The Story of Photosynthesis…
Take a look at how plants make their food. The food plants made from photosynthesis
are called CARBOHYDRATES.
If we look at the word…….CARBOHYDRATE… we can tell quite a lot about it..
Carbohydrates contain the atoms CARBON, HYDROGEN and OXYGEN
So, which part of the word means that it contains carbon? And which part of the word
means that it contains hydrogen? Now, can you suggest what the letters ATE mean
when placed on the end of a chemical name?
The diagram to the right is a
chemical picture of one
carbohydrate. The chemical has
how many
Carbon atoms?
Hydrogen atoms?
Oxygen atoms?
The carbohydrate is called glucose – it is a simple sugar and you are probably very
familiar with its taste if you have had candy, lemonade, soda, grapes, apples and just
about any other food that comes from a plant.
How Do Plants Make Carbohydrates (Glucose)?
If you were a plant and you had to make this carbohydrate what atoms are you going to need and where
could you get them from?
If we had some carbon dioxide, could we make carbohydrates from it?
What atoms would still be missing?
If we had some water as well as the carbon dioxide,
what extra atom could this supply?
Suppose we have the carbon dioxide
and some water – we would need to
split the water up to release the
hydrogen from it. The process of
splitting water into hydrogen and
oxygen is very difficult. However with the help of sunlight energy plants
can split the water and use the
hydrogen to put with the carbon and
oxygen from our carbon dioxide.
When light energy is used to split water, there is a product left over that is not
needed. What is this product?
You may have come across this idea before – it seems that photosynthesis
results in the production of carbohydrates (glucose) and also releases oxygen
into the air – which is a good thing for animals!
We know that plants use sunlight energy to split water (H2O) into hydrogen and
oxygen. The hydrogen is added to the carbon dioxide to make CARBOHYDRATES
(glucose). The oxygen produced from this splitting of water is released into our
atmosphere.
We summarise this using a chemical equation:
6 CO2
+ 6 H20
carbon
water
dioxide
--->
C6H12O6 + 6 O2
glucose
oxygen