Grade 7 Chapter 3: Properties of Natural Resources

Introduction

Natural resources are materials and components found in the environment that are used by living organisms. Air, water, and soil are three of the most vital natural resources, essential for sustaining life on Earth. Understanding their unique properties is crucial to appreciating their importance and managing them responsibly. This chapter will delve into the characteristics and functions of air, water, and soil.

Properties of Air

Composition of Air

Air is a mixture of several gases. The major components are:

• Nitrogen (N₂): Approximately 78%
• Oxygen (O₂): Approximately 21%
• Argon (Ar): Approximately 0.9%
• Carbon Dioxide (CO₂): Approximately 0.04%
• Other gases, water vapor, and dust particles in trace amounts.

Properties of Air

• Air has mass and weight: Although invisible, air exerts pressure due to its weight.
• Air occupies space: It can be compressed and expanded.
• Air is a homogeneous mixture: Its components are uniformly distributed.
• Atmospheric Pressure: The pressure exerted by the weight of the air column above a given area. It decreases with altitude.
• Scattering of Light: Air particles (dust, gases) scatter sunlight, which is why the sky appears blue and sunsets are reddish.
• Temperature Regulation: Air helps maintain the Earth's temperature, preventing extreme heat and cold.
• Transmission of Sound: Sound travels through air as vibrations.
• Humidity: The amount of water vapor in the air. The capacity of air to hold moisture depends on its temperature.

Properties of Water

States of Water

Water exists in three states: solid (ice), liquid (water), and gas (water vapor).

Properties of Water

• Universal Solvent: Water can dissolve a large number of substances, making it an excellent solvent for many biological and chemical processes.
• No Fixed Shape, but Definite Volume: Water takes the shape of its container but maintains its volume.
• Anomalous Expansion of Water: Unlike most liquids, water expands when it freezes (from 4°C to 0°C). This makes ice less dense than water, causing it to float. This property is crucial for aquatic life in cold regions.
• Density: The density of water is highest at 4°C.
• Boiling Point and Freezing Point: Pure water boils at 100°C and freezes at 0°C at standard atmospheric pressure.
• Importance for Life: Water is essential for all living organisms for various metabolic activities, transport of substances, and temperature regulation.
• Purity: Pure water is tasteless, odorless, and colorless.

Properties of Soil

Soil Formation

Soil is formed from the weathering of rocks and the decomposition of organic matter over long periods.

Types of Soil

Soil can be classified based on particle size and composition:

• Sandy Soil: Contains a high proportion of sand particles. It has large spaces between particles, leading to good aeration but low water-holding capacity.
• Silty Soil: Contains a high proportion of silt particles. It feels smooth and holds water better than sandy soil.
• Clayey Soil: Contains a high proportion of clay particles. It has very small spaces between particles, leading to poor aeration but high water-holding capacity. It is sticky when wet.
• Loamy Soil: A mixture of sand, silt, and clay. It is considered ideal for plant growth due to its balanced water retention, aeration, and nutrient content.

Properties of Soil

• Soil Structure: The arrangement of soil particles into aggregates. Good soil structure allows for proper aeration, water infiltration, and root penetration.
• Soil Texture: Refers to the relative proportions of sand, silt, and clay particles.
• Water Holding Capacity: The ability of soil to retain water. Clayey soil has high capacity, sandy soil has low capacity.
• Aeration: The presence of air spaces in the soil, important for root respiration.
• pH of Soil: Measures the acidity or alkalinity of the soil.
  • Acidic Soil: pH less than 7.
  • Neutral Soil: pH equal to 7.
  • Alkaline Soil: pH greater than 7.
  The pH affects nutrient availability to plants.
• Humus: Decomposed organic matter in soil, which improves soil fertility and water retention.

Importance of Soil

• Agriculture: Provides nutrients and support for plant growth, essential for food production.
• Habitat: Home to countless microorganisms, insects, and other animals.
• Water Filtration: Filters water as it percolates through the ground.
• Nutrient Cycling: Plays a vital role in the decomposition and recycling of organic matter.

Summary

• Air is a mixture of gases with mass, weight, and occupies space; it helps in scattering light, regulating temperature, and transmitting sound.
• Water exists in three states, is a universal solvent, exhibits anomalous expansion upon freezing, and is crucial for all life processes.
• Soil is formed from weathered rocks and organic matter; its properties include structure, texture, water-holding capacity, aeration, and pH.
• Good soil structure and appropriate pH are vital for plant growth and overall ecosystem health.
• Natural resources like air, water, and soil are indispensable for sustaining life and require careful management.