1. Testing only one variable
A controlled variable means its the one that stays the same. In a controlled experiment, it means there is only one manipulated, (changed) variable.
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 answer is <span>C.silent.
Nonsense, missense, silent, and frameshift mutations are point mutations. The point mutations are the change in a single nucleotide base on the DNA molecule. In a missense mutation, the change in a single nucleotide base results in a codon coding for a different amino acid. In a nonsense mutation, the change in a single nucleotide results in a stop codon or in a nonsense codon. Frameshift mutation, due to addition or deletion of a base, results in the change of reading frame and totally different translation. In all these cases, the change could lead to different of nonfunctional protein translation.
Silent mutation, on the other, means that change in a nucleotide base will no affect amino acid. It will result in a different codon, but the one that code for the same amino acid, so the same protein will be produced.
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