GT BIOLOGY 2008

SR.CELL.6H

THE IMPORTANCE OF CELL SIZE

INTRODUCTION

Your parents might remember a movie called “The Blob.” Could a giant amoeba-like organism really take over the world? Today you will examine why most cells, regardless of the size of the organism, are all relatively the same microscopic size.

HYPOTHESIS:

Your teacher has prepared three different-sized agar cubes using a pH indicator called bromothymol blue (BTB). When BTB comes in contact with an acid, it turns yellow. The three cubes are placed in a vinegar solution for 25 minutes. Hypothesize which size cube (1cm, 2 cm or 3 cm) you think will turn yellow the fastest. Use proper format and include appropriate cell transport vocabulary.

DIRECTIONS:

Use the models provided by your teacher to determine the surface area and volume of three different cube-shaped “cells” and answer the questions that follow.

1. Equations: Fill in the components you will use to calculate these parameters.

Surface area: ______X ______X ______

Volume: ______X ______X ______

2. Calculations: Determine the surface area and volume measurements for the “cells” in Table 1 (on the next page). Then calculate the surface area-to-volume ratio for each “cell.” Show all of your work in the boxes.

3. Anything that the cell takes in, such as oxygen and food, or releases, such as carbon dioxide, must go through the cell membrane. Which characteristic of the cube from Table 1 best represents how much cell membrane the models have? Why?

4. The cell contents, including the cytoplasm and organelles, use the oxygen and food brought through the membrane. Which characteristic of the cube from Table 1 best represents the cell contents? Why?

Table 1

Figure / Calculate the Surface Area / Calculate the Volume / Calculate the Surface Area–to–Volume Ratio
2 cm by 2 cm by 3 cm
6 cm by 2 cm by 1 cm

4 cm by 3 cm by 1 cm

5. As cells grow larger, what happens to the Total Surface Area-to-Volume ratio?

6. Why can’t cells survive when the Total Surface Area-to-Volume Ratio becomes too small?

7. Compare the results of the BTB-cube demonstration to your hypothesis. Do the data support your hypothesis? Why or why not?

8. The distance that the vinegar diffuses into each cube is the same (the concentration gradient is the same for each cube, regardless of size). Why, then, did the smallest cube turn yellow faster? Use the calculations you have completed from this activity to support your answer.

analysis

1.  In order for a cell to continue being efficient at exchanging materials, what must it do as it grows to maintain its surface area-to-volume ratio?

2.  Are elephants bigger than mice because they have larger cells? Use data from today’s activity to support your answer.

3.  Circle which of the following cell shapes will be most efficient at exchanging materials with its environment. Assume that all of the shapes have the same volume. Justify your choice.

i. ii. iii.

4. Use the knowledge you have gained from this activity to explain these cell specializations. For each example, discuss a connection between the cell’s specialized structure and a life process.

a. Cells that line the small intestine have finger-like extensions called microvilli.

b. Red blood cells have a biconcave shape, like doughnuts, as opposed to a spherical shape.

EXTENSION

Most absorption of food nutrients occurs in the small intestine. The lining of the small intestine is covered with tiny fingerlike projections called villi, which give it the feel and appearance of velvet fabric. The cells covering each villus also have projections on their outer surface. These microscopic projections are called microvilli. Together, the villi and microvilli of the small intestine greatly increase the suitable area available for absorption of nutrients.

Examine the diagrams of epithelial cells, villi, and microvilli below.

·  Which structure (villi or microvilli) is the most effective in absorbing materials in the small intestine? Your answer should be based on the two structures functioning independently. Use the knowledge gained from today’s lab to guide your thinking.

·  What impact would damage to the villi or microvilli have on the health of the organism? Relate your response to a topic covered during our Biochemistry Unit.

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