function, for example, if it becomes too acidic (too many __________ ions, H + ) or to basic (too many ___________ ions, OH - ). Unless the pH is correct, the chemical reactions that must take place inside the cell are disrupted, and the cell could die. When the concentrations of hydrogen ions and hydroxide ions in a solution are equal, the solution is neither acidic nor basic; it is said to be ______________________. Biology12: pH lab Page 1
Transcript
Biology 12 ACIDS BASES AND CELLS Name _________________
Organisms are often very sensitive to the effect of acids and bases in their environment. They need to maintain a stable internal pH in order to survive—even in the event of environmental changes. Many naturally occurring biological, geological, and man-made chemicals are capable of stabilizing the environment’s pH. This may allow organisms to better survive in diverse environments found throughout the earth. It is very important for cells to maintain the correct pH in order to survive and function properly; however, many of the metabolic reactions that occur in cells tend to shift the pH away from the ideal position.
Objective of this lab: Use different methods of pH measurement.Measure the pH of some biological chemicals. To investigate the extent to which certain substances resist changes in pH.To investigate how cells maintain the correct pH in spite of metabolic activities that shift the pH towards either the acidic or basic end of the scale? In other words, how do cells maintain homeostasis with respect to pH?
Prelab To be completed before starting the lab. Living cells need to maintain a fairly constant internal environment. This is called _________________________________. The cell will not function, for example, if it becomes too acidic (too many __________ ions, H+) or to basic (too many ___________ ions, OH-). Unless the pH is correct, the chemical reactions that must take place inside the cell are disrupted, and the cell could die.
When the concentrations of hydrogen ions and hydroxide ions in a solution are equal, the solution is neither acidic nor basic; it is said to be ______________________.
We measure the hydrogen ion concentration of a solution by means of a scale called the pH scale. Neatly draw a diagram of the pH scale to illustrate your understanding of it.
The pH scale is geometric. This means that the numbers on the scale differ by factors of 10. How much more acidic will a solution of pH 5 be than a solution of pH 7? _________How many times more basic is a solution with a pH of 12 than one with a pH of 8? ________XWhat are substances that resist change in pH called? _________________
Biology12: pH lab Page 1
Write a formal hypothesis for the following questions:
(Use your textbook to refresh your memory about writing hypotheses, page 9 and 10. Remember a formalized hypothesis focuses on two variables that may be related. It makes a prediction of how manipulating one variable, independent, will affect the other variable, dependent. ‘If’ and ‘then’ should be used. )
1. Part A: What is the pH of most biological materials?
Part A. Measuring pH and Determining the pH of Some Living Materials
1. Dip pieces of blue and pink litmus paper into the solutions of 0.1 M HCl (an acid), 0.1 M NaOH (a base), tap water and distilled water. Record the colour of the indicator papers in Table 1 below. Also, use the pH indicator paper and the Vernier pH meter to measure the actual pH of the solutions.
2. Use the pH indicator paper to determine the pH of each of the biological materials listed in Table 2. Record the pH of each sample, and indicate whether it is acidic or basic.
Table 1. Measure pH using various indicator papers and Vernier pH meter
0.1 M HCl
0.1 M NaOH
Tap water Distilled water
Colour of blue litmus paper
Colour of pink litmus paper
pH determined from pH
indicator paper
pH determined from Vernier pH
meter
Table 2. pH of Various Living Materials
Biological Sample Tested pH(use pH paper)
Acidic or Basic?
Saliva
Tears
Urine
Lemon juice
Milk
Liver, ground
Potato, ground
Egg
Biology12: pH lab Page 3
Part B. Investigating how cells maintain homeostasis in acidic and basic environments
1. Pour 25 ml of tap water into a 50 ml beaker. Record its initial pH using the Vernier pH meter. Add 0.1 M HCl one drop at a time and determine the pH after each drop has been added, until 10 drops of acid have been used. Then record the pH after every 5 drops, until 30 drops have been added in all.
2. Rinse the beaker and repeat step 1 using 25ml 0.1 M NaOH.3. Rinse the beaker and repeat step 1 using 25 ml of liver homogenate instead of tap water.
Liver is one of the most metabolically active tissues of the body and has been blended into a homogenate for your use (10 g of liver per 100 ml of water and put in a blender).
4. Repeat step 3, but use NaOH.5. Repeat the test with potato homogenate (10 g potato blended with 100 g water).6. Repeat the test with an inorganic solution of sodium phosphate. 7. Make a simple graph, plotting two lines for the change of pH in tap water against the
number of drops of acid and base solutions added. Use a solid line for acid changes and a dashed line for changes with NaOH. On the same graph, plot the data for liver homogenate, potato homogenate, and inorganic sodium phosphate solution, using a different colour for each different solution, and solid lines for acid and dashed lines for base. Put an appropriate title on your graph.
Biology12: pH lab Page 4
Table 3. Maintaining homeostasis in acidic and basic environments
5. Did the biological samples (such as the liver and potato homogenates) respond in the same way as the tap water when acid or base was added. Explain.
6. Does the inorganic sodium phosphate solution respond to additions of acid or base more like the tap water, or more like the organic (biological) samples? Explain how you know. Did your results in this activity support your original hypothesis?
7. The sodium phosphate solution is called a buffer. There are many different kinds of buffers, but they all show the same property as the sodium phosphate solution when acids or bases are added. Based on your observations, do you think that there are buffers in living systems? How do you know? (Your answer must be based on your observations in this lab.)
Biology 12: Rubric for pH and Buffer lab Name: _______________Rubric Component 4 3 2 1
Completion of prelab.
Accurate and written with insight, goes beyond the problem.
Accurate and written with insight.
Accurate Partially accurate
Identifies and summarizes the
problem/questions at issue.
Accurately identifies theproblem/questions and provides well-developedexplanations.
Accurately identifies the problem/questions and provides a brief explanation.
Identifies the problem/questions and provides a poor summary or identifies an inappropriate problem/question.
Does not identify or summarize the problem/questions accurately if at all.
HypothesisClear explanation of purpose; educates by providing context.
Gives a correct purpose with some framework
Declares a purpose that is correct. Purpose is incorrect.
Identifies and assesses the quality of supporting
data/evidence
Provides a well-developedexamination of the evidence/data and questions its accuracy, relevance, and completeness. Clearly distinguishes between fact and opinion.
Examines evidence andquestions the quality. Distinguishes between fact and opinion.
Merely repeats information provided. Does not justify position or distinguish between fact and opinion.
Does not identify or assess the quality of supporting evidence.
Identifies and evaluates
conclusions, implications, and
consequences
Accurately identifies conclusions, implications, and consequences with a well-developed explanation. Provides an objective reflection of own assertions.
Accurately identifies conclusions, implications, and consequences with a brief evaluative summary.
Does not explain, provides inaccurate information, or merely provides a list of ideas; or only discusses one area.
Does not identify or evaluate any conclusions, implications or consequences.
Clarity of data tables and graphs
Graph correctly titled and labeled
Graph correctly titiled but not labeled.
Graph labeled but contains errors in units, axes or headings. No pencil.
Graph present but not titled nor labeled.
Participation during lab
Focused for entire lab/ followed all instructions and cleaned up.
Partly focused and partly cleaned up
Watched others and did gave instructions did not clean up.
Very little participation/ mind on other things
Research 100% Accurate Adequate Complete but inaccurate
Incomplete
Writing skills Full sentences, good grammar, answer the questions accurately.
Full sentences, poor grammar, answers questions accurately
