Tell why you may be able to survive a bitter cold day in snow-cave."

First you need to know that the warm air is less dense than the colder air and thus it tends to rise; so snow-caves are constructed in some way that the tunnel entrance is below the main space, and so the warm air can be retained into the cave. In a typical snow-cave, you can reach temperatures over 0°C even when the temperature outside are under zero degrees celsius.

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.