CBSE Class 7 Science Heat Transfer in Nature (Class 7 NCERT New) Quiz 5

1. Two animals live in the Arctic: one has thick blubber and dense fur, while the other has thin skin and no fur. If the outside temperature drops to , which animal is more likely to survive and why, based on principles of thermal insulation?

A The thin-skinned animal, because it can absorb more radiation from the environment B The thick-furred animal, because its insulation traps air and reduces heat loss through conduction and convection, maintaining body temperature C The thin-skinned animal, because less insulation allows faster convection to warm the body D Both animals survive equally because radiation from the Sun provides enough heat for both

2. A forest ecosystem receives solar radiation during the day. The soil absorbs heat and slowly releases it at night. Which of the following best explains why the temperature near the forest floor does not drop as drastically at night compared to an open desert?

A The forest trees reflect all radiation back into the atmosphere, keeping the ground warm B The tree canopy reduces convection of warm air away from the forest floor, and the soil slowly conducts stored heat upward, moderating the temperature C The desert sand conducts heat better than forest soil, causing the desert to cool faster through conduction D Forests produce their own heat through photosynthesis, which replaces the lost solar radiation at night

3. Consider a coral reef ecosystem where water temperature rises by above normal due to increased solar radiation. Using your knowledge of the effects of temperature on organisms, which of the following outcomes and reasoning is most scientifically sound?

A All fish will immediately leave the reef because fish cannot survive any temperature change B The coral may experience bleaching because the elevated temperature stresses the symbiotic algae living in coral tissues, disrupting the ecosystem's energy flow C The increased temperature will improve photosynthesis for all organisms, making the ecosystem healthier D The water will begin convecting so rapidly that all organisms will be carried away from the reef

4. A scientist measures the rate of heat conduction through two types of soil: dry sandy soil and wet clay soil. She finds that wet clay conducts heat faster than dry sandy soil. Which of the following best explains this finding and predicts how it would affect organisms living in each soil type during a cold night?

A Wet clay conducts heat faster because water is a better conductor than air; organisms in wet clay soil would lose body heat more quickly than those in dry sandy soil B Dry sandy soil conducts heat faster because sand particles are larger; organisms in sandy soil would stay warmer at night C Both soils conduct heat at the same rate because soil composition does not affect conduction D Wet clay conducts heat faster because clay reflects more radiation; organisms in wet clay would gain more heat at night

5. Birds that migrate to warmer climates in winter are responding to changes in temperature. Which of the following best explains how heat transfer principles are connected to this migration behavior?

A Birds migrate because cold regions have more radiation from the Sun, which is harmful to birds B In cold regions, birds lose body heat rapidly through conduction, convection, and radiation; migrating to warmer climates reduces heat loss and lowers the energy needed to maintain body temperature C Birds migrate because convection currents in warm regions push food sources toward colder areas D Birds migrate to warmer climates to increase conduction of heat from the ground into their bodies

6. A student claims that a thermos bottle keeps hot drinks warm by eliminating all three types of heat transfer. Evaluate this claim using your knowledge of heat transfer in nature. Which answer best assesses the student's claim?

A The student is correct; a thermos eliminates conduction, convection, and radiation completely, making it a perfect insulator B The student is partially correct; a thermos significantly reduces conduction by using insulating walls, reduces convection by sealing the liquid, and reduces radiation with reflective surfaces, but cannot eliminate heat transfer entirely C The student is incorrect; a thermos only reduces radiation and has no effect on conduction or convection D The student is incorrect; a thermos only works by increasing convection inside the bottle to keep the temperature uniform

7. During winter, small mammals such as mice huddle together in groups. Using principles of heat transfer, which of the following best explains why huddling helps these animals survive cold temperatures?

A Huddling increases the surface area exposed to cold air, allowing more radiation to warm the group B Huddling reduces the total surface area exposed to the cold environment, decreasing heat loss through conduction, convection, and radiation, and allowing shared body heat to keep the group warmer C Huddling increases convection between the animals, which generates more heat for the group D Huddling allows the animals to absorb more solar radiation by forming a larger dark mass

8. A plant in a greenhouse absorbs solar radiation and converts some of it into heat. The greenhouse glass traps this heat inside. Which of the following best explains the role of each heat transfer process in keeping the greenhouse warm, and how this relates to natural ecosystems?

A Radiation from the Sun enters the greenhouse; conduction through the glass traps the heat; this is similar to how deserts stay warm at night through conduction of stored heat B Radiation from the Sun enters and warms surfaces inside; convection circulates warm air within the greenhouse; the glass reduces heat loss by radiation back to the outside; this is similar to how Earth's atmosphere traps heat through the natural greenhouse effect C Convection from the Sun warms the greenhouse; conduction through plants distributes the heat; this is similar to how ocean currents distribute heat in ecosystems D Radiation warms the greenhouse, and the glass increases conduction to the outside, cooling the greenhouse; this is similar to how animals use fur to conduct heat away from their bodies

9. Which of the following is a good conductor of heat?

A Wood B Plastic C Iron D Rubber

10. Heat is transferred in liquids and gases mainly by:

A Conduction B Convection C Radiation D Reflection