# Agar Cube Lab Report

Investigating the Relationship between Cell Size and Rate of Diffusion

Ban Madi

11 Dp Biology SL

Research Question: How does the size of the cell affect its efficiency in exchanging substances through several ways, like diffusion?

Aim: To plan and carry out an investigation to show the relationship between volume/Cm3, surface area, and diffusion using agar cubes measured in time/s; and to demonstrate, using diffusion, why the size of cells is limited, keeping the room temperature and pressure constant.

Hypothesis: I expect to find that when the surface area to volume of a cell reaches a certain level, diffusion alone won't be able to supply the cell materials needed, and as single-celled organisms take in and release substances by means of diffusion across the cell membrane, this process limits cell size. I predict that as the rate of diffusion will be too slow to deliver materials to the center of the cell in the larger cells, it could result in cell malfunction.

Variables:

The independent variables are the dimensions of surface area to volume ratio of the agar cube. (1cm,1.5cm,2cm)

The dependant variable, the variable I am observing/recording, is the time of diffusion (NaOH turns the agar cube pink as it disperses into it).

The controlled variables will be keeping the concentrations of the Sodium Hydroxide constant, to use agar jelly from the same batch. Also, there’s the room temperature which is kept constant and the room pressure.

Materials:

250 ml beaker

Measuring tape

Dull knife

Stirring rod

Phenolphthalein agar cubes (2x2x2 cm, 1.5cm,1cm)

Hydrochloric acid (1m)

Paper towel

Ruler

Procedure:

1- Obtain agar cubes and hydrochloric acid from your lab instructor.

2- Cut the cubes so that one has a length of 1.00 ±0.05 cm, another 1.50 ±0.05 cm, and the 3rd 2.00 ±0.05 cm.

3- Examine the cubes closely and then place them in the 250ml beaker.