Exercise Questions and Answers
Q1: What is one major reason Mars cannot currently support life like Earth?
(i) It has too many volcanoes.
(ii) It is too close to the Sun.
(iii) It lacks a thick atmosphere and liquid water.
(iv) Its magnetic field is too strong.
A1: Mars cannot support life like Earth because it lacks a thick atmosphere and liquid water, essential for life as we know it. Its thin atmosphere (100 times thinner than Earthβs) and position at the edge of the habitable zone limit liquid water availability (Pages 6-7).
Answer: (iii) It lacks a thick atmosphere and liquid water.
Q2: Which of these is an example of geodiversity?
(i) Variety of bird chirping in a forest.
(ii) Different landforms like mountains, valleys, and deserts.
(iii) Changing weather during monsoons.
(iv) Number of different types of fish in a pond.
A2: Geodiversity refers to the variety of landforms, rocks, and soils. Different landforms like mountains, valleys, and deserts are examples of geodiversity, as they create unique habitats (Page 10, Fig. 13.9).
Answer: (ii) Different landforms like mountains, valleys, and deserts.
Q3: If the Earth were smaller with the same density, what might happen to its atmosphere?
(i) It would become thicker and hotter.
(ii) It would escape into space due to weaker gravity.
(iii) It would become frozen.
(iv) It would cause stronger winds.
A3: A smaller Earth with the same density would have weaker gravity, unable to retain atmospheric gases, causing them to escape into space, as seen with Mars (Page 7).
Answer: (ii) It would escape into space due to weaker gravity.
Q4: In sexual reproduction, why are offspring different from their parents?
(i) They grow in different climates.
(ii) They eat different food.
(iii) They acquire new instructions after birth.
(iv) They get mixed instructions (genes) from both parents.
A4: Offspring in sexual reproduction differ from parents because they receive a mix of genetic instructions (genes) from both parents via gametes, creating unique combinations of traits (Page 13).
Answer: (iv) They get mixed instructions (genes) from both parents.
Q5: You notice tiny green plants growing on cracks on your school wall after the monsoon. Where do you think the seeds came from? What conditions helped these plants grow there?
A5:
- Seed origin: Seeds likely came from nearby plants, carried by wind, birds, or animals (e.g., birds eating fruits and excreting seeds). They settled in wall cracks (Page 13).
- Conditions for growth: Monsoon rains provided water, and cracks retained moisture and soil particles. Sunlight and nutrients in the cracks supported seed germination and growth, as learned in seed germination studies (Page 13).
Answer: Seeds were carried by wind, birds, or animals. Monsoon water, retained moisture, sunlight, and nutrients in cracks helped plants grow.
Q6: 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?
A6:
- Local climate: Deforestation reduces trees that absorb carbon dioxide and produce oxygen, increasing local temperatures (less shade) and altering rainfall patterns due to reduced transpiration (Page 10).
- Biodiversity: Loss of forest habitat displaces or endangers animals, plants, and microbes, reducing species diversity and disrupting food webs (e.g., herbivores lose food, affecting predators) (Page 14).
- Water availability/quality: Fewer trees lead to soil erosion, reducing water retention and increasing runoff, which lowers groundwater levels. Runoff may carry pollutants from construction, degrading water quality in nearby rivers or lakes (Pages 10, 15).
Answer: Deforestation raises temperatures, alters rainfall, reduces biodiversity by displacing species, lowers groundwater due to erosion, and degrades water quality with pollutants.
Q7: 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?
A7: While Earth has experienced natural climate changes over millions of years (e.g., ice ages), todayβs global warming is different because it is primarily driven by human activities, like burning fossil fuels, which release excessive greenhouse gases (carbon dioxide, methane). These gases intensify the greenhouse effect, causing rapid warming, melting ice caps, rising sea levels, and extreme weather, unlike slower natural changes. Deforestation and pollution further exacerbate this, threatening ecosystems and biodiversity (Pages 14-15, Chapter 12). The Paris Agreement (2015) highlights the urgency to limit warming to 1.5Β°C, but current efforts are insufficient, making human-induced climate change a unique and urgent crisis (Page 15).
Answer: Todayβs global warming is human-driven, caused by fossil fuel emissions and deforestation, leading to rapid, severe changes unlike slow natural climate shifts, threatening ecosystems and requiring urgent action.
Q8. Imagine Earthβs magnetic field suddenly disappeared. What kinds of problems could arise for life on Earth? Explain.
A8: The Earthβs magnetic field acts like a protective shield. If it suddenly disappeared, these problems could arise:
1. Radiation from the Sun (Solar Wind)
- The magnetic field deflects charged particles from the Sun (solar wind).
- Without it, these harmful particles would directly strike Earthβs atmosphere.
- This could increase exposure to radiation, affecting humans, animals, and plants (higher risks of cancer, DNA damage).
2. Loss of Atmosphere
- Over long times, solar wind could strip away Earthβs atmosphere, just like it happened on Mars.
- This would reduce oxygen and make Earth less habitable.
3. Disruption of Technology
- Satellites and communication systems rely on protection from magnetic shielding.
- Without it, solar storms could cause power grid failures, GPS errors, and satellite damage.
4. Auroras Everywhere
- Normally, auroras (Northern and Southern Lights) are limited to polar regions where charged particles interact with the atmosphere.
- Without a magnetic field, auroras could appear across the globe β beautiful, but a sign of dangerous solar radiation.
5. Navigation Problems
- Many animals (like birds, turtles, and even bees) use Earthβs magnetic field to migrate.
- Without it, their navigation systems would fail, disturbing ecosystems.
Q9. 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?
A9: Letβs imagine we are building a human settlement on Mars. To make it habitable, weβd need to recreate some key Earth-like conditions:
Three things needed:
- Breathable Atmosphere
- Mars has a very thin atmosphere, made mostly of carbon dioxide (COβ).
- We need to create enough oxygen for humans to breathe, and maintain air pressure similar to Earth.
- Liquid Water Supply
- Water is essential for drinking, farming, hygiene, and producing oxygen + rocket fuel (via electrolysis).
- On Mars, water exists mostly as ice, so weβd need systems to extract, melt, and purify it.
- Suitable Temperature & Protection
- Mars is extremely cold (average β60 Β°C) and has no strong magnetic field to protect against harmful solar radiation.
- Weβd need insulated habitats, greenhouses, and radiation shielding (underground bases or domes with protective layers).
Hardest to Replicate- The hardest to recreate is a protective atmosphere + magnetic shielding.
Reason:
- Oxygen can be produced (from COβ or water) with technology.
- Water can be extracted from Martian ice.
- But creating a thick, stable atmosphere with radiation protection requires altering the entire Martian environment (a huge task, called terraforming).
- Without this shield, humans must live in sealed domes or underground, relying on artificial systems.
Q10. 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.
A10: What could be causing the change?
- Global Climate Change: Rising greenhouse gases (like COβ, methane) trap heat, leading to higher temperatures and disturbed rainfall patterns.
- Local Causes:
- Cutting down trees (deforestation) reduces rainfall and increases heat.
- Overuse of groundwater and poor farming practices dry up soil.
- Pollution from industries or vehicles can also affect local weather.
Two ways the village could adapt:
- Water Management & Conservation
- Build rainwater harvesting systems, ponds, or check dams to store rain when it does fall.
- Use drip irrigation and water-efficient crops to reduce wastage.
- Climate-Resilient Farming
- Shift to drought-resistant or short-duration crops that need less water.
- Practice crop diversification so that even if rains fail, some crops survive.
- Plant more trees (agroforestry) to cool the local environment and improve rainfall.
Q11. If there were no atmosphere on the Earth, would it affect life, temperature, and water on the planet? Explain.
A11: Yes , if Earth had no atmosphere, it would affect life, temperature, and water very severely.
Effect on Life
- The atmosphere provides oxygen for breathing and carbon dioxide for plants.
- Without it, no plants, animals, or humans could survive.
- Harmful solar radiation (UV rays, cosmic rays) would directly hit Earth, making it impossible for life to exist on the surface.
Effect on Temperature
- The atmosphere traps heat through the greenhouse effect, keeping Earth warm.
- Without it, daytime temperatures would become extremely hot (like the Moon, ~120 Β°C in sunlight) and nights extremely cold (β170 Β°C).
- This huge fluctuation would make Earth unlivable.
Effect on Water
- The atmosphere helps maintain water in liquid form by controlling pressure and temperature.
- Without it, liquid water would boil away or freeze, leaving Earth dry and barren.
Q12. Discuss five examples of vegetative propagation.
A12: Five Examples of Vegetative Propagation:
- Potato (Stem Tubers)
- New potato plants grow from the “eyes” (buds) on the tuber.
- Farmers use pieces of potato with eyes for planting.
- Onion & Garlic (Bulbs)
- Each bulb contains a short stem and fleshy leaves.
- When planted, the bulb grows into a new plant.
- Ginger & Turmeric (Rhizomes)
- These underground stems store food and have buds.
- Buds sprout into new shoots and roots, forming new plants.
- Bryophyllum (Leaf Buds)
- Small buds grow on the edges of leaves.
- When leaves fall on soil, the buds grow into new plants.
- Sugarcane (Stem Cuttings / Setts)
- Sugarcane stems have nodes with buds.
- Farmers cut the stem into pieces and plant them; each node can grow into a new plant.