Water: A Precious Resource Class 7 Notes Science Chapter 16
Water: A Precious Resource Class 7 Notes Science Chapter 16
Preview of the chapter
Water is one of the most prevalent and practical materials in our environment and is necessary for all life forms to live. On March 22, World Water Day is observed to raise awareness of the significance of water conservation. In order to raise awareness of freshwater conservation and to emphasize the fact that life cannot exist on earth without water, 2003 was designated as the International Year of Freshwater. Knowing how much water is available on our globe is crucial before analyzing why water is becoming scarce.
Water: Introduction
Water is a colorless, tasteless, and odorless liquid that is essential to life on Earth. It is the most abundant substance on our planet, covering approximately 71% of the Earth's surface. Water is a unique substance due to its physical and chemical properties, which make it an excellent solvent and a vital component in many biological and geological processes.
Water is composed of two hydrogen atoms and one oxygen atom, giving it the chemical formula H2O. It exists in three states: solid, liquid, and gas, depending on temperature and pressure. At standard temperature and pressure, water is a liquid, but it can also exist as a solid (ice) and gas (water vapor).
Origin of water
- It is discovered that a specific sort of meteorite is where water first formed.
- Lakes, rivers, ponds, and other water bodies are the main sources of water for human consumption.
- Earth's water shares the same chemical makeup as some meteorites.
Water Availability
Freshwater and saltwater
Water on Earth is found in two main forms: freshwater and saltwater. Freshwater is water that contains a very low concentration of dissolved salts, less than 0.05%. It is found in rivers, lakes, streams, and groundwater. Freshwater is essential for life and is used for drinking, irrigation, and many other purposes.
Saltwater, on the other hand, is water that contains a high concentration of dissolved salts, typically around 3.5%. Saltwater is found in oceans and seas, which cover about 71% of the Earth's surface. Saltwater is not suitable for most human uses, as it is too salty to drink or use for irrigation without first undergoing desalination processes.
Statistics of availability of water
1. 71 % of Earth consists of water<
2. Out of this 71 %, 97% water is in oceans and seas, remaining 3 % is the freshwater in forms of lakes, rivers.
3. Out of this 3 % of freshwater, 30% is groundwater(not easily accessible), 69% are in the form glaciers, icebergs.( not accessible), out of the remaining 1% of water only 0.006% is used by the people for their uses.
Water Cycle
Physical properties of water
- Water has several unique physical properties that make it essential to life and many natural processes.
- Some of these properties include: High heat capacity: Water has a high heat capacity, which means it can absorb a lot of heat without changing temperature.
- Excellent solvent: Water is an excellent solvent for many substances, due to its polar nature.
- Density: Water has a unique density property.
- It is densest at 4°C and less dense at both higher and lower temperatures.
Water cycle
The water cycle is the overall process, in which water circulates and is maintained for years to use.
The various processes involved in the water cycle are:
- Evaporation
- Condensation
- Precipitation
- Transpiration
Evaporation/Transpiration
- Evaporation is the process by which liquid water is converted into water vapor, while transpiration is the process by which plants release water vapor into the air through their leaves.
Condensation
Condensation is the process by which water vapor in the air is converted into liquid water, typically occurring when warm, moist air cools and loses its capacity to hold water vapor, causing the water vapor to condense into liquid droplets. This process is responsible for the formation of clouds, dew, and fog, among other phenomena.
Precipitation
Precipitation refers to any form of water that falls from the atmosphere and reaches the Earth's surface, such as rain, snow, sleet, or hail. Precipitation occurs when clouds become saturated with water vapor and the water droplets or ice crystals in the clouds grow large enough to fall to the ground under the force of gravity. Precipitation is a critical component of the water cycle, as it replenishes the Earth's freshwater supply and helps maintain ecosystems and human societies.
Ground Water
Ground water
Groundwater is the water present underground or beneath the Earth’s surface in soil spaces and rock formations.
1. Water table - The water table is the portion of the ground above that which is submerged in water.
2. Infiltration - Infiltration is the term used to describe the process by which water seeps into the earth from the soil's surface.
3. Aquifer - The areas where groundwater is held in reserve between rock strata below the water table.
Effect of water scarcity on plants
- Stunted growth: Water is essential for plant growth, and a lack of water can stunt growth and development.
- Wilting: Plants can wilt when they do not receive enough water, as they lose the ability to maintain turgor pressure in their cells.
- Reduced yield: Water scarcity can lead to a reduction in crop yield, as plants are not able to produce as much fruit or grain.
- Increased susceptibility to pests and diseases: Water-stressed plants are more vulnerable to pests and diseases, as they are weaker and less able to defend themselves.
- Premature death: If plants do not receive enough water for an extended period, they can die prematurely.
Water Management
Water management
Water management is the effective planning, distribution and use of water resources.
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