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.
Answer:
5.) What is the process by which the egg is released called?
A.) Ovulation
6.) When does ovulation occur?
A.) Ovulation typically occurs about 14 days before the start of the next menstrual period.
<u>-TheUnknownScientist</u>
Answer:
a.Many mitochondrial genes resemble proteobacteria genes, while the genes in the chloroplast resemble genes found in some photosynthetic bacteria.
c.Mitochondria and chloroplasts both have their own circular DNA and 70S ribosomes that are similar to those found in bacteria.
d.Mitochondria and chloroplasts replicate by a process similar to mitosis.
Explanation:
Endosymbiotic theory states that mitochondria and chloroplast which are organelles of eukaryotic cells were once independently living micro-organisms but with due course of time eukaryotic cells engulfed them and they become an integral part of these eukaryotic cells.
The resemblance between mitochondrial genes with those of proteobacteria and chloroplast genes with photosynthetic bacteria strongly support endosymbiotic theory. Apart from this, the presence of their own DNA that too circular just like prokaryotic microbes and 70 S ribosomes also support this theory. Also just like prokaryotic cells, before cell division mitochondria and chloroplasts undergo replication by means of a process known as binary fission.
<span>The sequence of alternation of generation is; gametes->zygote->sporophyte->spores->gametophyte->gametes.
The attached diagram shows clearly this looped cycle. Alternation of generation
occurs in a more advanced land plant that
has distinct
haploid and diploid phases in their life
cycle. The diploid phase usually involves
the sporophyte while the haploid phase involves the gametophyte</span>
MUTATIONS lead to duplications actually increase the number of genes in a genome.
