My Classroom Material 137 - BIOLOGY JUNCTION

Diffusion and Osmosis

Diffusion and Osmosis

Introduction:
In this exercise you will measure diffusion of small molecules through dialysis tubing, an example of a semi permeable membrane. The movement of a solute through a semi permeable membrane is called dialysis. The size of the minute pores in the dialysis tubing determines which substance can pass through the membrane. A solution of glucose and starch will be placed inside a bag of dialysis tubing. Distilled water will be placed in a beaker, outside the dialysis bag. After 30 minutes have passed, the solution inside the dialysis tubing and the solution in the beaker will be tested for glucose and starch. The presence of reducing sugars like glucose, fructose, and sucrose will be tested with Benedict’s Solution. The presence of starch will be tested with Lugol’s solution (iodine-potassium-iodide).

Procedure:

Obtain a 30 -cm piece of 2.5-cm dialysis tubing that has been soaking in water. Tie off one end of the tubing to form a bag. To open the other end of the bag, rub the end between your fingers until the edges separate.
Place 15 mL of the 15% glucose/ 1% starch solution in the bag. Tie off the other end of the bag, leaving sufficient space for the expansion of the bag’s contents. Record the color of the solution in Table 1.1.
Test the 15% glucose / 1% starch solution in the bag for the presence of glucose. Your teacher may have you do a Benedict’s test. Record the results in Table1.1.
Fill a 250 mL beaker or cup 2/3 full with distilled water. Add approximately 4 mL of Lugol’s solution to the distilled water and record the color in Table 1.1. Test the solution for glucose and record the results in Table 1.1.
Immerse the bag in the beaker of solution.
Allow your set up to stand for approximately 30 minutes or you see a distinct color change in the bag or the beaker. Record the final color of the solution in the bag, and of the solution in the beaker, in Table 1.1.
Test the liquid in the beaker and in the bag for the presence of glucose. Record the results in Table 1.1.

Table 1.1

	Initial Contents	Initial Solution Color	Final Solution Color	Initial Presence of Glucose	Final Presence of Glucose
Bag	15% Glucose & 1% starch
Beaker	H2O + IKI

Analysis of Results:
1. Which substance(s) are entering the bag and which are leaving the bag? What experimental evidence supports your answer?

_______________________________________________________________________

2. Explain the results you obtained. Include the concentration differences and membrane pore size in your discussion.

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3. Quantitative data uses numbers to measure observed changes. How could this experiment be modified so that quantitative data could be collected to show that water diffused into the dialysis bag?

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4. Based on your observations, rank the following by relative size, beginning with the smallest : glucose molecules, water molecules, IKI molecules, membrane pores, starch molecules.

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5. What results would you expect if the experiment started with glucose and IKI solution inside the bag and only starch and water outside? Why?

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Osmosis:
In this experiment you will use dialysis tubing to investigate the relationship between solute concentration and the movement of water through a semi permeable membrane by the process of osmosis. When two solutions have the same concentration of solutes, they are said to be isotonic to each other. If the two solutions are separated by a semi permeable membrane, water will move between the two solutions, but there will be no net change in the amount of water in either solution. If two solutions differ in the concentration of solutes that each has, the one with more solute hypertonic to the one with the less solute. The solution that has less solute is hypotonic to the one with more solute. These words can only be used to compare solutions.

Procedure:
1. Obtain six 30-cm strips of presoaked dialysis tubing.

2. Tie a knot in one end of each piece of dialysis tubing to form six bags. Pour approximately 25 mL of each of the following solutions into separate bags:

Distilled water
0.2 M sucrose
0.4 M sucrose
0.6 M sucrose
0.8 M sucrose
1.0 m sucrose

Remove most of the air from the bags by drawing the dialysis bag between two fingers. Tie off the other end of the bag. Leave sufficient space for the expansion of the contents in the bag.

3. Rinse each bag gently with distilled water to remove any sucrose spilled during filling.

4. Carefully blot the outside of each bag and record in Table 1.2 the initial mass of each bag.

5. Fill six 250 mL beakers 2/3 full with distilled water.

6. Immerse each bag in one of the beakers of distilled water and label the beaker to indicate the molarity of the solution in the dialysis bag. Be sure to completely submerge each bag.

7. Let them stand for 30 minutes.

8. At the end of 30 minutes remove the bags from the water. Carefully blot and determine the mass of each bag.

9. Record your group’s results in Table 1.2. Obtain data from the other lab groups in your class to complete Table 1.3: Class Data.

Table 1.2 Dialysis Bag Results: Individual Data

Contents in Dialysis Bag	Initial Mass	Final Mass	Mass Difference	% Change in Mass
a). Distilled Water
b). 0.2 M
c). 0.4 M
d). 0.6 M
e). 0.8 M
f). 1.0 M

To Calculate:

% change in mass

Final Mass-Initial Mass

100

———————–

Initial Mass

Table 1.3 Dialysis Bag Results: Class Data

percent change in Mass of Dialysis Bags

Bag Contents	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6	Total	Class Average
Distilled Water
0.2 M
0.4 M
0.6 m
0.8 M
1.0 M

10. Graph the results for both your individual data and class average on the following graph. For this graph you will need to determine the following:

a). the independent variable. __________________________________

b). the dependent variable. ___________________________________

Graph Title ______________________________________________

Analysis of Results:
1. Explain the relationship between the change in mass and the molarity of sucrose within the dialysis bag.

________________________________________________________________________

2. Predict what would happen to the mass of each bag in this experiment if all the bags were placed in a 0.4 M sucrose solution instead of distilled water. Explain your response.

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3. Why did you calculate the per cent change in mass rather than using the change in mass?

________________________________________________________________________

4. A dialysis bag is filled with distilled water and then placed in a sucrose solution. The bag’s initial mass is 20 g. and its final mass is 18 g. Calculate the percent change of mass, showing your calculations in the space below.

5. The sucrose solution in the beaker would have been ___________________ to the distilled water in the bag.

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Edible Cell Instructions

Edible Cells!

Construct a 3 dimensional, edible, eukaryotic cell that includes the following structures:
* cell membrane
*nucleus
*nucleolus
*chromatin
*rough ER
*smooth ER
*free ribosomes
*mitochondria
*lysosome
*Golgi bodies
*storage vacuole or vesicle

Make sure you use sanitary conditions when constructing your cell because we will eat them in class!

Include a key to your model and a short paper explaining the function of each cellular part.

Click here for photos of edible cells

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DNA Code for Insulin

DNA’s Instructions for Insulin

Introduction:

Below are two partial sequences of DNA bases (shown for only one strand of DNA) Sequence 1 is from a human and sequence 2 is from a cow. In both humans and cows, this sequence is part of a set of instructions for controlling the production of a protein. In this case, the sequence contains the gene to make the protein insulin. Insulin is necessary for the uptake of sugar from the blood. Without insulin, a person cannot use digest sugars the same way others can, and they have a disease called diabetes.

Materials:

paper, pencil, codon table

Procedure:

Using the DNA sequence given in table 1, make a complimentary RNA strand for the human. Write the RNA directly below the DNA strand (remember to substitute U’s for T’s in RNA).
Repeat step 1 for the cow. Write the RNA directly below the DNA strand in table 2.
Use the codon table in your book to determine what amino acids are assembled to make the insulin protein in both the cow and the human. Write your amino acid chain directly below the RNA sequence.

Table 1

Sequence 1 Human
DNA	C C A T A G C A C G T T A C A A C G T G A A G G T A A
RNA
Amino Acids

Table 2

Sequence 1 Cow
DNA	C C G T A G C A T G T T A C A A C G C G A A G G C A C
RNA
Amino Acids

Analysis:

1. The DNA sequence is different for the cow and the human, but the amino acid chain produced by the sequence is almost the same. How can this happen?

2. Diabetes is a disease characterized by the inability to break down sugars. Often a person with diabetes has a defective DNA sequence that codes for the making of the insulin protein. Suppose a person has a mutation in their DNA, and the first triplet for the gene coding for insulin is C C C (instead of C C A). Determine what amino acid the new DNA triplet codes for. Will this person be diabetic?

3. What if the first triplet was C A A ?

4. How is it that a code consisting of only four letters, as in DNA ( A, T, G, C ) can specify all the different parts of an organism and account for all the diversity of organisms on this planet?

DNA sequences are often used to determine relationships between organisms. DNA sequences that code for a particular gene can vary widely. Organisms that are closely related will have sequences that are similar. Below is a list of sequences for a few organisms:

Human	CCA TAG CAC CTA
Pig	CCA TGG AAA CGA
Chimpanzee	CCA TAA CAC CTA
Cricket	CCT AAA GGG ACG

5. Based on the sequences, which two organisms are most closely related?

6. An unknown organism is found in the forest, and the gene is sequenced, and found to be C C A T G G A A T C G A , what kind of animal do you think this is?

Edible Cell Pictures

Edible Cell Models




	Cell Page	Notes page

DNA Model

Structure of DNA Lab

Introduction:

Deoxyribonucleic acid (DNA) is one of the two types of nucleic acids found in organisms and viruses. The structure of DNA determines which proteins particular cells will make. The general structure of DNA was determined in 1953 by James Watson and Francis Crick. The model of DNA that they constructed was made of two chains now referred to as the double helix. Each chain consists of linked deoxyribose sugars and phosphates units. The chains are complementary to each other. One of four nitrogen-containing bases connects the chains together like the rungs of a ladder. The bases are cytosine, guanine, thymine, and adenine. The DNA molecule looks like a spiral staircase. The structure of DNA is illustrated by a right handed double helix, with about 10 nucleotide pairs per helical turn.

DNA is a polymer. The monomer units of DNA are nucleotides. Each nucleotide consists of a 5-carbon sugar (deoxyribose), a nitrogen containing base attached to the sugar, and a phosphate group. (See Table 1.) There are four different types of nucleotides found in DNA, differing only in the nitrogenous base. Adenine and guanine are purines. Purines are the larger of the two types of bases found in DNA. They have two rings of carbons & nitrogens. Cytosine and thymine are pyrimidines and have a single carbon-nitrogen ring. (See Table 2.) The sequence of these bases encodes hereditary instructions for making proteins—which are long chains of amino acids. These proteins help build an organism, act as enzymes, and do much of the work inside cells.

Table 1

DNA Nucleotide
(Sugar + Phosphate + Base)

Table 2

Pyrimidine (single ring of C & N)	Purine (double ring of C & N)

Materials:

Colored paper (any 5 different colors to run templates), scissors, transparent tape, coat hanger, hole punch, string or fishing line

Procedure:

Use the section of DNA you have been assigned (Human hemoglobin or Chicken Hemoglobin), and figure out the sequence of bases present on the complementary strand of this molecule Table 1.

Human Hemoglobin		Chicken Hemoglobin
Left Strand	Complementary Strand	Left Strand	Complementary Strand
TAA		GTT
TGT		TGT
CGA		CCG
CCG		CCG
CTG		CGA
GTC		GTC
CAA		TAT
GTC		CGA
CTT		TTG
TGA		AGG

Count the number of bases (A, T, C, and G) you will need for both strands of the DNA model your group has been assigned, and cut out these bases. (60 total)
Cut out a sugar and a phosphate for each of your DNA bases. (120 of each)
Construct a nucleotide for each base that you have cut (sugar + phosphate + base) by taping these together. (20 total nucleotides)
Using your assigned DNA sequence from Table 1, line up the nucleotides in the right order forming he left strand of your DNA molecule. (30 nucleotides)
Add the other complementary nucleotides to form the right strand by taping the bases together (A bonds with T; C bonds with G).
Once the strand is complete, secure it by adding more transparent tape or ask your teacher to laminate your model.
Punch two holes at the top of your model, and attach the DNA model to a coat hanger with string.
Carefully twist your model into a double helix (5 base pairs in a 1/2 turn and 10 in a complete turn).
Attach thin fishing line to the sides of the nucleotides to hold the turns in place.
Hang your model from the ceiling using the top of your coat hanger.

TEMPLATES:

Adenine

Thymine

Cytosine

Guanine

Phosphate

Sugar

Questions & Observations:

1. What 2 molecules make up the sides of the DNA molecule?

2. What nitrogen bases form the rungs of the DNA double helix?

3. What is meant by the complementary strand of DNA?

4. What sugar makes up DNA nucleotides?

5. How are nucleotides named?

6. DNA is the instructions for building what molecule in our cells?

7. What would happen if one or more bases on the DNA strand were changed?

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