BIOLOGY 102: General Biology
Investigation 3
Cell Structure and Cell Membranes

Part 1 - Cells [20 points]

Specimen Number | Organism | Eukaryote or Prokaryote | Where Organism is Found | How Organism Obtains Nutrients | Image 9 | Spirogyra | Eukaryote | Freshwater, free-floating | Autotrophy | Image 7 | Diatom | Prokaryote | Oceans, freshwater, soils and damp places | Heterotrophy | Image 6 | Paramecium | Eukaryote | Freshwater, brackish and marine environments, often very abundant in stagnant basins and ponds | Heterotrophy | Image 2 | Lactobacillus | Prokaryote | Vagina and the gastrointestinal tract | Heterotrophy | Image 10 | Euglena | Eukaryote | Fresh and salt waters, abundant in quiet inland waters | Both (Mixotrophy) | Image 11 | Trypanosoma | Eukaryote | Generally found in intestine, but normally occupy the bloodstream or an intracellular environment | Heterotrophy | Image 13 | Volvox | Eukaryote | Ponds and ditches | Autotrophy | Image 4 | Radiolaria | Eukaryote | Found as zooplankton throughout the ocean and their skeletal remains | Heterotrophy | Image 1 | Amoeba | Eukaryote | Stagnant water | Heterotrophy | Image 12 | Plant cells with nucleus (chloroplasts absent) | Eukaryote | Plants | Autotrophy |

List two similarities between plant cells and animal cells

1. Both plant and animal cells have a nucleus.

2. Both plant and animal cells have ribosomes, mitochondria, and a Golgi apparatus.

List two differences between plant and animal cells

1. Animal cells do not have a cell wall or chloroplasts, but plant cells do.

2. Plant cells have one large central vacuole while animal cells have one or more small vacuoles.

Part 2 – Diffusion and Osmosis

Diffusion [4 pts] Boiling water (Right Side) | Cold water (Left Side) | * Absorbed tea bag rapidly | * Slowing absorbed tea bag | * Instant change in color | * After 3 minutes, slight change in color | * Tea bag sinks into cup after tea is equally distributed | -Tea bag stayed a float on top of water |
*Note: Lipton 100% All Natural Tea bags were used. To begin… 3 minutes later…

Boiling water… In the cup of boiling water, it is my assumption that the molecules within the tea bag are moving faster due to the excessive temperature. Because these molecules are bouncing around so rapidly in such a confined space, they are released from the tea bag into the cup and this is where we notice the water begins to change colors. The molecules are moving rapidly from the tea bag to the water until the molecules are equally distributed within the cup, and that is why we notice that the water stops changing color and our tea is brewed.

Cold water…. In the cold water, on the other hand, the molecules are not moving as rapidly because the temperature is not high enough. Due to the slow motion working of the molecules, it takes longer for them to escape the tea bag and equally distribute themselves within cup as you saw above, after three minutes the color of the water only changed slightly. Ultimately, the temperature affects the rate of diffusion.

Osmosis

Label your 4 plastic cups A, B, C & D
Cut 4 small pieces of paper and using a pencil label them A, B, C & D. These labels will go inside your dialysis tubing.
Prepare your dialysis tubing as follows: * Soak your dialysis tubing in distilled water until it is flexible * Take a piece of dialysis tubing and tie a tight knot in one end * Open the other end of the tubing by rolling it between your thumb and finger * Fill bag A with 10mL of 1% sucrose solution. Insert label A and squeeze out any air bubbles then tie a tight knot in the end of the tubing to seal it * Check for leaks, blot dry and set aside * Fill bag B with 10mL of 1% sucrose solution and complete procedure as before * Fill bag C with 10mL 25% sucrose solution and complete procedure as before * Fill bag D with 10mL 50% sucrose solution and complete procedure as before
Make a visual assessment of each bag at time zero, i.e. before placing it into the solution in the cup, and take notes.
Prepare the experimental setup as follows * Fill cup A with 50% sucrose solution * Fill cups B, C & D with 1% sucrose solution * Add bag A to cup A; bag B to cup B and so on
Leave your experiment undisturbed for 60 minutes. Now carefully remove each bag from the cup with its respective solution and blot dry. Measure the volume of liquid inside each bag using your graduated cylinder and record your data in the table below. Be sure to blot dry your graduated cylinder between measurements.
[2 pts]

| Beginning volume (milliliters) | End Volume (milliliters) | Difference (milliliters) | Bag A | 10 | 7 | (-) 3 | Bag B | 10 | 10.1 | (+) 0.1 | Bag C | 10 | 12 | (+) 2 | Bag D | 10 | 14 | (+) 4 |
* When I cut open Bag A, I dropped the bag and water spilled out of bag.

1. Did water move into or out of all of the bags? [1 pt]

For the most part, other than the bag I spilled, water moved into all of the bags.

2. Which bags demonstrated osmosis? Draw a diagram to show water movement in each of the bags. [3 pts] Bags B, C, and D demonstrated osmosis.

3. Which bags showed the most rapid movement of water across the membrane? Explain your answer [3 pts]

Bags C and D showed the most rapid movement of water across the membrane because there was more sugar within the bag than in the cup so the water moved from the low sugar concentration to the high sugar concentration.

4. Apply the information you have learned and briefly discuss why it is important for animal cells and plant cells to have the ability to balance water intake with water loss. [5 pts]

It is important for animal cells and plant cells to have the ability to balance water intake with water loss because if a cell has too much water it may burst and cells can be killed if they do not have enough water. This process of balancing water is called osmoregulation.

Part 3 – Cell Membranes

For all 6 treatments
Arrange your tubes in ascending intensity of red color. Determine a scale for yourself on a scale of 0 (no color) to 10 (darkest red color) and quantify the colors observed in your tubes. Record your results in the space below.

Tube Number | Treatment | Color Intensity (scale 0-10) | 1 | 70oC | 1 | 2 | 55oC | 2 | 3 | 40oC | 2 | 4 | 20oC | 3 | 5 | 4oC (refrigerator) | 4 | 6 | -5oC (freezer) | 8 |

1. Which treatment caused most membrane damage as reflected by color intensity? [2 pts] The -5°C freezer treatment (Tube #6) caused the most membrane damage as reflected by its color intensity.

2. Which treatment caused least membrane damage as reflected by color intensity? [2 pts] The 70°C treatment (Tube #1) caused the least membrane damage as reflected by color intensity.

3. In what way does extreme heat damage the membrane allowing the contents to leak out of cells? [3 pts] Extreme heat, surprisingly, did not damage the membrane as rapidly as I had anticipated. Rather it slowly damaged the membrane by only releasing trace amounts of red pigments.

4. How does extreme cold damage the membrane allowing the contents to leak out of cells? [3 pts] Extreme cold, on the other hand, takes its toll on the membrane immediately.

5. Apply this knowledge to a situation that may arise in your daily life or in nature and briefly explain your reasoning in the space below. [2 pts]

The first thing that came to mind when I thought of this lab experiment and how it may arise in my daily life was regarding over-exposure to heat and freezing temperatures. When our bodies come into too much contact with sunlight we experience either a tan or as most of us do, we burn. This over-exposure of sunlight can overtime cause skin cancer that damages our body’s cells while even the slightest exposure to freezing temperatures can cause hypothermia and take effect immediately and cause death to a person.