Part 5. Solvents, solutions, and conductivity

Part 6. pH of water and common solutions

Materials

• 
  pH meter/probe or pH paper
  
• 
  Beakers or test tubes
  
• 
  Stir rods
  
• 
  Five liquids
  

• 
  Deionized water
  
• 
  Vinegar
  
• 
  Ammonia
  
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  Citric acid (lemon juice, freshly squeezed)
  
• 
  Milk
  

• 
  Water samples taken from various sources (e.g., tap, well, pond, stream, lake)
  

Procedure

2. Using the pH meter/probe or pH paper, test the pH of the deionized water. Record your observations in the Student Data Table. Then, test the pH of the other four liquids, and record your observations.

3. Repeat for water samples taken from other sources.

Extension activity

References on pH: tables and definitions

• 
  http://www.mpcfaculty.net/mark_bishop/pH_equilibrium.htm
  
• 
  http://www.engineeringtoolbox.com/ph-25_483.html
  
• 
  http://www.albion.edu/chemistry/CH121/pHvalues.htm
  

Macromolecules

Objectives

• 
  list the six elements that are the main components of a living cell: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur;
  
• 
  explain carbon’s atomic structure and its role in forming the macromolecules of life, and provide examples of compounds;
  
• 
  recognize that cells can make a variety of macromolecules from a relatively small set of monomers;
  
• 
  identify and describe the following macromolecules and their structures:
  

• 
  Carbohydrates provide and store energy.
  
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  Lipids insulate, store energy, and make up cell membranes.
  
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  Proteins may be structural or may function in transport, movement, defense, or cell regulation.
  
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  Nucleic acids (DNA and RNA) control cell activities by directing protein synthesis.
  

• 
  give examples of each specific protein function;
  
• 
  recognize the following:
  

• 
  Proteins are polymers made by linking together amino acid monomers.
  
• 
  A protein’s structure depends on its specific conformation.
  

• 
  generalize the structure and function of enzymes, including their
  

• 
  definite three-dimensional shape, which allows binding with a substrate
  
• 
  ability to control the rate of metabolic reactions by acting as catalysts;
  

• 
  understand that pH and temperature are important to cell functioning because
  

• 
  most organisms can tolerate small changes in pH;
  
• 
  most cells function best within a narrow range of temperature and pH;
  
• 
  at very low temperatures, reaction rates are too slow;
  
• 
  high temperatures or extremes of pH can change the structure of proteins and consequently their function.
  

Materials needed

• 
  Copies of the attached student activity sheet
  
• 
  Materials listed on the activity sheet (optional)
  

Instructional activity

Content/Teacher Notes

Students need to study molecular structures to be familiar with each monomer molecule. They should understand that the presence of carbon is the basis for all the structures. They should appreciate the intricate complexity of the polymeric molecules and understand why they are called “macromolecules.” Based on the middle and high school Science SOL, students should have an understanding of the atomic models and bonding. Nevertheless, students may need refreshers on these topics as well as an introduction to Lewis models.

Introduction

2. Ask students to brainstorm what each of these foods does for the body. List their responses.

3. Then, write the four macromolecules on the board, and ask students which part of the sandwich fits in the different categories. Students should be able to categorize all components of the sandwich except, perhaps, the vegetables.

Procedure

Observations and Conclusions

Sample assessment

• 
  Use the student activity sheet for assessment. The answer key follows:
  

Type of Macromolecule	Elements (C, H, O, N, S, P)	Monomer (example)	Polymer (example)	Functions
Carbohydrate	C, H, O	Glucose, fructose, galactose	Starch, glycogen, chitin, cellulose	Provide and store energy Provide protection and support
Lipid	C, H, O, (P — phospholipids)	Fatty acids, glycerol	Triglycerides, phospholipids, steroids	Is key component of cell membranes Provide long-term energy storage Provide insulation
Protein	C, H, O, N (S)	Amino acids	Polypeptides (proteins) Coils (pleated sheet)	Provide enzymes (chemical reactions) Provide hormones Provide storage (egg whites of birds, reptiles; seeds) Provide transport (hemoglobin) Are contractile (muscle) Are protective (antibodies) Provide membrane proteins (receptors, membrane transport, antigens) Are structural, assist movement Provide toxins (botulism, diphtheria)
Nucleic acid	C, H, O, N, P	Nucleotide (base, sugar, phosphate)	DNA, RNA	Translate genetic information Provide sequence for amino acids and protein synthesis

1. C, H, O, N, S, P

2. C, H, O

3. Bohr model showing appropriate orbital number and electron distribution

4. Lewis model showing four available electrons from hybrid orbitals

5. Four electrons; can hybridize and form four bonds; bonds well with itself to form rings and chains

6. Amino acids

7. General structure of amino acid either drawn, copied and pasted on the computer, or made from a molecular model kit

(Answers will vary.)

1. Benedict’s test is for simple (reducing) sugars. The iodine test is to indicate complex carbohydrates (starch).

2. Qualitative

3. Carbohydrates are important. They give cells energy to carry on respiration, a requirement for life.

1. 2H₂O₂  in the presence of peroxidase 2H₂O + O_{2 (gas)}

2. Hydrogen peroxide

3. An enzyme catalyzes and lowers the activation energy required for the decomposition reaction to occur.

4. The bonds in the peroxidase were broken. The peroxidase was denatured (changed shape). The enzyme could no longer work normally.

5. The bonds in the peroxidase were broken. The peroxidase was denatured (changed shape). The enzyme could no longer work normally.

6. Tubes 5 and 6 were the controls.

7. If the pH of the peroxidase environment is low, then the enzyme peroxidase will not be able to break the bonds in the hydrogen peroxide to produce water and oxygen gas.

Or

If the enzyme peroxidase is placed in an environment of boiling water, then the peroxidase will be denatured and will not be able to break the bonds in the hydrogen peroxide to produce water and oxygen gas.

(Answers will vary.)

Follow-up/extension

• 
  Students should be able to relate the terms Active Site, Substrate, and Product to the function of protein.
  
• 
  Students may want to investigate competitive and non-competitive inhibition and allosteric changes in enzyme functioning.
  
• 
  If time allows, amylase action on starch and its changes in the Iodine or Benedict’s Reagent reaction may be observed.
  

Resources

• 
  Organic Chemistry, Biochemistry. The Biology Web. http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20100/Bio%20100%20Lectures/Biochemistry/biochemi.htm. Provides good background information on the structures of all macromolecules.
  

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