Category: 1st Semester

pH in Living Systems

 

 

pH and Living Systems

 

Introduction:

Scientists use something called the pH scale to measure how acidic or basic a liquid is. The scale goes from 0 to 14. Distilled water is neutral and has a pH of 7. Acids are found between 0 and 7. Bases are from 7 to 14. Most of the liquids you find every day have a pH near 7. They are either a little below or a little above that mark. When you start looking at the pH of chemicals, the numbers go to the extremes. Substances with the highest pH (strong bases) and the lowest pH (strong acids) are very dangerous chemicals. Molecules that make up or are produced by living organisms usually only function within a narrow pH range (near neutral) and a narrow temperature range (body temperature). Many biological solutions, such as blood, have a pH near neutral.

The biological molecule used in this lab is a protein found in milk. Proteins are used to build cells and do most of the cell’s work. They also act as enzymes. For proteins to work, they must maintain their globular shape. Changing the shape of a protein denatures and the protein will no longer work.

Materials:

Small squares of wide-range pH paper, pH color chart, paper towels, 4 dropper bottles, ammonia, lemon juice, skim milk, distilled water, forceps, 50 ml beakers, small squares of narrow-range pH paper, 2 stirring rods

Procedure (part A): Testing the pH of Substances

  1. Line up 4 squares of wide-range pH paper about 1 cm apart on a paper towel.
  2. Put one drop of distilled water on the pH square.
  3. Compare the color of the pH paper to the color chart and record the pH in data table 1.
  4. Repeat this procedure for the ammonia, lemon juice, and skim milk.

Questions (Part A): Determining the pH of Solutions

  1. Which substance was the most acidic?
  2. Which substance was the most basic?
  3. Did any of the substances have a pH close to neutral? Name them.

Procedure (part B): Showing the Effect of pH on a Biological Molecule (Milk Proteins)

  1. Place 100 drops of skim milk in a 50 ml beaker.
  2. Pick up a piece of narrow-range pH paper with forceps.
  3. Touch the pH paper to the milk and remove it.
  4. Compare the color of the pH paper to the pH color chart.
  5. Record the initial pH in data table 2.
  6. Add a drop of lemon juice to the milk in the cup & stir with a stirring rod. Keep track of how many drops you add to the milk!
  7. Measure and record the pH of the solution with the narrow-range pH paper.
  8. Repeat step 7 until you notice an obvious change in the appearance of the milk. record this final pH and appearance of the milk in your data table.
  9. Repeat steps 1-8 using a clean 50 ml beaker and fresh milk, and substitute ammonia for the lemon juice.
  10. Add drops of ammonia to the milk until the change in pH of the milk is equal to the change in pH you measured in step 8. Be sure to keep track of the number of drops added. HINT: If the pH changed by 2 units with the lemon juice, then add ammonia until you also get 2 pH units of change!

Data:

Table 1

 

Substance Tested pH Acid Base Neutral

 

Table 2

Substance Tested Substance used to Produce Change Starting pH of Milk Final pH of Milk Original Appearance of Milk Final Appearance of Milk Total Number of drops added to Produce the change
100 drops Skim Milk Lemon Juice
100 drops Skim Milk Ammonia

Questions:

1. Which substance tested from table 1 was the most acidic?

2. Which substance was most basic?

3. Did any substance from table 1 have a neutral, or near neutral pH? If so, which substance was neutral?

4. Why did you use narrow-range pH paper to measure the milk’s change in pH?

 

5. Describe the change in appearance of the milk as more lemon juice was added. Explain why this change occurred.

 

 

6. How much did the pH of milk change when lemon juice was added?

7. Why do you think lemon juice “curdled”  (precipitated out the proteins) from the milk?

 

8. Did you get the same change when ammonia was used? Why or why not?

 

 

 

Mrs Nerg

 

      Seven Life Processes
Movement

Reproduction

Sensitivity

Nutrition

Excretion

Respiration

Growth

 Mrs Nerg

MRS NERG
 

What one MAIN characteristic do ALL organisms have in common?
They’re all made of cells!

Nucleotide Model preap

 

Model of a Nucleotide

 

Introduction

Nucleotides consist of three parts — a pentose sugar, a nitrogen-containing base, and a phosphate group. A pentose sugar is a five-sided sugar. There are 2 kinds of pentose sugars — deoxyribose and ribose. Deoxyribose has a hydrogen atom attached to its #2 carbon atom (designated 2′), and ribose has a hydroxyl group atom there. Deoxyribose-containing nucleotides are the monomers of DNA, while Ribose-containing nucleotides are the monomers of RNA.

A nitrogen-containing ring structure is called a base. The base is attached to the 1′ carbon atom of the pentose. In DNA, four different bases are found — two purines, called adenine (A) and guanine (G) and two pyrimidines, called thymine (T) and cytosine (C). RNA contains The same purines, adenine (A) and guanine (G).  RNA also uses the pyrimidine cytosine (C), but instead of thymine, it uses the pyrimidine uracil (U).

 

The Purines The Pyrimidines

The combination of a base and a pentose is called a nucleoside.  A phosphate group is attached to the 5′ carbon of the pentose sugar.

Objective

Students will construct a 3-dimensional model of a single nucleotide, the monomer of which nucleic acids are composed.

Materials

Various materials may be used for the atoms that make up a nucleotide such as styrofoam balls, plastic coke bottle caps, beads, etc. Bonds between atoms may be made from toothpicks, plastic stirring sticks, popsicle sticks, etc. Single & double bonds must be represented by the correct number of “sticks”. The atoms and bonds may NOT be made of any food item. Your model should be glued together to make the model rigid for hanging. Attach string and a label with the nucleotide’s name to your model. Models must be sturdy, light weight, and small enough to hang from the ceiling.

Color Code for atoms:

CARBON – BLACK
HYDROGEN – YELLOW
OXYGEN – RED
NITROGEN – BLUE

Structural Formulas of Nucleotides:

Uracil Nucleotide (Ribose ) & Thymine Nucleotide (Deoxyribose)

 
Adenine Nucleotide (Deoxyribose)
Cytosine Nucleotide (Deoxyribose)
Guanine Nucleotide (Deoxyribose)
 

 

 

Natural Selection Activity

 

Survival of the Fittest

 

Introduction:

  Within a population, organisms will vary.  Charles Darwin stated that in the struggle for existence, those variant organisms that have favorable variations are “better adapted” to their environment and will survive and reproduce in greater numbers.  Favorable variations may mean that they are faster, or stronger, or able to eat different types of food, or better camouflaged to avoid predators.  In this lab you will simulate the effect of predation by a hawk on a large population of assorted mice.  Your population of mice will consist of black, white, and speckled mice.  You will represent the hawk.

Objectives:

  –to simulate the effect of hawk predation on the appearance of mice
-to simulate the natural selection of traits

Materials:

large sheet of newspaper  4 hawks (students)
30 white mice (paper squares) 1 petri dish
30 speckled mice (paper squares)
30 black mice (paper squares)

Procedure:

  1. Open your sheet of newspaper and place it on the lab table.  This will serve as the environment for your mice.
  2. Place the petri dish on the other side of the lab table.  This will be the nest.
  3. Select one person from your group to act as a hawk.  This person should stand by the nest.
  4. Spread the mice on their environment evenly.
  5. The hawk now swoops over and has 1 minute to pick up as many mice as possible. The hawk may only pick up one mouse at a time, and must place it in their nest (a petri dish) before flying back to pick up another.  The goal is to pick up as many mice as possible in the time period.
  6. When the time is up record the number of mice left in the environment in the data table below.
  7. Repeat this procedure for each person in the lab group or 4 times. 
  8. After all data is collected, construct a bar graph. Be sure to label the graph and its axes.
  9. Data:

 

White
mice
Speckled mice
Black
mice
Hawk #1  

 
Hawk #2  

 
Hawk #3  

 
Hawk #4  

 
Total  

 

 

Conclusion:
 Write a paragraph describing;

* the purpose of the lab

* what you thought the results would be

* what the results were (discussing numbers from data)

*how the mouse population and hawk population may change over time from natural selection

 

Natural Selection Peanut Activity

 

Natural Selection Within a Species

 

Introduction:

Natural selection is the evolutionary process by which the most adaptable individuals survive. An adaptation is an inherited variation that helps an organism to survive. When the organism survives, its chances of reproduction are increased as well as its ability to pass on its inherited traits.  All members of a species are different from one another.  In this activity, you will investigate two variations among peanut plants — length of shell and number of seeds per shell.   Most shells contain a certain number of seeds which is an adaptation to its survival.  

Objective:

Students will investigate natural selection in peanuts.

Materials:

50 peanuts in shells, metric ruler, pencil, graph paper

Procedure:

  1. Count out 50 peanuts in their shells.
  2. Use a metric ruler to measure the length of each shell in millimeters.  Put a check mark in Table 1 in the space indicating the length of the shell.
  3. Open the shell and count the number of seeds inside.  Put a check mark in Table 2 in the space next to the number of seeds that you counted. 
  4. Repeat steps 1 – 3 for the other 49 peanuts.
  5. Set up two bar graphs using the headings from each table as the axes for each graph.
  6. Plot a bar graph from the data in each table.

Data:

Table 1

 

Length of Shell
(mm)		 Number of Shells
5-10
10-15
15-20
20-25
25-30
30-35
35-40
40-45
45-50
50-55
55-60
60-65
65-70
70-75

 

 

Table 2

 

Number of Seeds Per Shell Number of Shells
1
2
3

 

 

 

Title: ________________________________________________________

 

Title: ________________________________________________________

 

Questions:

  1. What is the most common length of the shells you measured?
  2. What was the most common number of seeds in the peanut shells that you opened?
  3. What might happen if each shell contained fewer than normal seeds and why?
  4. What might happen if each shell contained more than the normal number of seeds and why?
  5. Was there a relationship between the most common length of shells and the number of seeds they contained? Explain your answer.
  6. Write 1-2 paragraphs explaining how shell length and seed number in peanuts illustrates natural selection within this species.