State the important functions of roots. What is a modified root? Give suitable examples.

Read the passage given below and answer the question that follows.
You come home from school one hot summer day and notice that your favourite potted plant, kept near your window, looks dull and droopy. You get a jug of water and lovingly pour the water into the soil around the plant. Then with concerned glances during the rest of the afternoon you notice how your plant slowly picks itself up and by the evening looks like its old self.
What brought about the changes in your plant?