Heat — Science STD 7 — Question

Figure shows a part of a forest.


Write any three activities going on in the forest on the basis of this figure.

A food stall owner was preparing dough for making bhaturas. He added a pinch of yeast and sugar to the dough and left it in a warm place. After few hours, the dough had risen. There was a sour smell too.
(i) Why did the dough rise?
(ii) Why did the dough smell sour?
(iii) Why was sugar added to the dough?
(iv) What would have happened if the dough was kept in the refrigerator, soon after it was prepared?

During the summer vacations, Gaurav visited his native village. He observed that farmers were using pesticides in their field. He contacted the village head and explained him the effects of such substances in causing soil pollution. Next day, the village head called a meeting of all the villagers and convinced the villagers not to use chemicals and pesticides.

1. Why is there a ban to demand the polythene bags and plastics.
2. List some substances which pollute the soil.
3. What are the values shown by Gaurav?

Harish went to visit his grandfather in village where he saw that his grandfather’s field of wheat are infected with fungus but no one is aware of this. Harish rushed to his grandfather’s side and told him that the field have been infected with fungi. He should use an antifungal agent in his fields to stop this infection.

1. What is fungus?
2. Can fungus only cause diseases or can it be helpful also?
3. What values are shown by Harish?

Explain weathering of rocks.

Draw a neat and clean diagram of Amoeba showing the correct location of the following components: nucleus, vacuole, pseudopodia.

Name the source from which litmus solution is obtained. What is the use of this solution?

List the ways in which wastewater present in sewage is generated and the kind of contaminants present in each.