These three lab experiments were assigned for my BIO156 class, but they became a fun family project for our Science Saturday. The kids were lab assistants, and enjoyed being able to participate by writing down their own hypotheses. when the projects were done we discussed what had happened and why which was a great learning experience for us all, and was a great way for me to review as well! These are all ones that kids can do with help, so feel free to try them!
LAB
MILK, JUICE, CARROT
This
exercise has three parts. As you work, please take photographs of what you are
doing and record your results. Three or
four photographs of each part should be enough to show the steps and your final
result. For each experiment, you will be asked to formulate a hypothesis. Make
sure you understand what this is. Write complete, proper sentences, please.
Have fun!
Part 1 Milk
Objective: Observe and
explain changes occurring in milk due to biological influences
Materials:
Milk
Shallow cup or jar
1.
Pour ½ cup milk into a shallow cup or
jar.
2.
Place in a warm, dark place for about
three days.
3.
Record what you think will happen to the milk and why you believe
this will happen. This is your hypothesis.
4.
At the end of the three days, observe the milk and record what your senses detect.
5.
Explain why any changes (if any)
occurred.
6.
List any factors that are playing a
part. What could you call what you made (if you had a change in the milk)? Really
think about this in terms of cell respiration and any organisms which could
play a role.
7.
Record your
hypothesis, observations, explanation, and factors separately from these
instructions. You will see a place for them on the last page.
Part 2 Juice
Objective:
Witness the mixing action of molecules and describe the process
Materials:
3
cups or jars
6
cups water
½
cup fruit juice—grape, cranberry, or another that is dark in color
1.
Set up the jars or cups as follows:
Pour
2 cups of room temperature water in Cup 1
Pour
2 cups of ice water in Cup 2
Pour
2 cups of boiling water in Cup 3
2.
Slowly pour one-third of the juice into Cup 1. Observe and record
3.
Repeat for Cup 2 and Cup 3.
4.
Give detailed observations and comparisons between the behaviors
of the solutions in the three cups.
5.
Explain why the differences have occurred in terms of the behavior
of molecules and what might influence their behavior.
6.
Write your observations and explanation
separately from these instructions. You will see a place for them on the last
page.
Part 3 Carrot
Before you begin, review the main parts of a
cell and particle movement.
Objective: Investigate cellular functions and cellular
structures using a carrot
Materials:
2
jars or cups
string
water
salt
masking tape
carrot
knife
ruler
1.
Pour two cups of water into two jars or cups. Add one teaspoon of
salt into one and label it "Salt Water" with a piece of masking tape.
Label the other beaker "Fresh Water."
2.
Cut a fresh carrot in half. Measure the length and width of both
pieces and record this measurement on the answer sheet. Tie a piece of string
just below the cut side of the carrot on both pieces. Tie the string tightly.
3.
Set one carrot with the cut-end side down into one jar and the
other with the cut-end side down in the second jar. Allow the carrots to sit in the jars for 24
hours.
4.
Before you observe results of the experiment, write down what you
think will happen to each carrot in this experiment and why you believe this
will happen. This is your hypothesis.
5.
Remove the carrots and examine the tightness of the strings.
Re-measure the carrots and record the findings.
6.
Note if there are any differences in the tightness of the strings
and the textures for both carrot pieces. Observe which type of water caused an
increase in carrot size. Observe which type of water caused a decrease in
carrot size.
7.
Initial length and width of carrot pieces:
Piece 1
Piece 2
After-experiment length and width
of carrot pieces:
Piece 1
Piece 2
Record your hypothesis, tightness of string and texture observations and
measurements separately from these instructions. You will see a place for them on the last
page.
Answers
Record your answers here, space out as
needed, and copy and paste them into your blog. Include three or so photos for
each part to illustrate the process of the experiment. Thanks!
Milk: Record your
hypothesis, observations, explanation, and factors here.
Hypothesis: The milk will curdle creating a semi-solid curd of the condensed white blood cells, lipids, etc and a watery whey will come to the top.
Observations:
The milk created a semi-solid in the center bottom of the cut and a cloudy, watery liquid collected on the top. The solid portion dislodged from the bottom and made the water a little cloudier when I move it from the location where is sat during the test to take this photo.
Although I knew that milk curdles, and knew to expect this result before performing the test (with 4 kids I have had more than one sippy cup lost under the couch for a couple of days) I wasn't quite sure why this happens. It turns out that the reason that the milk proteins associate and form into the curd is because the pH of the milk changes. As bacteria grows in the milk, they bacteria produces lactic acid which raises the pH and causes the normally disassociated milk proteins (casein) to start to clump together. This process can be artificially produced with other acids such as lemon juice.
Source:
Why Does Milk Curdle?. Bethany Moncel. http://foodreference.about.com/od/Dairy/a/Why-Does-Milk-Curdle.htm. Accessed 18 February 2013.
Juice: Write
your observations and explanation here.
Hypothesis: The warmer the water the faster the juice will diffuse into solution.
Observations:
| Materials ready for the juice lab- ice water, room temp water, boiling water (left to right). |
When juice was added to the ice water the juice went to the bottom and mixed with the water. There was still clear water on the top, but below that the juice a water mixed. Right after pour the juice in it could be seen swirling in the jar and mixing with the water.
The juice added to the room temperature water could be seen swirling and mixing with it and seemed to turn into a complete solution with the water rather quickly.
This really didn't photograph well, but in the boiling water the juice blended with the water but resulted in a solution that faded through the jar. It was darkest at the bottom and then still looked like clear water at the top.
Diffusion is the mixing of two substances through kinetic means. The particles of each are moving, and eventually intermingle enough to create a solution where they are evenly distributed. Thermal energy can speed this process. The juice added to the ice water was taking much longer to disperse evenly with the juice because at a lower temperature the molecules are moving more slowly. At higher temperatures the molecules are more excited and are moving much faster due to thermal energy. I was puzzle though by the gradiated color in the boiling water jar.
Source:
Diffusion. Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html. Accessed 18 February 2013.
Carrot: Record your hypothesis, tightness of string
and texture observations and measurements, and what type of water caused
shrinkage or expansion here.
Hypothesis: The carrot in fresh water will remain firm and fresh, while the carrot in salt water will behome dehydrated and shrivel.
Observations:
Initial
length and width of carrot pieces:
Piece
1: 9 cm long, 7.5 cm circumference (Fresh Water)
Piece
2:
After-experiment
length and width of carrot pieces:
Piece
1: 9.5 cm long 8 cm
Piece
2: 9 cm long, 7.3 cm circumference (Salt Water)
After soaking in their respective jars for 28 hours the carrots were observed a second time. There was measurable shrinkage in the circumference of the carrot that had been submerged in salt water, while the carrot that had been submerged in fresh water had increased in size. Before tying the string on the carrots, it was soaked in water to allow for any stretching the might occur when it got wet. After the testing period the string was still very tight on the fresh water sample. On the salt water sample, the string still stayed in place, but could be moved down towards the cut end of the carrot with minor effort. When it was moved the area where it had been tied was obviously indented with markings from the string. The area towards the cut end of the salt water sample also felt somewhat more pliable than before the test, and as compared to the other sample.
The sample that was in the salt water lost volume because of diffusion. The water was a salt solution, meaning that there was a higher sodium content outside of the carrot than inside. This will pull water out of the carrot through osmosis to try and make the NaCl levels even between the two areas. As water leaves the carrot cells they become dehydrated and lose their normal structure and functionality. In the fresh water sample water moves into the carrot through osmosis as in a somewhat opposite process. Because the water is not pure H2O it is unlikely that it will overfill the cells and burst them, but in a pure environment this would happen.
Source:
Human Biology Sixth Edition: Structure and Function of Cells (p58). Michael D. Johnson. print.
