Discover, Design and Debate — Projects — "Our Home: Earth, a Unique Life Sustaining Planet"

1. 14 marks

   Design an 'Earth Survival Kit' for a tiny model of Earth built for another planet. What must it include, and why, based on everything this chapter says Earth needs to support life?

   Hint. Pull directly from the chapter's own list of what makes Earth habitable — position, size, atmosphere, magnetic field, water.

   ✦ An Earth Survival Kit, based on this chapter, would need: a source of liquid water (since the habitable zone's whole purpose is keeping water liquid), a breathable atmosphere containing oxygen and enough carbon dioxide for plant photosynthesis, a way to trap just enough heat via a mild greenhouse effect (to avoid both freezing and Venus-style overheating), some form of shielding from cosmic rays and solar wind (recreating the role Earth's magnetic field plays), and soil/geosphere materials rich enough in nutrients to support plant growth. Each item directly maps to one of the specific factors — position, size/atmosphere, magnetic field, and geosphere — that this chapter identifies as necessary for Earth to sustain life.

2. 24 marks

   India's Chandrayaan-4 mission plans to bring back lunar soil samples. If the Moon had water, could plants grow in that soil? Design an experiment to explore whether plant growth is possible in Moon soil.

   Hint. Structure the experiment as a comparison, changing one variable (the soil type) while keeping everything else about the growing conditions the same.

   ✦ To test this, you could set up two identical growing trays under the same light, water, and temperature conditions — one with regular Earth soil and one with a sample of lunar soil (real or simulated 'lunar regolith simulant,' since real Moon soil is scarce) — and plant the same type of seeds in each, ensuring both get identical water, sunlight, and air access. By keeping every other factor (light, water, temperature, seed type, air) the same and changing only the soil type, any difference in germination rate, growth speed, or plant health between the two trays could be attributed specifically to differences in the soil itself, such as its nutrient content or texture — testing whether soil is really the limiting factor, given that this chapter states plants also need water, air, sunlight, and the right temperature, not soil alone.

3. 33 marks

   Flowers are often brightly coloured and have a pleasant smell. How do these features help the plant reproduce?

   Hint. Connect these features to the very first step of sexual reproduction in plants — getting pollen to move at all.

   ✦ Bright colours and pleasant smells attract pollinators like insects, birds, and bats to visit the flower, since this is exactly what pollination requires — the chapter states pollen is carried between flowers by wind, insects, or animals. By making themselves noticeable and appealing to these pollinators, flowers increase the chances that pollen will actually be carried from their anther to another flower's ovule, making fertilisation (and ultimately seed and fruit production) far more likely than if the flower were plain and unnoticed.

4. 43 marks

   Why do animals like fish and frogs lay hundreds or even thousands of eggs at a time, while other animals lay only a few? What might be the advantages and disadvantages of laying so many eggs?

   Hint. Connect this to the external-fertilisation strategy the chapter describes for these specific animals, and what risks that strategy carries.

   ✦ Fish and frogs use external fertilisation, releasing eggs and sperm directly into open water where they combine and then develop with no protection from either parent — this leaves both the unfertilised eggs and the developing embryos highly exposed to predators, water currents, and environmental hazards. Laying hundreds or thousands of eggs is an advantage because it increases the chance that at least some offspring survive despite this high exposure and lack of protection. The disadvantage is that producing so many eggs requires significant energy and resources, and most of those eggs or young will likely not survive to adulthood — a very different trade-off from animals that invest heavily in protecting a small number of offspring instead.

5. 53 marks

   Birds like sparrows build nests and care for their eggs and chicks, while reptiles like snakes usually lay their eggs and leave them without protection. How might this difference in parental care affect the chances of survival for the young ones in each case?

   Hint. Weigh direct protection and feeding against how many offspring each strategy can realistically support.

   ✦ Sparrow chicks, protected and fed in a nest by their parents, likely have a higher individual chance of survival, since active parental care can defend eggs and chicks from predators and provide food they couldn't find on their own yet. Snake eggs, left without protection, face much higher individual risk from predators and environmental hazards, but this strategy typically requires less energy investment per egg from the parent, potentially allowing more eggs to be laid overall — meaning the two strategies represent different trade-offs between investing heavily in fewer, better-protected offspring versus producing more offspring with less protection for each.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity — Textbook of Science for Grade 8, Chapter 13 (hecu113.pdf), Reprint 2026-27, pages 210-228. Questions are referenced from the NCERT textbook for identification.