The atmospheric layer that protects the Earth against danger of the rocks is the mesosphere. This layer is above the stratosphere. The temperature drops in this layer to about -100 degrees Celsius. This is the coldest region of the atmosphere. The mesosphere burns up most meteors and asteroids before they are able to reach the earth's surface. It becomes cold enough to freeze water vapor in its atmosphere into ice clouds.
The mesosphere is the lowest layer of the stratosphere and coldest layer of atmosphere. The incoming meteors and debris from the space are burned away in this layer. As the debris passes the layers of the atmosphere, the friction causes them to burn and destroy before these reach the surface thereby protecting the Earth's surface. On the bodies like mercury and moon, we can find the surface has many impact craters. This is because there is no atmosphere on mercury and moon which could protect their surfaces.
Passive transport moves molecules from one side of the membrane to the other with the energy of the chemical gradient (or concentration gradient). Otherwise, active transport uses the hydrolyzation of ATP to gain energy in order to move molecules across the membrane without taking into account the gradient.
