<P> Biochemistry deals with the chemistry of the growth and activity of living organisms . It is a chemistry where most reactions are controlled by complex proteins called enzymes and are moderated and limited by hormones . The chemistry is always highly complex and is still not fully understood . Decomposition of organic material is also within the scope of biochemistry although in this case it is the growth and activity of fungi, bacteria and other micro-organisms that is involved . Typical types of change include all the process involved in photosynthesis, a process in which carbon dioxide and water are changed into sugars and oxygen by plants, digestion in which energy rich materials are used by organisms to grow and move, Krebs cycle which liberates energy from stored reserves, protein synthesis which enable organisms to grow using processes controlled by RNA etc . </P> <P> The following can indicate that a chemical change has taken place, although this evidence is not conclusive: </P> <Ul> <Li> Change of odor . </Li> <Li> Change of color (for example, silver to reddish - brown when iron rusts). </Li> <Li> Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat . </Li> <Li> Change of composition - paper turning to ash when burned . </Li> <Li> Light and / or heat given off . </Li> <Li> Formation of gases, often appearing as bubbles in liquids . </Li> <Li> Formation of a precipitate (insoluble particles). </Li> <Li> The decomposition of organic matter (for example, rotting food). </Li> <Li> The change is difficult or impossible to reverse . </Li> </Ul> <Li> Change of odor . </Li>

What are some signs that a chemical reaction has occured