Why do stinging nettles sting?

Why do stinging nettles sting?

There are actually over 30 species of stinging nettle, with the most common being Urtica dioica, existing throughout the northern hemisphere.

How do stinging nettles sting?

If you look closely, you can see tiny hairs covering each nettle. The long hairs found on stinging nettles are called trichomes. These trichomes are the parts of a stinging nettle that stings you. (1) The stinging structure of the nettle is similar to the hypodermic needle. (2) Each hair is just a single cell that is elongated into a fine point. The walls of this point contain a material that glass is made of, called silica. Therefore, the sting is essentially a tiny glass needle. At the tip of the hair, there is a tiny glass bobble. Below the tiny glass bobble, there is a point of weakness in the cell wall, meaning that when the tip of the hair is touched, the glass bobble breaks off, leaving a sharp edge which can then penetrate skin. The sting is not just due to the fact that the skin is being pierced; it is also due to toxic substances which are present in a swollen sac at the bottom of the hair. It is the injection of these toxins that makes the stinging nettle sting.   The main toxins in this liquid seem to be histamine, serotonin, acetyl choline, and formic acid. This liquid full of toxic substances is under pressure. Therefore, when the top of the hair is knocked off, the toxins are released into the skin. The needle is pushed down as it penetrates the skin, which squeezes the sac at the base of the hair, increasing the pressure of the liquid. This helps to push the liquid up the hair and into the skin. This is similar to pushing down onto the plunger of a syringe (the increase in pressure forces liquid out). (1)

 

                  (7)                                                                                                

                                                                                                                                   (8)

                                                                                                                                 

Little is known regarding the cellular and molecular mechanisms that occur when an organism is stung. It is thought that histamine causes the initial reaction when an organism is stung. However, it is believed that further reactions occur between an organism and the stinging nettles chemicals. It is thought that stinging nettles may contain additional toxic substances that are toxic to the nerves, causing a secondary release of other toxins. (7)

Being able to sting is an effective way for stinging nettles to avoid being eaten. (3)

Information about the toxins in stinging nettles

•  Histamine causes inflammation, which is why we tend to take antihistamines against allergies.
• Serotonin and acetyl choline are neurotransmitters so they fire off our nervous system. (1)
• Serotonin and acetyl choline combine to make histamine stronger, causing an allergic reaction in most people who get stung by stinging nettles. (4)
• Ants produce formic acid, which is the substance that makes their bites hurt.

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The toxins trigger the pain receptors in skin, which causes inflammation and irritation. If you are badly stung, the effects can last to up to twelve hours. (1)

So, why can we sometimes pick stinging nettles up without being stung?

The hairs on the stinging nettles grow in a certain direction. On the stem, they tend to grow upwards. On the leaves, they tend to grow outwards. (6) If you stroke the plant in the direction of these tiny hairs, the stinging nettle tends to not sting you. (5)

By Lauren Watmough 

<!--[if !supportLists]-->     (1)    <!--[endif]-->http://www.bbc.co.uk/programmes/p00gj39c

<!--[if !supportLists]-->     (2)    <!--[endif]-->http://www.nettles.org.uk/nettles/lore.asp

<!--[if !supportLists]-->     (3)    <!--[endif]-->http://www.bbc.co.uk/nature/life/Stinging_nettle#intro

<!--[if !supportLists]-->     (4)    <!--[endif]-->http://www.wisegeek.com/what-is-a-stinging-nettle.htm

<!--[if !supportLists]-->     (5)    <!--[endif]-->http://www.wisegeek.com/what-is-a-stinging-nettle.htm

<!--[if !supportLists]-->     (6)    <!--[endif]-->http://en.wikipedia.org/wiki/Stinging_nettle

<!--[if !supportLists]-->     (7)    <!--[endif]-->http://bioweb.uwlax.edu/bio203/2011/homolka_kail/adaptation.htm

<!--[if !supportLists]-->     (8)    <!--[endif]-->http://www.psmicrographs.co.uk/stinging-nettle-hair-or-trichome--urtica-dioica-/science-image/80012472

The Science behind a Good Meaty Steak

By Jack Scott

We know from observation and experience, that when you cook food, it changes colour, releases aromas, and transforms the taste. Common sense would say that when exposed to heat, something is clearly happening at a chemical level to change the product. But what exactly? And is the same for all foods? 

Louis-Cammile Maillard

In the early twentieth century, a scientist named Louis-Cammile Maillard noticed that when he heated sugars and amino acids together, the mixture slowly turned brown. What he had discovered was the Maillard effect (What a coincidence!) This reaction gave a scientific explanation behind what everyone intrinsically knew, that as food is cooked, it changes it's colour, taste, and chemistry. It wasn't until 1953 however, when an american chemist published a paper on the subject, that a mechanism for the Maillard reaction became established(1). 

The Maillard reaction is not a single reaction, but a complex series of reactions between amino acids and reducing sugars, usually at increased temperatures. In the process, hundreds of different flavour compounds are created. These compounds in turn break down to form yet more new flavour compounds, and so on. Each type of food has a very distinctive set of flavour compounds that are formed during the Maillard reaction(3).

The breakdown of Sugars and Amino Acids which produce the Maillard Reaction

If we take meat as an example, the denatured proteins on the surface of the meat recombine with the sugars present. The combination creates the "meaty" flavour and changes the colour. For this reason, it is also called the browning reaction. When meat is cooked, the outside reaches a higher temperature than the inside, triggering the Maillard reaction and creating the strongest flavours on the surface(1). The Maillard reaction occurs most readily at around 200° C, although in the case of marinating, the acids in the marinade can 'cook' the outer surface of some meats.

The meat has been changed by the Maillard reaction, whilst the onions have been caramelised.

Maillard reactions are (partly) responsible for the flavour of bread, cookies, cakes, beer, chocolate, popcorn, cooked rice. In many cases, such as in coffee, the flavour is a combination of Maillard reactions and caramelisation. Caramelisation is the browning of sugar, a process used extensively in cooking for the resulting nutty flavour and brown colour(2). As the process occurs, volatile chemicals are released, producing the characteristic caramel flavour. Like the Maillard reaction, caramelisation is a type of non-enzymatic browning. However, unlike the Maillard reaction, caramelisation only takes place above 120-150 °C, whereas Maillard reactions could occur at room temperature.

Although studied for nearly one century, the Maillard reactions are so complex that still many reactions and pathways are unknown. Many different factors play a role in the Maillard formation and thus in the final colour and aroma; pH (acidity), types of amino acids and sugars, temperature, time, presence of oxygen, water, water activity (aw) and other food components all are important(4).

1 http://www.exploratorium.edu/cooking/meat/INT-what-makes-flavor.html

2 http://www.exploratorium.edu/cooking/candy/caramels-story.html

3 http://www.food-info.net/uk/colour/maillard.htm

4 http://web.archive.org/web/20041029235215/http://www.agsci.ubc.ca/courses/fnh/410/colour/3_82.htm

What happens when we cook an egg?

 

Cooking an egg.

 

Last week in the woods we cooked an egg using half an orange peel as a container, but what was happening whilst it cooked?

 What is in an egg?

As an egg is the place where an embryo will develop until it is ready to be born it contains almost everything that is required for life (2). Proteins form around 12% of an egg, these are made up of one or more long chains of amino acids. The order and type of these acids effects the shape of the protein and therefore what job it will do within the cell. These jobs range from the replication of DNA to acting as gateways through cell walls (remember the photosynthesis song).

The bonds between various amino acids causes the chains to bend into structures known as an Alpha- helix or a beta- sheets (4).

Amino acids forming an Alpha- helix (1)

Amino acids forming a Beta-sheet. (1)

 

Some parts of these structures are what is known as ‘hydrophobic’ this means they will repel water and will cause the protein to bend in on itself. This creates the complex 3d shape that allows a protein to fulfil its function (4).

A complex protein made from two chains of amino acids.

Changes during cooking.

 When heated the molecules in a protein begin to vibrate more vigorously this breaks the bonds between amino acids causing the protein to ‘denature’ and loose its shape. 

New bonds are then formed between the long chains amino acids creating a solid mass that we can now eat (3). You can see this happen as the clear 'egg white' turns opaque. 

Beating an egg.

 We do not always cook our eggs before we eat them, a chocolate moose contains 'raw' egg. So what happens when we beat an egg that allows us to eat it? 

The answer is very similar to cooking an egg, this time instead of a heat source providing the energy to break bonds, the action of beating itself will denature the proteins stretching them into long chains which trap air creating a moose (5).

Rob Jones

1) Answers.com

2) http://www.nutritionandeggs.co.uk/basic/nutritional-value-eggs
3)http://voices.yahoo.com/the-kitchen-chemist-happens-fry-egg-2969005.html
4) http://www.nlm.nih.gov/medlineplus/ency/article/002467.htm
5) http://cooking.stackexchange.com/questions/11305/what-does-beating-eggs-actually-do-chemically-speaking

How ancient people first used Metals

How ancient people first used Metals

How did metallurgy begin?

There is a theory to how this began and it is called the Campfire theory, this theory states that ores were accidentally used to build stone enclosures around cooking fires, and that people noticed new metals appearing from the ashes. It also says that this would be fine to smelt mercury and lead but would not work for copper or iron as the temperatures around a fire are not high enough. However the most likely setting to discover smelting was when using pottery kilns, where mineral pigments used in colouring and glazing pottery would occasionally have been chemically reduced to pure metal.

Iron in ancient times:

The first smelting of iron took place around about 1500bc, but was only available to the ancients through meteorites that fell to earth. Iron-making itself didn't become an everyday process until 1500bc when hematite, an oxide of iron was used by the ancients to make beads and ornaments. Wrought iron is the first iron known to man. The product of reaction was a spongy mass of iron intermixed with slag. This was then reheated and hammered to expel the slag and then forged into the desired shape. The use of iron weapons revolutionized warfare when it became cheaper to produce as before iron was more expensive than gold.

Copper in ancient times:

The first smelting of copper took place in 4200bc, and was used to create the first tools, implements and weapons. By 3600 BC the first copper smelted artifacts were found in the Nile valley and copper rings, bracelets, chisels were found. By 3000 BC weapons, tools etc. were widely found. Tools and weapons of utilitarian value were now within society, however, only kings and royalty had such tools; it would take another 500 years before they reached the peasants.

Sources:

http://neon.mems.cmu.edu/cramb/Processing/history.html

http://www.uwgb.edu/dutchs/westtech/xancient.htm

Sam Long

An interesting video which helped me understand the Physics behind Fire.

Jack Scott

Combustion

Just a quick reply to an issue which was raised in a previous post surrounding 'incomplete combustion'.

Complete combustion

In complete combustion, the burning fuel will produce only water and carbon dioxide (no smoke or other products). The flame is typically blue. For this to happen, there needs to be enough oxygen to combine completely with the fuel gas.

Many of us use methane gas (CH₄), commonly known as natural gas, at home for cooking. When the gas is heated (by a flame or spark) and if there is enough oxygen in the atmosphere, the molecules will break apart and reform totally as water and carbon dioxide.

Incomplete combustion

If there is not enough oxygen available during a chemical reaction, incomplete combustion occurs, and products such as carbon (C) and carbon monoxide (CO) as well as water and carbon dioxide are produced. Less heat energy is released during incomplete combustion than complete combustion. In incomplete combustion, the burning flame is typically yellow or orange and there is smoke.

Hope this answers your query!

Jack Scott

http://www.sciencelearn.org.nz/Contexts/Fire/Science-Ideas-and-Concepts/What-is-fire

Why use Alloys?

Why do we Alloy Metals?

 

One of the first alloys used by mankind was Bronze (1). Copper had been worked in the years preceding this by some cultures. However the softness of this metal meant that’s its uses beyond the decorative were very limited. Bronze, an alloy of copper and tin, was the answer.

An alloy is a mixture of two or more metals that together produce a mixture where the desired characteristics are improved (3). For example if tin and lead are alloyed, as we will demonstrate in our experiment, they produce an alloy that will scratch both of its constituents demonstrating its increased hardness.

Why are they harder?

The different types of atoms within an alloy disrupt the usual pattern of its structure. ‘Smaller’ atoms fit between the arrangements of ‘larger’ atoms to create a closely locking pattern (2). This makes it more difficult for the layers of atoms to slide over one another increasing hardness (2).

The change in the structure of metals also changes melting point, density and magnetism, corrosion resistance and many other characteristics. As such an Alloy can be tailor made to the exact specifications required for each use.

What else do we use Alloys for?

Alloys are all around us, we use them for thousands of different uses sometimes without even knowing it. Some examples of hidden alloys include.

• Silver jewellery. Think that necklace is pure silver? Unlikely, silver is extremely soft in its natural state, mixed with copper it becomes ‘Sterling silver’ (4).
• Everyone knows Airliners are made from Aluminium, but have you heard of Duralumin? Manganese, Magnesium and Copper combine with Aluminium to increase its strength, making you safer in the air (5)

Some Alloys have amazing properties. Nitinol, an alloy of Nickel and Titanium possesses the ability to be bent out of shape, only to return to its original shape when heated or an electrical current is passed through it. This makes it useful for things like reading glasses. Can you think of any more possible uses?

 

These Nitinol tubes are used by Doctors to keep your cardio vascular system working (6).

 Alloys have thousands of uses within our society, in fact many things would not be possible without them, try to imagine a world without satelites, computers, or even a stainless steel spoon.

Rob Jones

 

1: http://www.ancient.eu.com/Bronze_Age/

2: Http://www.bbc.co.uk/schools/gcsebitesize/science/

3: Concise oxford dictionary 1964.

4: http://www.buzzle.com/articles/types-of-alloys-and-their-uses.html

5: http://www.britannica.com/EBchecked/topic/174106/duralumin

6: http://www.saesgetters.com/applications/superelastic-medical-devices

 

Our experiment.

This week we will be trying very hard to create an Alloy, whilst at the same time teaching others about how and why we would do this. The Alloy we have chosen is Solder, created from a mixture of Lead and Tin.

We will be using:

• Charcoal
• Lead
• Tin
• Carbon Powder
• Casting sand
• Crucible
• Tongs and heat resistant gloves.

The experiment itself should look like this:

• We make a very hot fire using our charcoal.
• Secondly we must prepare our casting sand for the Alloy.
• Placing 1g of lead into our crucible (terracotta pot i found at a garden centre) we heat this in the fire until the lead is molten.
• Whilst this happens we can explain how things melt.
• We then add a spoon full of Carbon powder, this will prevent the lead forming a skin.
• Next we must add 1g of Tin and allow that to melt.
• When everything is molten we move the crucible out of the fire and stir our metals together.
• Before it cools we must then pour the metal into our casting sand.
• When the Solder cools we will be able to demonstrate its increased hardness and reduced density.

The result of our efforts will hopefully demonstrate to the group that 'working with metals' is possible in a Forest environment.

                                                         Lead
      Solder wire.
Tin

Rob Jones

Tin

Tin

Next week, we will be demonstrating the melting points of tin and lead. We will also be discussing alloys. To teach our peer’s about this, we need to know a bit more about tin ourselves.

A bit about tin

Tin (Sn) is a silvery/white metal. It is malleable and slightly ductile, with a crystalline structure. When a bar of tin is bent, a “tin cry” is heard due to the breaking of these crystals. (4) There are twenty-two known isotopes of tin, with nine of these being stable isotopes. Tin has a melting point of 231.9681˚C and a boiling point of 2270˚C. (5)

                 

                                                                             (4)

                                                                               (7)

How long has tin been around?

Tin has been around since the formation of the Earth. It began to be used during the Bronze Age, starting around 3000 B.C. The first metals to be discovered and used by ancient men were gold, silver, copper and lead. Following these, tin, iron and mercury were then discovered and used. (1)

Where is tin found?

During ancient times, Europe obtained most of its tin from the British Isles. The major producers of tin today are China, Indonesia, Peru, Brazil and Bolivia. (2) The primary source of tin is found in cassiterite (tin dioxide). (1) Cassiterite is found in vein deposits, granitic rocks, and pegmatites.

                                                                             (6)

 How is tin extracted?

Tin can be extracted from the ore through smelting, which is heating to extract the ore. (1) An ore is a compound from which an element can be extracted.
Smelting: Cassiterite is reduced with carbon in a reverberatory furnace. A temperature of over 1200˚C is required. Cassiterite is hardly ever produced entirely free from other minerals. Many minerals are reduced to metals at the same time, forming alloys with tin. The tin therefore needs to be refined in order to become commercially useful. Iron is removed by passing steam through the metal when it is molten. Arsenic and antimony are removed by adding aluminium alloy. Copper is removed with sulphur. Very impure tin can be refined using electrolysis. (4)
Tin can be extracted from cassiterite by heating cassiterite with charcoal. The carbon reacts with and removes the oxygen from the cassiterite, leaving behind pure tin. Iron also occurs in very small amounts in cassiterite. If this is not removed, a very hard, useless form of tin is produced. Cassiterite is heated with oxygen to oxidize any iron. The iron is converted to iron (III) oxide and tin is left. (2)

                                                                             (8)

Uses of tin

Tin is not easily oxidized, or easily affected by the sea, water, soft tap water or weak acids. Therefore, it is used to protect other metals from rusting or corroding. (1) Metals can be plated with tin in two ways. The metal can simply be dipped in molten tin and then pulled out. A thin layer of molten tin sticks to the metal and then cools to form a coating. The second method is electroplating. The base metal is suspended into tin sulphate solution, or a similar compound. An electric current is passed through the solution, causing the tin to be deposited on the surface of the base metal. (2)
Tin can be made into bronze. The earliest bronze had a small amount of tin in it. It was soon found that tin added to metals, especially copper, making them stronger and easier to cast. Combing tin and copper made bronze. This brought metalworking from the Copper Age to the Bronze Age. Gold, copper, silver, lead, tin, iron and mercury were used by the Egyptians, Mesopotamians, Romans and Greeks.
Tin is easily mixed with other metals, so it is a good alloy. Tin chloride is used in the manufacture of dyes, textiles and polymers; in the silvering of mirrors; as a food preservative; as an additive of the perfumes used in soap; and as an anti-gumming agent used in lubricating oil. Tin oxide is used in the manufacture of special types of glass, glazes and colours, perfumes, cosmetics, in textiles, and as a polishing material for glass, steel and other materials. Tin fluoride is used as an additive in toothpaste to help protect against cavities. (2) Amalgams in dentistry are made of tin, silver, mercury and sometimes zinc. (1)
Tin is widely used for soldering because it bonds with many metals below their melting points. (1)
One application of tin is that of tin foil. Tin foil is a very thin sheet of tin used to wrap foods. The tin protected the products from spoiling through exposure to the air. Today, most tin foil is made of aluminium as this metal is less expensive.
The majority of today’s toys are made from plastic. However, beginning in the 1800s and during World War Two, many of the best toys were made from tin-plated metal. (2)
Tin is also used in paint, plastics and pesticides. (1) Tin has many uses, due to this, not all of them have been discussed above.

Health effects of tin

Tin bonds with organic substances. This is bad for our bodies. Humans can absorb tin through the skin, by breathing and through eating. The effects of tin include: 

•          Breathlessness
•          Eye and skin irritations
•         Urination problems
•          Dizziness
•          Stomach aches
•          Severe sweating
•          Headaches

More severe effects include:

•          Liver damage
•          Damage to chromosomes
•          Brain damage
•          Red blood cells shortage
•          Depression
•          Weakening of the immune system (1)

Tin in the environment

Tin is pretty much non-biodegradable. It is toxic to living things and damages aquatic ecosystems by interfering with reproduction, growth and feeding patterns. Organic tin compounds build up in the upper part of the ocean. (1)

By Lauren Watmough

     (1)    http://science.yourdictionary.com/articles/who-discovered-tin.html 

     (2)    http://www.chemistryexplained.com/elements/T-Z/Tin.html#ixzz2Lk3dh0TA

     (3)    http://www.carnmetl.demon.co.uk/tin.htm

     (4)    http://www.webelements.com/tin/

     (5)    http://chemistry.about.com/od/elementfacts/a/tin.htm

     (6)    http://en.wikipedia.org/wiki/File:Tin-ancient-sources.svg

     (7)    http://en.wikipedia.org/wiki/Tin

     (8)    http://emilydong.en.made-in-china.com/product/hbUxEqrXvpRc/China-Ferromanganese-Smelting-Furnace.html