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

Explanation:
The correct answer is Humus. Here is the detailed explanation:
1. Dark-coloured substance:
- Humus is a dark-coloured substance that is typically brown or black in appearance.
2. Formed from dead remains of plants and animals:
- Humus is formed through the decomposition of organic matter, such as dead plants and animals.
- It is the end product of the decomposition process, where microorganisms break down the organic matter.
3. Characteristics of humus:
- Humus is rich in nutrients and organic matter.
- It has a high carbon content and is a vital component of healthy soil.
4. Importance of humus:
- Humus improves soil structure by enhancing its ability to retain water and nutrients.
- It increases soil fertility and promotes the growth of plants.
- Humus also helps in preventing soil erosion and contributes to the overall health of ecosystems.
5. Difference between humus and other options:
- Gravel: Gravel is not a dark-coloured substance formed from dead remains of plants and animals. It is a type of coarse rock particle.
- Loam: Loam is a type of soil that has a balanced mixture of sand, silt, and clay. It contains organic matter, but it is not solely composed of dead remains of plants and animals.
- Clay: Clay is a type of soil particle that is fine and sticky when wet. It does not necessarily contain dead remains of plants and animals.

Therefore, the correct answer is Humus, as it is the dark-coloured substance formed from dead remains of plants and animals.

Layers of soil that support plant growth:
1. Topsoil: This is the uppermost layer of soil and is rich in organic matter. It is typically dark in color and contains the most nutrients required for plant growth. Topsoil has a loose texture, which allows roots to penetrate easily and access water and nutrients.
2. Subsoil: Located beneath the topsoil, subsoil is less fertile but still provides some support for plant growth. It contains a lower amount of organic matter and nutrients compared to topsoil. Subsoil is important for plant growth as it helps with water drainage and root development.
3. Bedrock: Bedrock is the solid rock layer that lies beneath the soil. While bedrock does not directly support plant growth, it plays a role in determining soil composition and fertility. The depth and type of bedrock can affect the depth of the topsoil and the availability of nutrients for plants.
Conclusion: The layer of soil that primarily supports plant growth is the topsoil. It provides essential nutrients and a suitable environment for roots to thrive. While subsoil also contributes to plant growth, it is the topsoil that is most crucial for healthy and productive plants. Bedrock, although important in determining soil characteristics, does not directly support plant growth.

The water holding capacity is highest in:
Answer: C. Clayey soil
Explanation:
The water holding capacity of soil refers to the ability of soil to retain water for plant uptake. Clayey soil has the highest water holding capacity compared to other soil types. Here is why:
1. Particle size:
- Clayey soil has the smallest particle size among different soil types. Its particles are fine and compact, allowing for more water retention.
- Sandy soil, on the other hand, has larger particles, which creates larger gaps between them, leading to poor water retention.
2. Pore spaces:
- Clayey soil has smaller pore spaces between particles compared to sandy soil.
- The small pore spaces in clayey soil can hold onto water more effectively, preventing it from draining away quickly.
3. Absorption:
- Clayey soil has a high absorption capacity due to its chemical composition and surface area.
- The clay particles have a high affinity for water molecules, allowing them to attract and hold on to water.
4. Hydration:
- Clay minerals have the ability to absorb and retain water within their crystal structure through a process called hydration.
- This hydration process further contributes to the water holding capacity of clayey soil.
In summary, clayey soil has the highest water holding capacity due to its small particle size, smaller pore spaces, high absorption capacity, and the ability of clay minerals to hydrate.

Why is organic matter (humus) an important part of soil?
Organic matter, also known as humus, plays a crucial role in soil health and fertility. Here are the key reasons why it is important:
1. Nutrient-rich:
- Organic matter contains a wide range of essential nutrients such as nitrogen, phosphorus, and potassium, which are vital for plant growth and development.
- These nutrients are released slowly as organic matter decomposes, providing a steady supply of nutrients to plants over time.
2. Soil structure and moisture retention:
- Organic matter improves soil structure by binding soil particles together, creating aggregates that allow for better water infiltration and drainage.
- It also helps to prevent soil erosion by reducing the impact of rain or irrigation water on the soil surface.
- Additionally, organic matter acts as a sponge, holding moisture in the soil and increasing its water-holding capacity.
3. Microbial activity:
- Organic matter serves as a food source for beneficial soil microorganisms, such as bacteria and fungi.
- These microorganisms break down organic matter further, releasing nutrients in forms that plants can readily absorb.
- They also contribute to the overall health of the soil ecosystem and help suppress harmful pathogens.
4. pH buffering:
- Organic matter has a buffering effect on soil pH, helping to maintain it within the optimal range for plant growth.
- It can neutralize both acidic and alkaline soils, creating a more favorable environment for plants.
5. Pollutant breakdown:
- While not as significant as other functions, organic matter can contribute to the breakdown of certain organic pollutants in the soil, reducing their harmful effects.
Overall, the presence of organic matter in soil is essential for maintaining soil fertility, improving water infiltration, enhancing soil structure, and supporting healthy plant growth.

Soil erosion:
Soil erosion refers to the process of the removal and transportation of soil particles by wind, water, or other natural forces. It is a harmful process that can have detrimental effects on the environment and agricultural productivity. Here is a detailed explanation of soil erosion:
Causes of soil erosion:
- Water: Heavy rainfall, runoff, and flooding can wash away the topsoil and cause erosion.
- Wind: Strong winds can pick up loose soil particles and carry them away.
- Human activities: Deforestation, improper agricultural practices, construction, and mining can contribute to soil erosion.
Effects of soil erosion:
- Loss of fertile topsoil: Eroded soil often contains essential nutrients necessary for plant growth. When this topsoil is lost, it affects agricultural productivity.
- Reduced water quality: Eroded soil particles can end up in rivers, lakes, and other bodies of water, leading to sedimentation and decreased water quality.
- Increased flooding: With the loss of vegetation and topsoil, water can quickly accumulate and lead to increased flooding.
- Damage to infrastructure: Erosion can undermine the stability of buildings, roads, and other structures.
Prevention and control measures:
- Contour plowing: Plowing along the elevation contours of the land can help slow down water runoff and prevent erosion.
- Terracing: Creating level platforms on steep slopes can help reduce the speed of water runoff and control erosion.
- Planting cover crops: Planting crops like grasses or legumes during fallow periods can help protect the soil from erosion.
- Mulching: The use of organic materials like straw or wood chips can help protect the soil from erosion by reducing the impact of raindrops and wind.
- Conservation tillage: Reducing or eliminating tillage can help maintain soil structure and reduce erosion.
Conclusion:
Soil erosion is a harmful process that involves the removal and transport of soil particles by wind and water. It can have significant environmental and agricultural consequences. Implementing proper erosion control measures is essential to protect the soil and maintain its fertility.

Fossil fuels formed over a long period of time when heat and pressure were applied to:
- Bacteria on top of the mud: This option is incorrect because bacteria on top of the mud do not contribute to the formation of fossil fuels.
- Carbon filtered through limestone: This option is incorrect because carbon filtering through limestone is not the primary process involved in the formation of fossil fuels.
- Organisms buried in the ground: This option is correct. Fossil fuels are primarily formed from the remains of ancient plants and animals that were buried deep in the ground. Over millions of years, the heat and pressure from the layers of sediment above them caused the organic matter to undergo chemical processes, transforming it into fossil fuels such as coal, oil, and natural gas.
- Nitrogen mixed in the water: This option is incorrect because nitrogen mixed in the water does not play a significant role in the formation of fossil fuels.
In summary, the correct answer is C: Organisms buried in the ground. Fossil fuels are formed from the remains of ancient plants and animals that were buried deep in the ground and subjected to heat and pressure over millions of years.

Terrace farming helps in reducing soil erosion by water.
- What is terrace farming?
Terrace farming is a method of agriculture where sloped land is transformed into a series of flat terraces or steps. These terraces help in preventing soil erosion and allow for cultivation on steep slopes.
- How does terrace farming reduce soil erosion by water?
1. Contouring: Terrace farming involves creating terraces that are level or gently sloping across the slope of the land. This helps in slowing down the flow of water and prevents it from gaining enough speed to erode the soil.
2. Retention of water: The terraces act as barriers and retain water on each level, allowing it to soak into the soil instead of running off and causing erosion.
3. Preventing runoff: The flat surfaces of the terraces reduce the amount of surface runoff, as the water is absorbed into the soil gradually. This prevents the force of running water from eroding the soil and carrying it away.
4. Diverting excess water: Terrace farming also involves the construction of channels or drains to divert excess water away from the terraces. This prevents waterlogging and further erosion.
Terrace farming is an effective technique to reduce soil erosion by water, as it helps in controlling the flow of water, retaining moisture, and preventing runoff. It allows for sustainable agriculture on steep slopes that would otherwise be prone to erosion.

Definition of a flash flood:
A flash flood is a sudden and unexpected flood that occurs for a short duration.
Characteristics of a flash flood:
- Caused by heavy rain: Flash floods are primarily caused by heavy rainfall, often in a short period of time. This excessive rainfall overwhelms the capacity of the local drainage system to handle the water, leading to rapid flooding.
- Not caused by the flooding of a river: Unlike regular floods, which are caused by the overflowing of rivers and streams, flash floods are not directly caused by the flooding of a river. They are typically localized events that occur in low-lying areas, urban areas, or areas with poor drainage.
- Occurs suddenly and unexpectedly: Flash floods can occur with little to no warning, making them highly dangerous. They can develop rapidly, within minutes or hours, and catch people off guard.
- Short duration: Flash floods are typically short-lived, lasting from a few minutes to a few hours. However, during this short period, they can cause significant damage due to the intensity of the rainfall and the rapid rise in water levels.
Examples of flash flood triggers:
- Intense or prolonged rainfall
- Thunderstorms
- Dam or levee failures
- Rapid snowmelt
- Urbanization and the blocking of drains or stormwater systems
In conclusion, a flash flood is a type of flood that occurs suddenly and unexpectedly, usually as a result of heavy rainfall. It is characterized by its short duration and can cause significant damage due to the rapid rise in water levels. Flash floods are not caused by the flooding of a river but rather by localized factors such as heavy rain or blocked drainage systems.

Environmental Consequences of Floods:
There are several environmental consequences associated with floods. These include:
1. Dispersal of weed species:
- Floodwaters can carry seeds and plant fragments, leading to the dispersal of weed species.
- These weed species may invade new areas and outcompete native vegetation, disrupting the balance of ecosystems.
2. Erosion of soil:
- Floods can cause significant erosion of soil, especially in areas with steep slopes or when the ground is already saturated.
- The force of the water can wash away the top layer of soil, leading to loss of fertile land and degradation of agricultural fields.
- Erosion can also result in sedimentation in rivers and streams, affecting aquatic habitats and water quality.
3. Release of pollutants into waterways:
- Floodwaters can pick up various pollutants, such as chemicals, fertilizers, and sewage, from urban and agricultural areas.
- These pollutants are then carried into rivers, lakes, and other water bodies, causing contamination and potential harm to aquatic ecosystems and the organisms living in them.
- The release of pollutants can also have long-term effects on water quality, posing risks to human health and the environment.
4. Damage to infrastructure:
- Floods can cause extensive damage to infrastructure, including roads, bridges, buildings, and utilities.
- This damage not only disrupts the functioning of communities but also contributes to environmental consequences, such as the release of hazardous materials from damaged structures.
Conclusion:
Floods have significant environmental consequences that can impact ecosystems, water quality, and human activities. The dispersal of weed species, erosion of soil, and release of pollutants into waterways are among the key environmental consequences associated with floods. It is important to implement effective flood management strategies to mitigate these environmental impacts and protect the environment and human well-being.

The false statement among the given options is:
A: Weather forecasts for a small region are more accurate than those for a large region
Explanation:
- Weather forecasts for a small region are more accurate than those for a large region:
- This statement is false. Weather forecasts for a small region are generally less accurate than those for a larger region. Forecasting weather for a larger area allows for the consideration of a wider range of data and atmospheric conditions, which can lead to more accurate predictions.
- Weather forecasts are more accurate in Melbourne than in Darwin:
- This statement is true. Weather forecasts in Melbourne are generally more accurate than in Darwin due to the variability of weather patterns and the influence of tropical climate in Darwin.
- Forecasts of temperature are more accurate than forecasts of rainfall:
- This statement is true. Forecasting temperature is generally more accurate than rainfall as temperature forecasts rely on numerical models that are based on well-understood physical processes. Rainfall forecasts, on the other hand, are more uncertain due to the complex nature of precipitation.
Therefore, the false statement is A: Weather forecasts for a small region are more accurate than those for a large region.