Biology Case

Internal Assesment - Task 2C

In this experiment I am investigating the relationship between surface area and the volume of a model cactus and to determine whether this relationship affects the loss of water. We used oasis blocks, an absorbant material used by florists as a substitute for a cactus, that would soak up the water, and thus ideally show the percentage water loss by weighing the before and after evaporation weights.

Independent Variable

The independent variable is the total surface area for each size of the blocks and I think this will affect the dependent variable as larger blocks, I hypothesize, will have less water loss by evaporation as there is less surface area for it, as opposed to the smaller (2cm x 2cm x 2cm) blocks, that have a larger total surface area for water to evaporate. Dependent Variable

The dependent variable is the percentage loss of water, and I think this will be affected by the independent variable, the total surface area of the blocks, because I hypothesize that the larger the total surface area, the more water loss will occur, as the oasis will have more places for the evaporation to take place. Control Variables

The control variables are the size and shape of the oasis blocks within each category, the size of the tray, and the conditions that the blocks are left in to saturate and evaporate, and these are important to keep controlled as the shape and size can alter the surface area, which will in turn distort the results. this is the same of the size of the tray, which could potentially alter water distribution, and the conditions that the trays are left in could drastically change the rate of evaporation.

I will change the independent variable in the way that I will test three different sizes of blocks: - 1 x (8cm x 8cm x 4cm)

- 4 x (4cm x 4cm x 4cm)

32 x (2cm x 2cm x 2cm)

I will use a metal ruler with as much accuracy as possible to ensure that the

test is fair. I will control the controlled variables by:

Ensuring that the shape and size is constant within the different variant groups of the independent variable, by measuring all sides with a ruler. Re-using the same tray (after cleaning it each time).

Leaving the tray for two days in the same place each time to control the environment to the fullest of my ability.

Controlling of Variables

Unfortunately, in the time frame we had to complete and document this experiment there was not enough time to repeat the experiment in order to carry out an error analysis by use of standard deviation. The apparatus I will use to control the pre-mentioned variables are as