Key Concept: Atmospheric Conditions

b) By absorbing and reflecting harmful ultraviolet rays
[Solution Description] Earth’s atmosphere, containing ozone, acts as a shield by preventing harmful ultraviolet radiation from reaching the Earth’s surface. This protection is crucial for sustaining life as it prevents damage to living organisms.

Key Concept: Advanced Reasoning, Numerical and Analytical Difficulty

b) 160 km
[Solution Description]
Let’s analyze the analogy using proportions based on dimensions given:
1. **Apple’s Skin-to-Radius Ratio**: The apple’s skin is $0.1 \, \text{cm}$ thick with a radius of $4 \, \text{cm}$, producing a ratio of
$\frac{0.1}{4} = 0.025$
2. **Apply this Ratio to Earth**: Using Earth’s mean radius ($6400 \, \text{km}$), calculate the crust’s estimated thickness:
$\text{Crust Thickness} = 0.025 \times 6400 \, \text{km} = 160 \, \text{km}$
This calculation equates Earth’s crust to be roughly $160 \, \text{km}$ thick, captured accurately by option b).

Key Concept: Earth’s Surface and Life

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
Assertion is true because Earth is indeed the only known planet where we observe an atmosphere containing significant levels of oxygen. This is unique compared to other planets in our solar system.
The Reason provided is also true as oxygen is crucial for the process of respiration, allowing living organisms to convert glucose into energy necessary for survival. However, while both statements are true, the reason given does not directly explain why Earth has an oxygen-containing crust. The crust’s composition and atmospheric oxygen level are results of biological processes over millions of years rather than being inherently related by causation.
Therefore, the correct answer is: Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

Key Concept: Earth’s Surface and Climate

a) It allows Earth to remain within the habitable zone
[Solution Description] The Earth’s nearly circular orbit keeps it at a constant distance from the Sun throughout the year. This constancy in distance ensures that Earth experiences relatively stable temperatures, avoiding extreme cold or heat that would be inhospitable for life. As a result, this stable climate facilitates the consistent presence of liquid water, which is essential for sustaining life.

Key Concept: Concept of Earth’s Crust

c) It supports life by providing essential resources
[Solution Description] The Earth’s crust is a very thin layer when compared to the entire size of Earth, similar to how the skin of an apple relates to the whole fruit. This thin crust is where all life exists because it contains essential elements like soil and minerals that are necessary for plants and other organisms. It also holds water bodies and supports the atmosphere, which is crucial for life. Without this thin but resource-rich layer, life as we know it would not be possible on Earth.

Key Concept: Photosynthesis Process

b) Carbon dioxide
[Solution Description] Plants use carbon dioxide from the atmosphere during photosynthesis. In the presence of sunlight, carbon dioxide and water are converted into glucose and oxygen by plants.

Key Concept: Reason for Earth’s uniqueness

c) It supports various life forms
[Solution Description] Earth is unique because it has a delicate, life-supporting crust where diverse life thrives. No other known planets have this capability of sustaining such diverse life forms.

Key Concept: Comparison of Earth’s crust to an apple’s skin

d) The skin of the apple
[Solution Description] The statement compares Earth’s crust to an apple’s skin. The crust is the thin outermost layer of the Earth where all terrestrial life resides. This comparison highlights how relatively thin the crust is in relation to the entire size of the planet.

Key Concept: Planetary Atmospheres

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion states that Venus is the hottest planet in our solar system, which is true. Even though Mercury is closer to the Sun, Venus has a thick atmosphere rich in carbon dioxide, causing a strong greenhouse effect that traps heat and makes it hotter than Mercury.
The reason given is that Venus is closest to the Sun. This statement is false because Mercury is actually the closest planet to the Sun, not Venus.
Therefore, the correct answer is that the Assertion is true, but the Reason is false.

Key Concept: What Do the Planets of Our Solar System Look Like?

d) Assertion is false, but Reason is true.
[Solution Description]
The assertion states that Venus is the hottest planet because of its closeness to the Sun. However, Mercury is actually closer to the Sun than Venus. Despite being further from the Sun compared to Mercury, Venus is hotter due to its dense atmosphere composed primarily of carbon dioxide, which efficiently traps heat through the greenhouse effect. Therefore, the reason provided correctly explains why Venus is the hottest planet and not because it’s closest to the Sun. Hence, both the Assertion is false as it incorrectly attributes heat to distance from the Sun, while the Reason is true as it gives the correct explanation for Venus’s high temperature.

Key Concept: Order of Planets by Distance from the Sun

c) Mars
[Solution Description] The planets in order of their distance from the Sun are Mercury, Venus, Earth, and then Mars. Therefore, Mars is the fourth planet from the Sun.

Key Concept: Planetary Atmospheres

a) Mercury
[Solution Description] Mercury does not have an atmosphere. While most other planets have atmospheres of varying thickness and composition, Mercury is too small and close to the Sun to retain one.

Key Concept: Temperature and Atmosphere of Planets

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion that Jupiter is colder than Earth is true. Jupiter, being much farther from the Sun compared to Earth, receives less solar energy per unit area, which contributes to its lower average temperature.
The reason states that the distance from the Sun determines a planet’s temperature. This is also true, as planets closer to the Sun generally receive more sunlight and hence tend to be warmer. However, this alone does not account for all temperature variations because factors like atmospheric composition also significantly affect temperature, as seen in Venus having a higher temperature due to its greenhouse effect despite not being closest to the Sun. Therefore, while both statements are individually correct, the reason is not the sole or direct explanation for the specific temperature comparison between Jupiter and Earth.
Thus, the correct answer is: Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

Key Concept: Atmospheric Composition, Temperature Variation

b) Because of dense CO$_2$ atmosphere causing heat retention
[Solution Description]
Venus experiences extremely high temperatures primarily due to its dense atmosphere composed almost entirely of carbon dioxide, creating a strong greenhouse effect. This gas traps heat very efficiently, causing temperatures on Venus to be higher than those on Mercury, which lacks a significant atmosphere to retain heat. Mars, with a much thinner atmosphere and lower capability to trap heat, cannot match Venus’s temperatures either.

Key Concept: Temperature Characteristics of Gas Giants

d) Neptune
[Solution Description] Neptune is the farthest from the Sun among the gas giants and has the coldest average atmospheric temperature due to its great distance from the Sun.

Key Concept: Comparison of Gas Giants

d) Saturn
[Solution Description] Saturn is well-known for its extensive and visible ring system, which is a distinguishing feature compared to the other gas giants in our solar system.

Key Concept: Characteristics of Venus and its comparison to Earth

d) Venus is slightly smaller than Earth and has a thick carbon dioxide atmosphere
[Solution Description]
Venus has a radius that is 0.95 times that of Earth. This means Venus is slightly smaller than Earth in terms of size. The atmosphere of Venus is primarily composed of carbon dioxide, which creates a strong greenhouse effect, making it the hottest planet despite being second from the Sun.

Key Concept: Temperature characteristics of rocky planets

c) Venus because of its dense carbon dioxide atmosphere
[Solution Description]
Although Mercury is closer to the Sun, Venus experiences higher average temperatures due to its thick atmosphere rich in carbon dioxide, which leads to a runaway greenhouse effect. Therefore, Venus has a higher average temperature than any other planet in our solar system.

Key Concept: Differences in temperature and atmospheric conditions across planets

Correct Answer option Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Assertion states that Venus is the hottest planet. Observations show this is true because its surface temperature is higher than any other planet in our solar system. The reason given is the presence of a thick carbon dioxide-rich atmosphere causing a significant greenhouse effect. This explanation directly links to why Venus is the hottest, as the trapped heat raises temperatures more than on Mercury, even though Mercury is closer to the Sun. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Atmospheric conditions of planets

c) Its thick atmosphere traps heat
[Solution Description] The primary reason Venus experiences such high temperatures is due to its dense atmosphere rich in carbon dioxide. This gas forms a strong greenhouse effect, trapping heat and making the planet extremely hot.

Key Concept: Magnetic field of the Earth, Position of the Earth

Correct Answer option b) Deflects harmful particles and radiation
[Solution Description]
Earth’s magnetic field deflects high-energy particles from space, such as cosmic rays and solar winds, which could strip away the atmosphere or increase harmful UV radiation on the surface. Earth’s favorable position also keeps it within a safe range where these fields can effectively protect the planet from extensive atmospheric erosion and biological damage.

Key Concept: Position of the Earth and Magnetic Field

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion mentions that Earth’s position relative to the Sun is crucial because it permits water to remain in a liquid state, which is essential for life. This is true as water in its liquid form is necessary for biochemical processes.
The reason states that the Earth’s magnetic field protects the planet by deflecting harmful particles, such as cosmic rays and solar wind, thereby maintaining the integrity of the atmosphere. This is also true.
However, while both statements are correct, the reason given does not directly explain why the Earth’s distance from the Sun allows water to stay liquid. Therefore, the correct answer is: Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

Key Concept: Habitable Zone, Liquid Water

Correct Answer option b) No, the temperatures are too low for liquid water.
[Solution Description]
A planet located at twice the Earth-Sun distance ($2$ AU) would receive significantly less solar energy compared to Earth. According to the inverse square law, the energy received is inversely proportional to the square of the distance from the Sun.
Calculation:
Energy received at $2$ AU = $\frac{1}{{2}^2}$ = $\frac{1}{4}$ or $25\%$ of the energy Earth receives.
With such reduced solar irradiation, it’s highly probable that any water present on the planet’s surface would freeze, given the lower temperatures expected at that distance.
Therefore, under similar atmospheric conditions to Earth, liquid water is unlikely to exist on the surface due to insufficient warmth to prevent freezing.

Key Concept: Position of the Earth, Liquid Water

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description] The assertion states that Earth’s distance from the Sun allows it to support life by being in the habitable zone, ensuring water remains liquid. The reason explains why liquid water is essential: it’s necessary for all life forms as we know them. Both statements are true and the reason directly explains why Earth’s position makes it suitable for life; liquid water is indeed vital for life development. Therefore, both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Earth’s distance from the Sun, Habitable zone

Correct Answer option b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description] The assertion states that Earth’s position enables water to be in liquid form, which is crucial for life. This is true because Earth’s location within the habitable zone allows temperatures that prevent all water from evaporating or freezing completely, making it suitable for various forms of life. The reason given claims that the habitable zone is defined by retaining an atmosphere. While the presence of an atmosphere is important for maintaining temperature and pressure for liquid water, the primary definition of a habitable zone is based on the distance from the star allowing liquid water on the surface. Thus, both statements are independently true, but the reason does not directly explain the assertion.

Key Concept: Earth’s Distance From the Sun, Liquid Water Stability

b) Liquid water enables efficient nutrient transport and chemical reactions
[Solution Description]
Liquid water is vital for life as it acts as a solvent, facilitating chemical reactions necessary for biological processes. On planets farther from the Sun, where water predominantly exists in solid form, these essential reactions are severely limited. Solid water does not allow molecules to move freely or interact effectively. The presence of liquid water creates a conducive environment for sustaining metabolic activities critical for life.

Key Concept: Habitable Zone

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that Earth is in the habitable zone, facilitating the presence of liquid water. This is true because the habitable zone, also known as the Goldilocks zone, is the range where conditions are just right for liquid water to exist, crucial for life as we know it.
The reason provides a different aspect of Earth’s suitability for life by mentioning the effects of Earth’s size on gravitational force. It states that if Earth were significantly larger, gravity could potentially crush human bones due to increased force, which is also true.
However, the reason does not explain why Earth is in the habitable zone—it rather explains another factor related to Earth’s habitability linked to its size and gravitational pull. Therefore, while both statements are true, they address different aspects of Earth’s habitability, and the reason is not the correct explanation of the assertion.

Key Concept: Atmosphere, Oxygen, Ozone Layer

Correct Answer option (a) Increase in skin-related health issues among living organisms.
[Solution Description] The ozone layer plays a crucial role by absorbing harmful ultraviolet (UV) radiation from the Sun, thus protecting living organisms from potential cellular damage caused by UV exposure. Without ozone, there would be an increase in UV radiation reaching the Earth’s surface, leading to heightened risks of skin cancer and other health issues for humans and animals, along with detrimental effects on plant life, which rely on specific light wavelengths for photosynthesis. Ecosystems could face severe disruptions due to these factors.

Key Concept: Earth’s Gravitational Force and Bone Integrity

a) Bones might weaken, leading to fractures under normal loads
[Solution Description] An increase in Earth’s size will result in a higher gravitational force due to the relationship $g = \frac{GM}{R^2}$, where $g$ is gravitational acceleration. Larger size with unchanged density increases mass $M$ significantly more than the square of the radius $R$, enhancing gravitational pull. Constant exposure to stronger gravity could lead to excessive pressure on bones, potentially causing structural damage or deformation due to the body’s inability to withstand the increased stress over prolonged periods.

Key Concept: Size of the Earth

Correct Answer option Assertion is true, but Reason is false.
[Solution Description]
The Assertion states that the Earth’s size is crucial in maintaining its atmosphere, which is accurate. A suitable gravitational force due to Earth’s size retains the atmosphere, essential for sustaining life. The Reason claims that if the Earth were larger, gravity would be too weak, which is incorrect. In reality, a larger planet would have stronger gravity, not weaker. Therefore, while the Assertion is true, the Reason provided is false.

Key Concept: Earth’s size allows it to support a stable atmosphere

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
Assertion states that Earth’s gravity is sufficient to retain its atmosphere. This is true because the Earth’s mass and size are such that its gravitational force is capable of retaining atmospheric gases.
The reason given is about Mars having a much thinner atmosphere due to its smaller size and weaker gravitational pull, which is a true statement as well.
Here, both statements are true, and the Reason is the correct explanation for the Assertion since it highlights how a planet’s size (and consequently its gravity) affects its ability to maintain an atmosphere. The lack of stronger gravity on Mars leads to a thinner atmosphere compared to Earth.
Therefore, the answer is: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Key Concept: Effect of Earth’s Size on Atmosphere

c) Gases might escape into space
[Solution Description] If Earth were much smaller, its gravitational pull would be weaker, making it difficult to retain the gases in its atmosphere. As a result, these gases might escape into space, and without a stable atmosphere, life as we know it could not be sustained.

Key Concept: The role of gravity in holding the atmosphere

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that Earth’s gravity is capable of holding the atmospheric gases, which is true. This is because the gravitational force exerted by Earth is sufficient to prevent these gases from escaping into space.
The reason provided is also correct as it explains a hypothetical scenario: if Earth had been much smaller, its gravity wouldn’t have been adequate to keep the atmospheric gases intact. This explanation highlights how the size and corresponding gravitational force of Earth are crucial for maintaining its atmosphere.
Therefore, both the Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.

Key Concept: Magnetic Field and Atmospheric Protection, Gravity Influence

c) Protecting atmosphere from solar winds, reducing gas loss.
[Solution Description]
Earth’s magnetic field acts as a shield protecting the atmosphere from solar winds — streams of charged particles emitted by the Sun. Without this protection, these high-energy particles could strip away the atmosphere over time.
Gravity keeps the atmospheric gases close to Earth, while the magnetic field ensures they’re not blown away into space. Solar winds carry enough energy to impart momentum to gas particles, but the magnetic field deflects these charged particles, minimizing their impact on the atmosphere.
Therefore, the combination of gravity holding the gases and the magnetic field preventing external stripping is crucial for atmospheric retention.

Key Concept: Impact of Ozone Layer Depletion

c) Increased exposure to ultraviolet rays causing health issues
[Solution Description] Significant depletion of the ozone layer would result in more ultraviolet rays reaching Earth’s surface. This increase in UV radiation exposure could lead to higher rates of skin cancer, eye cataracts, and other health issues among humans and wildlife, as well as affecting ecosystems and food chains.

Key Concept: Formation of Ozone, Role of Oxygen

c) It breaks apart under UV light to form ozone
[Solution Description] The formation of ozone in the atmosphere begins with oxygen molecules ($O_2$). When high-energy UV rays strike an $O_2$ molecule, it splits into two individual oxygen atoms. These free oxygen atoms can then collide with other $O_2$ molecules to form ozone ($O_3$). Thus, atmospheric oxygen is essential for the creation of ozone and consequently, the formation of the ozone layer.

Key Concept: Magnetic Field of the Earth

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
Both statements are true. The Earth’s magnetic field does act as a protective shield against harmful high-energy particles such as cosmic rays and solar wind. This protection is crucial for maintaining the atmosphere and supporting life on Earth. Additionally, the Reason provided explains that the origin of the Earth’s magnetic field is due to the movement of molten iron in the core, which is a scientifically accepted explanation. However, while both statements are true and related, the reason does not directly explain the assertion’s focus on protection from particles but rather describes the cause of the magnetic field itself.

Key Concept: Protection by Earth’s Magnetic Field

d) By deflecting harmful solar particles
[Solution Description] The Earth’s magnetic field deflects high-energy charged particles such as those from solar winds away from the Earth. This shielding effect reduces the potential damage these particles could cause to the ozone layer, which serves as a barrier against harmful UV rays.

Key Concept: Magnetic field of the Earth

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that Earth’s magnetic field acts as a protective shield against harmful cosmic rays and solar wind particles, which is true. These high-energy particles can damage the atmosphere and increase UV radiation exposure, but the magnetic field deflects many of them, safeguarding life.
The reason given is that the movement of molten iron in Earth’s core generates its magnetic field. This statement is also true. The geodynamo effect, caused by convection currents in the liquid outer core, is responsible for creating Earth’s magnetic field, which aligns with both statements being correct. However, while both are true, the generation of the magnetic field is not the direct explanation of how it protects from cosmic rays and solar winds; instead, it describes the origin of the magnetic field itself.
Therefore, both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

Key Concept: Earth’s Magnetic Field Origin

b) Movement of molten iron in the Earth’s core
[Solution Description] The Earth’s magnetic field is believed to originate from the movement of molten iron in its core. This movement generates electric currents, which in turn create the magnetic field. This process is known as the dynamo effect.

Key Concept: Protection from harmful particles

c) More harmful UV rays would reach Earth.
[Solution Description] Without Earth’s magnetic field, the high-energy particles from cosmic rays and solar wind could directly hit the atmosphere, damaging it and depleting the ozone layer. This would lead to increased levels of harmful UV radiation reaching the surface, posing a threat to life forms.

Key Concept: Protection from harmful cosmic rays and solar wind

b) By deflecting harmful particles
[Solution Description] Earth’s magnetic field acts as a protective shield by pushing away many harmful high-energy particles from space, like cosmic rays and solar winds, thus protecting our atmosphere and supporting life.

Key Concept: Balance and Interaction of Elements on Earth

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description] The assertion states that the habitability of Earth’s biosphere is due to a balance between living and non-living elements. This is true because life on Earth indeed relies on such balance where different components interact synergistically. The reason explains one aspect of this interaction—where decomposers recycle nutrients to sustain plant life. This statement is also accurate. However, while both statements are true, the reason does not directly explain why the entire biosphere remains habitable; instead, it provides an example of a process within this system. Therefore, the reason is an important detail but not the direct cause of the overall balance mentioned in the assertion.

Key Concept: Plants, animals, and microorganisms; Importance of balance

c) By returning essential nutrients to the soil
[Solution Description]
Decomposers, such as bacteria and fungi, break down dead organisms and organic waste material, converting them into simpler substances that are returned to the soil. This decomposition process recycles nutrients, making them available for plant growth, which in turn supports herbivores and higher trophic levels in the food chain. By breaking down complex organic matter into inorganic forms, decomposers help maintain soil fertility and nutrient cycles, ensuring ecosystem sustainability and supporting diverse life forms.

Key Concept: Photosynthesis, Greenhouse Effect

a) Photosynthesis
[Solution Description] The process that highlights the joint role of air and sunlight is photosynthesis. During photosynthesis, plants absorb sunlight and use it to convert carbon dioxide from the air and water from the soil into glucose and oxygen. This not only provides food but also releases oxygen, essential for animal respiration. Moreover, through the greenhouse effect, sunlight warms the Earth’s surface, allowing water to remain liquid and facilitating this entire cycle.

Key Concept: Photosynthesis and Air

d) They release oxygen during photosynthesis
[Solution Description] Plants take carbon dioxide from the air and water from the soil, using sunlight to perform photosynthesis. During this process, they produce glucose and release oxygen as a byproduct. This oxygen is then added to the atmosphere, crucial for the respiration of most living organisms.

Key Concept: Nutrients in Soil

a) Nitrogen
[Solution Description] The syllabus indicates that soil is rich in nutrients such as nitrogen and potassium, which are essential for plant growth. These elements help plants perform photosynthesis and create proteins.

Key Concept: Source of Nutrients

c) From the decomposition of materials
[Solution Description] The syllabus mentions that nutrients such as nitrogen and potassium are released into the soil through the slow breakdown of rocks and organic matter from dead plants and animals. This process enriches the soil with necessary elements for plant growth.

Key Concept: Plants, Animals, and Microorganisms

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion discusses how Earth’s capability to support various forms of life is largely attributed to the ongoing processes of reproduction and evolution among plants, animals, and microorganisms. This is true because these processes ensure survival and adaptation over time, enabling life to thrive despite environmental changes.
The reason, however, claims that reproduction results in identical offspring, which contributes to genetic uniformity. While asexual reproduction may lead to genetically similar offspring, sexual reproduction combines genetic materials from two parents, resulting in offspring with genetic variations. Genetic diversity, rather than uniformity, is crucial for adaptability and evolution, allowing species to cope with changing environments.
Thus, the Assertion is true as it highlights the importance of reproduction and evolution in sustaining life. However, the Reason is false because it incorrectly represents the outcome of reproductive processes by suggesting genetic uniformity rather than diversity.

Key Concept: Biosphere Components, Environmental Balance, Impact of Human Activity

b) Geosphere changes cause atmospheric instability impacting ecosystems
[Solution Description] Deforestation affects the geosphere by removing trees, which play a crucial role in the hydrological cycle by releasing water vapor during transpiration. Reduced tree cover decreases this moisture return to the atmosphere, affecting rainfall patterns (hydrosphere). This leads to drier conditions impacting the biosphere by reducing available water for organisms and changing habitats, and the atmosphere becomes dustier due to loss of vegetation cover. This demonstrates the intricate balance where the geosphere, hydrosphere, biosphere, and atmosphere interact to sustain life.

Key Concept: Balance in Ecosystems

c) Assertion is true, but Reason is false.
[Solution Description]
Assertion states that the balance between various natural elements is crucial for sustaining life on Earth, which is true because ecosystems are interconnected systems where each component supports others to maintain environmental equilibrium. This balance ensures the availability of resources like clean air, water, and soil, necessary for life.
Reason claims that the destruction of forests does not affect the air quality and biodiversity of a region, which is false. Forests play a significant role in maintaining air quality by absorbing carbon dioxide and releasing oxygen during photosynthesis. They also provide habitat and resources for diverse species, contributing to biodiversity. Therefore, deforestation can lead to a decrease in air quality and loss of biodiversity.
Since the assertion is true but the reason provided is false, the correct option is: Assertion is true, but Reason is false.

Key Concept: What keeps life from disappearing?

c) Reproduction among organisms
[Solution Description] Reproduction is essential for maintaining the continuity of life on Earth. It allows for the production of new individuals, ensuring that each type of organism continues to exist across generations.

Key Concept: Asexual Reproduction

c) Offspring are genetically identical to the parent
[Solution Description] In asexual reproduction, only one parent is involved in producing offspring. This process leads to the creation of exact genetic copies or clones of the parent because there is no mixing of genetic material from two parents, as seen in sexual reproduction. A good example of this is binary fission in bacteria.

Key Concept: Asexual vs Sexual Reproduction, Continuity of Life

c) Organism B’s method promotes adaptability and resilience
[Solution Description]
Asexual reproduction involves a single parent producing genetically identical offspring, ensuring rapid population growth but limited genetic variation. This mode of reproduction is efficient for stable environments with little change. On the other hand, sexual reproduction, involving two parents, results in offspring with genetic variation due to the combination of genes from both parents. This genetic diversity is crucial for adapting to changing environments, thus enhancing the long-term survival and evolution of a species. The presence of both reproductive strategies allows life to be sustained across varying conditions on Earth.

Key Concept: Reproduction, Genetic Variation

a) By combining alleles from different parents
[Solution Description]
Sexual reproduction involves the combination of genetic material from two parents through the process of fertilization. Each parent contributes half of their genetic material to the offspring. This mixing of genetic information creates new combinations of genes, leading to variation among offspring. Such genetic recombination during processes like meiosis increases the genetic diversity within a species, which can enhance the ability of individuals to adapt and survive in changing environments.

Key Concept: Asexual Reproduction in Simple Animals

b) Budding
[Solution Description] Hydra reproduce asexually by budding. In this process, a small outgrowth develops on the body of the parent hydra, which will eventually detach and become a new individual. This method allows hydras to produce offspring that are genetically identical to the parent.

Key Concept: Asexual Reproduction, Genetic Consistency

c) Mitosis duplication preserves genetic traits
[Solution Description]
Vegetative propagation produces offspring that are genetically identical to the parent because it involves mitosis, where the genetic material is duplicated exactly. Each cell division during this process results in two daughter cells with the same genetic code as the parent. This method ensures consistency in traits but limits genetic diversity because it doesn’t involve the mixing of genes found in sexual reproduction. Consequently, while it allows for the rapid proliferation of plants with desirable traits, it can make populations more susceptible to diseases or environmental changes.

Key Concept: Concept: Vegetative Propagation

c) Stem
[Solution Description]
In vegetative propagation, parts like the stem, leaf, or root can be used. For instance, the ‘eyes’ of a potato, which are actually buds on its surface, can grow into new plants when planted. This makes the stem an essential part for vegetative propagation.

Key Concept: Vegetative propagation in plants

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion states that vegetative propagation leads to rapid reproduction and helps preserve desired traits. This is true because vegetative propagation allows plants to reproduce quickly without going through a seed stage, ensuring that the exact genetic makeup of the parent plant is passed on.
The reason given is that genetic material is exchanged between two parents, which is false in the context of vegetative propagation. In vegetative propagation, there is no exchange of genetic material as it involves only one parent, producing clones of itself. Hence, the reason does not apply to the scenario described by the assertion.
Therefore, the correct answer is that the Assertion is true, but the Reason is false.

Key Concept: Examples of Vegetative Propagation

d) Seed germination
[Solution Description]
Examples of vegetative propagation include stem cutting of a money plant, using the eyes of a sprouted potato, and a piece of ginger. Seed germination does not involve vegetative propagation as it is a sexual reproduction process involving seeds.

Key Concept: Reproduction Methods

c) It uses only one parent plant’s material
[Solution Description]
Vegetative propagation produces offspring that are genetically identical to the parent because it involves mitotic division where no exchange of genetic material occurs. Unlike sexual reproduction, which combines genes from two parents through meiosis and fertilization, vegetative propagation uses parts of a single parent plant, preserving its genetic makeup completely.

Key Concept: Asexual reproduction in microbes and simple animals

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that asexual reproduction allows for rapid population growth but lacks genetic diversity. This is true because asexual reproduction involves a single parent replicating to produce offspring, leading to quick multiplication of individuals in favorable conditions. However, since there is no exchange or recombination of genetic material from two different parents, all offspring are genetically identical to the parent, resulting in no genetic variation.
The reason given is that organisms undergoing asexual reproduction produce identical offspring by precisely replicating their genetic material. This is also true, as during asexual reproduction, the DNA of the parent cell is copied exactly into the offspring cells, ensuring they are clones of the parent.
Both the assertion and the reason are accurate statements about asexual reproduction. However, while the reason supports the claim about lack of genetic diversity, it does not directly explain the concept of allowing for rapid population growth. Hence, the reason is NOT the correct explanation of the assertion.

Key Concept: Asexual reproduction

c) Assertion is true, but Reason is false.
[Solution Description] The assertion that “Hydra can reproduce by budding” is true because Hydra, a simple animal, reproduces asexually through a process called budding. During budding, a new individual grows out of the body of the parent organism and eventually detaches to become an independent organism. However, the reason provided is incorrect. Budding does not involve the fusion of two identical individuals. Instead, it involves the development of a new organism from a bud on the parent organism. Therefore, the reason is false.

Key Concept: Asexual reproduction in microbes

c) $4000$
[Solution Description] The initial number of bacteria is $500$. The doubling time is $20$ minutes, so we have $3$ doubling periods in $1$ hour ($60$ minutes).
First Doubling:
$500 \times 2 = 1000$
Second Doubling:
$1000 \times 2 = 2000$
Third Doubling:
$2000 \times 2 = 4000$
Therefore, the number of bacteria after $1$ hour is $4000$.

Key Concept: Pollination, Genetic Material, Zygote Formation

a) No seed formation and risk to species continuity
[Solution Description] Pollination involves the transfer of pollen grains from the anther to the stigma, and for successful fertilisation, the pollen tube must grow towards the ovule where it releases sperm cells to fertilise the egg. If the pollen tube fails to reach the ovule, fertilisation cannot occur, preventing the formation of a zygote. Without zygote formation, seeds do not develop, halting seed production and consequently affecting the continuation of the plant species as no next generation seeds would be produced.

Key Concept: Sexual Reproduction in Animals

c) Fertilization takes place internally within the female
[Solution Description] In mammals, fertilization is an internal process where the sperm from the male is deposited inside the female’s reproductive system. The sperm then swims towards and fertilizes the egg produced by the female.

Key Concept: Sexual Reproduction in Animals and Plants

Correct Answer option Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
In sexual reproduction, gametes from two parents combine during fertilization. Each parent produces a specialized reproductive cell known as a gamete (sperm or egg in animals; pollen or ovule in plants). These gametes contain only half of the parent’s genetic material. When the male and female gametes fuse during fertilization, they form a zygote with a complete set of genetic instructions, which is necessary for proper development. Therefore, both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Key Concept: Fertilization process

d) In water
[Solution Description] In fish and frogs, fertilization occurs externally in water. Both male and female release their gametes into the water where the sperm meets the egg forming a zygote.

Key Concept: Role of gametes in sexual reproduction

c) Assertion is true, but Reason is false.
[Solution Description] In sexual reproduction, each parent contributes only half of their genetic material through specialized cells called gametes (sperm and egg). This prevents the doubling of genetic instructions in each generation. Therefore, the assertion is true as it correctly describes the role of gametes. However, the reason given states that each parent passes all their genetic material, which contradicts the concept of gametes carrying only half the genetic material. Thus, the reason is false.

Key Concept: Gamete specialization, Sexual reproduction in animals

b) Sperm cells are motile, while egg cells provide nutrients for development
[Solution Description] Sperm and egg cells are highly specialized for their respective roles in mammalian reproduction. Sperm cells are small and motile, equipped with flagella enabling them to swim towards the egg for fertilization. They are streamlined to travel efficiently through the female reproductive tract. Egg cells, on the other hand, are larger and non-motile, providing nutrients and cellular components necessary for early development post-fertilization. Their size allows them to contain sufficient resources needed for the initial stages of growth after fertilization occurs.

Key Concept: Genetic material transfer in sexual reproduction

d) Due to the combination of genetic material from two parents
[Solution Description] In sexual reproduction, offspring receive half of their genetic material from each parent. The combination of different alleles from two parents creates genetic variation among the offspring. This mixing of genes allows for new traits to appear, contributing to differences between offspring and their parents.

Key Concept: Mechanism of gamete transfer, environment influence

c) Aquatic environments promote external fertilization as they allow easy dispersion of gametes in water.
[Solution Description]
In aquatic environments, many animal species utilize external fertilization, a process where both sperm and eggs are released into the water. This method benefits from the surrounding water medium for several reasons:
– Water facilitates the movement and dispersal of gametes, increasing the likelihood of sperm encountering eggs.
– It enables large numbers of gametes to be released simultaneously, boosting chances of fertilization.
– As water provides a supportive medium, it negates the need for specialized internal structures for fertilization.
Species like fish and amphibians often rely on this method due to these advantageous environmental conditions provided by their aquatic habitats.
Conversely, in terrestrial environments, internal fertilization is more common due to the lack of a fluid medium for gamete transport, necessitating direct transfer mechanisms.
Therefore, the aquatic environment profoundly influences the reliance on external fertilization in many species inhabiting such regions.

Key Concept: Concept of Reproductive Cells in Plants

b) Anther
[Solution Description] In flowering plants, the pollen grains found inside the anther of a flower contain the male gametes.

Key Concept: Special cells for reproduction

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The process of sexual reproduction requires gametes from both parents to combine and form a zygote. Each gamete contains half the genetic material, i.e., haploid number of chromosomes. When they fuse, a diploid zygote is formed, restoring the full set of chromosomes characteristic of the species. This mechanism prevents the doubling of genetic information with each generation. Hence, both the assertion and reason are true statements, and the reason provides an accurate explanation for why gametes contain half the genetic material.

Key Concept: Sexual reproduction in plants

c) Pollen and Ovules
[Solution Description] In sexual reproduction, both male and female gametes are formed with half of the parent’s genetic material. These specialized reproductive cells ensure that the offspring does not receive a double set of genes. In flowering plants, these gametes are pollen grains from the male part and ovules from the female part.

Key Concept: Special cells for reproduction

c) By having male and female parts that produce gametes
[Solution Description] Flowering plants have distinct male and female parts, which produce gametes necessary for sexual reproduction. The male part produces pollen, which contains the male gametes, while the female part produces ovules containing female gametes. Fertilization occurs when pollen reaches an ovule, leading to seed formation.

Key Concept: Pollination

c) Insects
[Solution Description] The process of pollination involves the transfer of pollen grains from the anther of one flower to the stigma of another. This transfer can occur through various agents, such as wind, insects, birds, or animals. Insects are particularly significant in this role due to their interaction with flowers, often attracted by nectar.

Key Concept: Pollination and Fertilisation

a) They carry pollen from the anther of one flower to the stigma of another.
[Solution Description] Insects assist in the transfer of pollen from the male part of one flower to the female part of another flower. This is crucial for fertilisation because it allows the sperm cells within the pollen to reach the ovules in the other flower. Without this transfer, fertilisation may not occur, and seeds would not form.

Key Concept: Seed Dispersal

c) It assists seeds in finding nutrient-rich environments away from the parent plant.
[Solution Description] Animals consume fruits and subsequently excrete the seeds at a distance from the parent plant. This process helps in spreading the plant’s seeds over a larger area. The seeds can then germinate in new locations, reducing competition with the parent plant and increasing the chances of successful reproduction.

Key Concept: Fertilisation, Zygote Formation, Embryo Development

b) Gamete release $\rightarrow$ Fertilization in water $\rightarrow$ Zygote formation $\rightarrow$ Embryo development
[Solution Description] The process begins with the adult male and female releasing their gametes into the water. The sperm then swims towards the egg, leading to external fertilization. This creates a zygote in the aquatic environment. Following this, the zygote undergoes several rounds of cell division (cleavage) while still in the water, progressing to form an embryo. Therefore, the sequence is: Gamete release $\rightarrow$ Fertilization in water $\rightarrow$ Zygote formation $\rightarrow$ Embryo development.

Key Concept: Zygote, Genetic Variability, Reproduction Continuity

c) It introduces genetic variation, increasing adaptability and survival chances
[Solution Description] Sexual reproduction involves the fusion of two distinct gametes, sperm and egg, each contributing half of the genetic material to the offspring. This leads to a combination of different alleles, creating genetic diversity within a population. Such diversity enhances adaptability and survival in changing environments, offering a significant advantage over asexual reproduction, which produces genetically identical offspring with limited ability to adapt to new conditions. Consequently, the presence of varied characteristics increases the likelihood of some individuals surviving adverse changes, ensuring species continuity.

Key Concept: Internal vs External Fertilisation

c) Internal fertilization involves sperm meeting eggs inside the female’s body, while external occurs outside
[Solution Description] Internal fertilization involves the deposition of sperm inside the female’s body, which is common among many terrestrial animals and some aquatic species like mammals and birds. Conversely, external fertilization takes place in the external environment, often in water, where both gametes are released and meet outside the parents’ bodies. This is typical of many fish and amphibians.

Key Concept: Pollution, Ecosystem Impact, Biodiversity Loss

Correct answer option d) Pollution $\rightarrow$ Ecosystem disturbance $\rightarrow$ Resource scarcity $\rightarrow$ Biodiversity loss
[Solution Description] Pollution from industrial waste, agricultural runoff, and plastic debris influences terrestrial and aquatic ecosystems. Pollutants can lead to soil degradation and water contamination. For instance, excess fertilizers in water bodies can cause algal blooms, depleting oxygen levels, and harming aquatic life. On land, soil pollution reduces crop yields, impacting food supply for herbivores. Consequently, predators depending on these herbivores face starvation. This disruption extends through the food chain, reducing biodiversity. Therefore, pollution triggers a cascade starting with ecosystem disturbance, leading to resource scarcity, and culminating in biodiversity loss.

Key Concept: Climate Change, Greenhouse Gases, Global Warming Impact

Correct answer option a) Emission of gases $\rightarrow$ Temperature rise $\rightarrow$ Flooding $\rightarrow$ Human displacement
[Solution Description] The burning of fossil fuels releases greenhouse gases such as carbon dioxide and methane into the atmosphere. These gases trap heat from the sun, leading to an increase in Earth’s average temperature, known as global warming. This warming effect can cause ice caps to melt, resulting in rising sea levels. As a consequence, coastal cities may become flooded, and extreme weather conditions could occur more frequently. Biodiversity is also affected as habitats change; some species may not be able to adapt quickly enough, leading to population declines or extinction. Thus, the sequence starts with emission of gases, followed by temperature rise, habitat alteration, and finally impacts on both biodiversity and human settlements.

Key Concept: Reproduction, Climate Change

c) Assertion is true, but Reason is false.
[Solution Description]
The assertion correctly states that reproduction is essential for the continuation of life on Earth. Without it, the existing populations of organisms would die out without being replaced by new offspring, ultimately leading to the disappearance of life.
However, the reason provided claims that the increase in global temperatures due to climate change enhances the reproduction rates of all species uniformly. This statement is false. While some species may experience increased reproduction rates with slight temperature increases, others might suffer negative impacts on reproductive success. Increased temperature can disrupt ecosystems, alter habitats, and negatively affect species not adapted to warmer conditions, thus having a variable impact rather than a uniform one across all species.
Therefore, while the assertion is true, the reason provided is false.

Key Concept: Pollution, Ecosystem Balance

b) By reducing the availability of essential resources
[Solution Description] Pollution from industrial waste, plastic debris, and agricultural runoff introduces harmful substances into water bodies, disrupting aquatic ecosystems. These pollutants can lead to oxygen depletion, harming fish and other marine organisms. Furthermore, toxic substances accumulate in the food chain, affecting even top predators. As aquatic life struggles, the balance within these ecosystems shifts, with some species declining and others potentially becoming invasive, further destabilizing the environment.

Key Concept: Air Pollution, Climate Change

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
The assertion states that burning fossil fuels increases greenhouse gases, contributing significantly to climate change. This is true because carbon dioxide (CO$_2$), one of the principal greenhouse gases, results from the combustion of coal, oil, and gas, which enhances the greenhouse effect, thus warming the planet.
The reason mentions that air pollution primarily leads to direct crop damage. While it is true that air pollution can affect crops through mechanisms like acid rain or smog reducing photosynthesis, this is not the primary concern associated with air pollution’s contribution to climate change. Thus, while both statements are true individually, the reason does not correctly explain the assertion since the key link between fossil fuel burning and climate impact lies in greenhouse gas emissions more than direct crop damage.
Therefore, both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

Key Concept: Threats to Life on Earth

b) Carbon Dioxide (CO$_2$)
[Solution Description] One of the primary gases that contribute to global warming is carbon dioxide (CO$_2$). When fossil fuels are burned, they release CO$_2$ into the atmosphere. This gas traps heat from the sun, preventing it from escaping back into space, thereby causing Earth’s temperature to rise—a phenomenon known as the greenhouse effect.

Key Concept: Biodiversity Loss

c) Weakens ecological balance
[Solution Description] Biodiversity loss occurs when natural habitats are destroyed or species become extinct. This affects ecosystems because each living thing plays a specific role in maintaining ecological balance. For example, if plants disappear, herbivores that feed on them struggle to survive, leading to a decline in predator populations as well. A decrease in biodiversity weakens nature’s ability to support life and maintain ecosystem stability.

Key Concept: Climate change and Pollution

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that global warming causes the melting of polar ice caps, which results in rising sea levels threatening coastal areas. This is a true statement because as temperatures rise due to global warming, ice caps melt, contributing to higher sea levels.
The reason explains that the main cause of global warming is pollution from burning fossil fuels releasing greenhouse gases such as carbon dioxide. This reason is also true since burning fossil fuels is indeed a significant contributor to the increased concentration of greenhouse gases in the atmosphere.
Moreover, the reason given correctly explains why the assertion happens; the release of greenhouse gases from burning fossil fuels traps more heat in the atmosphere, leading to global warming, which subsequently causes ice cap melting and sea level rise.
Therefore, both the Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.

Key Concept: Pollution, Ozone Layer Recovery, and International Protocols

c) 70 million metric tons
[Solution Description]
The annual reduction in CFC emissions is $10 – 3 = 7$ million metric tons. Over a decade (10 years), the cumulative reduction is $7 \times 10 = 70$ million metric tons.

Key Concept: Effects of burning fossil fuels and global warming

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion is that burning fossil fuels contributes to global warming. This statement is true because when fossil fuels like coal and oil are burned, they release greenhouse gases such as carbon dioxide and methane. These gases have the property of trapping heat in the Earth’s atmosphere, thereby increasing the overall temperature — a phenomenon known as global warming.
The reason provided supports this assertion by explaining the mechanism: the combustion of fossil fuels leads to the release of these greenhouse gases, contributing directly to the heat-trapping effect.
Therefore, both the Assertion and the Reason are true, and the Reason given is indeed the correct explanation for the Assertion.

Key Concept: Concept of Greenhouse Gases and Global Warming

c) Carbon Dioxide
[Solution Description] Burning fossil fuels releases several greenhouse gases, with carbon dioxide ($CO_2$) being a major contributor. Carbon dioxide is known for its ability to trap heat in the Earth’s atmosphere, leading to an increase in global temperatures, which is a significant factor in global warming.

Key Concept: Climate change consequences

c) Melting of polar ice caps
[Solution Description] Burning fossil fuels releases excess carbon dioxide, contributing to climate change. One direct consequence of this process is the melting of polar ice caps, which results in rising sea levels and potential flooding.

Key Concept: Pollution and Ecosystems

c) Decreases resource availability and causes additional stress
[Solution Description] Pollution adds further stress to ecosystems already weakened by deforestation. Air pollutants can inhibit plant growth, while water and soil pollutants degrade the quality of essential resources needed by remaining plants and animals. These combined stresses reduce biodiversity even further, potentially leading to ecosystem collapse. The compounded negative effects from both pollution and deforestation make it difficult for ecosystems to recover and maintain balance.

Key Concept: Deforestation, Ecosystem Disturbance, Biodiversity

b) It destroys habitats leading to reduced biodiversity
[Solution Description] Deforestation results in habitat loss, which directly affects plant and animal species that reside in those habitats. Without their natural environment, these species struggle to find food, reproduce, and survive, leading to a decline in population or even extinction. This loss of species reduces biodiversity, which weakens ecosystem resilience by diminishing ecological roles such as pollination, seed dispersal, and nutrient cycling. Consequently, the overall health of the ecosystem degrades, making it more vulnerable to environmental changes and reducing its ability to support life.

Key Concept: Deforestation and Habitat Destruction

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
[Solution Description]
The assertion states that “Deforestation leads to increased carbon dioxide levels in the atmosphere.” This is true because when trees are cut down, they can no longer absorb carbon dioxide. Furthermore, if these trees are burned or decay, the stored carbon is released back into the atmosphere as carbon dioxide.
The reason given is “Trees absorb carbon dioxide during photosynthesis, reducing atmospheric carbon dioxide.” This is also true. Photosynthesis involves the absorption of carbon dioxide by plants to produce glucose and oxygen, thereby reducing the amount of carbon dioxide in the atmosphere.
Because both statements are true and the reason correctly explains why deforestation causes an increase in atmospheric carbon dioxide, the correct answer is option a).

Key Concept: Climate Change

Correct Answer option a) Carbon dioxide
[Solution Description] When fossil fuels like coal and oil are burned, they release greenhouse gases, primarily carbon dioxide, into the atmosphere. This contributes significantly to global warming.

Key Concept: Water Pollution Effects

Correct Answer option c) Habitat destruction for fish
[Solution Description] Plastic waste in water bodies poses significant threats to aquatic life. Animals may ingest plastics, mistaking them for food, which can lead to choking, entanglement, or death due to digestive blockages.

Key Concept: Pollution, Global Warming, Ecosystem Impact

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.
[Solution Description]
In this Assertion-Reason question, we need to analyze both the assertion and the reason provided.
The assertion states that the burning of fossil fuels contributes significantly to air pollution and accelerates climate change by increasing greenhouse gases in the atmosphere. This statement is correct because when fossil fuels like coal and oil are burned, they release carbon dioxide and other pollutants into the atmosphere. These gases trap heat, contributing to the greenhouse effect and leading to global warming. Therefore, the assertion is true.
The reason states that climate change leads to habitat destruction, which is one of the causes of biodiversity loss. This statement is also correct. As global temperatures rise due to climate change, ecosystems can be disrupted. For instance, increased temperatures can lead to melting ice caps, rising sea levels, and altered weather patterns, all of which can destroy habitats and thus contribute to a loss of biodiversity. Therefore, the reason is also true.
However, while both statements are true, the reason provided is about the effects of climate change on ecosystems, not directly explaining how the burning of fossil fuels specifically increases greenhouse gases, which was the focus of the assertion. Thus, the reason, although true, is not the direct explanation for the assertion.
Hence, the correct option is that both the assertion and reason are true, but the reason is NOT the correct explanation of the assertion.