NCERT MCQ Solutions for Class 8 Science Curiosity Chapter 13 Our Home: Earth, a Unique Life Sustaining Planet

The habitable zone, also called the Goldilocks zone, is the distance from a star where conditions are just right for liquid water to exist.
Earth lies in this zone, allowing water to stay mostly in liquid form, which is essential for sustaining life in all forms.

Life on Earth exists on a very thin layer of the crust, like the skin on an apple. This narrow zone contains mountains, forests, oceans and all life forms.
Despite being thin, this layer supports diverse ecosystems and is essential for life to thrive.

Earth appears blue from space because about 70% of its surface is covered by water in the form of oceans, seas and rivers.
This abundant water presence is unique and crucial for sustaining life, making Earth distinct among the known planets.

Oxygen is essential for respiration in humans, animals and many microorganisms. It is part of Earth’s atmosphere and is also released by plants during photosynthesis.
The presence of oxygen in suitable amounts is vital for life to survive on Earth.

The ozone layer, made of O₃ molecules, is located in the Earth’s atmosphere and blocks harmful ultraviolet (UV) rays from the Sun.
These rays can damage living cells and DNA. The ozone layer acts like a protective shield for all life forms on Earth.

Earth’s magnetic field is generated by molten iron in its core and protects the planet by deflecting high-energy particles such as cosmic rays and solar wind. This shielding effect helps prevent damage to the atmosphere and supports life on Earth.

During photosynthesis, plants absorb carbon dioxide and water, and use sunlight to produce food. In this process, they release oxygen as a by-product.
This oxygen is essential for the respiration of living organisms and helps maintain life on Earth.

The atmosphere surrounds Earth with gases like oxygen, nitrogen and carbon dioxide.
It protects life by maintaining temperature, blocking UV rays and enabling respiration. Without this envelope of gases, life as we know it could not survive.

The greenhouse effect is caused by gases like CO₂ trapping heat radiated from Earth’s surface.
This natural process keeps Earth warm enough for water to remain liquid, making the planet habitable. Without it, Earth would be too cold for most life forms.

Although Venus is not the closest to the Sun, it is the hottest planet due to its thick atmosphere filled with CO₂.
This traps heat intensely through the greenhouse effect, making Venus even hotter than Mercury.

Geodiversity refers to the variety of landforms, rocks, soils and minerals.
This diversity supports unique ecosystems and influences climate, water availability and the distribution of species. It plays a key role in shaping life on Earth.

The hydrosphere includes all water on Earth, such as oceans, rivers, lakes and groundwater.
It supports aquatic life, aids in agriculture, and is essential for climate regulation and sustaining living organisms.

The geosphere includes the Earth’s crust, rocks, minerals and soil.
It provides the foundation for terrestrial ecosystems and is the source of nutrients and raw materials required for human activities and plant growth.

Life on Earth is supported by the interaction of air, water, soil, temperature and living organisms.
These systems are interconnected, and any imbalance in one affects the others. This interdependence sustains ecosystems and helps life thrive.

Vegetative propagation is a form of asexual reproduction where new plants grow from parts like roots, stems or leaves.
The new plants are genetically identical to the parent. This method ensures rapid and efficient reproduction without the need for seeds.

Earth is uniquely suited for life because it has liquid water, oxygen-rich air and a temperature range that supports diverse life forms.
These essential conditions result from Earth’s location in the habitable zone and the balance of gases in its atmosphere.

Plants absorb carbon dioxide (CO₂) from the atmosphere during photosynthesis. Using sunlight, they convert CO₂ and water into food and release oxygen.
This process is central to life on Earth and keeps the carbon-oxygen cycle in balance.

The biosphere includes all regions on Earth where life exists — land, water and air. It interacts with the geosphere, hydrosphere and atmosphere to support ecosystems.
This life zone includes humans, animals, plants and microorganisms.

Nitrogen is a major component of amino acids and nucleic acids, which are essential for life. Plants absorb nitrogen from the soil in usable forms and animals obtain it through the food chain.
The nitrogen cycle maintains this balance in ecosystems.

Earth rotates once every 24 hours on its axis. This rotation causes different parts of the planet to face the Sun at different times, resulting in the cycle of day and night.
This natural rhythm regulates temperature and life activities.

The biosphere is the sphere of life. It contains all living organisms — from plants and animals to fungi and bacteria — across land, air and water.
It interacts with the non-living components of Earth to form balanced ecosystems.

Condensation is the process by which water vapor cools and changes into liquid droplets, forming clouds.
This purified water then falls as precipitation. Step in the water cycle as essential for distributing fresh water across the planet.

When greenhouse gases like CO₂ increase beyond natural levels, more heat is trapped in the atmosphere.
This leads to a rise in Earth’s average temperature, known as global warming. This can disturb weather patterns and threaten ecosystems.

Earth’s natural systems include the atmosphere (air), hydrosphere (water), geosphere (land) and biosphere (life). A smartphone network is a man-made system and not a part of Earth’s physical or biological systems .

The Sun provides energy that drives weather, ocean currents and supports photosynthesis.
Nearly all life depends directly or indirectly on solar energy. The Sun as Earth’s primary energy source that sustains ecosystems and natural processes.

Earth’s systems — atmosphere, hydrosphere, lithosphere and biosphere — are interconnected. A change in one affects the others. For example, pollution in air can affect rainfall and soil fertility. 

Plant roots bind the soil, preventing it from being washed away by rain or blown by wind. This helps maintain soil fertility and reduces erosion.
This function as essential in conserving Earth’s natural resources.

Many plants rely on animals like birds or mammals to spread their seeds.
This is an example of interdependence, where living things depend on each other to survive and reproduce.
The chapter includes such relationships as vital to nature’s balance. 

The Earth’s crust is its outermost layer and supports all known life. It is where plants grow, animals roam and humans build.
Although thin compared to Earth’s full volume, the crust contains all terrestrial ecosystems and human civilization.

Earth is special because of its balanced and interconnected systems — air, water, soil and living beings.
Maintaining this harmony is essential for sustaining life. Any imbalance affects the entire system, including humans, plants and animals.