SCI-FACT 1:
Cows need to eat about one-half of a kilogram of dry forage to
produce each litre of milk. But to produce each kilogram of dry
forage, pasture plants use about 0.5 kilolitres of water. It
follows that it takes a minimum of about 250 litres of water to
produce the pasture required by a cow to produce each litre of
milk.
SCI-FACT 2: Atoms
consist of a nucleus containing neutrons and protons with electrons
spinning around this central nucleus. All atoms are electrically
neutral, containing the same numbers of electrons (negatively charged
particles) and protons (positively charged particles). However, their
mass is determined by the number of neutrons and protons contained in
the nucleus, and the nuclei of atoms of the same chemical element can
contain different numbers of neutrons. These atoms, which have
different masses, are known as isotopes. Some atoms can absorb
neutrons, becoming heavier isotopes of the same element whilst others
can emit neutrons, becoming lighter isotopes of the same element.
Uranium
was the first element which we found could absorb neutrons. The
nucleus of the 235U isotope of uranium can absorb a
neutron to become the short-lived 236U isotope, whose
nucleus immediately divides into two smaller nuclei. As it divides it
releases more neutrons and energy, and if there are sufficient atoms
of the 235U isotope packed together they can absorb these
neutrons from the decaying 236U. If there is nothing else
to absorb the neutrons released by the 236U a “chain reaction” can
start, resulting in the explosive release of energy. However, if the
chain reaction can be controlled and the heat generated by the
236U atoms as they breakdown can be harvested we have a new
controllable source of energy. This is the very simple basis of all
nuclear power stations. read more
on this topic
SCI-FACT 3: Plutonium
is a highly radioactive metal produced from uranium in nuclear
fuel rods. A lump of plutonium about half the size of a litre
carton of milk will spontaneously explode (“go critical”) with a
force equivalent to 20 kilotons of TNT.
read more on this topic
SCI-FACT 4:
Sun-light is a transient form of energy. However, the chemicals
which make up plant dry-matter are stable provide and a good store
of the sun-light that has been captured by the plants and used to
produce them. The “fossil fuels” (coal, oil and methane gas)
represent stored sun-light, they are the buried residues of plants
that grew on Earth many, many years ago.
Approximately ½ kilogram of hydrocarbon or coal can be produced from
1 kilogram of plant dry-matter,
that is every
kilogram of fossil hydrocarbon fuel or coal represents about 4000 MJ
of stored sun-light.
The energy released
when we burn fossil hydrocarbons (their heat of combustion) is
typically between 40 and 50 MJ/kg and that of coal about 8 MJ/kg.
It follows that when we burn fossil fuels we only recover ¼ - 1% of
the sun’s energy that was used to produce them. read more on this topic
SCI-FACT 5: All
plants transpire water whilst photosynthesising. They all produce
about one kilogram of new dry matter when they harvest 2000 MJ of
PAR. A C3 plant will transpire about 0.5 kilolitre of
water whilst a C4 plant about transpire only about 0.25
kilolitre of water.
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SCI-FACT 6: A
C3 plant will
struggle to harvest the incident sunlight it receives during a month
if the ratio of rainfall (measured in mm or L/m2) to
incident PAR (in MJ/m2) is less than one, and a
C4 plant will struggle if the ratio is less than on-half
(0.5).
read more on this topic
