Q1.
Many useful changes happen in our daily life. For example, the changing of milk into curd, ripening of fruits, cutting of fruits, and cooking of food. All these are desirable changes. Can you think of some other desirable changes happening around you?
Answer
Yes — many changes around us are wanted and useful.
- At home: curd being churned into butter, dough rising with yeast to make bread fluffy, wet clothes drying in the sun, water boiling for drinking, rice cooking, tea leaves giving colour to water.
- On the farm and in the garden: a seed germinating into a seedling, buds opening into flowers, grain ripening, kitchen waste and dry leaves rotting into compost.
- In the workshop and factory: clay being shaped and baked into pots and bricks, iron being melted and cast into tools, cotton being spun into thread and woven into cloth, sugarcane juice becoming jaggery.
- In our own body: the digestion of food, the healing of a wound, growth in our height.
Some changes are undesirable — the rusting of iron, the decay of food during storage, the souring of milk in summer, paint drying and releasing substances that pollute the air, and the rise of carbon dioxide in the atmosphere because of the fuel burnt by cars, trains and aeroplanes.
Why it happens: Desirable and undesirable are not properties of the change itself — they depend on the situation. Decomposition of food is undesirable in the kitchen, but it is exactly what we want in a compost pit. Rusting is undesirable on a gate, but the same reaction gives the beautiful red layer on basalt rock that the chapter shows in Fig. 5.10b.