The effect of size and shape of an object on the time take for a substance to diffuse to its centre.
Diffusion is a very important process for organisms. (docx.) Cells in organisms are so small that they are about 25 µm. (adapaproject.org, 2014) In this activity, we will explore the relationship between the surface area, volume and SA:V of a cell between the diffusion of nutrients, oxygen, carbon dioxide, waste products into the cells, and investigate the cell size limitations.
In this activity, the size of organisms will be replaced by using blocks of agar jelly. The time taken for the jelly to discolourise is a measure of the rate of diffusion of acid into the jelly which indicates the rate of diffusion of nutrients into the cells.
To investigate the relationship between the size and shape of an object and the time taken for a substance to diffuse to its centre.
If the size and shape of an object is bigger, then the time taken for a substance to diffuse to its centre is longer.
Materials and equipment:
0.1 M sulphuric acid
4 small beakers
clear plastic ruler
The jelly is placed on the cutting tile.
The jelly is cut into correct sized blocks, which are 20mm x 20mm x 20mm, 12mm x 12mm x 12mm, 20mm x 30mm x 3mm, 10mm x 18mm x 10mm, using the scalpel.
Enough acid is added into each of the four beakers, which is about 25mm deep.
Each block is lowered into its own beaker of acid, using the spoons. The block is made sure that it is completely covered by the acid. The stopwatch is started as soon as the blocks are added to the acid.
After 5 minutes, all the blocks are removed from the acid using the plastic spoons. The blocks are placed on paper towel to dry.
Each block is cut in half, using the scalpel. Then, the thickness of the discolouration is measured, using the ruler. This indicates how quickly the acid diffused into the block.
The agar and acid are disposed properly.
Safety and ethical assessment:
I tied my long hair.
I tied back loose clothing.
I wore covered shoes into the lab.
I wore labcoat before I started doing the experiment.
I used the apparatus in a correct manner.
Table 1: The results on the blocks after immersing in the acid for 5 minutes
Dimensions of block Surface area (mm2) SA Volume (mm3)
Vi SA:VThickness of coloured section (mm) Volume of coloured section Vr (mm) Volume of discoloured section Vd% of block diffused with acid
A 20x20x20 mm 2400 8000 0.30 18 3744 4256 46.8%
mm 864 1728 0.50 5 125 1603 92.8%
mm 1500 1800 0.83 3 0 1800 100%
mm 920 1800 0.51 3 84 1716 95.3%
Table 1 shows the results on the blocks after immersing in the acid for 5 minutes. It clearly shows that the block with the larger volume and smaller SA:V has less percentage of diffusion of acid into the block in 5 minutes (that is block A with 46.8% of diffusion) than the block with smaller volume but bigger SA:V (that is block C with 100% of diffusion).
Analysis and discussion:
The bigger the volume of the block, the less the amount of diffusion of acid in 5 minutes. Block A has the biggest volume, that is 8000mm3, only 46.80% of the block is diffused with acid after 5 minutes, meanwhile Block B has the smallest volume, it has 92.80% of the block is diffused with acid after 5 minutes.
The bigger the surface area of the block, the more the amount of diffusion of acid in 5 minutes, when the volume of the block is the same. Block C has larger surface area than Block D, that is 2400, 100% of the block is diffused with acid in 5 minutes, meanwhile Block D, surface area of 920, 95.30% of the block is diffused with acid after 5 minutes.
The bigger the SA:V of the block, the more the amount of diffusion of acid in 5 minutes. Block C has the largest SA:V, that is 0.83, 100% of the block is diffused with acid in 5 minutes, meanwhile Block A has the SA:V, that is 0.30, only 46.80% of the block is diffused with acid after 5 minutes
Supported. Block A has the largest volume, in 5 minutes, only 46.8% of block is diffused with acid, so it means it will take longer time to diffuse to its centre of the block.
Cells tend to be very small in size to maximize the rate of diffusion of nutrients into the cell. Most cells are not bigger than 1mm in diameter because if they were, then the time taken for the nutrients and oxygen to diffuse into the cell would be so long until the cell couldn’t even survive.
Firstly, we wore disposable gloves to protect our hands from contamination. Secondly, we made sure we know where is the safety equipment in the lab and how to use it, incase when something happens, we can treat it immediately in a correct and safe way. Thirdly, we made sure we dispose the lab waste properly, because certain types of waste can be dangerous and can contaminate the environment and cause diseases if it is not handled properly.
First, we can repeat our experiment for at least 3 times to get the average data to a more reliable result. We can also control our concentration of the sulphuric acid. If the concentration of the sulphuric acid is high, the rate of diffusion of acid into the jelly is high. The volume of sulphuric acid can be controlled also, so that the rate of diffusion is not affected by the the pressure of larger volume of sulphuric acid. Prepare everything in advance, record everything down during the experiment, and analyze the data to improve the quality of data.
We can control other variables that might affect the rate of diffusion, such as temperature of surrounding, volume of acid, concentration of acid. In addition, we can use a small container or beaker to make sure every side of block is immersed in the acid.
On cold days, animals curl up tightly to decrease their surface area expose to the cold weather, they have less surface area to volume ratio, so they can retain the heat and lose heat more slowly. In hot days, many animals stretch out, it increases their surface area, the surface area to volume ratio increases, the can lose more heat and lost heat faster.
The hypothesis is supported. When the block has the smallest size, the percentage of the block diffused with acid is the most. When the block has the biggest SA:V, the percentage of the block diffused with acid is the most. So, the cells are tend to be so small so that they have bigger SA:V which will help maximize the rate of diffusion of nutrients, oxygen, carbon dioxide, waste products between the cells and the environment.
https://www.quora.com/During-the-winter-animals-curl-into-a-circle-Why (Stephen Foskey , 2017)