Class 8 Science Chapter 1 Crop Production and Management

Key Concept: Sprinkler System, Drip System

a) Sprinkler System

[Solution Description]

The sprinkler system is designed to work efficiently on uneven land where water distribution can be challenging. It uses rotating nozzles to sprinkle water over the crops, simulating rainfall. This method ensures that water is evenly distributed across the field, even in areas with varying elevations. Additionally, it helps conserve water by delivering it directly to the crops without excessive runoff or evaporation. Therefore, the sprinkler system is the most suitable method for the farmer’s field.

Key Concept: Sprinkler System

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The sprinkler system is a modern method of irrigation that is particularly beneficial on uneven land where water availability is insufficient. The system consists of perpendicular pipes with rotating nozzles attached to the main pipeline at regular intervals. When water is allowed to flow through the main pipe under pressure, it escapes from the rotating nozzles and is sprinkled over the crops, simulating rainfall. This method is highly effective for lawns, coffee plantations, and various other crops. Both the assertion and reason are true, and the reason correctly explains why the sprinkler system is useful on uneven land.

Key Concept: Sprinkler System, Water Pressure

b) 2 bar

[Solution Description]

The total length of the main pipe is 100 meters, and the pressure loss is 0.1 bar per 10 meters. The number of intervals is $100 / 10 = 10$. The total pressure loss is $10 \times 0.1 = 1$ bar. Therefore, the pressure at the farthest perpendicular pipe is $3 – 1 = 2$ bar.

Key Concept: Agriculture Definition, Food Security

c) The cultivation of land to produce crops

[Solution Description]

Agriculture refers to the practice of cultivating land to produce crops and rearing animals for food, fiber, and other products. This practice allowed early humans to settle in one place and develop civilizations by ensuring a stable food supply.

Key Concept: Cropping Patterns, Kharif and Rabi Crops

d) Assertion is false, but Reason is true.

[Solution Description] The assertion states that paddy is cultivated during the winter season in India, which is incorrect. Paddy is a kharif crop and is sown during the rainy season, typically from June to September. The reason given is that paddy requires a lot of water for its growth, which is true but does not support the assertion since the assertion itself is false. Therefore, the correct answer is that the assertion is false, but the reason is true.

Key Concept: Cropping Patterns

c) Winter season

[Solution Description]

Rabi crops are grown during the winter season, which spans from October to March. Examples of rabi crops include wheat, gram, pea, mustard, and linseed.

Key Concept: Historical Background of Farming

c) The ability to cultivate land and produce crops

[Solution Description]

Humans transitioned from nomadic lifestyles to settled agricultural practices primarily because they learned to cultivate land and produce crops like rice and wheat. This allowed them to have a stable food source, reducing the need to wander in search of food.

Key Concept: Kharif Crops, Water Requirements

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

Paddy is a Kharif crop that is sown during the rainy season (June to September) in India. It requires a significant amount of water for its growth, which is naturally provided by the monsoon rains. The winter season (October to February) in India is generally dry with minimal rainfall, making it unsuitable for paddy cultivation. Therefore, both the Assertion and Reason are true, and the Reason correctly explains why paddy cannot be grown in the winter season.

Key Concept: Kharif Crops

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

Paddy is indeed a Kharif crop, and Kharif crops are specifically sown during the rainy season, which in India spans from June to September. Therefore, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Rabi Crops

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that wheat is a rabi crop, which is true as wheat is indeed grown during the winter season. The reason explains that rabi crops are cultivated from October to March, which is also correct and directly supports the assertion. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Harvesting, Storage, Rabi Crops

c) Spoilage due to moisture

[Solution Description]

Proper drying of harvested grains is essential before storage to prevent spoilage. If grains are stored without drying, they may retain moisture, which can lead to the growth of microorganisms and pests. This makes the grains unfit for consumption or germination. Therefore, the potential consequence of storing wheat without proper drying is spoilage due to moisture.

Key Concept: Agricultural Practices

c) Spinach

[Solution Description] Vegetables like spinach are cool-season crops and are not suitable for summer cultivation.

Key Concept: Agricultural Practices

d) They thrive in warm temperatures

[Solution Description] Vegetables like okra and cucumber thrive in warm temperatures, ensuring higher yield and quality during summer.

Key Concept: Preparation of Soil

c) To allow roots to penetrate deep and bring nutrient-rich soil to the top

[Solution Description]

Tilling or ploughing the soil helps in loosening and turning the soil, which allows the roots to penetrate deep into the soil. It also helps in the growth of earthworms and microbes, which further loosen the soil and add humus to it. Additionally, tilling brings nutrient-rich soil to the top, making it accessible for plant growth.

Key Concept: Preparation of Soil

b) Brings nutrient-rich soil to the surface

[Solution Description]

Tilling or ploughing the soil is important because it loosens the soil, allowing roots to penetrate deeply and breathe easily. It also brings nutrient-rich soil to the top, which is essential for plant growth. Additionally, it helps in the growth of earthworms and microbes, which further loosen the soil and add humus. Thus, tilling improves soil fertility and aids in better crop cultivation.

Key Concept: Soil Organisms

a) They help in turning and loosening the soil

[Solution Description]

Earthworms and microbes turn and loosen the soil, which helps in aeration and adds humus to the soil. This process improves soil fertility and structure, making it more suitable for crop cultivation.

Key Concept: Plough

b) Plough

[Solution Description]

The plough is a tool that has been used since ancient times for tilling the soil, adding fertilisers, removing weeds, and turning the soil.

Key Concept: Appropriate Distance Between Seeds

c) To avoid overcrowding of plants

[Solution Description]

Maintaining an appropriate distance between seeds during sowing prevents overcrowding of plants. This ensures that each plant gets sufficient sunlight, nutrients, and water from the soil, leading to healthier growth.

Key Concept: Sowing

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that seeds that float on water are damaged and hollow. This is true as damaged seeds lose their density and become hollow, making them lighter. The reason explains that damaged seeds become lighter due to being hollow, which is the correct explanation for why they float. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Adding Manure and Fertilisers

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that manure is an organic substance obtained from the decomposition of plant or animal wastes, which is a true statement as per the syllabus. The reason states that manure improves the water holding capacity of the soil, which is also true according to the syllabus. Additionally, the reason correctly explains why manure is beneficial for the soil, as it enhances its water retaining capacity.

Key Concept: Crop Rotation and Soil Replenishment

c) To maintain soil fertility through nutrient replenishment

[Solution Description]

Crop rotation involves growing different crops alternately in the same field. This practice helps in replenishing the soil with nutrients. For example, growing legumes in one season and wheat in the next season helps in fixing atmospheric nitrogen into the soil, thereby maintaining its fertility. Hence, crop rotation is encouraged to maintain soil fertility.

Key Concept: Irrigation Methods

c) Sprinkler system

[Solution Description]

The sprinkler system is the most suitable method for uneven land where water availability is limited. It uses perpendicular pipes with rotating nozzles that sprinkle water over the crops, similar to rain. This method ensures efficient water usage and uniform distribution across the field.

Key Concept: Irrigation Methods

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the drip system is more efficient than the sprinkler system for watering fruit plants. This is true because the drip system delivers water directly to the roots of the plants, ensuring minimal water wastage and optimal usage. The reason provided explains that in the drip system, water falls drop by drop directly near the roots, which minimizes water wastage. This is indeed the correct explanation for why the drip system is more efficient for watering fruit plants. Therefore, both the assertion and the reason are true, and the reason correctly explains the assertion.

Key Concept: Weeds and their Effects

c) To prevent competition with crop plants for resources

[Solution Description]

Weeds are undesirable plants that grow naturally in crop fields. They compete with the crop plants for essential resources like water, nutrients, space, and light. This competition negatively affects the growth and yield of the crop. Additionally, some weeds can interfere with harvesting and may even be poisonous to animals and humans. Therefore, the primary reason for removing weeds is to prevent them from competing with the crop plants for resources.

Key Concept: Weeding, Weedicides

c) Applying weedicides and manual weeding before the weeds flower and seed

[Solution Description] Manual weeding involves physically removing weeds by uprooting or cutting them close to the ground, which is effective if done regularly. Weedicides like $2,4-D$ are chemicals sprayed to kill weeds and are most effective when applied during the vegetative growth of weeds before they flower and seed. Therefore, combining both practices before flowering and seeding ensures maximum weed control.

Key Concept: Harvesting, Threshing, Combine Machine

c) Harvesting the crop and separating grain from chaff

[Solution Description] A combine machine is designed to perform both harvesting and threshing. It cuts the mature crop (harvesting) and separates the grain from the chaff (threshing) in a single operation, making the process more efficient and reducing manual labor.

Key Concept: Storage

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

According to the syllabus, harvested grains have more moisture, and if they are stored without drying, they may get spoilt or attacked by organisms. Therefore, grains are dried in the sun before storage to reduce moisture, which helps in preventing the attack by insect pests, bacteria, and fungi. Hence, both the Assertion and Reason are true, and the Reason correctly explains the Assertion.

Key Concept: Storage Methods

c) To protect grains from pests

[Solution Description]

Dried neem leaves are used in grain storage because they have natural pesticidal properties. They help protect the grains from pests and microorganisms, ensuring longer shelf life and safety of the stored grains.

Key Concept: Addition of Manure

c) To enhance the soil’s fertility by providing nutrients

[Solution Description]

Adding manure before tilling ensures that it gets properly mixed with the soil. This enhances the soil’s fertility by providing essential nutrients, which are crucial for healthy plant growth. Proper mixing also improves soil structure and water retention capacity.

Key Concept: Agricultural Implements, Plough, Tractor-driven Cultivator

c) It saves labour and time while providing precise tilling.

[Solution Description]

In modern agriculture, the use of a tractor-driven cultivator is preferred over traditional wooden ploughs because it saves both labour and time. A tractor-driven cultivator can cover larger areas of land more quickly and efficiently compared to manual or animal-drawn ploughs. Additionally, the cultivator provides more precise control over the depth and uniformity of tilling, leading to better soil preparation for crop cultivation. This efficiency and precision make the tractor-driven cultivator a more effective tool for modern farming practices.

Key Concept: Levelling of Soil

c) Leveller

[Solution Description] A leveller is the tool commonly used for levelling the soil in agricultural fields. It is designed to create a uniform surface by smoothing out irregularities in the soil, which is essential for effective irrigation and sowing.

Key Concept: Decomposition of Manure

b) Bacteria and fungi

[Solution Description]

Microorganisms such as bacteria and fungi break down plant and animal waste into simpler organic compounds, converting them into nutrient-rich manure that can be used to enrich the soil.

Key Concept: Plough

b) Ploughshaft

[Solution Description]

The plough consists of several parts, including the ploughshare (a strong triangular iron strip) and the ploughshaft (a long log of wood). The question asks for the part of the plough that is made of wood. The correct answer is the ploughshaft.

Key Concept: Plough Function

b) Tilling the soil

[Solution Description]

The primary function of a plough is to till the soil, which involves loosening and turning the soil. This process helps in preparing the field for sowing seeds, adding fertilisers, and removing weeds. The plough is an ancient tool made of wood or iron and is drawn by animals such as bulls.

Key Concept: Hoe Operation

c) Pulled by animals

[Solution Description]

A traditional hoe is pulled by animals or manually pushed by the farmer to remove weeds and loosen the soil.

Key Concept: Cultivator, Labour and Time Saving

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that a tractor-driven cultivator reduces the time required for ploughing compared to traditional methods. This is true because a tractor-driven cultivator is designed to operate at a higher speed and cover more area efficiently. The reason explains that this efficiency is due to the high speed and capability of the cultivator, which directly supports the assertion. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Nursery, Appropriate Distance

b) Grow seeds in a nursery and transplant later

[Solution Description] The farmer should first grow paddy seeds in a nursery to allow them to develop into seedlings. Maintaining an appropriate distance between plants is crucial to prevent overcrowding, ensuring each plant gets sufficient sunlight, nutrients, and water from the soil.

Key Concept: Tools Used for Sowing, Seed Drill

c) It sows seeds uniformly at equal distances and depths

[Solution Description]

The seed drill ensures uniform distribution of seeds at equal distances and depths. It also covers seeds with soil, protecting them from being eaten by birds and saving time and labor compared to traditional methods.

Key Concept: Selection of Seeds

c) Stirring seeds in water and observing which ones float

[Solution Description]

Damaged seeds are lighter and hollow, causing them to float on water. Good seeds are heavier and sink in water. This method separates good seeds from damaged ones based on their buoyancy.

Key Concept: Nursery

c) To ensure better growth and survival

[Solution Description]

Paddy seeds are first grown in a nursery because they require controlled conditions to germinate and grow into seedlings. Once they have grown sufficiently, they are transplanted to the field manually. This method ensures better growth and survival rates for the paddy plants.

Key Concept: Floating Damaged Seeds

b) They are lighter than water

[Solution Description]

Damaged seeds become hollow and lighter due to the loss of internal material. This makes them less dense than water, causing them to float.

Key Concept: Traditional Method of Sowing

c) Assertion is true, but Reason is false.

[Solution Description] The Assertion describes the traditional tool used for sowing seeds, which is indeed shaped like a funnel with sharp-ended pipes that pierce into the soil to place seeds. This is correct as per the syllabus. However, the Reason states that the funnel-shaped tool ensures even distribution of seeds, promoting uniform growth. While the tool does help in placing seeds into the soil, the primary function of the tool is to place seeds at a certain depth, not necessarily to ensure even distribution or uniform growth. Therefore, the Assertion is true, but the Reason is false.

Key Concept: Components of Traditional Sowing Tool

b) Two or three

[Solution Description] The traditional sowing tool typically has two or three pipes that allow the seeds to pass through and be placed in the soil.

Key Concept: Modern Method of Sowing

c) It saves labour and time

[Solution Description]

The primary advantage of using a tractor-driven cultivator for ploughing is that it saves both labour and time. This method is efficient and reduces the manual effort required in traditional ploughing methods.

Key Concept: Seed Drill Benefits

c) Increases the risk of seeds being exposed on the surface

[Solution Description]

Using a seed drill saves time and labour, ensures uniform sowing, and protects seeds from being eaten by birds. It does not increase the risk of seeds being exposed on the surface.

Key Concept: Seed Drill

c) To sow seeds uniformly at equal distance and depth

[Solution Description]

The primary purpose of using a seed drill is to sow seeds uniformly at equal distances and depths. This ensures that seeds are covered by soil after sowing, protecting them from being eaten by birds and saving time and labour.

Key Concept: Sowing and Seed Drill

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The seed drill is a modern agricultural tool used for sowing seeds efficiently. It ensures that seeds are placed at uniform distances and depths, which helps in proper germination and growth. Additionally, the seed drill covers the seeds with soil immediately after sowing. This covering of seeds with soil is crucial because it prevents birds from accessing and eating the seeds. Therefore, both the Assertion and Reason are true, and the Reason correctly explains why the Assertion is important in agriculture.

Key Concept: Seed Drill

b) Saves time and labour

[Solution Description]

The primary advantage of using a seed drill is that it saves time and labour by sowing seeds uniformly at equal distances and depths. It also ensures that seeds are covered by soil, protecting them from being eaten by birds.

Key Concept: Spacing Between Seeds, Overcrowding

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The assertion states that maintaining an appropriate distance between seeds is essential for ensuring that each plant receives adequate sunlight, nutrients, and water. This is true because proper spacing prevents overcrowding, which can hinder the growth and development of plants. The reason given is that overcrowding leads to competition for resources, resulting in weaker growth and reduced yield. This is also true and directly explains why maintaining appropriate spacing is crucial. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Avoiding Overcrowding

b) To prevent plants from competing for resources

[Solution Description]

Maintaining an appropriate distance between seeds ensures that each plant gets sufficient sunlight, nutrients, and water from the soil. Overcrowding can lead to competition for these resources, resulting in poor growth and reduced yield.

Key Concept: Seed drill, Nursery, Overcrowding

b) Birds moved some seeds to certain areas, causing uneven distribution

[Solution Description] The seed drill ensures uniform sowing at equal distances and depth, which helps in preventing overcrowding initially. However, overcrowding can still occur due to factors like uneven germination rates or external disturbances such as birds or animals moving the seeds. Additionally, if the seeds are not covered properly by soil, they might be exposed to external factors leading to uneven growth.

Key Concept: Manure, Fertiliser

c) Substitute fertilisers with organic manure and adopt crop rotation

[Solution Description]

The farmer has been using inorganic fertilisers, which, over time, have made the soil less fertile due to excessive use. To improve soil fertility and crop yield, the farmer should adopt practices that replenish soil nutrients and improve soil texture. Organic manure enhances soil’s water holding capacity, makes it porous, increases friendly microbes, and improves soil texture. Additionally, crop rotation helps in replenishing soil nutrients naturally. Therefore, substituting fertilisers with organic manure and adopting crop rotation are effective solutions.

Key Concept: Need for Nutrients in Soil

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

Continuous cultivation of crops without allowing the soil to rest or adding nutrients leads to nutrient depletion. Manure is added to replenish these lost nutrients, ensuring healthy plant growth. Both the assertion and reason are true, and the reason correctly explains why continuous cultivation depletes soil nutrients.

Key Concept: Manure and Fertilizers, Continuous Cropping

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

Continuous cropping without allowing the soil to recover naturally depletes essential nutrients required for plant growth. This occurs because crops absorb nutrients from the soil, and repeated cultivation without adding nutrients back leads to nutrient deficiency. Manure, being an organic substance derived from decomposed plant and animal waste, helps in replenishing these nutrients. It not only provides essential nutrients but also improves soil structure, water retention, and microbial activity. The reason correctly explains why manure is effective in addressing nutrient depletion caused by continuous cropping.

Key Concept: Manuring replenishes soil nutrients

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion states that manure improves the water holding capacity of the soil, which is true as per the syllabus. The reason states that manure enhances the porosity of the soil, facilitating gas exchange, which is also true according to the syllabus. However, while both statements are true, the reason does not directly explain why manure improves the water holding capacity of the soil. Therefore, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

Key Concept: Fertilisers vs Manure

d) Fertilisers are chemical-based.

[Solution Description]

The main difference between manure and fertilisers is that manure is organic and obtained from the decomposition of plant or animal waste, while fertilisers are chemicals produced in factories and are rich in specific nutrients.

Key Concept: Manure, Soil Porosity

c) It makes the soil porous

[Solution Description]

Adding manure makes the soil porous, which means it increases the air spaces within the soil. This improvement in soil porosity facilitates the exchange of gases, such as oxygen and carbon dioxide, between the soil and the atmosphere. Better gas exchange is crucial for root respiration and overall plant health.

Key Concept: Adding Manure and Fertilisers

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

Manure is an organic substance derived from the decomposition of plant or animal waste. It improves the soil’s water holding capacity, making the soil porous and enhancing its texture. The reason correctly explains that manure is obtained from the decomposition of cattle dung and plant residues. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Difference Between Fertiliser and Manure

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description] According to the syllabus, fertilisers are indeed man-made inorganic salts prepared in factories, making the Assertion true. Additionally, it is also mentioned that fertilisers do not provide any humus to the soil, making the Reason true. However, the Reason does not explain why fertilisers are man-made inorganic salts or why they are prepared in factories. Therefore, the Reason is not the correct explanation of the Assertion.

Key Concept: Adding Manure and Fertilisers

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The assertion states that adding manure replenishes essential nutrients for plant growth, which is true because manure contains organic matter that decomposes to release nutrients. The reason states that continuous cultivation depletes the soil of its nutrients, which is also true as plants absorb nutrients from the soil during growth. The reason correctly explains why adding manure is necessary, as it compensates for nutrient depletion caused by continuous cultivation. Therefore, both the Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.

Key Concept: Advantages of Manure, Soil Texture, Water Holding Capacity

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that manure improves the water holding capacity and soil porosity, which is true as per the syllabus. The reason mentions that manure increases the number of friendly microbes, which also contributes to better soil texture and water retention. Both the assertion and reason are correct, and the reason correctly explains why manure improves these properties of the soil. Therefore, the correct answer is that both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Sources of Irrigation

c) Sprinkler System

[Solution Description]

Traditional sources of water for irrigation include wells, tubewells, ponds, lakes, rivers, dams, and canals. Modern irrigation methods like the sprinkler system and drip system are not considered traditional sources as they involve advanced technology and equipment.

Key Concept: Sources of Irrigation

a) Rainwater

[Solution Description]

The sources of water for irrigation include wells, tubewells, ponds, lakes, rivers, dams, and canals. These are all traditional and widely used sources. However, rainwater itself is not directly considered a source of irrigation since it has to be collected in structures like ponds or lakes first.

Key Concept: Traditional Methods of Irrigation

b) Chain pump

[Solution Description] The chain pump is a traditional irrigation method where a series of buckets attached to a chain are used to lift water from wells or canals.

Key Concept: Moat (Pulley System

c) 3

[Solution Description]

The mechanical advantage (MA) of a pulley system is given by the ratio of the load lifted to the input force applied:

$\text{Mechanical Advantage} = \frac{\text{Load}}{\text{Input Force}}$

Substituting the given values:

$\text{Mechanical Advantage} = \frac{180 \, \text{N}}{60 \, \text{N}} = 3$

Therefore, the mechanical advantage of the pulley system is 3.

Key Concept: Chain Pump, Traditional Methods of Irrigation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the chain pump is less efficient compared to modern irrigation methods due to its reliance on human or animal labor. This is true because traditional methods like the chain pump are labor-intensive and cannot match the speed or consistency of mechanized systems. The reason explains that modern irrigation methods utilize electricity, diesel, biogas, or solar energy, which enhance their efficiency by reducing manual effort and increasing operational capacity. Both statements are true, and the reason correctly explains why modern methods are more efficient than traditional ones.

Key Concept: Dhekli, Efficiency

c) 4.08 W

[Solution Description]

First, calculate the work done to lift the water: Work = Force $\times$ Distance. The force required is equal to the weight of the water, which is mass $\times$ gravity. The mass of 500 liters of water is 500 kg. So, Force = $500 \times 9.8 = 4900$ N. The distance is the height of the well, which is 10 m. Therefore, Work = $4900 \times 10 = 49000$ J.

Next, calculate the time taken in seconds: 2 hours = $2 \times 3600 = 7200$ s. The actual power output is Work / Time = $49000 / 7200 \approx 6.81$ W. However, the dhekli has an efficiency of 60\%, so the effective power output = $6.81 \times 0.60 \approx 4.08$ W.

Key Concept: Rahat System

c) It is cheaper but less efficient than modern methods.

[Solution Description]

The Rahat system is a traditional irrigation method that is cost-effective but less efficient compared to modern methods. It uses a lever system and depends on human or animal labor.

Key Concept: Sprinkler System

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The Assertion states that the sprinkler system is useful for uneven lands where sufficient water is not available. This is true because the syllabus explicitly mentions that the sprinkler system is more useful on uneven land where sufficient water is not available. The Reason states that the rotating nozzles in the sprinkler system spray water like rainfall, making it suitable for lawns, coffee plantations, and other crops. This is also true as per the syllabus, which describes how water escapes from the rotating nozzles and gets sprinkled on the crop as if it is raining. Furthermore, the Reason correctly explains why the sprinkler system is useful for uneven lands, as the rainfall-like distribution of water ensures uniform irrigation even on uneven terrain. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Modern Irrigation Methods

b) Drip system

[Solution Description]

The drip system is the most suitable irrigation method for regions with poor water availability because it minimizes water wastage by delivering water directly to the plant roots.

Key Concept: Drip Irrigation, Water Efficiency

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The assertion states that drip irrigation is the most efficient method for watering fruit plants and trees. This is true because drip irrigation delivers water directly to the root zone, reducing losses due to evaporation and runoff. The reason explains that water is delivered drop by drop directly near the roots, which minimizes evaporation and ensures minimal wastage. Since the reason correctly explains why drip irrigation is efficient, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Drip System, Water Conservation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the drip irrigation system is the most efficient method of irrigation for fruit plants and trees. This is true because drip irrigation delivers water directly to the plant roots, reducing water loss due to evaporation and runoff. The reason explains why drip irrigation is efficient: it minimizes evaporation and runoff by delivering water directly to the roots. Therefore, both the assertion and the reason are true, and the reason correctly explains the assertion.

Key Concept: Modern Methods of Irrigation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that the drip system is more efficient than the sprinkler system in water usage. This is true because the drip system delivers water directly to the roots, which reduces water loss due to evaporation and runoff. The reason explains why the drip system is more efficient by stating that it delivers water directly to the roots, minimizing evaporation and runoff. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Irrigation

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The Assertion states that the sprinkler system is more useful in uneven lands where sufficient water is not available. This is true because the sprinkler system is designed to distribute water evenly across uneven terrains, ensuring that all parts of the field receive adequate water. The Reason explains that the sprinkler system allows water to be sprinkled on the crop as if it is raining, which helps in efficient water usage. This is also true because the sprinkler system mimics natural rainfall, reducing water wastage and ensuring that water reaches the crops effectively. Furthermore, the Reason correctly explains why the Assertion is true, as the ability to sprinkle water like rain is what makes the sprinkler system suitable for uneven lands with limited water availability.

Key Concept: Weeds, Weeding Methods

c) Uprooting or cutting weeds with a khurpi

[Solution Description]

Manual removal of weeds involves physically uprooting or cutting them close to the ground using tools like a khurpi. This method is effective for small-scale weeding and helps in reducing competition for resources between weeds and crops.

Key Concept: Weeding and Weedicides

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that weeding is necessary before weeds produce flowers and seeds. This is true because removing weeds at this stage prevents them from spreading further through seeds. The reason explains that once weeds produce flowers and seeds, they become more difficult to control and can spread rapidly. This is also true and directly explains why weeding should be done before flowering and seed formation. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Weeding, Weedicides

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion claims that the use of weedicides is the most effective method for controlling weeds in crops. While weedicides are indeed effective, this statement is subjective because effectiveness can vary based on the type of crop, weed, and other factors. Manual weeding and tilling are also effective methods. The reason states that weedicides are sprayed during the vegetative growth of weeds before flowering and seed formation, which is true. However, this does not necessarily make weedicides the most effective method universally. Thus, both the assertion and reason are true, but the reason does not correctly explain the assertion.

Key Concept: Manual Removal, Weeding

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The assertion states that manual removal of weeds is most effective when done before the weeds produce flowers and seeds. This is true because once weeds produce flowers and seeds, they can spread their seeds to other parts of the field, leading to a higher weed population and making weeding more challenging. The reason explains why the assertion is true by detailing the consequence of not removing weeds before they flower and seed. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Weedicides, Health Precautions

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion states that weedicides like $2,4-D$ are used to kill weeds without harming crops, which is correct as per the syllabus. The reason mentions that farmers should use protective measures like covering their nose and mouth during spraying to avoid health risks. This is also true because weedicides can be harmful to human health if inhaled or absorbed through the skin. However, the reason does not directly explain why weedicides are effective against weeds; it only highlights a precautionary measure. Therefore, both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

Key Concept: Storage Methods, Neem Leaves

c) By repelling insects and pests

[Solution Description]

Dried neem leaves act as a natural pesticide. They repel insects and pests, preventing them from infesting the stored grains. This method is effective for small-scale storage in homes, ensuring the grains remain safe and usable over time.

Key Concept: Storage of Produce

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The syllabus states that freshly harvested grains have high moisture content, which can lead to spoilage or pest attacks if not dried properly. Drying the grains in the sun reduces moisture, making them safe for storage and preventing damage from insects, bacteria, and fungi. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Pest Control

c) Dried neem leaves

[Solution Description]

Dried neem leaves are commonly used at home to store food grains and protect them from pests. Chemical treatments are used in large godowns, and silos and granaries are used for large-scale storage.

Key Concept: Winnowing, Small-scale storage, Moisture control

c) The grains will spoil due to microbial growth caused by high moisture.

[Solution Description]

Winnowing helps in separating grain from chaff, but it does not reduce the moisture content of the grains. High moisture content in stored grains can lead to the growth of microorganisms like fungi and bacteria, which can spoil the grains. Therefore, the primary risk is spoilage due to microbial growth caused by high moisture.

Key Concept: Storage of Grains

c) To reduce moisture and prevent spoilage

[Solution Description] Harvested grains have high moisture content, which can lead to spoilage or attack by microorganisms. Drying reduces the moisture, preventing such damage and ensuring safe long-term storage.

Key Concept: Chemical treatments, Moisture control

c) To protect grains from pests and microorganisms

[Solution Description]

Chemical treatments are primarily used to protect grains from pests and microorganisms. While drying reduces moisture content, it does not completely eliminate the risk of pests or microbial attack. Chemical treatments act as an additional layer of protection, ensuring that grains remain safe and usable for longer periods, especially in large godowns where natural methods like drying may not suffice.

Key Concept: Chemical treatment, Pest control

d) Applying chemical treatments

[Solution Description]

In large-scale storage, chemical treatments are specifically used to protect grains from pests and microorganisms. While drying reduces moisture, it does not fully protect against pests. Neem leaves are used for small-scale storage, and jute bags are not sufficient for large-scale protection. Thus, the correct method is chemical treatment.

Key Concept: Storage of Grains

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that silos are used for large-scale storage of grains to protect them from pests and moisture. This is true as silos are specifically designed to store grains safely by keeping them dry and free from pests. The reason explains that silos are airtight structures that prevent pests and reduce moisture, which is also true. Moreover, the reason correctly explains why silos are effective for grain storage. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Storage of Grains

c) To reduce moisture and prevent spoilage

[Solution Description]

Freshly harvested grains contain a high amount of moisture, which can lead to spoilage or attack by microorganisms and pests if stored without drying. Drying the grains reduces moisture content, preventing such attacks and ensuring the grains remain fit for use or germination.

Key Concept: Chemical Treatments for Pest Prevention

c) To protect the grains from pests and microorganisms

[Solution Description] The primary reason for using chemical treatments in large-scale grain storage is to protect the grains from pests and microorganisms. These chemicals are specifically designed to prevent infestations that can lead to significant loss of stored grains. They are used in big godowns where natural methods like dried neem leaves are insufficient.

Key Concept: Pest Control in Grain Storage

b) Dried neem leaves

[Solution Description]

Dried neem leaves are commonly used to store food grains at home to protect them from pests like insects and rats.

Key Concept: Animal Husbandry

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The concept of animal husbandry revolves around the rearing of animals for food production. This process includes providing proper care, shelter, and food to the animals, which is essential for their well-being and productivity. Therefore, both Assertion (A) and Reason (R) are true, and Reason (R) provides a correct explanation for Assertion (A).

Key Concept: Animal Husbandry

b) Animal husbandry

[Solution Description]

The practice of rearing animals for food is known as animal husbandry. This involves providing proper food, shelter, and care to animals on a large scale.

Key Concept: Egg Production

b) To obtain eggs and meat

[Solution Description]

The primary purpose of rearing poultry birds in animal husbandry is to obtain eggs and meat for human consumption. Poultry farming focuses on raising domesticated birds such as chickens, ducks, and turkeys primarily for their eggs and meat. This contributes significantly to the food supply.

Key Concept: Apiculture

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] Honeybees play a crucial role in the pollination of many agricultural crops, which is a well-established fact. The reason states that pollination by honeybees increases the yield of crops, which is also true. Moreover, the reason correctly explains why honeybees are essential for agriculture, as their pollination activity directly contributes to higher crop yields. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Crop Classification

c) Soyabean

[Solution Description]

Kharif crops are grown during the monsoon season in India. Examples include rice, maize, and soyabean. Among the given options, soyabean is a kharif crop.

Key Concept: Source of Food for Animals

c) From plants or other animals

[Solution Description]

Animals cannot produce their own food, so they depend on plants or other animals for their nutrition. They consume these sources directly or indirectly to fulfill their dietary needs.

Key Concept: Food Storage, Animal Husbandry

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The assertion states that large-scale storage of grains in silos and granaries is primarily done to protect them from pests like rats and insects. This is true as silos and granaries are designed to provide a safe environment for grain storage by minimizing exposure to pests. The reason mentions that chemical treatments are used in large godowns to prevent the growth of microorganisms and pests in stored grains. This is also true because chemical treatments are commonly employed in large-scale storage facilities to ensure the grains remain free from infestations. Furthermore, the reason correctly explains why such measures are necessary in large godowns, thus providing a valid explanation for the assertion. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Agricultural practices

a) Crop rotation and proper irrigation

[Solution Description]

Regular food production on a large scale requires effective agricultural practices such as crop rotation, proper irrigation, and the use of quality seeds and fertilizers. These practices help in maintaining soil fertility, managing water resources efficiently, and ensuring high yields, which are crucial for feeding a large population.

Key Concept: Preparation of Soil, Agricultural Implements

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

Tilling or ploughing is a fundamental agricultural practice that involves turning and loosening the soil. This process helps in bringing the nutrient-rich soil to the top layer, which is crucial for plant growth. Additionally, tilling allows roots to penetrate deeply and breathe easily. The plough, an ancient agricultural tool made of wood or iron, is specifically designed for this purpose. It is typically drawn by animals such as bulls or horses, making it an effective implement for tilling. Therefore, both the assertion and reason are true, and the reason correctly explains why tilling is essential for crop production.

Key Concept: Finding Infinite Rational Numbers Between Two Numbers, Distributivity of Rational Numbers

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description] To determine the correctness of the assertion and reason, let’s analyze both statements. First, consider the assertion: “Between any two rational numbers $a$ and $b$, there exists an infinite number of rational numbers.” This statement aligns with the property of rational numbers that there are infinitely many rational numbers between any two given rational numbers. Now, consider the reason: “The mean of two rational numbers is always a rational number.” The mean of two rational numbers $a$ and $b$ is calculated as $\frac{a + b}{2}$. Since the sum of two rational numbers is rational, and division by 2 (a rational number) also results in a rational number, the mean is indeed a rational number. However, while the mean provides one method to find a rational number between two given rational numbers, it does not explain why there are infinitely many rational numbers between them. Thus, both the assertion and reason are true, but the reason is not the correct explanation of the assertion.