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Science MagazineScience MagazineScience MagazineScience Magazine
Interesting
experiments and
Chemistry Jokes
available!
What are yellow
explosive—the
TNTs?
The HOT topic—
Nuclear Crisis in
Japan
Learn more
about Hormones
Cooperated with Biology Society
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Preface
Thank you for supporting the Science Magazine published
in the 1st term of the academic year. Knowing that students
are pursuing knowledge of Science, we - members of the
Science Society and Biology Society work hard to publish
the 2nd Science Magazine in the second half of the
academic year.
In an attempt to provide you with more amazing science
information, the Science Society and the Biology Society
worked on the 2nd term magazine together. To provide
all-round science knowledge to you, we give details about
light, nuclear crisis in Japan, the yellow explosive in
Chemistry and the hormone in biology. Last but not least,
we have prepared an interesting topic which you are going
to love it. You are sure to have a lot of fun in the world of
chemistry. Do not hesitate! Let’s enjoy the Science
Magazine and discover the world around us!
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Content
Physics
1. How fast can light travel? P.4-5
Chemistry
1. The Japan Earthquake and Nuclear Crisis P.6-10
2. Having fun in Chemistry P.11-13
3. Yellow explosive- TNT P.14-17
Biology
1. Hormones in Organisms P.18-34
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HOW FAST CAN LIGHT TRAVEL?HOW FAST CAN LIGHT TRAVEL?HOW FAST CAN LIGHT TRAVEL?HOW FAST CAN LIGHT TRAVEL?
We sometimes describe fast-moving objects moving as fast as light,
but actually how fast is light? 10,000 ms�� ? 1,000,000 ms-1?
10,000,000 ms-1? Or actually infinity? This question has puzzled
numerous scientists for centuries. In the 19th century Hippolyte
Fizeau developed a method to determine the speed of light based on
time-of-flight measurements on Earth and reported a value of
315,000 kms-1. His method was improved upon by Léon Foucault who
obtained a value of 298,000 kms-1 in 1862. How could they measure
the speed of light? Let’s discover!
Diagram of the Foucault apparatus
A method of measuring the speed of light is to measure the time
needed for light to travel to a mirror at a known distance and back.
This is the working principle behind the Foucault apparatus
developed by Hippolyte Fizeau and Léon Foucault.
The setup as used by Fizeau consists of a beam of light directed at a
mirror 8 kilometres (5 miles) away. On the way from the source to the
mirror, the beam passes through a rotating cogwheel. At a certain rate
of rotation, the beam passes through one gap on the way out and
another on the way back, but at slightly higher or lower rates, the
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beam strikes a tooth and does not pass through the wheel. Knowing
the distance between the wheel and the mirror, the number of teeth
on the wheel, and the rate of rotation, the speed of light can be
calculated.
The method of Foucault replaces the cogwheel
by a rotating mirror. Because the mirror keeps rotating while the light
travels to the distant mirror and back, the light is reflected from the
rotating mirror at a different angle on its way out than it is on its way
back. From this difference in angle, the known speed of rotation and
the distance to the distant mirror the speed of light may be
calculated.
Nowadays, using oscilloscope with time resolutions of less than one
nanosecond, the speed of light can be directly measured by timing the
delay of a light pulse from a laser or an LED reflected from a mirror.
This method is less precise (with errors of the order of 1%) than
other modern techniques, but it is sometimes used as a laboratory
experiment in college physics classes.
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The Japan Earthquake and Nuclear Crisis
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History of Nuclear Power in Japan
In 1954, Japan budgeted 230
million yen for nuclear energy,
marking the beginning of the
program. The first nuclear
reactor in Japan was built by
the UK's General Electric
Company. In the 1970s the
first Light Water Reactors
were built in co-operation
with American companies.
These plants were bought
from U.S. vendors such as General Electric or Westinghouse with
contractual work done by Japanese companies, who would later get a
license themselves to build similar plant designs. Developments in
nuclear power since that time has seen contributions from Japanese
companies and research institutes on the same level as the other big
users of nuclear power.
Since 1973, nuclear
energy has been a
national strategic
priority in Japan, as
the nation is heavily
dependent on
imported fuel, with
fuel imports
accounting for 61%
of energy production.
In 2008, after the
opening of 7 brand new nuclear reactors in Japan (3 on Honshu, and
1 each on Hokkaido, Kyushu, Shikoku, and Tanegashima) Japan
became the third largest nuclear power user in the world with 55
nuclear reactors. These provide 34.5% of Japan's electricity.
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How to Prevent Nuclear Crisis in Japan
Following an earthquake, tsunami,
and the failure of cooling systems at
the Fukushima I Nuclear Power Plant
on March 11, 2011, a nuclear
emergency was declared. This was the
first time a nuclear emergency had
been declared in Japan, and 140,000
residents within 20 km of the plant
were evacuated. The amount of
radiation released is unclear, and the
crisis is still ongoing.
With the loss of power at reactors, and with its valves and pumps
damaged by the tsunami, the fuel rods in the reactors are still under
high temperature. Because of the high temperature, the radiation is
given out from the fuel rods. In order to avoid the spreading of
radiation, the emergency workers were pumping in seawater to cool
down the fuel rods. At the same time, they mixed the water with an
element Boron.
Boron is the chemical element with atomic number 5 and the
chemical symbol B. Because of its high neutron cross-section,
boron-10 is often used to control fission in nuclear reactors as a
neutron-capturing substance. In this crisis, Boron is used to disrupt
the nuclear chain reactions in the reactors, and then the fuel rods can
be cooled down.
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Can Apply Iodine Solution onto the body surface
prevent or treat radiation-related injuries?
When there is an
accident involving
damage to the nuclear
reactor causing
leakage, radioactive
materials in the
reactor core may be
released into the
atmosphere. The
radioactive caesium
(Cs-137) and
radioactive iodine
(I-131) are the most
abundant radionuclides that may be released into the atmosphere
during the accident. Recently, many people buy iodine solution to
prevent the radiation-related injury.
131I decays with a half-life of 8.02 days with beta and gamma
emissions. This nuclide of iodine atom has 78 neutrons in nucleus;
the stable nuclide 127I has 74 neutrons. On decaying, 131I transforms
into 131Xe:
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Iodine in food is absorbed by the body and preferentially
concentrated in the thyroid where it is needed for the functioning of
that gland. When 131I is present in high levels in the environment
from radioactive fallout, it can be absorbed through contaminated
food, and will also accumulate in the thyroid. As it decays, it may
cause damage to the thyroid. The primary risk from exposure to high
levels of 131I is the chance occurrence of radiogenic thyroid cancer in
later life.
There is no scientific evidence that eating salt or applying iodine
onto the body surface can prevent or treat radiation-related injury.
Applying iodine solution onto body surface may cause skin irritation.
More information on Japan nuclear crisis:
http://www.bbc.co.uk/news/world-asia-pacific-13017282
http://en.wikipedia.org/wiki/Japan_nuclear_crises
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Having Fun in Chemistry
It seems that it’s a bit boring when we study chemistry. However,
beyond the textbook, Chemistry is full of fun and interesting! Let’s get
into the Fun Chemistry World!
MAGIC: Get Away PEPPER!!
It may be the easiest magic in the world. You can find all the ‘magic’
tools you need at home.
• black pepper
• water
• detergent (dishwashing liquid)
• plate or bowl
Steps:
1. Fill the plate or bowl with water until it is
FULL.
2. Spread some pepper on the water.
3. Dip your finger into the centre of the water, there will be not
much effects.
4. Put a drop of detergent on your finger and dip it into the centre
of the water. The pepper will move away from your finger!
Notes:
If you are doing this trick, you may first
prepare a clean finger (for step 3) and a
finger with detergent (for step 4). It makes
your trick more realistic!
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Principle behind the GREAT trick:
Normally, there is a surface tension
on the water surface and the tension
makes the water bugles up a bit. The
tension ‘holds’ the water in the plate.
When you add detergent into the
water, the tension becomes lower
than usual and hence the water wants
to spread out. As the water flattens on
the plate, the pepper then floats up
and moves (carried by water) to the
edge of the plate as if by magic.
Hey magicians! Show this magic to your friends in lunchtime!
Chemistry Jokes
Don’t think chemists are just boring guys! They have a great sense of
humor!
Do you have a chemistry joke or riddle or are you looking for one?
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Helium
Helium walks into a bar and orders a beer, the bartender says, "Sorry,
we don't serve noble gases here." He doesn't react.
Chemical formula of water
Teacher: What is the chemical formula of water?
Pupil: HIJKLMNO (H2O , ‘H to O’)
What solution is it?
How do you call a tooth suspended in a litre of water?
Answer:a 1 molar solution
Neutron
A neutron walks into a shop,
"I’d like a 'coke', he says.
The shop keeper serves up the coke.
"How much will that be?" Asked the neutron.
"For you?" Replied the shop keeper, "No charge!"
Why chemists are great
Why are chemists so great at solving problems?
Answer: Because they have all the solutions.
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The Yellow Explosive – TNT Trinitrotoluene (abbreviated as TNT), or more specifically, 2, 4, 6 -
trinitrotoluene, is a chemical compound with the formula C6H2
(NO2)3CH3. This yellow-coloured solid is sometimes used as a reagent
in chemical synthesis, but it is best known as a useful explosive
material with convenient handling properties. The explosive yield of
TNT is considered to be the standard measure of strength of bombs
and other explosives.
TNT was first prepared in 1863 by German
chemist Julius Wilbrand and originally used as
a yellow dye. Its potential as an explosive was
not appreciated for several years mainly
because it was so difficult to detonate and
because it was less powerful than alternatives.
TNT can be safely poured when liquid into
shell cases, and is so insensitive that in 1910, it
was exempted from the UK's Explosives Act
1875 and was not considered an explosive for
the purposes of manufacture and storage. The
German armed forces adopted it as a filling for
artillery shells in 1902. TNT-filled
armor-piercing shells would explode after they
had penetrated the armor of British capital
ships, whereas the British lyddite-filled shells
tended to explode upon striking armor, thus
expending much of their energy outside the
ship. The British started replacing lyddite with
TNT in 1907. TNT is still widely used by the United States military
and construction companies around the world. The majority of TNT
currently used by the US military is manufactured by Radford Army
Ammunition Plant near Radford, Virginia.
It is a common misconception that TNT and dynamite are the same,
or that dynamite contains TNT. In fact, whereas TNT is a specific
chemical compound, dynamite is an absorbent mixture soaked in
nitroglycerin (硝化甘油) that is compressed into a cylindrical shape
and wrapped in paper.
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Upon detonation, TNT decomposes as a mix of follows:
2 C7H5N3O6 → 3 N2 + 5 H2O + 7 CO + 7 C
2 C7H5N3O6 → 3 N2 + 5 H2 + 12 CO + 2 C
The reaction is exothermic but has high activation energy. Because of
the production of carbon, TNT explosions have a sooty appearance.
Because TNT has an excess of carbon, explosive mixtures with
oxygen-rich compounds can yield more energy per kilogram than
TNT alone. During the 20th century, amatol, a mixture of TNT with
ammonium nitrate was a widely used military explosive.
Detonation of TNT can be done using a high velocity initiator or by
efficient concussion.
For many years, TNT used to be the reference point for the Figure of
Insensitivity. TNT has a rating of exactly 100 on the F of I scale.
However, the reference has since been changed to a more sensitive
explosive called RDX (旋風炸藥/黑索金 or Hexogen) , which has an F
of I of 80.
TNT contains 4.7 megajoules per kilogram. The energy density of
TNT is used as a reference-point for many other types of explosives,
including nuclear weapons, the energy content of which is measured
in kilotons (~4.184 terajoules) or megatons (~4.184 petajoules) of
TNT equivalent.
For comparison, gunpowder contains 3 megajoules per kilogram,
dynamite contains 7.5 megajoules per kilogram, gasoline contains
47.2 megajoules per kilogram (though gasoline requires an oxidant,
so an optimized gasoline and O2 mixture contains 10.4 megajoules
per kilogram), and butter contains 30 megajoules per kilogram (but
not an explosive).
TNT is one of the most commonly used explosives for military and
industrial applications. It is valued because of its insensitivity to
shock and friction, which reduces the risk of accidental detonation.
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TNT melts at 80 °C (176 °F), far below the temperature at which it
will spontaneously detonate, allowing it to be poured as well as safely
combined with other explosives. TNT neither absorbs nor dissolves
in water, which allows it to be used effectively in wet environments.
Additionally, it is stable compared to other high explosives.
TNT is poisonous, and skin contact can cause skin irritation, causing
the skin to turn into a bright yellow-orange colour. During the First
World War, munitions workers who handled the chemical found that
their skin turned bright yellow, which resulted in their acquiring the
nickname "canary girls" or simply "canaries."
People exposed to TNT over a prolonged period tend to experience
anemia and abnormal liver functions. Blood and liver effects, spleen
enlargement and other harmful effects on the immune system have
also been found in animals that ingested or breathed trinitrotoluene.
There is evidence that TNT adversely affects male fertility, and TNT is
listed as a possible human carcinogen. Consumption of TNT produces
red urine through the presence of breakdown products and not blood
as sometimes believed.
Some military testing grounds are contaminated with TNT.
Wastewater from munitions programs including contamination of
surface and subsurface waters may be coloured pink because of the
presence of TNT. Such contamination, called "pink water", may be
difficult and expensive to remedy.
TNT is prone to exudation of dinitrotoluenes (DNT) and other
isomers of trinitrotoluene. Even small quantities of such impurities
can cause such effect. The effect shows especially in projectiles
containing TNT and stored at higher temperatures, e.g. during
summer. Exudation of impurities leads to formation of pores and
cracks (which in turn cause increased shock sensitivity). Migration of
the exudates liquid into the fuse screw thread can form fire channels,
increasing the risk of accidental detonations; fuse malfunction can
result from the liquids migrating into its mechanism.
Industrially, TNT is synthesized in a three-step process. First,
toluene is nitrated with a mixture of sulfuric and nitric acid to
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produce mono-nitrotoluene or MNT. The MNT is separated and then
renitrated to dinitrotoluene or DNT. In the final step, the DNT is
nitrated to trinitrotoluene or TNT using an anhydrous mixture of
nitric acid and oleum. Nitric acid is consumed by the manufacturing
process, but the diluted sulphuric acid can be reconcentrated and
reused. Subsequent to nitration, TNT is stabilized by a process called
sulphitation, where the crude TNT is treated with aqueous sodium
sulfite solution in order to remove less stable isomers of TNT and
other undesired reaction products. The rinse water from sulphitation
is known as red water and is a significant pollutant and waste
product of TNT manufacture.
Control of nitrogen oxides in feed nitric acid is very important
because free nitrogen dioxide can result in oxidation of the methyl
group of toluene. This reaction is highly exothermic and carries with
it the risk of runaway reaction and explosion.
In the laboratory, 2, 4, 6-trinitrotoluene is produced by a two step
process. A nitrating mixture of concentrated nitric and sulphuric
acids is used to nitrate toluene to a mixture of mono- and
di-nitrotoluene isomers, with cooling to maintain careful temperature
control. The nitrated toluenes are separated, washed with dilute
sodium bicarbonate to remove oxides of nitrogen, and then carefully
nitrated with a mixture of fuming nitric acid and sulphuric acid.
Towards the end of the nitration, the mixture is heated on a steam
bath. The trinitrotoluene is separated, washed with a dilute solution
of sodium sulphite and then recrystallized from alcohol.
Detonation of the 500-ton TNT explosive
charge as part of Operation Sailor Hat in
1965. The white blast-wave is visible on the
water surface and a shock condensation
cloud is visible overhead
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Hormones Do you know why eating chocolate can make you less stressful and happier? Do you
know why a plant can grow towards sunlight? Do you know why you would tremble
and your heart beats faster when you are keyed up? If you don’t, you should take a
look at these articles concerning hormones. Living organisms’ daily lives are closely
related to hormones. A small act made by a person, the coordination of your body,
your emotion or even your health are also coordinated or controlled by hormones. Not
only in animals, are hormones also present in plants and fruits. Different types of
hormones have different functions. As we could see, hormones are greatly related to
our daily lives!
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A hormone is a chemical released by a cell or a gland in one part of the body that sends
out messages affecting cells in other parts of the organism. Only a small amount of
hormone is required to alter cell metabolism. In essence, it is a chemical messenger that
transports a signal from one cell to another. All multicellular organisms produce
hormones; plant hormones are also called phytohormones. Hormones in animals are
often transported in the blood.
-Hormones transported in blood
Cells respond to a hormone when they express a specific receptor for that hormone. The
hormone binds to the receptor protein,
resulting in the activation of a signal transduction mechanism that ultimately leads to
cell type-specific responses.
Endocrine hormone molecules are secreted directly into the bloodstream, whereas
exocrine hormones are secreted directly into a duct, and, from the duct, they flow either
into the bloodstream or from cell to cell by diffusion in a process known as paracrine
signalling.
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-Exocrine hormones are secreted directly into a duct
Recently it has been found that a variety of exogenous modern chemical compounds
have hormone-like effects on both humans and wildlife. Their interference with the
synthesis, secretion, transport, binding, action, or elimination of natural hormones in
the body are responsible of homeostasis, reproduction, development, and behavior
changes in the same way as the endogenous produced hormones.
Hormone cells are typically of a specialized cell type, residing within a particular
endocrine gland, such as thyroid gland, ovaries, and testes. Hormones exit their cell of
origin via exocytosis or another means of membrane transport. Cellular recipients of a
particular hormonal signal may be one of several cell types that reside within a number
of different tissues, as is the case for insulin, which triggers a diverse range of systemic
physiological effects. Different tissue types may also respond differently to the same
hormonal signal. Because of this, hormonal signalling is elaborate and hard to dissect.
-Exocytosis and endocytosis
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Physiology of hormones
In physiology, the endocrine system is a system of glands, each of which secretes a
type of hormone directly into the bloodstream to regulate the body. The endocrine
system is in contrast to exocrine system, which secretes its chemicals using ducts. It
derives from the Greek words endo (Greek ένδο) meaning inside, within, and crinis
(Greek κρινής) for secrete. The endocrine system is an information signal system like
the nervous system, yet its effects and mechanism are classifiably different. The
endocrine systems effects are slow to initiate and prolonged in their response, lasting
for hours to weeks. Hormones are substances (chemical mediators) released from
endocrine tissue into the bloodstream where they travel to target tissue and generate a
response. Hormones regulate various human functions, including metabolism, growth
and development, tissue function, and mood. The field of study dealing with the
endocrine system and its disorders is endocrinology, a branch of internal medicine.
Most cells are capable of producing one or more molecules, which act as signalling
molecules to other cells, altering their growth, function, or metabolism. The classical
hormones produced by cells in the endocrine glands are cellular products, specialized to
serve as regulators at the overall organism level. However, they may also exert their
effects solely within the tissue in which they are produced and originally released.
Hormone secretion can be stimulated and inhibited by other hormones, plasma
concentrations of ions or nutrients, binding globulins, neurons and mental activity, and
environmental changes.
-Negative feedback mechanism
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The rate of hormone biosynthesis and secretion is often regulated by a homeostatic
negative feedback control mechanism. Such a mechanism depends on factors that
influence the metabolism and excretion of hormones. Thus, higher hormone
concentration alone cannot trigger the negative feedback mechanism. Negative
feedback must be triggered by overproduction of an "effect" of the hormone.
To release active hormones quickly into the circulation, hormone biosynthetic cells
may produce and store biologically inactive hormones in the form of pre- or
prohormones. These can then be quickly converted into their active hormone form in
response to a particular stimulus.
Functions of hormones
1. Stimulation or inhibition of growth.
2. Mood swings.
3. Induction or suppression of apoptosis (programmed cell death).
4. Activation or inhibition of the immune system.
5. Regulation of metabolism.
6. Preparation of the body for mating, fighting, fleeing, and other activities.
7. Preparation of the body for a new phase of life: puberty, parenting, and menopause.
8. Control of the reproductive cycle.
9. Hunger cravings.
10. Regulate the production and release of other hormones.
11. Control the internal environment of the body through homeostasis.
Endocrine organs and secreted hormones
-Endocrine glands in the human head, neck and the hormones secreted
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-Endocrine glands of alimentary system and the hormones secreted
-Endocrine glands of reproductive system and the hormones secreted
-Hormones for calcium regulation -Hormones for other metabolic activities
24
Chemical classes of hormones
Vertebrate hormones fall into three chemical classes:
Peptide hormones consist of chains of amino acids. Examples of small peptide
hormones are TRH and vasopressin.
-Thyrotropin-releasing hormone’s chemical structure
Peptides composed of scores or hundreds of amino acids are referred to as proteins.
Examples of protein hormones include insulin and growth hormone.
-Insulin model
More complex protein hormones bear carbohydrate side-chains and are called
glycoprotein hormones. Luteinizing hormone, follicle-stimulating hormone and
thyroid-stimulating hormone are glycoprotein hormones. There's also another type of
hydrophilic hormones. They are called non-peptide hormones. Although they don't
have peptide connections, they are assimilated as peptide hormones.
Lipid and phospholipid-derived hormones derive from lipids such as linoleic acid,
arachidonic acid and phospholipids. The main classes are the steroid hormones that
derive from cholesterol and the eicosanoids. Examples of steroid hormones are
testosterone and cortisol.
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-Testosterone’s chemical structure
Sterol hormones such as calcitriol are a homologous system. The adrenal cortex and
the gonads are primary sources of steroid hormones. Examples of eicosanoids are the
widely studied prostaglandins.
-Monoamine’s chemical structure
Monoamines derived from aromatic amino acids like phenylalanine, tyrosine,
tryptophan by the action of aromatic amino acid decarboxylase enzymes. Examples of
monoamines are thyroxine and adrenaline.
Diseases of abnormal hormonal functioning
Diseases of the endocrine system are common, including conditions such as diabetes
mellitus, thyroid disease, and obesity. Endocrine disease is characterized by
deregulated hormone release (a productive pituitary adenoma), inappropriate response
to signalling (hypothyroidism), lack of a gland (diabetes mellitus type 1, diminished
erythropoiesis in chronic renal failure), or structural enlargement in a critical site such
as the thyroid (toxic multinodular goitre). Hypo-function of endocrine glands can occur
as a result of loss of reserve, hypo-secretion, agenesis, atrophy, or active destruction.
Hyper-function can occur as a result of hyper-secretion, loss of suppression,
hyperplastic or neoplastic change, or hyper-stimulation.
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-Hyperthyroidism
As the thyroid, and hormones have been implicated in signalling distant tissues to
proliferate, for example, the estrogen receptor has been shown to be involved in certain
breast cancers. Endocrine, paracrine, and autocrine signalling have all been implicated
in proliferation, one of the required steps of oncogenesis.
-Diabetes -Obesity
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Animal Hormones
Androgen
Androgen, also called testoid, is usually a steroid hormone presented in males’ testes
of animals. It controls and stimulates the development as well as the maintenance of
male characteristic in vertebrates by binding to the androgen receptors. The activity of
male sex organs and the development of male secondary sex characteristics (body hair,
deep voice) are also included in androgen’s functions. The most well-known androgen
is testosterone, which can be found in mammals, birds, reptiles and other vertebrates.
Human androgens have a wide range of functions from birth to death. These steroids
are essential to life and function as we have come to understand it. They are also
abused extensively because of their virilizing effect and other body image enhancing
properties. They have been banned in competitive sports but continue to be used
widely.
Androgens inhibit fat deposition. Most of us are aware that males have less fat tissue
than females. This is due to the fact that androgens inhibit the ability of fat cells to
store lipids. This occurs because androgens block the transduction pathway which
normally supports adipocyte function in mammals.
Androgens increase muscle mass. Generally males have greater
amounts of muscle tissues than females due to higher amount of
androgens present. Androgens are known to promote the
enlargement of skeletal muscle cells by acting in a coordinated
manner to enhance muscle functions by acting on many
different types of cells.
Athletes who abuse androgens gain muscle mass over a short
period of time. One must be alert to mood changes in such
clients as hormone levels rise and fall in unpredictable patterns.
Androgens act on the brain too. Circulating androgens affect human behaviour.
Higher levels of androgens are associated with more aggression, energy levels and
drive to achieve goals. This happens because androgens influence human neurons by
making them more sensitive to steroid hormones. Many studies show that androgen
levels are directly proportional to human aggression.
28
Insensitivity to androgens is fairly rare but does occur. Androgen resistance
syndrome is a disorder due to a mutation of gene encoding. It is called androgen
resistance. This results in under verilization or infertility in XY persons of either sex.
Insensitivity to androgens can also result in several types of intersex conditions.
Oxytocin
Oxytocin is a hormone that humans naturally create in the body, that also functions as
a neurotransmitter in the hypothalamus located deep in the brain, which regulates
specific physiological functions like body temperature, hunger, thirst, as well as fight
or flight emotions like fear and trust.
It is released naturally particularly in females who are in labour during child birth,
and it plays an important part in breastfeeding. It is also released in both males and
females during sexual activity and orgasm. The hormone is also released naturally
during hugging and pleasant physical touching between individuals, and the bonding
of a mother and her new born baby.
Oxytocin is best known for roles in female reproduction: 1) it is released in large
amounts after distension of the cervix and uterus during labour, and 2) after
stimulation of the nipples, facilitating birth and breastfeeding. Recent studies have
begun to investigate oxytocin's role in various behaviours, including orgasm, social
recognition, pair bonding, anxiety, and maternal behaviours. Therefore, it is often
referred to as the ‘love hormone’. It is known to directly affect human communication
through the eyes, which is an integral part of emotional interaction between
individuals.
29
Oxytocin is responsible for the increase in levels of
trust between people, which increases social
bonding and may be a viable antidote for depression,
social phobias and shyness. It also plays a part in the
social recognition of facial expressions, some think by
altering the firing of the amygdala, which is the part of
the brain that is primarily responsible for stimulating
emotion.
Oxytocin also stimulates contractions of the smooth muscle tissue in the wall of the
uterus during childbirth. Prior to the late stages of pregnancy, the uterus is relatively
insensitive to oxytocin. As the time of delivery approaches, the muscles become
sensitive to increased secretion of oxytocin. After delivery, oxytocin stimulates the
ejection of milk from the mammary glands. The suckling of an infant stimulates the
nerve cells in the brain to release oxytocin. Once oxytocin is secreted into the
circulatory system, special cells contract and release milk into collecting chambers
from which the milk is released. This reflex is known as the milk let-down reflex.
Thyroxine
The thyroid hormones are tyrosine-based hormones produced by the thyroid
gland primarily responsible for regulation of metabolism. An important component in
the synthesis of thyroid hormones is iodine.
Most of the thyroid hormone circulating in the blood is bound to transport proteins.
Only a very small fraction of the circulating hormone is free (unbound) and
biologically active, hence measuring concentrations of free thyroid hormones is of
great diagnostic value.
Thyroid hormones are lipophilic substances that are able to traverse cell
membranes even in a passive manner. However, at least 10 different active, energy
30
dependent and genetic
regulated iodothyronine
transporters have been identified in
humans. They guarantee that
intracellular levels of thyroid
hormones are higher than in blood
plasma or interstitial fluids.
The thyronines act on nearly every
cell in the body. They act to increase
the basal metabolic rate,
affect protein synthesis, help
regulate long bone growth (synergy
with growth hormone), neuronal
maturation and increase the body's
sensitivity to catecholamines. The
thyroid hormones are essential to
proper development and
differentiation of all cells of the
human body. These hormones also
regulate protein, fat,
and carbohydrate metabolism,
affecting how human cells use
energetic compounds. They also
stimulate vitamin metabolism.
Numerous physiological and
pathological stimuli influence
thyroid hormone synthesis.
Thyroid hormone leads to heat
generation in humans. However,
the thyronamines function via some unknown mechanism to inhibit neuronal activity;
this plays an important role in the hibernation cycles of mammals and
the molting behaviour of birds. One effect of administering the thyronamines is a
severe drop in body temperature.
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Plant hormones
Plant hormones are signal molecules produced within the plant, and occur in
extremely low concentrations. Hormones regulate cellular processes in targeted cells
locally and when moved to other locations, in other locations of the plant. Plant
hormones also determine the formation of flowers, stems, leaves, the shedding of
leaves, and the development and ripening of fruit. Plants, unlike animals, lack glands
that produce and secrete hormones, instead each cell is capable of producing
hormones.
Here we will introduce three special plant hormones: ethylene, auxins and cytokinin.
Ethylene
-Ethylene
Ethylene (IUPAC name: ethene) is a gaseous organic compound with the formula
C2H4. It is the simplest alkene (older name: olefin from its oil-forming property).
Because it contains a carbon-carbon double bond, ethylene is classified as an
unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant
hormone.
Ethylene has very limited solubility in water and does not accumulate within the cell
but diffuses out of the cell and escapes out of the plant. Its effectiveness as a plant
hormone is dependent on its rate of production versus its rate of escaping into the
atmosphere. Ethylene is produced at a faster rate in rapidly growing and dividing cells,
especially in darkness.
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-Sunflower seedling, just three days after germination
New growth and newly germinated seedlings produce more ethylene than can escape
the plant, which leads to elevated amounts of ethylene, inhibiting leaf expansion. As the
new shoot is exposed to light, reactions by phytochrome in the plant's cells produce a
signal for ethylene production to decrease, allowing leaf expansion.
Ethylene affects cell growth and cell shape; when a growing shoot hits an obstacle
while underground, ethylene production greatly increases, preventing cell elongation
and causing the stem to swell. The resulting thicker stem can exert more pressure
against the object impeding its path to the surface. If the shoot does not reach the
surface and the ethylene stimulus becomes prolonged, it affects the stems natural
geotropic response, which is to grow upright, allowing it to grow around an object.
Studies seem to indicate that ethylene affects stem diameter and height. When stems of
trees are subjected to wind, causing lateral stress, greater ethylene production occurs,
resulting in thicker tree trunks and branches.
Ethylene also affects fruit-ripening. Normally, when the seeds are mature, ethylene
production increases and builds-up within the fruit, resulting in a climacteric event just
before seed dispersal.
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Auxins
-Auxin
Auxins were the first class of growth regulators discovered. They are compounds that
positively influence cell enlargement, bud formation and root initiation in plant. They
also promote the production of other hormones and in conjunction with cytokinins, they
control the growth of stems, roots, and fruits, and convert stems into flowers. They
affect cell elongation by altering cell wall plasticity. Auxins decrease in light and
increase where it is dark. They stimulate cambium cells to divide and cause secondary
xylem to differentiate in stems. Auxins act to inhibit the growth of buds lower down the
stems (apical dominance), and also to promote lateral and adventitious root
development and growth. Auxins in seeds regulate specific protein synthesis, as they
develop within the flower after pollination, causing the flower to develop a fruit contain
the developing seeds.
-Lack of auxin can cause abnormal growth (right)
Auxins are toxic to plants in large concentrations. Auxins are commonly applied to
stimulate root growth when taking cuttings of plants. The most common auxin found in
plants is indoleacetic acid.
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Cytokinins
-Cytokinins
Cytokinins or CKs are a group of chemicals that influence cell division and shoot
formation. They were called kinins in the past when the first cytokinins were isolated
from yeast cells. They also help delay senescence or the aging of tissues, which are
responsible for mediating auxin transport throughout the plant, and affect intermodal
length and leaf growth. They have a highly synergistic effect in concert with auxins
and the ratios of these two groups of plant hormones affect most major growth periods
during a plant's lifetime. Cytokinins counter the apical dominance induced by auxins;
they are in conjunction with ethylene to promote abscission of leaves, flower parts
and fruits.
Potential Medical Applications of plant hormones
Plant stress hormones activate cellular responses, including cell death, to diverse stress
situations in plants. Researchers have found that some plant stress hormones share the
ability to adversely affect human cancer cells . For example, sodium salicylate has been
found to suppress proliferation of lymphoblastic leukemia, prostate, breast, and
melanoma human cancer cells. Jasmonic acid, a plant stress hormone that belongs to
the jasmonate family, induced death in lymphoblastic leukemia cells. Methyl jasmonate
has been found to induce cell death in a number of cancer cell lines.
-Sodium salicylate -Jasmonic acid
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References:
http://scienceray.com/biology/human-biology/human-androgens-fu
nctions-uses-and-abuses/2/
http://en.wikipedia.org/wiki/Androgen
http://www.answers.com/topic/what-are-the-functions-of-oxytocin
http://buyoxytocin.net/how-oxytocin-works
http://en.wikipedia.org/wiki/Thyroid_hormone
http://en.wikipedia.org/wiki/Hormones
http://en.wikipedia.org/wiki/Endocrine_system
http://en.wikipedia.org/wiki/Plant_hormone
http://legacy.owensboro.kctcs.edu/gcaplan/anat2/notes/APIINotes1
%20how%20endocrine%20works.htm
http://classes.midlandstech.com/carterp/courses/bio210/chap01/c
hap01.html
http://www.bbc.com/
http://chemistry.about.com/od/chemistrymagic/a/peppertrick.htm
http://chemistry.about.com/u/ua/chemistryfunhumor/Chemistry-Jo
kes.htm
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2010-2011 Committee
Science Society
Teacher advisors: Mr. Lui Kwok Keung
Mr. Yeung Tat Ming
Mr. Kong Kwok Hung
Chairman: 6B Shum Tsz Ho
5D Gast Felix
Vice-chairman: 6B Lam Wai Kit
Secretary: 6B Wu Wing Yan
Treasurer: 6B Chau Yu Chung
Publicist: 5D Yap Ling Fung
Contact: 5D Cheung Yi Ting
Committee: 6A Kwok Chi Kai 5D Chan Tsun Yui
6A Mok Kai Tung 5D Ho Chung Yan
5A Teng Chun Hang 5D Ng Yik Kwong
Biology Society
Teacher advisors: Miss Hui Man Chung
Chairman: 6B Lo Yee
Vice-chairman: 6B Lai Lok Yin
Committee: 6B Fan Sze Nok
6B Wan Tsz Yau
6B Chan Chun Ki
5A Cheung Chung Man
5A Sin Vivian
5A Teng Chun Hang
5D Yeung Tsz Yan
5D Chan Tsz Fung
5D Yap Ling Fung