How Big Can a Cell Get? Practical Discussion

Questions on How Big Can a Cell Get? Practical:

From the data, what can you conclude about the relationship between surface area:volume ratio and the rate of diffusion of the liquid?
As the surface area:volume ratio decreases (surface area-volume fraction), the rate of diffusion of the liquid decreases.

What is the size of the largest single cell organism? Explain why there is a cap on the maximum size of a living cell.
The largest single cell organism is a type of xenophyophore (a type of protozoa related to amoebas) measure 10cm across. They were discovered at depths of 10.6km deep in the Mariana Trench.
The ratio of cell volume to cell surface affects the maximum size of a cell. If the cell is too big, it will take too long for diffusion to take place and for necessary molecules to be transported from the cytoplasm through the cellulose cell membrane to the environment and vice versa. This can be proved by the results of the experiment. As the surface area:volume ratio of the agar block decreases, the rate of diffusion of the liquid decreases.

How does the concept of surface area to volume ratio be applied to the multi cellular organism and the specialisation of cells? Name some examples in our body that support your reasoning.
If a multi cellular organism is made up of solely cells clumped together, the cells in the middle would not be able to gain access to necessary molecules and diffusion would not take place, so they would die. The surface area would not be enough for the organism to survive. For it to survive, it would need to have a channel cutting through the mass of cells, like a tube, for necessary molecules and nutrients to reach the cells in the middle, allowing diffusion of these molecules to take place. The surface area of the cells mass exposed to the molecules would increase, increasing the rate of diffusion. Another way would be to develop a circulatory system, where specialised cells could pass the necessary molecules to other cells.
An example of this would be red blood cells. Red blood cells have a large surface area to volume ratio to allow rapid diffusion of oxygen, so that they can supply oxygen to other parts of our body, forming part of the circulatory system. Another example would be lung cells which are flatter, so they have a larger surface area:volume ratio. The rate of diffusion of oxygen as we breathe in would be faster so more oxygen can be taken in by the cells.

How Big Can a Cell Get? Practical

Today we did an experiment on the rate of diffusion of cells and the pH of some common liquids.
We used red cabbage juice agar because it changes to a variety of colours when mixed with different bases and acids. My group's liquids were white vinegar, baking powder solution and 100 plus.

PART 1

The agar block was cut into 3 pieces of each size: 5 x 5 x 5mm, 5 x 5 x 20mm and 10 x 10 x 10mm.
They were then placed into 3 petri dishes containing the 3 different liquids. We took down the amount of time taken for the agar blocks to change colour completely (to the core).

Table 1

Paper towel/ Agar block	5 x 5 x 5mm	5 x 5 x 20mm	10 x 10 x 10mm
Surface area (S)	150mm^2	450mm^2	600mm^2
Volume (V)	125mm^3	500mm^3	1000mm^3
S:V ratio	6:5	9:10	3:5
Time for agar block to change colour (vinegar)	3:38 min	4:15 min	7:59 min
Time for agar block to change colour (baking powder)	11:23 min	16:30 min	27:00 min
Time for agar block to change colour (100+)	2:35 min	3:23 min	5:38 min

PART 2

We also soaked 30 x 20mm paper towel strips in the cabbage juice, left them to dry, and then introduced a few drops of each liquid onto each paper strip. Finally we poured an equal amount of each liquid into 3 test tubes and added equal volumes of cabbage juice to each of them The colour changes of the agar blocks in part 1, the paper strips and the cabbage juice were recorded.

Table 2

Materials	Colour Change	Vinegar	Baking Powder	100+
Agar	Initial Colour	Dark purple
	Final Colour	Red	Green	Light purple
Paper towel	Initial Colour	Light purple-blue
	Final Colour	Darker purple	Green	Light purple
Cabbage juice	Initial Colour	Dark purple
	Final Colour	Red	Green	Pink-purple

Taxonomy and Ecology

Basically this is what I need to know about taxonomy:

Taxonomy is the naming and classifying of organisms. A taxon is a group of organisms in a classification system.
 
Key concept:
The current tree of life has three domains (Bacteria, Archaea, Eukarya)
 
- All living things bear scientific names that use the binomial signature (two parts, reflecting its genus and species)
- Linnaeus Classification System: Seven levels (need to remember all seven: Kingdom, Phylum, Class, Order, Family, Genus, Species)
- Linnaeus taxonomy does not account for molecular evidence
- Interpret data given from this classification system
- There are six kingdoms (Animalia, Plantae, Protista, Archaea, Bacteria, Fungi) and preceding that, 3 domains
- Domain Bacteria branches into the Bacteria kingdom
- Domain Archaea branches into the Archaeal kingdom
- Domain Eukarya (all eukaryotes) branches into the Protista, Animalia, Plantae and Fungi kingdoms
- Classification of living things is a work in progress.
 
And a little bit on ecology:

- Living things cannot exist alone, there must be a relationship between them.

- Living things are adapted to the environment where they live.
- Ecology is the study of how living things interact with each other and with their environment.
- Abiotic factors (light, temperature, water) & biotic factors (organisms)