Fuel cells can make an electricity from a simple electrochemical
reaction in which oxygen and hydrogen combine to form water. There are several
different types of fuel cell but they are all based around a central design
which consists of two electrodes, a negative anode and a positive cathode.
These are separated by a solid or liquid electrolyte that carries electrically
charged particles between the two electrodes. A catalyst, such as platinum, is
often used to speed up the reactions at the electrodes. Fuel cells are
classified according to the nature of the electrolyte. Every type needs
particular materials and fuels and is suitable for any applications. The
article below uses the proton exchange membrane fuel cell to illustrate the
science and technology behind the fuel cell concept but the characteristics and
applications of the other main designs are also discussed. Proton Exchange Membrane Fuel Cells (PEMFC)
The hydrogen ions permeate across the electrolyte to the
cathode, while the electrons flow through an external circuit and provide
power. Oxygen, in the form of air, is supplied to the cathode and this combines
with the electrons and the hydrogen ions to produce water. These reactions at
the electrodes are as follows:
Anode: 2H24H+ + 4e-
Cathode: O2 + 4H+ + 4e- 2H2O
Overall: 2H2 + O22H2O + energy
PEM cells operate at a temperature of around 80°C. At this
low temperature the electrochemical reactions would normally occur very slowly
so they are catalysed by a thin layer of platinum on each electrode.
The introduction of the herbivores would disrupt the genetic equilibrium in the population because the herbivores would act as a mechanism of natural selection.
The presence of anthocyanin in the stem is determined by the presence of the dominant allele ANL, so the genotypes of the plants that have anthocyanin are ANL/ANL and ANL/anl. The plants that do not have anthocyanin in their stems are homozygous for the anl allele and the herbivores would eat these plants more often, reducing the frequency of the anl allele in the population.
Errors in transcription are less potentially harmful compared to DNA replication errors because:
1. Unlike DNA, RNA does not permanently store genetic information in the cell.
2. RNA strands have a very short life span. Because of this the errors do not normally have serious impact on the body system.
Also, many copies of RNA are usually made.
She should use; File > Save As > Save
She can save the document with another name by using the following option;
1. Click ‘File’ in the top left-hand corner of the screen.
2. Choose ‘Save as’ from the menu option. The ‘Save as’ menu is used to save an existing document with another name.
3. A ‘Save as’ dialogue box will appear at the upper left-hand side. This box will show the folder where the document can be saved, and also where the document name can be changed. Once the new document name has been typed in, click on ‘save’ in order to save the changes.
The lungs are the main organ of the respiratory system