A student carried out an investigation using chicken eggs - AQA - GCSE Biology - Question 4 - 2018 - Paper 1

The percentage change in mass is calculated as follows:

$\text{Percentage change in mass} = \frac{75.7 - 72.4}{72.4} \times 100 = 4.6\%$

The masses of the eggs increased due to water entering the egg through osmosis. This happens when the egg is placed in distilled water, which has a lower concentration of solutes compared to the inside of the egg. As water moves from an area of high concentration (the surrounding solution) to an area of low concentration (inside the egg), the mass of the eggs rises due to the absorption of water.

The student could use five (or more) different concentrations of a salt or sugar solution in separate beakers. By plotting the percentage change in mass against the concentration of the solution, they could determine the concentration where the curve crosses the zero percentage change line.

Calcium ions are moved from the egg shell into the cytoplasm through a process known as active transport. This occurs against the concentration gradient, where calcium ions are transported from an area of low concentration in the egg shell to a higher concentration in the cytoplasm. This process requires energy, as the movement of ions is against their natural diffusion tendency.