I have often mentioned the importance of nitrogen (in the form of nitrate) to the growth of plants. It gets mentioned pretty regularly in the questions after several posts and when I wrote about crop circles, Fritz Haber and Norman Borlaug. Plant nutrients often appear as part of exam questions so please forgive me if I bang on about them some more.
Plants are remarkably simple things. They absorb water from the soil, carbon dioxide from the air then use the energy in sunlight to smash these two raw materials together to make glucose. Oxygen, the waste product of this process, is released freely into the atmosphere. This is how they make their food for respiration and as a result provide food and oxygen for all the other organisms on Earth.
It is not the whole story of course. In order to do this wonderful reaction they need to make a molecule called chlorophyll. This green pigment is capable of trapping and using sunlight to catalyse photosynthesis. Part of the molecule is four atoms of nitrogen which the plant needs to absorb from its environment. Nitrate, dissolved in water, is absorbed through the roots from the soil (or directly from the surrounding water in the case of aquatic plants). Nitrate is also needed to make the amino acids that are the building blocks of proteins such as the enzymes that catalyse every reaction within the plant’s cells.
There are other essential minerals in the soil. Obviously magnesium is needed as it forms the core of the chlorophyll molecule (in a similar way to how an iron atom holds haemoglobin molecules together). Potassium is involved in a huge number of biochemical processes in plants and is absorbed through the roots as dissolved potassium chloride, potassium sulphate or potassium nitrate. The non-metal element phosphorous is also vital to plants. It is absorbed from the soil by the roots as calcium phosphate dissolved into the groundwater. It is important because it makes up a vital part of the energy transferring molecules ADP and ATP (adenosine diphosphate and adenosine triphosphate). Without these molecules none of the energy produced during respiration would be able to be used by any other parts of the cell.
Shortages of any of these essential nutrients will cause plants to look unhealthy and their growth will be slowed.
More on deficiency symptoms next time…
Questions…
- Explain one of the many ways that nitrate can get into the soil.
- Name a non-metal element not mentioned in the passage above and tell me one characteristic of that element.
- What are the raw materials of aerobic respiration?
- Name an enzyme that you have studied. What job does it perform?
- What group of molecules are the building blocks of proteins?
Comments