Our Home: Earth, a Unique Life Sustaining Planet — Mastery

Q1. The cover image of Chapter 13 was taken by an Indian Space Research Organisation (ISRO) Earth Observation Satellite. The image was made by combining nearly

• A. 30 smaller images
• B. 3000 smaller images
• C. 300000 smaller images
• D. 3 smaller images

Q2. The ISRO Earth-observation image on the cover is described as a 'false colour image'. The chapter explains that scientists use false colours to

• A. Make satellite photographs look more artistic
• B. Hide actual data from common viewers
• C. Show different types of information using different colours
• D. Replace real Earth photographs because real photos are not possible

Q3. The chapter calls the Earth's distance from the Sun 'just right' for life. The word 'just right' specifically refers to the fact that

• A. Day and night have equal length throughout the year
• B. Earth's gravity is exactly 9.8 m/s²
• C. Earth rotates from west to east
• D. Temperature allows water to exist in liquid form

Q4. Scientists think Mars may have once supported simple life because

• A. Liquid water has been continuously available on Mars from the past until now
• B. Several spacecrafts and rovers have explored Mars but no proof of life yet has been found, while clues suggest that in the past Mars may have had liquid water — maybe even some lakes — and conditions that could support simple life forms
• C. Animals like dogs have been found alive in Martian soil
• D. Mars is the closest planet to the Sun and is the hottest

Q5. India's Mangalyaan (Mars Orbiter Mission), launched in 2013, was a big step in exploring Mars. According to the chapter, Mangalyaan showed the world that India could

• A. Carry humans to Mars in a single mission
• B. Do space science with smart, low-cost technology, and helped bring Mars closer to us
• C. Replace ISRO with private companies for Mars exploration
• D. Mine minerals from Mars and bring them to Earth

Q6. In the chapter, the term 'atmosphere' is best described as

• A. All the solid matter inside the Earth
• B. Only the layer of ozone above the Earth
• C. All the gases that surround the Earth
• D. Only the clouds in the sky

Q7. The chapter notes that soil may look like simple dirt but it is actually rich in nutrients that plants need. Two such nutrients explicitly named in the chapter are

• A. Carbon and helium
• B. Oxygen and chlorine
• C. Nitrogen and potassium
• D. Iron and silver

Q8. The chapter says that some of the Sun's heat is trapped by the atmosphere due to the greenhouse effect. For sustaining life on Earth, this effect is

• A. Mild but useful — it keeps the temperature just high enough for water to remain liquid
• B. Extremely harmful and should be removed completely
• C. Completely absent on Earth
• D. Only seen on planets with no atmosphere

Q9. The chapter recalls from Chapter 7 (Class 7) that water plays a key role in plants by

• A. Producing electric currents in the leaves
• B. Reflecting sunlight back to space to cool the plant
• C. Being a good solvent that transports nutrients from soil to leaves
• D. Acting as a magnetic field for the plant

Q10. Water vapour in the air forms clouds and brings rain or snow, refilling rivers, lakes and underground water. According to the chapter, the kinds of plants and animals that can live in a place are most strongly affected by

• A. The colour of the local soil
• B. The shape of nearby buildings
• C. The number of vehicles in the area
• D. Rainfall in that place

Q11. Single-celled organisms like bacteria and amoeba reproduce asexually by

• A. Dividing into two identical individuals
• B. Producing pollen grains
• C. Combining male and female gametes
• D. Forming a zygote inside a fruit

Q12. Planaria, a type of flatworm mentioned in the chapter, is interesting to scientists studying regeneration because it

• A. Lays large eggs like a hen
• B. Has bones that are crushed by gravity
• C. Can regrow from a fragment of its body
• D. Pollinates flowers in the Sundarbans

Q13. Priya places a stem cutting of a money plant in a glass container of water. Roots and tiny leaves soon appear. This is an example of

• A. Sexual reproduction in animals
• B. Vegetative propagation, a form of asexual reproduction
• C. Pollination by insects
• D. Fertilisation in birds

Q14. According to Fig. 13.11 of the chapter, two examples of vegetative propagation shown are

• A. Mango seed and apple seed
• B. Banyan and peepal
• C. Coconut and tamarind
• D. Ginger and potato

Q15. In flowering plants, when pollen is carried from the anther of one flower to another flower by wind, insects or animals, the process is specifically called

• A. Germination
• B. Fertilisation
• C. Transpiration
• D. Pollination

Q16. After fertilisation in a flowering plant, the chapter says the zygote becomes the seed and

• A. The fleshy part of the flower around the ovule develops into a fruit
• B. The roots of the plant immediately fall off
• C. The leaves change into pollen grains
• D. The plant stops making any new flowers ever

Q17. In most mammals, including humans, the development of the zygote into an embryo takes place

• A. In water outside the mother's body
• B. Inside the body of the female, where the mother provides all the food and oxygen the baby needs
• C. Inside an egg laid by the mother
• D. On a leaf, after pollination

Q18. The chapter explains that brothers and sisters in the same family can look different from each other because

• A. Each child eats different food after birth
• B. Different children grow in different climates
• C. Each gamete carries a different set of instructions, and instructions from sperm and egg mix in different ways each time
• D. Genes are different in summer and winter children

Q19. Air pollution from factories, vehicles and burning fuels can cause

• A. Increase in Earth's distance from the Sun
• B. Stronger ozone layer above the Earth
• C. Better and safer drinking water for cities
• D. Breathing problems, damage to crops, smog and acid rain

Q20. The chapter says that 'protecting the climate means cutting down on greenhouse gases'. From the options below, the most effective long-term action a city government can take is to

• A. Replace coal-fired power with renewable energy like solar and wind, improve energy use and encourage environmentally friendly travel
• B. Build more coal-based power plants quickly
• C. Cut down forests to make room for new petrol stations
• D. Discourage the use of cycles and public transport

Q21. Ms. Sharma asks her Class 8 students in a school in Rampur for the SINGLE best 'small action' from the chapter that any one of them can start TODAY to reduce pollution and waste. Which of the following best fits the chapter's advice?

• A. Wait until governments pass new laws and then act
• B. Reusing, repairing and recycling items like clothes and plastic, plus small habits like saving energy and water
• C. Throwing away all old clothes and buying only new ones
• D. Cutting trees to build a new playground

Q22. According to the chapter, the harmful chemicals that the Montreal Protocol (1987) reduced — Chlorofluorocarbons (CFCs) — were causing damage to which part of the atmosphere?

• A. The ground-level temperature
• B. The clouds in the troposphere
• C. The ozone layer
• D. The earth's magnetic field

Q23. The chapter says the Earth Summit (1992) led to international efforts on

• A. Outer-space tourism for private companies
• B. Mining of the Moon and Mars
• C. Sports cooperation between countries
• D. Climate change and biodiversity

Q24. A Class 8 student in Ravi's class says, 'If the crust is as thin as an apple's skin, then almost all of Earth is the crust.' Which of the following is the most pedagogically sound response based on the chapter?

• A. The student is right — the entire Earth is the crust
• B. The student has misread the analogy — the crust is the thin outer skin only; the inside is upper mantle, lower mantle, outer core and inner core
• C. The student should be told that the apple analogy is not used in the chapter
• D. The student should be told that crust means the same as biosphere

Q25. Many students think Venus must be cooler than Mercury because Mercury is closer to the Sun. To address this misconception in a Class 8 lesson, the chapter recommends using which key idea?

• A. The size of Venus matters more than distance
• B. Mercury is actually farther from the Sun than Venus
• C. Venus's thick CO₂ atmosphere traps heat through the greenhouse effect, making it hotter than Mercury
• D. Mercury rotates more slowly than Venus, so it stays cold

Q26. A teacher wants students to OBSERVE asexual reproduction (vegetative propagation) at first hand in the classroom. From Activity 13.3, the most appropriate setup is to

• A. Pollinate flowers using a paintbrush and count fruits in a week
• B. Watch a hen hatch chicks from eggs in class
• C. Plant a stem cutting of a money plant in a glass container of water (or moist soil) and observe new roots, stems and leaves daily for several days
• D. Dissect an animal to find sperm and egg cells

Q27. Bhoomi argues that Earth would still support life even WITHOUT a magnetic field, because the ozone layer alone can protect us. Using the chapter's reasoning, the MOST important counter is that

• A. Without a magnetic field, Earth would move closer to the Sun
• B. Without a magnetic field, the cosmic rays and solar wind would reach the atmosphere, damage it and reduce the ozone layer, letting in more UV — so ozone alone is not enough
• C. Without a magnetic field, gravity would disappear and bones would float
• D. Without a magnetic field, water would automatically become saline

Q28. The chapter notes that reproduction does more than produce more of the same kind of living being — it 'also allows for small changes that can help a plant or animal survive better in a new environment'. Which form of reproduction is the chapter pointing to here?

• A. Asexual reproduction, because copies are exact
• B. Vegetative propagation, because it does not need gametes
• C. Sexual reproduction, because mixing of instructions from two parents introduces variation
• D. Binary fission, because it doubles the number of organisms each time

Q29. The chapter's 'Discover, design, and debate' set notes India's Chandrayaan-4 mission bringing back Moon soil samples. If the Moon had water, could plants grow in that soil? The MOST scientifically sound first experiment a Class 8 group could design is to

• A. Send astronauts immediately to settle on the Moon
• B. Take Moon soil samples in a controlled greenhouse on Earth, add water, plant seeds and compare growth with Earth-soil controls under similar light and temperature
• C. Declare plant growth impossible without doing any experiment
• D. Pour acid on Moon soil to test if it dissolves

Q30. Consider the chapter's link between fossil-fuel burning and Earth's life-support system: I. Burning fossil fuels releases extra carbon locked underground for millions of years. II. Earth cannot absorb this extra carbon fast enough, so heat builds up in the atmosphere. III. A small temperature rise can melt ice caps, raise sea levels and cause extreme weather. Which are correct?

• A. I and II only
• B. II and III only
• C. All three
• D. I and III only