Time-lapse of agar:  https://youtu.be/Nr1cLJ3mCUM

Cells need to be small because they rely on diffusion for getting substances into and out of their cells. When a cell grows, there is less membrane for the substances to diffuse through resulting in the centre of the cell not receiving the substance that it needs. Diffusion is less efficient cell processes slow down and the cell stops growing. the cell then needs to divide into 2 smaller cells, which each have a larger surface area to volume ratio and can diffuse materials more efficiently.  As we see in our agar the smaller cube is all pink where as the bigger cube is not the same shade of pink throughout. Cells that are smaller are more efficient for diffusion. Their small size means they have a larger SA:V ratio and is important for the materials to move into and out of the cell by diffusion and active transport. Smaller molecules diffuse faster than larger molecules. The smaller molecules are able to move more quickly at a given temperature than larger molecules, allowing them diffuse across the membrane with greater speed.

 

As we see in this photo the smaller  pieces of agar and the same shade of pink throughout whereas the larger pieces have lighter shades of pink in the middle.

 

Some factors that can affect how materials diffuse into cells are:

1. Concentration gradient

2. Permeability of the cells to the materials

3. Mobility of the material (if it’s a solid that’s stuck onto something big, it’s not going to diffuse into a cell).

4. Temperature (if your tissue sample is frozen solid, you’re not going to be getting diffusion)

5. Pressure (this probably should come under “filtration” rather than “diffusion”)

6. Presence of transport proteins in the membranes of the cells for the materials

7. Cell size and volume

 

As we see in this photo we can see our agar cubes in a liquid of NaOH and they are at room temperature. We stirred it with a wooden stick at times.

When you increase the size you increase the surface area therefore increasing the volume. The larger the cell the harder to diffuse keeping the cell smaller will decrease the surface area to volume ratio making it easier to diffuse.

You have three cubes, A, B, and C.  They have surface to volume ratios of 3:1, 5:2, and 4:1 respectively.  Which of these cubes is going to be the most effective at maximizing diffusion, how do you know this?

The most effective cell would be cell C. Although the surface area is larger the volume is still small making diffusion possible effectively. The bigger SA with a small volume the better as it has more SA for diffusion to take place and a small volume.

Our cells are different shapes and have different purpose cells can adapt by diving.

Why can’t certain cells, like bacteria, get to be the size of a small fish?

Because the larger the cell the harder it is to undergo diffusion. Want to maintain a stable SA:V ratio.

 

What are the advantages of large organisms being multicellular?

Rate of diffusion is higher allows to be efficient and can be more specialized. Being larger has it benefits as it can minimize the risk of becoming prey. Being multicellular allows an organism to develop a higher level of adaptation to its surroundings. This is known as cell complexity and can lead to an organism becoming more intelligent via contact with its surroundings. When talking about evolution, this is where multicellular organisms have the advantage as the many types of cells contained in a complex cellular organism enable it to adapt, change and survive.This means that a single cell does not need to perform all of the functions required to survive and instead works in harmony with millions of other cells with each taking on its own unique role.