I will say mainly air pollution which destroys our ozone layer and let sun radiation come inside the earth...
A living cell is bigger. Life is made up of atoms, and a cell is living. Also, cells are made up of larger atoms than hydrogen, so a cell is bigger.
Around the age of six or seven years, our teeth start to loosen, eventually falling right out. These are what we call milk teeth. Their termination is not a cause for alarm, but rather, a natural process. Soon new teeth replace the ones that are lost. In fact, the deciduous teeth help the permanent teeth erupt in their normal position. Certain of the lower vertebrates, such as sharks and mud puppies, continuously produce new teeth. But most mammals have only two sets. It seems that as you go up on evolutionary scale, there is loss in capacity to replace teeth, scientists say. On the other hand, the teeth become more specialized. For example, in lower organisms, teeth are designed primarily for grabbing and slashing, while in higher animals, they are also adapted for chewing and grinding.
It has been known that in humans the first set of teeth do more than just allow a child to chew. They play a role in stimulating and guiding the growth and development of jawbones and permanent teeth. One of the biggest fallacies is the belief that because deciduous teeth are temporary, they are not important. If a child loses milk teeth prematurely, by accident or because of decay, his jaw and permanent teeth are likely to develop improperly. Prolonged treatment may be needed to set them right.
Another reason for our two sets of teeth is that there is not enough room in a child’s small mouth for the full set of permanent teeth – there are only 20 deciduous teeth, compared with 28 or 32 permanent teeth present in adults.
Hope this helps
While plants can produce their own energy using the process of photosynthesis, animals (and other organisms that can’t do photosynthesis) must eat to get energy from food molecules. Just like energy can be stored in the chemical bond between the second and third phosphate of an ATP molecule, energy can also be stored in the chemical bonds that make up food molecules. Most of the energy that we use comes from molecules of glucose, a simple sugar.
