A shell is considered as biotic (living) because it is a hard, rigid covering of many animals such as snail, sepia, pila, turtles, sea urchins. A shell is protective outer layer of these soft bodied animals.
Air pollution is a type of environmental pollution that affects the air and is usually caused by smoke or other harmful gases, mainly oxides of carbon, sulphur and nitrogen. In other words, air pollution is the contamination of air due to the presence or introduction of a substance which has a poisonous effect.
Air pollution can also cause long-term damage to people's nerves, brain, kidneys, liver, and other organs.
C. negative proteins inside the cell
The<em> cell membrane</em> controls the movement of substances in and out of cells and organelles. In this way, it is selectively permeable to ions and organic molecules.
