NCERT Solutions Class 8 Science Chapter 13 Our Home Earth

Concept used. A planet needs suitable temperature, liquid water and a protective atmosphere for Earth-like life. Mars has a very thin atmosphere and stable liquid water is not present on its surface today. The correct answer is (iii). Mars lacks a thick atmosphere and liquid water.

1. Earth supports life because it has liquid water, a suitable temperature range and a protective atmosphere.
2. Mars is near the edge of the habitable zone, but its atmosphere is much thinner than Earth's atmosphere.
3. A thin atmosphere cannot trap enough heat or protect the surface as effectively as Earth's atmosphere.
4. Liquid water is also not stable on the Martian surface today.
5. Therefore Mars cannot currently support Earth-like life mainly because it lacks a thick atmosphere and liquid water.

Concept used. Geodiversity means the variety of non-living Earth features. It includes landforms, rocks, soils, minerals and surface features. The correct answer is (ii). Mountains, valleys and deserts are landforms, so they show geodiversity.

1. Bird chirping and fish types are related to living organisms.
2. Weather during monsoon is a short-term atmospheric condition.
3. Mountains, valleys and deserts are landforms.
4. Landforms are non-living features of Earth.
5. So different landforms are examples of geodiversity.

Concept used. Gravity is the pull by which a planet holds objects and gases near it. A smaller Earth with the same density would have weaker gravity at its surface. The correct answer is (ii). Weaker gravity would make it difficult for Earth to hold its atmosphere.

1. Earth's atmosphere is made of gases around the planet.
2. These gases do not fly away easily because Earth's gravity pulls them inward.
3. If Earth were much smaller with the same density, its gravity would be weaker.
4. Weaker gravity would not hold atmospheric gases strongly.
5. Over time, many gases could escape into space.

Concept used. In sexual reproduction, two parents contribute genetic instructions. These instructions mix, so the offspring are not exact copies of either parent. The correct answer is (iv). Offspring receive mixed genes from both parents.

1. Asexual reproduction usually involves one parent.
2. Sexual reproduction involves two parents.
3. Each parent contributes genetic instructions to the offspring.
4. These instructions combine in a new way.
5. So the offspring may resemble the parents, but they are not exact copies.

Concept used. Seeds can be dispersed by wind, water, birds, animals or humans. Germination needs moisture, air, suitable temperature and some support for the young plant. The seeds may have been carried by wind, rainwater, birds or animals. Monsoon moisture, trapped soil, air and sunlight helped them grow.

1. Seeds from nearby plants may have reached the wall crack by wind.
2. Rainwater may also have washed small seeds into the crack.
3. Birds or animals may have dropped seeds after eating fruits.
4. Dust, soil particles and decaying matter can collect inside cracks.
5. During the monsoon, the crack stayed moist for many days.
6. The seeds also received air and some sunlight.
7. These conditions allowed the seeds to germinate and grow into tiny plants.

Concept used. Forests influence climate, biodiversity, soil and water. Trees cool the air, provide habitats, hold soil and help water enter the ground. The area may become hotter, drier and less biodiverse. Water availability may fall, and water quality may worsen due to runoff and soil erosion.

1. Trees give shade and cool the surroundings by releasing water vapour.
2. Removing a large forest patch can make the local area hotter.
3. Fewer trees may also reduce local moisture and affect rainfall patterns.
4. Many birds, insects, small animals and microbes lose food and shelter.
5. This reduces biodiversity in the area.
6. Tree roots hold soil and help rainwater soak into the ground.
7. Without roots, more rainwater runs off the surface and carries soil with it.
8. This can reduce groundwater recharge and make nearby water muddy or polluted.

Concept used. Climate can change naturally, but current global warming is strongly increased by human activities such as burning fossil fuels, deforestation and pollution. The rate of change matters. I would say natural climate changes happened before, but today's warming is faster and is mainly linked with human activities that add greenhouse gases.

1. It is true that Earth's climate has changed in the past.
2. But past changes often happened slowly over long periods.
3. Today's global warming is happening quickly compared with many natural changes.
4. Human activities add extra greenhouse gases such as carbon dioxide to the atmosphere.
5. Burning coal, petrol and diesel releases carbon dioxide.
6. Cutting forests removes trees that could absorb carbon dioxide.
7. Extra greenhouse gases trap more heat and disturb Earth's climate balance.
8. So present global warming is not just another ordinary natural change.

Concept used. Earth's magnetic field acts like a shield. It deflects many high-energy charged particles coming from the Sun and space. Life could face stronger harmful radiation, satellite and communication problems, and long-term damage to the atmosphere.

1. The Sun sends out high-energy charged particles.
2. Earth's magnetic field deflects many of these particles.
3. If the magnetic field disappeared, more particles could reach near Earth.
4. This could increase radiation danger for living beings and astronauts.
5. Satellites, communication systems and power grids could be affected.
6. Over long periods, the atmosphere could also become more vulnerable to loss.
7. Since atmosphere protects life and water, this would create serious risks for life.

Concept used. Human life needs breathable air, liquid water, suitable temperature, food, protection from radiation and safe pressure. Mars lacks many of these natural Earth conditions. We must recreate breathable air, liquid water and protected temperature-controlled habitats. The hardest is likely an Earth-like atmosphere because it needs pressure, gases and radiation protection at a huge scale.

1. First, humans need breathable air with enough oxygen.
2. Second, they need liquid water for drinking, hygiene, growing food and many life processes.
3. Third, they need a protected habitat with suitable temperature and pressure.
4. The habitat must also protect people from harmful radiation.
5. Food production would need soil or a growing system, nutrients and light.
6. Among these, an Earth-like atmosphere is hardest to recreate.
7. It must provide pressure, oxygen, heat balance and protection over a large area.

Concept used. Local weather patterns can be affected by climate change, deforestation, pollution and land-use changes. Adaptation means adjusting our practices to reduce harm from these changes. The change may be linked with climate change, tree loss and pollution. The village can store rainwater and grow heat-tolerant or drought-resistant crops.

1. Rising temperature and unpredictable rainfall can be signs of climate change.
2. Human activities such as burning fuels add greenhouse gases to the atmosphere.
3. Cutting trees can also make the local area hotter and drier.
4. Pollution and land-use changes may further disturb the local environment.
5. One adaptation is rainwater harvesting, so water is stored during heavy rains.
6. A second adaptation is growing crops that need less water and tolerate heat better.
7. The village can also use drip irrigation, protect trees and improve soil moisture.

Concept used. The atmosphere supplies gases, protects from harmful radiation, moderates temperature and helps maintain pressure needed for liquid water. Yes. Without the atmosphere, life would not get air or protection, temperatures would become extreme and liquid water would not remain stable.

1. Life would be affected because most organisms need oxygen for respiration.
2. The ozone layer in the atmosphere also blocks much harmful ultraviolet radiation.
3. Temperature would be affected because the atmosphere helps trap some heat.
4. Without it, days could become very hot and nights very cold.
5. Water would be affected because air pressure helps liquid water remain stable.
6. Without an atmosphere, liquid water could evaporate or freeze easily.
7. Clouds and rainfall would also not work normally without atmospheric water vapour.

Concept used. Vegetative propagation is a form of asexual reproduction in plants. A new plant grows from a vegetative part such as a stem, root, leaf, tuber, rhizome, bulb or runner. Examples include money plant stem cutting, potato tuber eyes, ginger rhizome, sugarcane stem cutting and onion bulb.

1. Money plant: A stem cutting with a node can grow roots in water or soil.
2. Potato: The eyes of a potato tuber are buds that can sprout into new plants.
3. Ginger: A piece of rhizome with a bud can grow into a new ginger plant.
4. Sugarcane: Stem cuttings with nodes are planted to grow new sugarcane plants.
5. Onion: The bulb can grow into a new onion plant when planted.
6. In all these cases, the new plant grows from a plant part, not from a seed formed by sexual reproduction.