Class 8 Science - Chapter 13 Practice Test

Habitable Zone (Goldilocks Zone): Earth's distance from the Sun provides the perfect temperature for water to exist in a liquid state. Not too hot (like Venus) and not too cold (like Mars).
Right Size and Gravity: Earth has enough gravity to hold onto its atmosphere. If it were smaller (like Mercury), the gases would escape into space. If it were too large, gravity would crush living things.
Magnetic Field: The movement of molten iron in Earth's core creates a magnetic shield. This protects the planet from harmful cosmic rays and solar winds.
Ozone Layer: A layer of three-atom oxygen molecules (O₃) that blocks harmful ultraviolet (UV) rays from the Sun.

Atmosphere: The layer of gases. Contains oxygen for respiration and carbon dioxide for photosynthesis. Also traps heat via the greenhouse effect, keeping Earth warm enough for life.
Hydrosphere: All water on Earth (oceans, rivers, groundwater). Essential for transporting nutrients and regulating temperatures.
Geosphere: The solid parts of the Earth (crust, rocks, soil, minerals). Provides a medium for plant growth and essential nutrients.
Biosphere: All living organisms and the environments they interact with.

Asexual Reproduction: A single parent produces new individuals that are exact copies. Example: Vegetative propagation (planting a stem, root, or leaf), or single-celled microbes dividing.
Sexual Reproduction: Involves two parents (male and female gametes). The male sperm and female egg combine (fertilisation) to form a zygote. This introduces genetic variations, helping species adapt to new environments over time.

Triple Planetary Crisis: The combination of climate change, biodiversity loss, and pollution.
Global Warming: Burning fossil fuels releases excess carbon dioxide and methane, enhancing the greenhouse effect. This traps more heat, leading to melting ice caps and extreme weather.
Pollution: Air, water, and soil pollution harm ecosystems, reduce crop yields, and endanger human health.

🌍 Chapter 13 Revision Notes