Processes of Life: How big can a cell get

First, we did an experiment on osmosis and diffusion.

1. Cut paper towels into 3 strips of about 30 x 20mm and soak them in cabbage juice (which is purple)
2. Cut your agar block (which has been soaked in cabbage juice) to the following dimensions
a. 3 pieces of 5 x 5 x 5 mm
b. 3 pieces of 5 x 5 x 20 mm
c. 3 pieces of 10 x 10 x10 mm
3. Immerse one of each dimension into the following solutions:

• 7 up
• Lemon
• Soap

4. Introduce a few drops of each of your 3 solutions onto a different strip of the cabbage juice soaked paper towel
5. Observe the colour change
6. Transfer 2cm^3 of each of the solution into separate test tubes. Add an equal volume of cabbage juice to each of these test tubes and record the colour change

Rate of Diffusion in different sizes of Agar

Agar Block	5 x 5 x 5mm	5 x 5 x 20mm	10 x 10 x 10mm
Surface Area (cm^2)	150	450	600
Volume (cm^3)	125	500	1000
Surface Area: Volume ratio	6:5	9:10	3:5
TIme for agar block to change colour completely (min)	20s	10s	1.10

Colour change of cabbage juice in a different medium

		7 up	Lemon Juice	Soap
Agar	Initial Colour	Purple	Purple	Purple
	Final colour	Slightly lighter purple	Pink	Blue
Paper towel	Initial Colour	Blue	Blue	Blue
	Final Colour	Light purple	Pink	Blue
Liquid	Initial colour	Colourless	Yellow	Yellowish

                       Final Colour     Light Purple               Pinkish-Orange  Light Purple

From this data, I can conclude that the higher the surface area to volume ratio, the faster the rate of diffusion.
There is a cap on the maximum size of a living cell as if the size of a living cell is too high, there will be a low surface area to volume ratio, causing inefficient diffusion.
The cell's surface area to volume ratio affects the rate of diffusion, which depends on the function of the cells. For example, the protusions on the large intestine increases the surface area and nutrients absorbed by the large intestines.

Osmosis and Diffusion (Experiment)

Today we did 3 experiments on Osmosis and Diffusion--
1. Osmosis in Plant tissues
2. Demonstration of Osmosis Processes in Non-living System Using an Osmometer
3. Osmosis in Plant cells

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1. In the first one, we used 3 potato strips of around 50 mm each.
We placed each one in different solutions, and found that Strip A increased in length, and Strip B and C decreased in length.
In the case of Strip C it was because the water molecules moved from a region of higher water potential (strip C) to a region of lower water potential (Solution) through a partially permeable plasma membrane. Thus the water potential in the Potato Strip decreased as the water molecules moved out of the cell and it became shorter.

2. In the second experiment, we observed two thistle funnels with cellophane paper tied over the mouth, and placed in a beaker.
Both the beakers were filled with distilled water. One thistle funnel has 50% sucrose solution, and the other with only distilled water.
After thirty minutes, the thistle funnel with sucrose solution in it had a higher water level.
This was because water molecules from there was a net movement of water molecules from the distilled water to the solution inside the funnel through the cellophane paper.

3. In the third experiment, we prepared a slide of a Hydrilla leaf. We observed it

Hydrilla leaf under 40x

Then we put it in saline solution

Hydrilla leaf in salt solution after 15 minutes