Download Why are Cells So Small Lab - District 279

Why Are Cells So Small?
Name:
Hour:
Introduction: When cells grow to a certain size, their rate of growth slows down until
they stop growing entirely. They have reached their size limit. When one of these
larger cells divides into two smaller cells, the rate of growth increases again.
Cells take in food and other molecules necessary for growth through the cell
membrane. The membrane covers the outside of the cell and equals the cell surface
area. The inside of the cell is filled with cytoplasm. The amount of cytoplasm equals
the cell’s volume.
If there is a lot of surface area, then a lot of food pass through the membrane to get
inside the cell. If there is a lot of cytoplasm (volume) then the cell needs lots of food.
Purpose: In the following experiment you will determine if there is a relationship
between size and surface area.
CUBE SIZE
(cm3)
3X3X3
SURFACE
AREA
(6 x s x s)
6 X 3 X 3=
54 cm2
VOLUME
(s x s x s)
27 cm3
AREA: VOLUME “FOOD
RATIO
DISTANCE”
54 : 27 = 2 : 1
2x2x2
1x1x1
0.1 x 0.1 x 0.1
Conclusion:
1. Which cube has the greatest surface area:
2. Which cube has the greatest surface area to volume ratio?
3. If the agar blocks were cells and the NaOH were a vital, substance such as food,
which block would have the most efficient ratio of surface area to volume?
4. What happens to the surface area to volume ratio of a cell as it grows?
5. Why does the growth rate of a cell slow down as it gets larger?
6. How does division affect the cell’s ability to absorb material for growth?
7. What final conclusion can you make about “why cells are so small”?
Diffusion: How Can You Model Permeability in Cells?
Introduction: In order for a cell to survive, materials need to be able to move in and
out of it. They pass through the cell membrane. The cell membrane is selective and
will only allow certain materials to pass through its border. One of the most
important functions of the cell membrane is to regulate the movement of dissolved
molecules from the liquid on one side of the membrane to the liquid on the other
side.
Purpose: In the experiment, you will observe some molecules moving through a
membrane, and determine why some molecules were not allowed to pass.
Materials: graduated cylinder, plastic sandwich bag, starch solution, 500 ml beaker,
iodine solution
Procedure:
1. Pour 50ml of starch solution into the plastic bag. Tie the bag with a twist tie.
2. Pour 250ml of water into a 500ml beaker.
3. Add 15 drops of iodine to the water in the beaker. CAUTION: Iodine is a
corrosive and irritating to the skin and can stain skin and clothing. Be careful
not to spill.
4. Place the sandwich bag of starch solution into the beaker of iodine solution.
Make observations about the sandwich bag:
Make observations about the iodine solution:
Predict what will happen:
5. After at least 20 minutes look at the bag and record observations.
Conclusion
1. What cell structure does the bag represent?
2. What cell structure does the starch solution represent?
3. Why was the iodine added?
4. What happened to the iodine over time? How do you know?
5. What happened to the starch solution? How do you know?
6. What changes occurred to the liquid in the beaker?
7. Iodine turns blue-black in the presence of starch. What process do you think
occurred that caused the results you observed? Explain your answer.