Class 8 Science Chapter 1 Crop Production and Management

Key Concept: Sprinkler System

b) Water is sprinkled over the crops

[Solution Description]

The sprinkler system is characterized by perpendicular pipes with rotating nozzles that sprinkle water on crops, simulating rain. It is particularly useful in uneven land where water availability is limited.

Key Concept: Sprinkler System

b) It distributes water uniformly over large areas

[Solution Description]

The sprinkler system is beneficial for uneven land because it can distribute water uniformly over large areas, regardless of the terrain’s irregularities, ensuring all parts of the crop receive adequate water.

Key Concept: Sprinkler System, Coverage Area

b) 706.86 square meters

[Solution Description]

The area of a circle is given by the formula $A = \pi r^2$. Here, the radius $r = 15$ meters. So, the area covered is $A = \pi \times 15^2 = \pi \times 225 \approx 706.86$ square meters.

Key Concept: Definition of Agriculture

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

[Solution Description] The assertion states that agriculture involves the cultivation of crops on a large scale, which is true as per the syllabus. The reason explains that when plants of the same kind are cultivated at one place on a large scale, it is called a crop. This is also true and directly supports the assertion by providing the definition of a crop, which is fundamental to understanding agriculture. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Impact of Agriculture, Societal Development

c) Led to the development of permanent settlements

[Solution Description]

The advent of agriculture allowed humans to settle in one place, leading to the development of permanent settlements and complex societies. It provided a stable food source, which supported population growth and the development of various technologies and social structures.

Key Concept: Agricultural Practices

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

[Solution Description]

The assertion states that the transition from nomadic life to settled agriculture was mainly because of the discovery of crop cultivation. This is true as the ability to grow crops provided a stable food source, which led to permanent settlements. The reason given is that crop cultivation allowed humans to produce food in a fixed location, thus removing the necessity for constant movement. This is also true and correctly explains the assertion because the production of crops in one place made it possible for early humans to settle down and stop their nomadic lifestyle.

Key Concept: Cropping Patterns

c) Kharif crops are sown in the rainy season, Rabi crops in winter

[Solution Description]

The primary difference between Kharif and Rabi crops lies in the seasons they are grown in. Kharif crops are sown during the rainy season (June to September), while Rabi crops are grown during the winter season (October to March).

Key Concept: Kharif Crops Examples

c) Paddy and Maize

[Solution Description]

Kharif crops include paddy, maize, soybean, groundnut, and cotton. Mustard and barley are Rabi crops, while wheat and barley are also Rabi crops. Paddy and maize are both Kharif crops.

Key Concept: Examples of Kharif Crops

b) Paddy and maize

[Solution Description] Kharif crops include paddy, maize, soybean, groundnut, and cotton. These crops are sown in the rainy season.

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: Rabi Crops

b) Wheat

[Solution Description]

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

Key Concept: Pulses and Vegetables

b) Cucumber

[Solution Description] Vegetables like cucumber and bitter gourd thrive in the summer season as they require warm temperatures for optimal growth.

Key Concept: Pulses and Vegetables, Summer Cultivation

b) Urad bean and okra

[Solution Description]

Pulses like moong bean and urad bean, along with vegetables like okra and bottle gourd, are commonly grown during the summer season due to their ability to withstand high temperatures and lower water requirements. These crops are well-suited for the climatic conditions prevalent in summer.

Key Concept: Preparation of Soil, Agricultural Implements

a) Water the soil to moisten it

[Solution Description]

The first step in preparing dry soil with large clumps is to moisten it before ploughing. Moistening the soil makes it easier to break the clumps and turn the soil effectively. Ploughing loosens the soil, allowing roots to penetrate deep and breathe easily. Therefore, the correct sequence is to water the soil first, then plough it.

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: 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: Manure Mixing, Tilling, Soil Preparation

d) Before tilling

[Solution Description]

Manure should be added to the soil before tilling. This allows the manure to be evenly mixed with the soil during the tilling process, ensuring that nutrients are distributed throughout the soil. Adding manure after tilling would not allow for thorough mixing, and adding it after levelling or sowing would disrupt the soil structure and may harm the seeds.

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: Seed Selection, Sowing Tools

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

[Solution Description]

The assertion states that damaged seeds float on water because they are hollow and lighter. This is correct as damaged seeds lose their internal structure, making them less dense than water, causing them to float.

The reason explains that floating seeds are separated during seed selection to ensure only healthy seeds are sown. This is also correct because separating floating seeds is a method used by farmers to remove damaged or unhealthy seeds before sowing.

The reason correctly explains the assertion because the process of separating floating seeds directly relies on the fact that damaged seeds are hollow and lighter, which makes them float. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Crop Rotation, Nitrogen Replenishment

c) Enriches the soil with nitrogen

[Solution Description]

Legumes have the ability to fix atmospheric nitrogen into the soil through symbiotic bacteria in their root nodules. When legumes are grown alternately with wheat, they enrich the soil with nitrogen, which is essential for wheat growth. This practice reduces the need for chemical fertilisers and maintains soil fertility.

Key Concept: Fertilisers

b) Urea

[Solution Description]

Fertilisers are chemicals rich in particular nutrients and are produced in factories. Examples include urea, ammonium sulphate, super phosphate, potash, and NPK (Nitrogen, Phosphorus, Potassium).

Key Concept: Irrigation Definition

b) Irrigation

[Solution Description]

The process of supplying water to crops at regular intervals is called irrigation. This helps in maintaining soil moisture for healthy crop growth.

Key Concept: Modern Methods of Irrigation

b) Drip system

[Solution Description]

The drip system is the best modern irrigation method for watering fruit plants, gardens, and trees. It delivers water drop by drop directly near the roots, minimizing water wastage.

Key Concept: Weedicides

c) Nose and mouth

[Solution Description]

Farmers should cover their nose and mouth with a piece of cloth during the spraying of weedicides to protect themselves from harmful chemicals.

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

c) Assertion is true, but Reason is false.

[Solution Description]

The assertion states that harvesting involves cutting or pulling mature crops close to the ground, which is correct as per the syllabus. The reason claims that harvesting is done to separate grain seeds from chaff using a machine called combine. However, separating grain seeds from chaff is actually a process called threshing, not harvesting. Therefore, while the assertion is true, the reason is false.

Key Concept: Storage Methods

b) Using silos and granaries

[Solution Description]

Farmers often use silos and granaries for large-scale grain storage. These structures protect the grains from pests like rats and insects, ensuring long-term preservation. Silos are particularly effective for bulk storage due to their design and ability to maintain grain quality.

Key Concept: Large-Scale Storage

c) Silos

[Solution Description]

Silos are large structures designed for bulk storage of grains. They provide protection against pests like rats and insects, and are commonly used for large-scale storage in granaries and godowns.

Key Concept: Importance of soil preparation

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

[Solution Description]

The assertion states that tilling or ploughing the soil is essential for crop cultivation, which is true as it loosens the soil and allows roots to penetrate deeper. The reason given is that tilling helps in bringing nutrient-rich soil to the top, which is also true as it facilitates better nutrient absorption by plants. Moreover, the reason correctly explains why tilling is essential for crop cultivation. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Agricultural Implements

c) Plough

[Solution Description]

The traditional tool used for tilling the soil is the plough. It is typically made of wood or iron and is drawn by a pair of bulls or other animals like horses and camels. The plough has a strong triangular iron strip called the ploughshare and a long wooden log known as the ploughshaft.

Key Concept: Assertion-Reason

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

[Solution Description]

The assertion states that levelling of soil helps in uniform distribution of water during irrigation. This is true because a levelled field ensures that water flows evenly across the entire area without pooling or running off. The reason explains that levelling prevents depressions or elevations in the field, which indeed prevents water stagnation and uneven watering. Since both the assertion and reason are true, and the reason correctly explains the assertion, the correct answer is option a).

Key Concept: Manure and Soil Nutrients

c) To properly mix nutrients with soil

[Solution Description]

Manure is added to the soil before tilling to ensure proper mixing of nutrients with the soil. This helps in replenishing the soil with essential nutrients required for healthy plant growth. Continuous cultivation depletes soil nutrients, and adding manure compensates for this loss.

Key Concept: Agricultural Implements

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

[Solution Description]

The assertion states that the use of a cultivator saves time and labour in ploughing fields, which is true because cultivators are designed to efficiently till the soil over large areas. The reason provided is that cultivators are tractor-driven implements that can cover large areas quickly, which is also true. Furthermore, the reason explains why the assertion is true, as the ability to cover large areas quickly directly leads to saving time and labour. Thus, both the assertion and the reason are true, and the reason correctly explains the assertion.

Key Concept: Soil Preparation

b) To make the soil fine for sowing

[Solution Description]

Crumbs are big clumps of soil formed after ploughing. Breaking them ensures that the soil becomes fine and suitable for sowing seeds, allowing better root penetration and nutrient absorption.

Key Concept: Hoe, Mechanical Advantage

c) 0.3

[Solution Description]

The mechanical advantage (MA) of the hoe is calculated as the ratio of the output force (force applied to loosen the soil) to the input force (force applied by the animal). Since the hoe covers an area of $0.09 \text{m}^2$ in one pass, the output force can be calculated using the pressure formula: $P = \frac{F}{A}$. Rearranging for $F$, we get $F = P \times A$. However, since the pressure is not given, we assume that the output force is directly proportional to the area covered. Therefore, the mechanical advantage is given by $MA = \frac{A_{\text{loosened}}}{A_{\text{blade}}} = \frac{0.09}{0.3} = 0.3$.

Key Concept: Modern Agriculture Tool

b) Cultivator

[Solution Description]

In modern agricultural practices, the cultivator is the tool that is typically attached to a tractor for ploughing the fields efficiently and effectively.

Key Concept: Selection of Seeds, Tools Used for Sowing

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

[Solution Description]

The assertion states that damaged seeds float on water because they are hollow and lighter. This is true as per the syllabus, which explains that damaged seeds become hollow and thus lighter, causing them to float. The reason mentions that the seed drill is a modern tool that ensures uniform sowing by placing seeds at equal distances and depths. This is also true as the syllabus explains that the seed drill sows seeds uniformly at equal distances and depths. However, the reason does not explain why damaged seeds float on water; it simply describes the functionality of the seed drill. Therefore, while both statements are true, the reason is not the correct explanation for the assertion.

Key Concept: Selection of Seeds

c) To ensure high yield and healthy crops

[Solution Description] Good quality seeds are selected to ensure high yield, health, and cleanliness of the crop. This helps in achieving better crop production.

Key Concept: Seed Selection, Seed Drill

c) Separate seeds using water and sow only the sinking seeds

[Solution Description] The farmer can use the water separation method to separate healthy seeds from damaged ones. Damaged seeds are lighter and hollow, so they float on water, while healthy seeds sink. Once the healthy seeds are separated, they can be used in the seed drill for sowing. This ensures uniform sowing and prevents the loss of yield due to damaged seeds.

Key Concept: Selection of Seeds

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

[Solution Description]

The assertion states that farmers prefer to use seeds which give high yield, which is true as high-yield seeds are selected to maximize crop production. The reason given is that high-yield seeds ensure a greater amount of crop production per unit area, which is also true and directly explains why farmers prefer such seeds. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Concept: Method for Seed Separation

b) Placing seeds in water and observing which float

[Solution Description] Placing seeds in water allows the damaged seeds to float because they are lighter and hollow, while the healthy seeds sink due to their higher density. This method is effective for separating the two types of seeds.

Key Concept: Seed Separation

c) Floating seeds on water

[Solution Description]

Floating damaged seeds on water is an effective method to separate them from good seeds. Damaged seeds are hollow and lighter, causing them to float, while healthy seeds sink.

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: Sowing: Modern Method

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

[Solution Description]

The assertion states that the use of tractor-driven cultivators reduces the time required for sowing, which is true because these machines are designed to cover more area in less time. The reason given is that tractor-driven cultivators operate at a faster speed compared to traditional methods, which is also true and directly explains why the assertion is correct. Therefore, both the assertion and the reason are true, and the reason correctly explains the assertion.

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: Uniform sowing depth

b) 4.72 grams

[Solution Description]

The volume of soil displaced by one seed can be calculated using the formula for the volume of a cylinder: $V = \pi r^2 h$. Assuming the seed occupies a cylindrical space with a radius of 0.5 cm and a depth of 5 cm, the volume is $V = \pi \times (0.5)^2 \times 5 \approx 3.93$ cubic centimeters. The weight of the soil displaced is then $3.93 \times 1.2 \approx 4.72$ grams.

Key Concept: Seed drill efficiency, Labor saving

c) 4 hours

[Solution Description]

The seed drill sows seeds at a rate of 0.5 hectares per hour. For a field of 2 hectares, the time taken by the seed drill is $2 / 0.5 = 4$ hours. Manual sowing takes 8 hours for the same area. Therefore, the time saved by using the seed drill is $8 – 4 = 4$ hours.

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

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

[Solution Description] The assertion states that maintaining appropriate distance between seeds ensures that plants receive adequate sunlight, nutrients, and water. This is true because proper spacing prevents overcrowding, which allows each plant to access sufficient resources. The reason explains that overcrowding leads to competition for resources, which hampers growth. This is also true and directly supports the assertion by explaining why proper spacing is necessary. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Avoiding Overcrowding

c) To ensure sufficient sunlight, nutrients, and water for each plant

[Solution Description]

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

Key Concept: Seed Drill

b) Ensures uniform sowing at equal distance and depth

[Solution Description]

The primary advantage of using a seed drill is that it sows the seeds uniformly at equal distance and depth. This ensures that seeds get covered by the soil after sowing, protecting them from being eaten by birds. Additionally, it saves time and labor.

Key Concept: Crop Rotation, Nitrogen Fixation

b) It replenishes the soil with nitrogen through biological fixation

[Solution Description]

Leguminous plants have Rhizobium bacteria in their root nodules, which fix atmospheric nitrogen into the soil. By growing legumes alternately with wheat, the farmer ensures that the soil is replenished with nitrogen, which is essential for plant growth. This practice of crop rotation helps in maintaining soil fertility without the need for additional chemical fertilisers.

Key Concept: Adding Manure and Fertilisers

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

[Solution Description]

The assertion states that manure is considered better than fertilisers because it improves soil texture and water retaining capacity. This is true as manure enhances the soil’s physical properties, including its texture and ability to retain water. The reason provided is that manure is a natural substance obtained by the decomposition of cattle dung and plant residues. This is also true as manure is indeed formed through the decomposition process involving microorganisms. However, while the reason correctly describes what manure is, it does not directly explain why manure is considered better than fertilisers. Therefore, both the assertion and reason are true, but the reason does not correctly explain the assertion.

Key Concept: Advantages of Manure

c) It makes the soil porous and improves its texture.

[Solution Description]

One of the key advantages of using manure over fertilisers is that manure improves the texture of the soil. Additionally, it enhances the water holding capacity and porosity of the soil, promotes the growth of friendly microbes, and provides humus. These benefits make manure a more holistic and sustainable option compared to synthetic fertilisers.

Key Concept: Assertion-Reason

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

[Solution Description] The assertion states that adding manure to the soil improves its water holding capacity, which is true as manure enhances the soil’s ability to retain water. The reason provided is that manure contains organic matter that enhances the soil’s porosity, which is also true. However, while increased porosity does contribute to better water retention, it is not the primary explanation for improved water holding capacity. The main reason for improved water holding capacity is the organic matter in manure itself, which directly increases the soil’s ability to retain moisture. Therefore, both the assertion and reason are true, but the reason does not fully explain the assertion.

Key Concept: Types of Nutrients, Manure Preparation

c) Decomposer bacteria

[Solution Description]

The decomposition of plant and animal waste into manure is primarily carried out by bacteria and fungi. These microorganisms break down the organic matter into simpler substances, releasing nutrients that can be absorbed by plants. This process transforms the waste into nutrient-rich organic manure, which improves soil fertility and structure.

Key Concept: Manure and its Advantages

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

[Solution Description] Adding manure to the soil improves its physical properties. One of the key advantages of manure is that it enhances the water holding capacity of the soil, as stated in the assertion. Additionally, manure makes the soil porous, which facilitates the exchange of gases, as mentioned in the reason. However, while both statements are true, the reason provided does not explain why manure increases the water holding capacity. Therefore, the reason is not the correct explanation of the assertion.

Key Concept: Crop Rotation

c) To replenish soil nutrients

[Solution Description]

Crop rotation helps in replenishing the soil with nutrients, especially nitrogen, by growing different crops alternately.

Key Concept: Fertiliser vs Manure

d) Fertilizers are man-made and do not provide humus, while manure is natural and provides humus.

[Solution Description]

Fertilizers are man-made inorganic salts prepared in factories, while manure is a natural substance obtained by decomposing cattle dung and plant residues. Fertilizers do not provide humus to the soil, whereas manure provides a lot of humus.

Key Concept: Adding Manure and Fertilisers, Vermicomposting

c) It enhances soil structure and microbial activity

[Solution Description] Vermicompost improves soil structure, water retention, and microbial activity while slowly releasing nutrients. Chemical fertilisers provide immediate nutrients but degrade soil health over time by causing salinity and reducing microbial diversity.

Key Concept: Advantages of Manure

d) It enhances the water holding capacity of the soil

[Solution Description]

Manure enhances the water holding capacity of the soil, making it beneficial for plant growth. This is one of the key advantages mentioned in the syllabus.

Key Concept: Irrigation Frequency

b) Due to increased rate of evaporation

[Solution Description]

In summer, the frequency of irrigation is higher due to the increased rate of evaporation of water from the soil and the leaves, as mentioned in the syllabus.

Key Concept: Sources of Irrigation

c) Tubewells

[Solution Description]

In areas with high groundwater levels, tubewells are commonly used as they can extract water from deeper underground. Wells are also used but tubewells are more efficient for tapping into deeper aquifers.

Key Concept: Traditional Methods of Irrigation

d) Rahat

[Solution Description] The rahat system, also known as the lever system, is a traditional irrigation method where water is lifted from wells using a lever mechanism.

Key Concept: Efficiency of Traditional Methods

c) They depend on human or animal labor

[Solution Description]

Traditional methods of irrigation, such as the moat, are less efficient because they rely on human or animal labor, which limits the amount of water that can be lifted and distributed. Modern methods, on the other hand, use pumps powered by diesel, biogas, electricity, or solar energy, which are more efficient and can handle larger volumes of water.

Key Concept: Chain Pump, Efficiency, Mechanical Advantage

b) 12250 J

[Solution Description]

First, calculate the useful work done:

$W_{\text{useful}} = mgh = 100 \, \text{kg} \times 9.8 \, \text{m/s}^2 \times 10 \, \text{m} = 9800 \, \text{J}$

Since the efficiency is 80\%, the total work done by the pump is:

$W_{\text{total}} = \frac{W_{\text{useful}}}{0.80} = \frac{9800}{0.80} = 12250 \, \text{J}$

Key Concept: Traditional Methods of Irrigation, Dhekli

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

[Solution Description]

The assertion states that the dhekli system is less efficient compared to modern irrigation methods, which is true because traditional methods like dhekli are labor-intensive and cannot cover large areas efficiently. The reason given is that the dhekli system relies entirely on human or animal labor for lifting water, which is also true. However, while the reason is correct, it does not fully explain why the dhekli system is less efficient compared to modern methods. Modern methods often use machinery and automation, which are more efficient in terms of time and coverage. Therefore, both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

Key Concept: Rahat – Lever System

c) Assertion is true, but Reason is false.

[Solution Description]

The Assertion states that the Rahat system is a traditional method of irrigation that uses a lever mechanism to lift water from wells. This is true as per the syllabus, which describes the Rahat system as one of the traditional methods of irrigation.

The Reason claims that the Rahat system is more efficient than modern pumps because it does not require any external energy source. This is false because the syllabus explicitly mentions that traditional methods like the Rahat system are less efficient compared to modern pumps, which use diesel, biogas, electricity, or solar energy for better efficiency.

Therefore, the Assertion is true, but the Reason is false.

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: 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 on uneven land where water availability is insufficient. This is true because the sprinkler system can efficiently distribute water over such terrains. The reason explains how the sprinkler system works: water flows through a main pipe under pressure and escapes from rotating nozzles, resembling rain. This is also true and correctly explains why the sprinkler system is effective on uneven land. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Drip Irrigation, Water Efficiency

c) 1000 hours

[Solution Description]

First, calculate the total water required for the orchard per day. Each tree needs 20 liters, and there are 100 trees. So, total water required = 20 L/tree × 100 trees = 2000 liters. The drip system delivers water at a rate of 2 liters per hour. To find the number of hours the system should run, divide the total water required by the delivery rate: 2000 L ÷ 2 L/hour = 1000 hours.

Key Concept: Application of Drip System

c) Mango trees

[Solution Description]

The drip system is particularly beneficial for fruit plants, gardens, and trees because it delivers water directly to the roots, ensuring efficient water use and minimizing wastage. This makes it ideal for fruit-bearing trees in an orchard.

Key Concept: Traditional Methods of Irrigation

d) Rahat

[Solution Description] The rahat system, also known as the lever system, is a traditional method of irrigation that uses a lever to lift water from wells or canals. This method is less efficient but cheaper compared to modern methods.

Key Concept: Irrigation Methods

c) Sprinkler System

[Solution Description]

The Sprinkler System is a modern irrigation method that is highly suitable for uneven land where water availability is limited. This system uses perpendicular pipes with rotating nozzles connected to a main pipeline. When water flows through the main pipe under pressure, it escapes from the rotating nozzles and is sprinkled over the crops, mimicking rainfall. This method ensures efficient water usage and is particularly useful in areas with uneven terrain.

Key Concept: Weeds and Weeding

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

[Solution Description] Weeding is indeed necessary as weeds compete with crop plants for essential resources such as water, nutrients, space, and light, which affects the growth of the crops. Additionally, some weeds are poisonous to animals and humans and can interfere with the harvesting process. Both the Assertion and Reason are true, and the Reason provides a correct explanation for why weeding is necessary.

Key Concept: Effects of Weeds

b) To ensure better growth of the crop by reducing competition for resources

[Solution Description]

Weeding is necessary because weeds compete with the crop plants for essential resources such as water, nutrients, space, and light. This competition affects the growth of the crop plants. Additionally, some weeds can interfere with harvesting and may be poisonous to animals and humans. Therefore, removing weeds ensures better growth and yield of the crops.

Key Concept: Manual Weeding, Weedicides

c) Applying weedicides before seed formation and manually removing visible weeds

[Solution Description]

Combining manual weeding with the careful use of weedicides can provide effective weed management. Manual weeding helps remove weeds physically, especially in areas where weedicides might not reach effectively. However, weedicides should be used during the vegetative growth stage of weeds, before they flower or produce seeds, to maximize their effectiveness. Farmers must also follow safety precautions, such as covering their nose and mouth, to minimize health risks from chemical exposure.

Key Concept: Manual Removal

c) Assertion is true, but Reason is false.

[Solution Description]

The assertion states that manual removal of weeds is effective because it physically removes the weeds from the ground, which is true as manual removal involves uprooting or cutting weeds close to the ground. The reason states that a seed drill can be used for manual removal of weeds. However, a seed drill is primarily used for sowing seeds and not for manual removal of weeds. Therefore, the assertion is true, but the reason is false.

Key Concept: Weedicides

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

[Solution Description] The assertion states that weedicides like $2,4-D$ are used to control the growth of weeds in crop fields, which is true as per the syllabus. The reason states that weedicides kill weeds without damaging the crops, which is also true. Furthermore, the reason correctly explains why weedicides are used, making it the correct explanation of the assertion.

Key Concept: Storage

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

[Solution Description]

The assertion states that proper storage of grains involves drying them to reduce moisture content, which is true as per the syllabus. The reason given is that drying grains prevents the attack by insect pests, bacteria, and fungi, which is also correct and directly explains why drying is necessary for proper storage. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Storage, Steps Before Storage

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

[Solution Description]

Freshly harvested grains naturally contain high moisture levels. If stored without drying, this moisture creates an environment conducive to the growth of microorganisms like bacteria and fungi, as well as attracting pests such as insects and rats. To prevent spoilage, grains are dried in the sun to reduce their moisture content. This process makes the grains less hospitable to microorganisms and pests, thereby ensuring longer storage life. Thus, drying is a critical step before storage to maintain grain quality.

Key Concept: Storage Precautions

b) To reduce moisture content

[Solution Description]

Harvested grains have more moisture, which can lead to spoilage or attack by organisms. Drying reduces moisture, preventing attack by insect pests, bacteria, and fungi.

Key Concept: Storage of Grains

b) To reduce moisture and prevent pest attack

[Solution Description]

Drying grains reduces the moisture content, which prevents the growth of pests, bacteria, and fungi. High moisture levels can lead to spoilage and make the grains unfit for use or germination.

Key Concept: Storage, Natural Insect Repellents

d) To repel insects and protect the grains from infestation.

[Solution Description] Neem leaves contain natural compounds that act as insect repellents. By adding them to the jute bags, the farmer aims to deter insects from attacking the stored wheat grains, ensuring their safety over a longer period.

Key Concept: Neem Leaves

b) Using dried neem leaves

[Solution Description]

Dried neem leaves are traditionally used at home for storing food grains. Neem leaves have natural properties that help in protecting grains from pests and insects.

Key Concept: Chemical Treatments

b) Chemical treatments

[Solution Description]

Specific chemical treatments are required for storing large quantities of grains in big godowns. These treatments protect the grains from pests and microorganisms.

Key Concept: Chemical Treatments

b) To protect grains from pests and microorganisms

[Solution Description]

Specific chemical treatments are necessary to protect large quantities of grains from pests and microorganisms. These treatments ensure that the grains remain safe and edible over extended periods by preventing infestation and spoilage, which can occur in large storage facilities like godowns.

Key Concept: Storage, Granaries, Moisture Control

b) 34.09 kg

[Solution Description]

To calculate the amount of water to be removed, we need to determine the initial and final weight of water in the wheat.

Initial weight of wheat = 500 kg, initial moisture content = 18%.

Initial weight of water = $500 \times \frac{18}{100} = 90$ kg.

Final moisture content = 12%. Let the final weight of wheat after drying be x kg.

Final weight of water = $x \times \frac{12}{100}$.

Since the dry matter remains the same, the dry matter initially is $500 – 90 = 410$ kg.

Final weight of wheat after drying = $\frac{410}{1 – \frac{12}{100}} = \frac{410}{0.88} = 465.91$ kg.

Final weight of water = $465.91 \times \frac{12}{100} = 55.91$ kg.

Water to be removed = Initial weight of water – Final weight of water = $90 – 55.91 = 34.09$ kg.

Key Concept: Chemical treatments, Pest prevention, Safety measures

a) Wearing a mask and gloves

[Solution Description] Chemical treatments for grain storage involve the use of hazardous substances that can pose significant health risks if not handled properly. Essential safety measures include wearing protective gear, ensuring proper ventilation, and avoiding direct inhalation of the chemicals. Among the options, wearing a mask and gloves is crucial to prevent exposure to harmful chemicals.

Key Concept: Food from Animals

c) Jute bags

[Solution Description]

Farmers often store grains in jute bags or metallic bins on a small scale to protect them from pests and insects. Large-scale storage involves silos and granaries, but for small-scale storage, jute bags and metallic bins are commonly used.

Key Concept: Animal Husbandry

d) Hen

[Solution Description]

Milk is obtained from animals like cows, buffaloes, she-goats, and she-camels. Hens are not a source of milk.

Key Concept: Animal Husbandry

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

[Solution Description]

The assertion states that animal husbandry involves rearing animals for food products such as milk, eggs, and meat. This is true as animal husbandry refers to the management and care of animals raised for food or other products. The reason explains that animals reared for food need proper food, shelter, and care to maintain their health and productivity. This is also correct because the well-being of animals directly impacts their ability to produce food. Furthermore, the reason logically explains why animal husbandry is practiced, as it ensures the animals are healthy and productive.

Key Concept: Egg Production, Nutritional Value

a) Protein

[Solution Description]

Egg whites are primarily composed of protein, with water making up the majority of the remaining content.

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: Seed Selection

c) They are hollow and 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. Healthy seeds are denser and thus sink when placed in water.

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 from marine sources

d) Vitamin D

[Solution Description]

Cod liver oil, which is obtained from fish, is particularly rich in vitamin D. This vitamin is essential for bone health and calcium absorption.

Key Concept: Food distribution, Agricultural practices

b) Improve storage facilities and transportation networks

[Solution Description]

Uneven food distribution can be mitigated by improving storage facilities, enhancing transportation networks, and adopting mixed farming practices. These measures ensure that food produced in surplus regions can be distributed efficiently to deficit areas.

Key Concept: Preparation of Soil, Tilling

a) Water the soil, till the soil, break the crumbs, level the field

[Solution Description]

The first step in preparing soil is tilling or ploughing, especially if the soil is dry. Dry soil may need watering before ploughing to make it easier to work with. After ploughing, the field may have big clumps of soil called crumbs, which need to be broken down. Levelling the field is beneficial for both sowing and irrigation. Finally, moistening the soil before sowing ensures better seed germination.

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.