## NCERT Exemplar Class 10 Science Solutions

##### Class X-Biology

Q.31. Indicate the flow of energy in an ecosystem. Why is it unidirectional? Justify.
Answer. Flow of energy in an ecosystem is as follows:
Sun → Producer → Herbivore → Carnivore
The flow of energy in the ecosystem is unidirectional. The energy enters the plants (from the sun) through photosynthesis during the making of food. This energy is then passed on from one organism to another in a food chain.
The energy given out by the organisms as heat is lost to the environment, it does not return to be used by the plants again. This makes the flow of energy in ecosystem ‘unidirectional’.
Q.32. What are decomposers? What will be the consequence of their absence in an ecosystem?
Answer. The microorganisms, comprising bacteria and fungi, break-down the dead remains and waste products of organisms. These microorganisms are the decomposers as they break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.
This decomposer acts as cleaning agents of environment by decomposing the dead bodies of plants and animals and help in recycling of materials, replenishment of soil’s nutrients etc.
Following are the consequence of their absence in an ecosystem:
Dead bodies and plants would keep lying and their number will keep on increasing. Their accumulation will cause land and water pollution. Also, substances from which these bodies are made such as soil and water will never be recycled.
Q.33. Suggest any four activities in daily life which are eco-friendly.
Answer. Four activities in daily life which are eco-friendly:
1. Using bags made of clothes or paper instead of plastic bags.
2. Use public transport, cycling or walking to travel.
3. Switch off fans and lights when not in use.
4. Dump off the biodegradable substances like vegetables and peels of fruits in ground.
Q.34. Give two differences between food chain and food web.

Q.35. Name the wastes which are generated in your house daily. What measures would you take their disposal?
Answer. Wastes which are generated in our house daily and measures for their disposal are as follows:
Raw vegetable and peels of fruits – can be disposed underground in a nearby garden which on decomposition enriches the soil with nutrients.
Paper wastes like newspaper, books etc – Can be recycled or can also be sold.
Plastic waste like polybags, plastic toys etc – Can be sold in suitable shops where they can be recycled.
Other household waste like pieces of glass, clothes etc – Should be safely dumped in garbage bins placed to collect non-biodegradable waste.
Q.36. Suggest suitable mechanism (s) for waste management in fertiliser industries.
Answer. Chemicals and harmful gases are the main pollutants which are produced in a fertilizer factory and a suitable waste management is essential for such industries.
These pollutants can be controlled at the point of generation within the factory or nearby treatment plant.
To control air pollution certain adsorption equipments may be fitted in chimneys of fertilizer industries which can absorb harmful pollutants before the smoke is released into atmosphere.
Water mixed with chemicals can be sent to water bodies after treatment in treatment plants within industries. Water can also be sent to any nearby treatment plants with the help of a suitable drainage system.
Q.37. What are the by-products of fertilizer industries? How do they affect the environment?
Answer.The by-products of the fertiliser industries are oxides of nitrogen and sulphur i.e., $SO_{2}, CO, NO_{x}, CO_{2}, H_{2}S$, other solid, liquid chemicals and some solid waste material.
These substances usually released in air or dump in river bodies or sea which causes water pollution. These substances when consumed by plants and animals enter the food chain.
By the process of bio magnification these harmful chemicals get concentrated at each trophic level. Human being omnivore eats both plants and animals (or aquatic animals) which is extremely harmful for health. SO2 gas released in atmosphere can cause acid rain which also effect monuments and buildings.
Q.38. Explain some harmful effects of agricultural practices on the environment.
Answer. Although agriculture is important but there are some harmful effects of agricultural practices on the environment which are as follows:
Excessive cutting down of trees for agricultural purposes causes deforesting and during rain fall it may also result in soil erosion.
Excess drainage of groundwater for irrigation purposes lowers the water table. This results in acute water shortage at many places.
Synthetic fertilizers and pesticides used in the field during rain fall washed away to rivers and other bodies which cause water pollution.
The chemical pesticides, being non-biodegradable accumulates in organisms in increasing amounts at each trophic level commonly known as bio magnification.