Class 6 Science Notes Chapter 14 (Chapter 14) – Examplar Problem Book
Detailed Notes with MCQs of Chapter 14, 'Water', from your Science Exemplar book. This chapter is fundamental, not just for your class but also forms the basis for environmental science questions in many government exams. Pay close attention as we break down the key concepts.
Chapter 14: Water - Detailed Notes for Exam Preparation
1. Importance of Water:
- Water is essential for the survival of all living organisms (plants, animals, humans).
- Our bodies are composed of about 70% water.
- Required for numerous life processes like digestion, excretion, and transport of substances within the body.
- Used for countless daily activities: drinking, cooking, bathing, washing, cleaning.
- Crucial for agriculture (irrigation) and industries.
- Helps regulate climate.
2. Sources of Water:
- Rain: The primary source of fresh water.
- Surface Water: Found on the Earth's surface.
- Rivers: Flowing bodies of water.
- Lakes & Ponds: Standing bodies of water.
- Oceans & Seas: Largest bodies of water, but the water is saline (salty) and not directly usable for drinking or irrigation without desalination.
- Groundwater: Water stored beneath the Earth's surface in the soil and rock layers.
- Accessed through wells, tube wells, hand pumps, and springs.
- The upper level of this groundwater is called the Water Table. The water table can rise or fall depending on rainfall and water extraction.
3. The Water Cycle (Hydrological Cycle):
This is the continuous circulation of water on, above, and below the surface of the Earth. Key processes involved:
- Evaporation: The process where liquid water changes into water vapour (gas) due to heat, primarily from the sun. Water evaporates from oceans, rivers, lakes, and soil.
- Transpiration: The process where plants release water vapour into the atmosphere through tiny pores (stomata) in their leaves.
- Condensation: The process where water vapour in the air cools down and changes back into tiny droplets of liquid water or ice crystals. These droplets gather to form clouds.
- Precipitation: When the water droplets or ice crystals in clouds become too heavy, they fall back to the Earth's surface in the form of rain, snow, sleet, or hail.
- Infiltration: Some rainwater seeps into the ground, replenishing groundwater. This process is called infiltration.
- Runoff: Water that flows over the land surface, eventually reaching rivers, lakes, or oceans.
4. Groundwater and Water Table:
- Groundwater: Water held underground in the soil or in pores and crevices in rock. It is a vital source of freshwater.
- Water Table: The upper surface/level of the saturated zone where groundwater occurs. Its depth varies with location, season, and amount of rainfall/extraction.
- Aquifer: A layer of permeable rock, sand, or gravel beneath the water table that holds groundwater.
- Recharge: The process by which groundwater is replenished, primarily through infiltration of rainwater. Deforestation and excessive concrete surfaces reduce infiltration and hinder recharge.
- Depletion: Excessive pumping of groundwater, especially when extraction exceeds recharge, leads to the lowering of the water table and depletion of groundwater resources.
5. States of Water:
Water exists naturally in three states:
- Solid: Ice, snow, frost (below 0°C).
- Liquid: Water (between 0°C and 100°C).
- Gas: Water vapour, steam (above 100°C, but evaporation occurs at lower temperatures too).
These states are inter-convertible through heating (melting, evaporation, boiling) and cooling (condensation, freezing).
6. Floods and Droughts:
- Floods: Occur when there is excessive rainfall over a short period, causing rivers, lakes, or reservoirs to overflow and submerge surrounding land.
- Causes: Heavy rains, melting snow, dam failures, poor drainage.
- Effects: Damage to property, crops, loss of life (human and animal), spread of waterborne diseases, soil erosion.
- Droughts: Occur when there is a prolonged period with little or no rainfall, leading to a severe shortage of water.
- Causes: Lack of rainfall, high temperatures leading to increased evaporation, excessive water usage.
- Effects: Crop failure, shortage of drinking water, scarcity of fodder for animals, migration, potential famine.
7. Water Scarcity:
- A situation where the demand for usable water exceeds the available supply.
- Causes:
- Uneven distribution of rainfall.
- Increasing population leading to higher demand.
- Deforestation (reduces rainfall and infiltration).
- Increased industrialization and agricultural needs.
- Water pollution (makes existing sources unusable).
- Wastage of water in daily activities.
- Depletion of groundwater.
8. Water Conservation:
- The practice of using water efficiently to reduce unnecessary water usage. It is crucial due to increasing scarcity.
- Methods:
- Reduce Wastage: Turn off taps while brushing/shaving, fix leaking taps and pipes immediately, use buckets instead of showers/hoses where possible.
- Reuse Water: Water used for washing vegetables can be used to water plants.
- Rainwater Harvesting: Collecting rainwater from rooftops or open spaces and storing it in tanks or allowing it to seep into the ground to recharge groundwater. This is a very effective technique, especially in areas with seasonal rainfall.
- Efficient Irrigation: Using methods like drip irrigation or sprinklers in agriculture reduces water loss compared to traditional flood irrigation.
- Planting Trees (Afforestation): Trees help maintain the water cycle and improve groundwater recharge.
- Protecting Water Bodies: Preventing pollution of rivers, lakes, and groundwater sources.
Multiple Choice Questions (MCQs):
-
The process by which plants release water vapour into the atmosphere is called:
(a) Evaporation
(b) Condensation
(c) Transpiration
(d) Precipitation -
The upper level of groundwater beneath the Earth's surface is known as the:
(a) Aquifer
(b) Water Table
(c) River bed
(d) Sea level -
Which of the following processes is responsible for the formation of clouds?
(a) Evaporation
(b) Condensation
(c) Infiltration
(d) Transpiration -
Excessive rainfall in a short period can lead to:
(a) Drought
(b) Water scarcity
(c) Flood
(d) Depletion of water table -
Which of these is NOT a primary cause of water scarcity?
(a) Increasing population
(b) Afforestation (Planting trees)
(c) Uneven distribution of rainfall
(d) Water pollution -
Collecting rainwater for future use or groundwater recharge is termed:
(a) Drip irrigation
(b) Water cycle
(c) Rainwater harvesting
(d) Condensation -
Water exists in gaseous form as:
(a) Ice
(b) Dew
(c) Water vapour
(d) Frost -
The continuous circulation of water between the Earth's surface and the atmosphere is called:
(a) Water conservation
(b) Water cycle
(c) Water table fluctuation
(d) Precipitation cycle -
A long period of abnormally low rainfall, leading to a shortage of water, is called:
(a) Flood
(b) Monsoon
(c) Drought
(d) Runoff -
Which human activity significantly hinders the recharging of groundwater?
(a) Planting trees
(b) Rainwater harvesting
(c) Building concrete roads and pavements
(d) Using drip irrigation
Answer Key for MCQs:
- (c) Transpiration
- (b) Water Table
- (b) Condensation
- (c) Flood
- (b) Afforestation (Planting trees) - This actually helps conserve water.
- (c) Rainwater harvesting
- (c) Water vapour
- (b) Water cycle
- (c) Drought
- (c) Building concrete roads and pavements - This prevents rainwater from seeping into the ground (infiltration).
Study these notes thoroughly. Understanding the water cycle, the importance of groundwater, and the methods of conservation are particularly important. Good luck with your preparation!