About Reactions

Biology Index

Where are we going with this? The information on this page should increase understanding related to the discussion of chemical reactions in biology.

About Reactions
(Hmm… this must be about reactions…)

Many topics in biology include the need to understand chemical reactions. So… let's discuss this!

A chemical reaction basically is taking some things and causing them become different things. More accurately, a chemical reaction is when an interaction involving substances and energy result in the production of one or more DIFFERENT substances.

Let's use the main photosynthesis reaction as an example.

Starting with carbon dioxide and water, light energy is used to produce glucose and oxygen.

There are, in any reaction two types of substances:

reactants and products.

So, let's take the above sentence and say it in a way that make it clear what are reactants and what are products. Also, let's add color!

Carbon dioxide and water react to produce glucose and oxygen.

So:

the reactants are carbon dioxide and water.

to produce indicates that a reaction occurred

glucose and oxygen are the products.

While there are chemical symbols for most reactions, in biology, the discussion sometimes is more conveniently carried on using the names of the substances. However, sometimes the chemical symbols are used. Let's look at that:

Carbon dioxide and water react to produce glucose and oxygen.

                                    CO2 + H2O ---> C6H12O6 + O2

Molecules are the string of letters and subscripts connected to each other without spaces. The letters come from the periodic table, are the atomic symbols. The little numbers are the subscripts which indicate how many of each type of atom are present in each molecule.  The ---> symbol indicates that the reaction took place.

Some sources will not make the subscripts small, so you might see something like this:

H20

In any case, the number in the middle or at the end of molecular notation applies ONLY to the element that comes immediately before it. Hence, in H2O, the 2 only applies to the H.

So, in H2O, there are 2 H atoms and 1 O atom.

To be most accurate, symbolic notations will include numbers called coefficients which indicate how many of each type of molecule is present. Let's have a look!

Carbon dioxide and water react to produce glucose and oxygen.

                                    6CO2 + 6H2O ---> C6H12O6 + 6O2

This notation means that it takes 6 molecules of carbon dioxide and 6 molecules of water make the reaction run.

Discussing biological reactions frequently attempt to describe what "goes in and what comes out."

So… Let's get our fancy color coded example again!

                                            PHOTOSYNTHESIS

Carbon dioxide and water react to produce glucose and oxygen.

                                 6CO2 + 6H2O  --->     C6H12O6 + 6O2

                                    Reactants   yield   Products

                                      Goes in       --->      Comes out