Solution to Activity 5.3 of NCERT Class 9 Science Chapter 5 The Fundamental Unit of Life

3. Complete Activity 5.3 (Page 52).

Osmosis with an egg

(a) Remove the shell of an egg by dissolving it in dilute hydrochloric acid. The shell is mostly calcium carbonate. A thin outer skin now encloses the egg. Put the egg in pure water and observe after 5 minutes. What do we observe?

(b) Place a similar de-shelled egg in a concentrated salt solution and observe for 5 minutes. The egg shrinks. Why?

Answer:

Aim: To observe what happens to the de-shelled egg in pure water and in concentrated salt solution and make conclusions based on that.

Materials Required: Two eggs, dilute hydrochloric acid, pure water, concentrated salt solution.

Procedure:

(i) The shells of the eggs are removed by dissolution in dilute hydrochloric acid in a jar.

(ii) Now, place one egg in pure water and observe what happens after 5 minutes.

(iii) Now, place the second egg in concentrated salt solution and observe what happens after 5 minutes.

Observations:

The egg in pure water swells in size.
The egg in concentrated salt solution shrinks in size.

The egg in pure water swells in size and the egg in salt solution shrinks.

Conclusions:

For the egg in pure water, the concentration of solute inside the egg is more than outside. Therefore, water enters the egg by the process of osmosis through the plasma membranes of the egg cells and the egg swells.
For the egg in concentrated salt solution, the concentration of solute outside the egg is more than inside. Therefore, water passes out of the egg in the salt solution by the process of osmosis through the plasma membranes of the egg cells and egg shrinks.
Thus, osmosis is the net diffusion of water across a selectively permeable membrane toward a higher solute concentration.

“Osmosis with an egg

(b) Place a similar de-shelled egg in a concentrated salt solution and observe for 5 minutes. The egg shrinks. Why?” – Solved.