Green Plants

Green plants absorb light energy using chlorophyll in their leaves. They use it to react carbon dioxide with water to make a sugar called glucose. The glucose is used in respiration, or converted into starch and stored. Oxygen is produced as a by-product.
This process is called photosynthesis. Temperature, carbon dioxide concentration and light intensity are factors that can limit the rate of photosynthesis.
Plants also need mineral ions, including nitrate and magnesium, for healthy growth. They suffer from poor growth in conditions where mineral ions are deficient.
Photosynthesis
Photosynthesis is the chemical change which happens in the leaves of green plants. It is the first step towards making food - not just for plants but ultimately every animal on the planet.
During this reaction, carbon dioxide and water are converted into glucose andoxygen. The reaction requires light energy, which is absorbed by a green substance called chlorophyll.
Photosynthesis takes place in leaf cells. These contain chloroplasts, which are tiny objects containing chlorophyll.

Cross-section through a leaf cell
Here is the equation for photosynthesis: carbon dioxide + water (+ light energy) → glucose + oxygen
'Light energy' is shown in brackets because it is not a substance. You will also see the equation written like this:

Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is used for respiration, while some is converted into insolublestarch for storage. The stored starch can later be turned back into glucose and used in respiration. Oxygen is released as a by-product of photosynthesis.

Plants and minerals
Plants need to take in a number of elements to stay alive. The most important are: * carbon * hydrogen * oxygen
Plants get hydrogen and oxygen from water in the soil, and carbon and oxygen from carbon dioxide and oxygen in the atmosphere. Water and carbon dioxide are used to synthesise food during photosynthesis. Oxygen is used to release energy from food during respiration.
In addition to these three elements, plants need a number of minerals for healthy growth. These are absorbed through the roots as mineral ions dissolved in the soil water. Two important mineral ions needed by plants are: * nitrate - for making amino acids, which are needed to make proteins * magnesium - for making chlorophyll
If a plant does not get enough minerals, its growth will be poor. It will suffer from deficiency symptoms: * deficient in nitrate - it will suffer from stunted growth * deficient in magnesium - it's leaves will turn yellow

The tomato plant on the left is healthy, the one on the right is growing in conditions where mineral ions are deficient

CO2 is absorbed, O2 is released, much like in a mammal respiratory system, O2 is absorbed, CO2 is released.
This is the chemical equation of photosynthesis from http://www.purchon.com/chemistry/chemical.htm:
Carbon Dioxide + Water = Glucose + Oxygen
6CO2 + 6H2O Light ...........= Chlorophyll C6H12O6
This is the chemical equation of cellular respiration from http://www.purchon.com/chemistry/chemical.htm:
Glucose + Oxygen = Carbon Dioxide + Water + Energy
C6H12O6 + 6O2 = 6CO2 + 6H2O + Energy
As you can see, the reactants of photosyntheis are the products of cellular respiration, and vise versa. The two chemical equations make a cycle, which sustains plant and animal life. Plants use carbon dioxide in photosynthesis, which produces oxygen through chemical reactions. Plants need carbon dioxide to live, and animals (indluding humans) require oxygen. Therefore, it is a beneficial cycle to both plants and animals. Good luck!

Read more: http://wiki.answers.com/Q/How_are_the_reactants_and_products_of_photosynthesis_related

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