Class 8 Science : Practice Questions and Answers

Power is the rate at which work is done or energy is transferred. The unit of power is the watt (W), which is defined as one joule of energy transferred per second.

A catalyst is a substance that accelerates a chemical reaction by lowering the activation energy, allowing the reaction to occur more easily. It remains unchanged after the reaction and can be used multiple times.

Convex mirrors are used in rear-view mirrors because they provide a wider field of view, allowing the driver to see more of the area behind the vehicle.

Solar energy is a renewable resource because it is constantly replenished by the Sun and does not deplete over time.

Sound waves need a medium, such as air, water, or solids, to travel. They cannot propagate through a vacuum because there are no molecules to transmit the vibrations.

Methane is a simple hydrocarbon with the molecular formula CH₄, consisting of one carbon atom bonded to four hydrogen atoms.

Stomata are small pores on the leaves that allow gases like oxygen and carbon dioxide to move in and out of the plant for processes like respiration and photosynthesis.

The cell membrane acts as a selective barrier, regulating the entry and exit of substances, thus maintaining the internal balance of the cell.

Leaves contain chlorophyll, a pigment that captures sunlight and facilitates the process of photosynthesis, which is essential for producing food in plants.

The heart is a muscular organ that pumps blood throughout the body, ensuring the distribution of oxygen and nutrients to various organs.

Roots anchor the plant in the soil and play a crucial role in absorbing water and essential minerals required for the plant's growth and survival.

Crop rotation involves growing different crops on the same piece of land during different seasons to prevent soil depletion and maintain its fertility. It's a sustainable farming practice that helps in managing pests and enhancing soil health.