In a chemical reaction, new materials are always formed. Sometimes these new materials are useful to us. Irreversible changes are permanent. They cannot be undone. For example, you cannot change a ...

For example, a question about fertilisers could include ideas about covalent substances, acids and alkalis, chemical calculations ... In the first experiment, they change the size of the calcium ...

Most cell signals are chemical in nature. For example, prokaryotic organisms have ... specialized cells in the human vascular system detect changes in blood pressure — information that the ...