SCIENCE CLASS- 8

CHAPTER-13 (Our Home: Earth, a Unique Life Sustaining Planet)

Question 1. What is one major reason Mars cannot currently support life like Earth?

Answer: (iii) It lacks a thick atmosphere and liquid water.

Explanation:

Life as we know it requires liquid water and a protective atmosphere. Mars has a very thin atmosphere and very little liquid water on its surface. Therefore, it cannot currently support life like Earth.

Question 2. Which of these is an example of geodiversity?

Answer: (ii) Different landforms like mountains, valleys, and deserts.

Explanation:

Geodiversity refers to the variety of geological features such as rocks, mountains, valleys, rivers, deserts, and landforms present on Earth.

Question 3. If the Earth were smaller with the same density, what might happen to its atmosphere?

Answer: (ii) It would escape into space due to weaker gravity.

Explanation:

A smaller Earth would have less mass and weaker gravitational force. The weaker gravity would be less capable of holding atmospheric gases, causing much of the atmosphere to escape into space.

Question 4. In sexual reproduction, why are offspring different from their parents?

Answer: (iv) They get mixed instructions (genes) from both parents.

Explanation:

In sexual reproduction, the offspring inherit genes from both parents. The combination of these genes creates variations, making offspring different from their parents.

Question 5. You notice tiny green plants growing in cracks of your school wall after the monsoon. Where do you think the seeds came from? What conditions helped these plants grow there?

Answer:

The seeds may have reached the wall cracks through:

• Wind
• Birds
• Insects
• Rainwater

Conditions that helped them grow:

• Availability of moisture after monsoon.
• Presence of dust and soil particles in cracks.
• Sufficient sunlight.
• Suitable temperature.

These conditions allowed the seeds to germinate and grow into small plants.

Question 6. A city has recently cut down a large patch of forest to build new roads and buildings. Discuss the possible effects this could have on the local climate and biodiversity. How might this affect water availability or quality in the area?

Answer:

Cutting down forests can have several harmful effects:

Effects on Local Climate

• Increase in temperature.
• Reduced rainfall.
• Lower humidity.
• More frequent heat waves.

Effects on Biodiversity

• Loss of habitat for animals and birds.
• Reduction in plant species.
• Disturbance of food chains.
• Possible extinction of local species.

Effects on Water Availability and Quality

• Reduced groundwater recharge.
• Increased soil erosion.
• More flooding during rains.
• Pollution of rivers and ponds due to soil runoff.

Therefore, deforestation negatively affects climate, biodiversity and water resources.

Question 7. A friend says, "The Earth has always had climate changes in the past, so today's global warming is nothing new." How would you respond using what you've learnt in this and other chapters of your science book?

Answer:

It is true that Earth's climate has changed naturally in the past. However, today's global warming is different because it is occurring much faster and is mainly caused by human activities.

Major causes include:

• Burning of fossil fuels.
• Deforestation.
• Industrial emissions.
• Increase in greenhouse gases such as carbon dioxide.

Scientific studies show that the current rate of warming is much higher than many natural climate changes in Earth's history.

Therefore, global warming is a serious issue that requires immediate action.

Question 8. Imagine Earth's magnetic field suddenly disappeared. What kinds of problems could arise for life on Earth? Explain.

Answer:

Earth's magnetic field protects us from harmful charged particles coming from the Sun.

If it disappeared:

• More harmful solar radiation would reach Earth.
• Communication and satellite systems could fail.
• Navigation systems would be affected.
• Many animals that use Earth's magnetic field for migration could become disoriented.
• The atmosphere could gradually be stripped away by solar wind.

Therefore, Earth's magnetic field is essential for protecting life.

Question 9. You are tasked with designing a new settlement for humans on Mars. Name three things you would need to recreate from Earth to support human life there. Which of these do you think is the hardest to replicate, and why?

Answer:

Three important things that must be recreated on Mars are:

• Breathable atmosphere containing oxygen.
• Liquid water supply.
• Suitable temperature and shelter.

Hardest to replicate:

A breathable atmosphere would be the hardest to replicate.

Reason:

Mars has a very thin atmosphere mainly composed of carbon dioxide. Creating and maintaining a large oxygen-rich atmosphere over an entire settlement would require advanced technology and enormous resources.

Question 10. In a village, the temperature has been increasing and rainfall has become unpredictable over the past few years. What could be causing this change? Suggest two ways the village could adapt to these new conditions.

Answer:

Possible Causes:

• Climate change.
• Deforestation.
• Increase in greenhouse gases.
• Changes in local land use.

Ways to Adapt:

1. Practice rainwater harvesting to store water.
2. Grow drought-resistant crop varieties.

These measures can help the village cope with changing climate conditions.

Question 11. If there were no atmosphere on the Earth, how would it affect life, temperature, and water on the planet? Explain.

Answer:

Effect on Life

• No oxygen for breathing.
• Life as we know it would not exist.

Effect on Temperature

• Extremely hot during the day.
• Extremely cold during the night.
• No atmosphere to regulate temperature.

Effect on Water

• Liquid water would not remain stable.
• Most water would evaporate into space or freeze.

Therefore, the atmosphere is essential for life, temperature balance and the water cycle.

Question 12. Discuss five examples of vegetative propagation.

Answer:

Vegetative propagation is a method of asexual reproduction in which new plants grow from vegetative parts such as roots, stems or leaves.

Examples:

1. Potato – grows from underground stem tubers.
2. Ginger – grows from underground stems called rhizomes.
3. Onion – grows from bulbs.
4. Sugarcane – grows from stem cuttings.
5. Bryophyllum – produces new plants from leaf margins.

Advantages of Vegetative Propagation:

• Produces plants quickly.
• New plants are identical to the parent plant.
• Useful for plants that do not produce viable seeds.
• Helps maintain desirable characteristics.

Key Concepts from the Chapter

• Mars lacks a thick atmosphere and stable liquid water.
• Geodiversity includes mountains, valleys, rivers and deserts.
• Gravity helps Earth retain its atmosphere.
• Genetic variation arises through sexual reproduction.
• Forests help maintain climate and biodiversity.
• Earth's magnetic field protects life from harmful solar radiation.
• Climate change is accelerated by human activities.
• The atmosphere is essential for life, water and temperature regulation.
• Vegetative propagation is a form of asexual reproduction.