Grade 7 Q&A: Chapter 3: Properties of Natural Resources

Concept Questions

Q1: List three important properties of air.

Answer: Three important properties of air are: it has mass and weight, it occupies space, and it exerts pressure (atmospheric pressure).

Q2: What is atmospheric pressure, and how does it change with altitude?

Answer: Atmospheric pressure is the force exerted by the weight of the column of air above a given area. It decreases with increasing altitude.

Q3: Explain the property of compressibility in air.

Answer: Compressibility in air means that its volume can be reduced by applying pressure. This property is utilized in devices like bicycle pumps and air brakes.

Q4: What are the three states in which water exists?

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

Q5: At what temperature does pure water freeze and boil at standard atmospheric pressure?

Answer: Pure water freezes at 0°C and boils at 100°C at standard atmospheric pressure.

Q6: Why is water called a 'universal solvent'?

Answer: Water is called a 'universal solvent' because it has the ability to dissolve a large number of substances, which is vital for many biological and chemical processes.

Q7: What is surface tension in water?

Answer: Surface tension is a property of water where molecules at the surface are more attracted to each other than to the air, creating a 'skin' on the surface. This allows some insects to walk on water.

Q8: Name the three main types of soil based on texture.

Answer: The three main types of soil based on texture are sandy soil, clayey soil, and loamy soil.

Q9: Which type of soil has good drainage but poor water retention?

Answer: Sandy soil has large particles, which results in good drainage but poor water retention.

Q10: What is the significance of water having its highest density at 4°C?

Answer: The fact that water has its highest density at 4°C is significant because it means ice (at 0°C) is less dense than liquid water, allowing ice to float. This insulates the water below, preventing entire bodies of water from freezing solid and allowing aquatic life to survive in cold climates.

Q11: What is the primary composition of air?

Answer: Air is primarily composed of nitrogen (approx. 78%), oxygen (approx. 21%), and small amounts of other gases like argon and carbon dioxide.

Q12: How does the elasticity of air manifest in everyday life?

Answer: The elasticity of air means that when compressed, it tends to regain its original volume once the pressure is released. This can be seen when a pumped-up tire springs back to shape after a slight deformation.

Q13: What is the importance of soil's water retention capacity for plants?

Answer: The water retention capacity of soil is crucial for agriculture because it determines how much water is available for plants to absorb, directly impacting their growth and survival.

Q14: What is loamy soil, and why is it considered ideal for plant growth?

Answer: Loamy soil is a balanced mixture of sand, silt, and clay particles. It is considered ideal for plant growth because it offers a good balance of drainage (from sand) and water retention (from clay), along with good aeration.

Q15: Besides mineral particles, what are the other main components of soil?

Answer: Besides mineral particles, the other main components of soil are organic matter (humus), water, and air.

Application-Based Questions

Q16: You are trying to fill air into a deflated football using a pump. Which property of air allows you to do this?

Answer: The property of air that allows you to fill a deflated football using a pump is its **compressibility**. Air molecules can be pushed closer together, reducing their volume and allowing more air to fit into the football.

Q17: During winter, a pond freezes from the top downwards. Explain how the unique density property of water helps aquatic animals survive beneath the ice.

Answer: Water has its maximum density at 4°C. As the temperature drops below 4°C, water becomes less dense. This means that ice (at 0°C) is less dense than the colder water just above freezing, so ice floats on top. This layer of ice acts as an insulator, preventing the entire pond from freezing solid and allowing aquatic animals to survive in the liquid water below.

Q18: A farmer wants to grow crops that require good drainage. Which type of soil would be most suitable for this, and why?

Answer: **Sandy soil** would be most suitable for growing crops that require good drainage. This is because sandy soil has larger particles with larger spaces between them, allowing water to pass through quickly and preventing waterlogging around the plant roots.

Q19: If you observe a syringe being used to draw liquid, which property of air is primarily responsible for the liquid being drawn up?

Answer: The property of air primarily responsible for the liquid being drawn up into a syringe is **atmospheric pressure**. When the plunger is pulled back, it creates a lower pressure inside the syringe. The higher atmospheric pressure outside then pushes the liquid into the syringe.

Q20: Why is it important for air to have specific heat capacity in relation to weather patterns?

Answer: It is important for air to have specific heat capacity because it influences how quickly air heats up or cools down. This property plays a crucial role in regulating atmospheric temperatures, forming convection currents, and ultimately affecting various weather patterns and climate conditions globally.

Q21: You notice that water droplets cling to the side of a glass after you pour water out. Which property of water explains this phenomenon?

Answer: This phenomenon is explained by the property of **adhesion** in water. Adhesion is the attraction between water molecules and molecules of other surfaces (in this case, the glass), causing the water to stick to the glass.

Q22: A gardener tests their soil and finds it is very acidic. How might this affect the growth of most plants, and what could they do to improve it?

Answer: A very acidic soil pH can negatively affect the growth of most plants because it can make essential nutrients less available for absorption. To improve it, the gardener could add liming materials (like agricultural lime) to the soil, which helps to increase the pH and make it more suitable for plant growth.

Q23: Why is the presence of air in the soil important for plant roots?

Answer: The presence of air in the soil is important for plant roots because roots, like other living cells, need oxygen for respiration. Respiration is the process that releases energy for root growth and nutrient absorption. Without sufficient air, roots can suffocate, leading to poor plant health or death.

Q24: Explain how the density difference between hot and cold air contributes to the formation of wind.

Answer: Hot air is less dense and tends to rise, while cold air is denser and tends to sink. This difference in density creates convection currents. As warm air rises, cooler, denser air rushes in to take its place, creating air movement, which we experience as wind.

Q25: Why is it beneficial for water to be a universal solvent for living organisms?

Answer: It is highly beneficial for water to be a universal solvent for living organisms because it allows for the dissolution and transport of essential nutrients, minerals, and gases within the body. For example, blood (mostly water) transports oxygen, nutrients, and waste products, and water also dissolves minerals in the soil for plant uptake.

Textbook Exercise Solutions

Fill in the Blanks:

1. The property of air that helps in filling a balloon is Air occupies space.
2. The property of water that helps in dissolving sugar is Universal solvent.
3. The property of soil that helps in holding water for plants is Water retention capacity.
4. The property of air that is useful in a bicycle pump is Compressibility.
5. The property of water that allows insects to walk on its surface is Surface tension.