Olympiad Test: Natural Resources And Calamities - 1 - Class 5 MCQ

Humus is a dark-colored, organic substance formed from the decomposition of dead plants and animals. It is rich in nutrients and plays a vital role in improving soil fertility, helping plants to grow. Humus also helps retain moisture in the soil and supports healthy soil structure.

• Gravel is made up of small, loose stones.
• Loam is a type of soil that contains a mixture of sand, silt, and clay.
• Clay is a fine-grained natural material that can become sticky when wet and is often used to make pottery.

Topsoil is indeed the layer that supports plant growth the most. Here's why:

• Topsoil contains the right mix of nutrients, organic matter (humus), and microorganisms needed for plants to grow. This is where most of the roots of plants are found.
• Subsoil and bedrock are typically not as rich in nutrients for plants, making them less suitable for plant growth.

So, the correct answer is B: Topsoil.

• Clayey soil has the highest water-holding capacity because its tiny particles are closely packed, allowing water to stay within the soil for a longer time.
• Loamy soil is a balanced mixture of sand, silt, and clay, and while it holds water well, it doesn't retain as much as clayey soil.
• Sandy soil has larger particles and doesn't hold water as effectively; it drains quickly.

So, clayey soil is the correct choice.

• Humus is the decomposed organic matter in soil. It is rich in nutrients like nitrogen, phosphorus, and potassium, which are essential for plant growth.
• It also improves soil structure, making it easier for plant roots to grow.
• While humus does help with water infiltration and supports microorganisms that can break down pollutants, its primary importance lies in enriching the soil with nutrients, boosting fertility.

• Soil erosion is the process where the top layer of soil, which is rich in nutrients, is carried away by natural forces like wind, water, or human activity.
• This leads to the loss of fertile soil, which can harm agricultural productivity and affect the ecosystem.
• It is a harmful process that reduces the land’s ability to support plant life.

Fossil fuels are formed from the remains of ancient plants and animals that were buried under layers of earth. Over millions of years, heat and pressure turned these remains into coal, oil, or natural gas.

• A: Bacteria on top of the mud – Bacteria help in decomposition but don’t directly form fossil fuels.
• B: Carbon filtered through limestone – Limestone doesn’t directly help in forming fossil fuels; it's a type of rock.
• D: Nitrogen mixed in the water – Nitrogen doesn’t play a role in fossil fuel formation.

Terrace farming involves creating steps on hilly or mountainous land, which helps prevent soil erosion by slowing down the flow of water. This method uses land more effectively and protects the soil from being washed away.

• B: Reducing soil erosion by deforestation – Deforestation increases soil erosion, not reduces it.
• C: Reducing soil erosion by water – Terrace farming reduces the harmful effects of water erosion, not promotes it.
• D: Reducing soil erosion by overgrazing – Overgrazing actually increases soil erosion.

A flash flood happens very quickly, often within six hours of heavy rain, and is usually short-lived. It can cause significant damage in a short amount of time due to rapid water flow.

• A: Is caused by heavy rain rather than from the flooding of a river – Flash floods can be caused by rain but they are more about the speed of the flood.
• B: Occurs in urban areas – Flash floods can occur anywhere, not just urban areas.
• D: Is caused by the blocking of drains – Blocked drains can worsen flooding, but they don't cause flash floods directly.

Floods can lead to various environmental consequences, including the dispersal of weed species, erosion of soil, and the release of pollutants into waterways, all of which can harm ecosystems.

• A: Dispersal of weed species – Floodwaters can carry weed seeds to new areas, spreading unwanted plant species.
• B: Erosion of soil – Floods can wash away the top layer of soil, causing erosion.
• C: Release of pollutants into waterways – Floods can carry pollutants like chemicals, sewage, and waste into rivers and lakes.

• A: Weather forecasts for a small region are more accurate than those for a large region: This is false. Weather forecasts for larger regions are generally more accurate because they account for broader atmospheric patterns and data, which help improve the prediction's reliability.
• B: Weather forecasts are more accurate in Melbourne than in Darwin: This is true. Melbourne's weather is influenced by temperate conditions, making it easier to predict compared to Darwin's tropical climate, which is more variable.
• C: Forecasts of temperature are more accurate than forecasts of rainfall: This is true. Temperature forecasting is generally more precise because it is based on well-understood physical processes, while rainfall is harder to predict due to its complex and variable nature.

Therefore, the false statement is A.