Why are top predators so rare and green plants so common

25 Jun Why are top predators so rare and green plants so common

Question
Materials Needed:

• Plastic baggie (like a sandwich baggie)

• Cornstarch (only 1 teaspoon)

• Iodine (at least 8 ounces — You can buy this at Walmart for a few $$!)

• 1 large potato

• Ruler and calculator

• Paper towel

PART A: Osmosis

Cornstarch & Iodine – In this lab you will observe the diffusion of a substance across a semi permeable membrane. Iodine is a known indicator for starch. An indicator is a substance that changes color in the presence of the substance it indicates.

Procedure:

1. Fill a plastic baggie with a teaspoon of cornstarch and half a cup of water and tie the bag.

2. Fill a cup halfway with water and add ten drops of iodine.

3. Place the baggie in the cup so that the cornstarch mixture is submerged in the iodine water mixture.

4. Wait fifteen minutes and answer the questions.

PART B: DIFFUSION & CELL SIZE

In this lab you will observe the relationship between cell size and extent of diffusion in potato cubes, and understand the necessity of microscopic cell size.

Math Formulas

* Surface area (mm2) = Length X Width X 6 (# of sides)

* Volume (mm3) = Length X Width X Height

Experimental Evidence:

1. Using a scalpel and paper towels, carefully cut 3 potato cubes using the dimensions in the calculations for Data Table 1 (0.5 cm3, 1 cm3, 2 cm3).

2. Submerge the potato cubes (cells) into the iodine solution for 20 minutes.

3. While you are waiting for 20 minutes, calculate the surface area, volume, and surface area to volume ratio for each of the 3 potato cubes (cells) in Data Table 1.

4. Carefully remove the potato cubes (cells) from the iodine solution and place them on absorbent paper towels.

5. Cut each cell in half and observe the inside. Note the color change from brown to clear that indicates the diffusion of diffusion medium (iodine) into the cube.

Using a metric ruler, measure the distance in centimeters that the diffusion medium diffused into each cube by measuring (in cm) how far the iodine penetrated into each cube. Record the data in Data Table 2. Next, record the total time of diffusion. Finally, calculate and record the rate of diffusion for each cube as centimeters per minute (divide centimeters/# of minutes).

Calculate the percentage of cell reached by diffusion for each cube.

a. Measure one side of the colored area of each cube. Calculate the volume of the colored area for each cube and record in Data Table 3.

b. Determine the volume of the cleared area of the cubes by subtracting the volume of the colored area from the total volume. Record in Data Table 3.

c. Finally, calculate the percentage of each cube into which the iodine diffused. Use this equation:

(total cube volume) – (volume of cube that has not changed color) X 100

(total cube volume)

6. Answer the remaining questions.

Questions

Define diffusion.

Describe the effect of temperature on the rate of diffusion.

Define turgor pressure.

Define hypertonic, hypotonic, and isotonic solutions.

Define Osmosis.

Is the baggie or beaker more concentrated in starch?

Iodine solution: is the baggie or the beaker hypertonic?

Select one:

a. beaker

b. liquid

c. baggie

Starch solution: is the baggie or the beaker hypertonic?

Select one:

a. beaker

b. starch

c. baggie

Which one is hypotonic in relation to starch, baggie or beaker?

Select one:

a. baggie

b. beaker

c. starch

Starting Color Color after 15 minutes

Solution in Beaker Orange Orange

Solution in Bag White Purple black

Based on your observations, which substance moved, the iodine or the starch?

Select one:

a. starch

b. iodine

c. glucose

How did you determine this?

Select one:

a. outside of bag changed colors

b. both sides of bag changed colors

c. inside of bag changed colors

The plastic baggie was permeable to which substance?

Is the plastic baggie selectively permeable? Explain.

In which cell (potato) did the iodine diffuse all the way to the center of the cube? Discuss the differences between the cells.

As cell size increases, what happens to the surface area to volume ratio? Give examples from the lab.

.

Based on your understanding of cell size and the rate (speed) of diffusion, explain why there are NO GIANT CELLS! Discuss diffusion in your answer.