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Class 8 Science Chapter 13 Our Home Earth A Unique Life Sustaining Planet Extra Questions
Class 8 Science Chapter 13 Extra Questions on Our Home Earth A Unique Life Sustaining Planet
Our Home Earth A Unique Life Sustaining Planet Class 8 Very Short Question Answer
Question 1.
Why is the Earth’s crust compared to the skin of an apple?
Answer:
The Earth’s crust is very thin compared to its total size, just like the skin of an apple compared to the entire fruit.
Question 2.
What is the Goldilocks zone and why is it important?
Answer:
The Goldilocks zone is the region around the Sun where liquid water can exist. It is important because liquid water is essential for life.
Question 3.
Which planet is called Earth’s sister planet and why?
Answer:
Venus is called Earth’s sister planet due to its similar size and structure, though its conditions are very different.
Question 4.
Why is the magnetic field called a protective shield of the Earth? (Competency Based Que.)
Answer:
The magnetic field deflects harmful charged particles from the Sun and cosmic rays, preventing them from reaching the surface.
Question 5.
What is the biosphere?
Answer:
The biosphere is the part of the Earth where all living organisms exist, interacting with air, water and land.
Question 6.
What is the role of water vapor in maintaining weather?
Answer:
Water vapor forms clouds, brings rainfall and helps regulate the water cycle, which is essential for life and farming.
Question 7.
What is the role of gametes in sexual reproduction?
Answer:
Gametes are special reproductive cells that carry half the genetic material of parents. When a male and female gamete fuse, they form a zygote with a complete set of chromosomes.
Question 8.
Why is sexual reproduction considered better for variations than asexual reproduction?
Answer:
Sexual reproduction combines genetic material from two parents, resulting in variations that help species adapt to changing environments.
Question 9.
What is the function of the zygote?
Answer:
The zygote is the first cell formed after fertilisation. It divides repeatedly and develops into an embryo.
Our Home Earth A Unique Life Sustaining Planet Class 8 Short Question Answer
Question 1.
How does Earth’s size affect its ability to support life?
Answer:
The size of Earth provides the perfect gravity to hold the atmosphere. If Earth were smaller, gases would escape into space as on Mercury. If it were larger, its gravity would be too strong, making conditions unbearable for life.
Question 2.
Explain how air, water and sunlight together support life.
Answer:
Air provides oxygen for animals and carbon dioxide for plants. Water supports life by hydrating organisms, helping in food production and regulating temperature. Sunlight provides energy for photosynthesis and warmth to maintain suitable living conditions.
Question 3.
What is geodiversity and why is it important?
Answer:
Geodiversity refers to the variety of landforms, rocks, soils and natural processes that shape them. It provides different habitats and resources like minerals and fertile soil that support various life forms.
Question 4.
How do satellites help in understanding Earth’s environment?
Answer:
Satellites take detailed images that reveal changes in weather, vegetation, oceans and pollution. They help monitor disasters like storms and oil spills and provide data for climate and environmental studies.
Question 5.
How is the greenhouse effect on Venus different from that on Earth?
Answer:
On Earth, the greenhouse effect is moderate and supports life. On Venus, a thick layer of carbon dioxide traps almost all heat, creating extreme surface temperatures that make the planet uninhabitable.
Question 6.
Why do birds lay eggs outside the female body, while humans develop embryos inside? (Competency Based Que.)
Answer:
Birds have evolved to lay fertilised eggs with protective shells, where the embryo develops outside. Humans, being mammals, have internal development where the embryo grows inside the mother’s uterus for better nourishment and protection.
Question 7.
How do pollinating agents benefit plants?
Answer:
Pollinating agents such as insects, birds, wind and water carry pollen grains to the stigma, ensuring fertilisation and the production of seeds for the next generation.
Question 8.
(i) Why are offspring from the same parents not identical?
(ii) How does sexual reproduction cause variations?
Answer:
(i) Offspring from the same parents inherit different gene combinations due to random mixing of genetic material.
(ii) Fusion of gametes from two parents introduces new genetic instructions, creating variations.
Question 9.
(i) Why is sexual reproduction considered better for the survival of species?
(ii) Give one example where variations are useful.
Answer:
(i) Sexual reproduction creates genetic variations that help organisms adapt to environmental changes.
(ii) Variation in crop plants helps them resist diseases and pests.
Our Home Earth A Unique Life Sustaining Planet Class 8 Long Question Answer
Question 1.
(i) Explain the process of sexual reproduction in humans.
(ii) Why do siblings have similarities and differences?
Answer:
(i) The male reproductive system produces sperms and the female reproductive system produces eggs. A sperm fuses with an egg in the fallopian tube to form a zygote. The zygote divides and becomes an embryo, which grows in the uterus until birth.
(ii) Siblings inherit genes from both parents, leading to similarities, but gene combinations differ, causing variations.
Question 2.
Describe the process of sexual reproduction in humans.
Answer:
The male reproductive system produces sperms, while the female reproductive system produces eggs. During fertilisation, a sperm and egg fuse in the fallopian tube to form a zygote. The zygote undergoes cell division and forms an embryo, which implants in the uterus and develops until birth.
Question 3.
(i) What is fertilisation?
(ii) Explain the process of fertilisation in flowering plants.
(iii) What happens to the ovule and ovary after fertilisation?
Answer:
(i) Fertilisation is the process where the male gamete fuses with the female gamete to form a zygote. This marks the beginning of a new individual.
(ii) In flowering plants, after pollination, the pollen grain germinates on the stigma and forms a pollen tube. This tube grows through the style and carries the male gamete to the ovule inside the ovary. The male gamete fuses with the egg cell (female gamete) present in the ovule, resulting in the formation of a zygote.
(iii) After fertilisation, the ovule develops into a seed which contains the embryo, while the ovary grows and transforms into a fruit to protect the seeds.
Question 4.
Last Sunday, Aarav was watching news about global warming and noticed that the polar ice caps are melting faster than before. His elder sister explained to him that the increase in greenhouse gases is responsible for this change. Aarav became curious and asked his sister about the role of greenhouse gases in maintaining life on Earth.
(i) What is the greenhouse effect and how is it useful for life on Earth?
(ii) Mention the values shown by Aarav’s sister.
Answer:
(i) The greenhouse effect is a natural process where gases like carbon dioxide and water vapor trap heat in the atmosphere, keeping Earth warm and suitable for life. Without it, Earth would be too cold for survival.
(ii) Aarav’s sister shows awareness about environmental issues and a caring attitude by explaining scientific concepts to him.
Question 5.
Ritu was in her garden and saw a honeybee sitting on a flower. She observed that the bee moved to another flower while carrying some yellow dust on its legs. Curious, she asked her mother why bees visit flowers and how they help plants reproduce. (Competency Based Que.)
(i) Explain how bees help in pollination.
(ii) What values are represented by Ritu here?
Answer:
(i) Bees carry pollen grains from the anther of one flower to the stigma of another. This process of transferring pollen is called pollination, which helps in fertilisation and seed formation.
(ii) Ritu shows curiosity, observation skills and interest in understanding nature.
Our Home Earth A Unique Life Sustaining Planet Class 8 Case Based Questions
Question 1.
The figure below shows a city with heavy traffic, factories emitting smoke and a thick layer of smog. Residents complain of irritation in eyes, breathing difficulties and cough. Doctors reported a rise in asthma and lung-related problems. (Competency Based Que.)
(i) Identify the main pollutants present in the smoke from factories and vehicles.
(ii) State any two harmful effects of smog on human health.
(iii) Suggest two ways to reduce air pollution in the city.
(iv) Name the law in India that provides the right to a clean environment.
Answer:
(i) Carbon monoxide, sulphur dioxide, nitrogen oxides and particulate matter.
(ii) Causes respiratory problems, irritation in eyes and asthma.
(iii) Using public transport, planting trees, using CNG/electric vehicles and installing filters in chimneys.
(iv) The Air (Prevention and Control of Pollution) Act, 1981.
Question 2.
The figure shows farmland where the farmer relies heavily on chemical fertilizers and pesticides to increase crop yield. With time, the excessive use of these chemicals has degraded soil fertility, killed beneficial microorganisms and reduced the natural nutrients present in the soil. Villagers living nearby report contamination of groundwater due to seepage of harmful chemicals. Crops have started showing signs of reduced growth and the farmer faces economic losses. Environmentalists have suggested using organic manure, crop rotation and vermicomposting as alternatives. Overuse of polythene bags and dumping of plastic waste in fields have further worsened soil quality, preventing proper water drainage and air circulation in the soil.
(i) Mention two harmful effects of using chemical fertilizers and pesticides.
(ii) Suggest any three eco-friendly measures to restore soil fertility.
(ii) Why does polythene cause damage to the soil environment?
(iv) Name one practice of sustainable agriculture that can prevent soil pollution.
Answer:
(i) Loss of soil fertility, contamination of groundwater and death of soil organisms.
(ii) Use of organic fertilisers (manure, compost), bio-pesticides and crop rotation.
(iii) Polythene blocks soil pores, reduces aeration and prevents water absorption, damaging soil health.
(iv) Organic farming or vermicomposting.
Skill Based Questions
Question 1.
Two identical plants are kept in sunlight, one in open air, the other under a transparent glass jar.
Thermometers show higher temperature inside the jar. (Knowledge Skill)
(i) Why is the temperature inside the glass jar higher than that of the uncovered plant pot, even though both receive the same sunlight?
(ii) How is this setup similar to the greenhouse effect occurring on Earth?
(iii) If the glass jar was made of black opaque material instead of transparent glass, what would be the possible outcome for the plant’s growth and temperature?
Our Home Earth A Unique Life Sustaining Planet Extra Questions for Practice
Very Short Answer Type Questions
Question 1.
What would happen if all decomposers vanished from Earth?
Question 2.
Why can Earth retain an atmosphere while Mercury cannot?
Question 3.
Why do seeds need to travel far from the parent plant?
Short Answer Type Questions
Question 1.
How does geodiversity contribute to life on Earth beyond just “landforms”?
Question 2.
Why is the Earth’s position in the solar system often compared to a ‘Goldilocks Zone’?
Question 3.
Compare how a greenhouse and Earth’s atmosphere trap heat, but differ in how they work.
Long Answer Type Question
Question 1.
How does Earth act like a connected team of systems to support life? Discuss using air, water, soil, sunlight and living organisms.