Class 8 practice
Class 8 science questions.
Science questions for Class 8, at the level of students aged 12–14, each with its answer and a short explanation. Try each one before opening the answer.
Blood vessels carry blood throughout our body. Which vessels have thick, elastic walls to withstand the high pressure of blood pumped directly from the heart?
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Answer: Arteries
Arteries carry oxygen-rich blood away from the heart under high pressure, so they need thick, elastic muscular walls. Veins have thinner walls and valves.
During an experiment, Priya ties a clear plastic bag over a green branch of a potted plant. Droplets of water soon appear on the bag's inner surface. Which process releases this water?
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Answer: Transpiration
Transpiration is the evaporation of excess water from plant leaves through microscopic pores called stomata.
Different regions of the Earth experience changing seasons throughout the year. What is the primary cause of these seasonal changes?
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Answer: The tilt of Earth's axis during revolution
Earth's axial tilt alters the angle and duration of sunlight reaching different hemispheres as Earth orbits the Sun, creating seasons.
Ananya plucks a guitar string gently, then plucks it much harder. How does the sound change when she plucks it harder?
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Answer: Its loudness increases while its pitch stays similar
Plucking harder gives more energy to the string, increasing the amplitude of vibration. Greater amplitude results in louder sound, while the frequency remains unchanged.
Deepa mixes baker's yeast and sugar into warm wheat flour dough. After an hour, the dough rises significantly in size. Which gas released during fermentation makes the dough puff up?
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Answer: Carbon dioxide
Yeast reproduces rapidly and respires anaerobically to break down sugars. This fermentation process produces carbon dioxide gas, which gets trapped in the dough and makes it rise.
A student watches the night sky in winter and spots a bright constellation shaped like a hunter with three distinct belt stars. Which constellation is this?
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Answer: Orion
Orion, also called the Hunter, is a prominent winter constellation easily identified by the three bright stars aligned straight across its middle.
During a lab experiment, Meera covers a healthy potted plant with a clear plastic bag. After two hours, water droplets form inside the bag. Which biological process caused these droplets?
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Answer: Transpiration
Transpiration is the release of water vapour from aerial parts of plants, mainly through microscopic leaf pores called stomata.
Ananya places a freshly cut balsam stem into water dyed with red ink. After two hours, red lines appear inside the leaves. Which plant tissue carried the red water upward?
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Answer: Xylem
Xylem vessels conduct water and dissolved minerals upward from roots to leaves. Phloem carries food manufactured in leaves to other parts of the plant.
Farmers in Punjab often plant legumes like gram or peas between cereal crops to enrich the soil. Which bacterium living in root nodules helps fix atmospheric nitrogen?
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Answer: Rhizobium
Rhizobium bacteria live in the root nodules of leguminous plants. They convert atmospheric nitrogen into usable nitrates, improving soil fertility naturally.
Meera observes onion peel cells under a compound microscope. She notices a clear, jelly-like substance filling the space between the cell membrane and the nucleus. What is this substance?
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Answer: Cytoplasm
Cytoplasm is the gel-like fluid that fills the interior of a cell and holds its cellular organelles.
Mountaineers climbing high peaks in the Himalayas sometimes suffer nosebleeds. What change in the surroundings causes this effect?
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Answer: Atmospheric pressure decreases at high altitudes
At high altitudes, external atmospheric pressure drops significantly. The higher blood pressure inside small nasal capillaries causes them to burst.
Iron water supply pipes in Indian cities are often coated with a thin layer of zinc to prevent rust. What is this protective process called?
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Answer: Galvanisation
Galvanisation is the process of coating iron or steel with zinc. The zinc layer protects the underlying metal from reacting with air and moisture.
- True or false?
A convex mirror always produces a virtual, erect, and smaller image of an object.
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Answer: True
Convex mirrors diverge light rays. They always produce diminished, erect, and virtual images, making them ideal as vehicle rear-view mirrors.
- True or false?
During anaerobic respiration, yeast converts glucose into lactic acid instead of alcohol.
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Answer: False
Yeast breaks down glucose anaerobically to produce ethanol (alcohol) and carbon dioxide. Muscle cells, not yeast, produce lactic acid during anaerobic respiration.
- True or false?
Pulmonary veins carry oxygen-rich blood from the lungs back to the left atrium of the human heart.
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Answer: True
Most veins carry oxygen-poor blood toward the heart. The pulmonary veins are an exception, carrying oxygenated blood from the lungs.
- Fill in the blank.
The green pigment that absorbs sunlight during photosynthesis inside plant leaves is ___ (begins with C).
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Answer: chlorophyll
Chlorophyll is the green pigment in chloroplasts that absorbs light energy required for photosynthesis in plants.
- Fill in the blank.
The mode of heat transfer in liquids and gases caused by the actual movement of particles is ___ (starts with 'c').
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Answer: convection
In convection, warmer fluid becomes less dense and rises, while cooler, denser fluid sinks.
- Fill in the blank.
The rear-view mirror used by motor vehicle drivers to see traffic behind them is a ___ mirror (starts with 'c').
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Answer: convex
Convex mirrors produce virtual, upright, and diminished images, providing drivers with a much wider field of view.
Which object's movement makes it the odd one out?
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Answer: Spinning top
A pendulum bob, a swing, and a plucked sitar string show oscillatory back-and-forth motion. A spinning top exhibits rotational motion around a central axis.
Which is the odd one out among these changes in matter?
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Answer: Melting of ice
Melting of ice is a reversible physical change where no new substance forms. The other three are irreversible chemical changes that create entirely new substances.
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