Excretion

Biology - Homeostasis & Excretion - Excretion

‘Excretion is the process by which waste products of metabolism are removed from the body’

Excretion happens in both animals and plants. Plants also oxygen (a waste product of the photosynthesis reaction) and carbon dioxide (from the respiration reaction). However, most of the detail here is about excretion in animals.


Nitrogenous waste has to be excreted by all animals.This is because it cannot be stored in the body in the same way that carbohydrates and fats can. Excess proteins are the main source of nitrogenous waste, and are converted either into carbohydrates or into urine.


Humans have a special excretory system. Most of the body's waste products are removed in sweat and urine.

Urine contains:

• ·       Urea
• ·       Ammonia
• ·       Other nitrogenous waste
• ·       Potassium (not nitrogenous)
• ·       Phosphate (not nitrogenous)

Filtration happens in 3 stages:

1.     Blood from the aorta (the largest artery in the body) enters the renal artery (renal meaning to do with the kidneys). This blood is carried to the kidneys.

2.     The kidney filters out the waste products

3.     The ‘clean’ blood leaves via the renal vein and enters the vena cava (a larger vein).

The urine travels down the ureters (connecting tubes) into the bladder. At the top of the urethra, the two sets of sphincter muscles control whether the urine can flow out of the body.
The voluntary sphincter muscles can be relaxed consciously, but the upper sphincter muscles relax when the bladder is full.

The kidney has 3 important types of structure:

Ø  Cortex. The blood flows into the cortex from the renal artery. The cortex contains blood vessels that branch from there, as well as nephrons (also known as kidney tubules)

Ø  Nephrons/kidney tubules run from the cortex to the medulla. The urine is emptied from there into the pyramids.

Ø  Pyramids join to the medulla, and they take the urine from there that has been filtered by the nephrons. The urine collects in the pelvis, which leads to the ureter.

RAMS and Moles

Chemistry - RAMS and Moles

A Mole is a unit of measurement used to express the amount of a substance. It is equal to the number of atoms or molecules in 12g of Carbon-12 (6.023×10^23). -1 This unit of measurement is used instead of grams because one mole of any substance contains the same number of molecules, regardless of its density.

The Relative Atomic Mass of an element is the weighted average mass of the isotopes of the element. It is measured on a scale on which a Carbon – 12 atom has a mass of exactly 12 units.

Relative Formula Mass is the term used to describe the RAM of a compound.

Number of Moles = mass (g)/mass of 1 mole (g)

Percentage Mass of an   = RAM × Number of that element/RFM of compound × 100                               element in a compound

Finding the Empirical Formula of a Compound

1.     List all the elements in the compound

2.     Underneath them, write their experimental masses or percentages

3.     Divide each mass or percentage by the RAM for that particular element

4.     Turn the results into a ratio (by dividing them all by the same number)

5.     Simplify the Ratio until you have it in its simplest form

Empirical Formula Calculations involving hydrated salts

When some substances crystallize from a solution, water becomes chemically bonded to the salt. The salt is said to be hydrated.

Finding the n in BaCl2.nH2O

To find n, the number of water molecules, you have to find the ratio of BaCl2 to the number of moles of water. It’s just another empirical formula!

1.     Find out the masses of water and the other substances in the solution

2.     Divide these by the respective RFM/RAM’s

3.     Turn the results into a ratio

4.     Find the Ratio in its simplest form

Moles in a Solution

A 1M Solution contains 1 Mole per litre; a 2M Solution contains 2 Moles per Litre etc. 

Number of Moles = Volume in Litres × Moles Per Litre of Solution

Focusing on near and far objects (accommodation)

Biology - Coordination - Eyes

The cornea does about 70% of the work involved in converging the light rays onto the retina. The lens will do the final adjusting. This is called Accommodation. Accommodation is a reflex action. The stimulus is the light, which is picked up by the rod and cone cells in the eye (the receptors). The signal as to whether the image is too far-focussed or short-focussed is sent via a sensory neurone to the CNS, which uses a relay neurone to send an impulse down a motor neurone to the effector, the muscles, which will relax or contract according to the original stimulus.

Accommodation is achieved through the relaxation and contraction of the antagonistic pair of muscles, the ciliary muscles and the suspensory ligaments.

Near Focusing: The ciliary muscles relax, and then the lens is pulled thin by the strain on suspensory ligaments exerted by the sclera under pressure from tissue fluid.

Far Focusing: The lens collapses more, due to its elasticity, when the strain on suspensory ligaments is reduced and ciliary muscles contract.

Long sighted people are unable to focus on near objects. Either the cornea or lens doesn’t bend the light enough, or the eyeball is too short. The image is brought into focus too far behind the retina.

Short sighted people cannot focus on distant objects. The cornea or lens bends the light too much or the eyeball is too long. The image is brought into focus in front of the retina.

With age, the lens loses flexibility and does not go back to a round shape as easily. This is why some older people have to wear reading glasses.

Making salts of different solubility

Chemistry - Acids, bases and salts - Salts of different solubility

This post is about how to make salts of different solubility through mixing compounds. Different methods are required for different levels of solubility and there are three categories namely: Insoluble salts, Soluble salts of low reactivity and Soluble salts of high reactivity. 

Insoluble salts

To make a pure sample of an insoluble salt, a precipitation reaction is used. A precipitate is a fine solid that is formed by a chemical reaction involving liquids or gases.

Two ionic solutions come together. In either of the pairs the attractions aren’t strong enough for the ions to stick together but now a pair is formed through strong bonds – the precipitate. The other ions have not changed at all, and are therefore spectator ions.

To choose what to mix, take one solution that has the appropriate positive ion and one solution that contains the negative ion.

To claim the salt, ‘filter, wash and dry the precipitate’.

Making Sodium, Potassium and Ammonium salts

This is why you can’t add an excess solid to a solution: the solid would react with the solution, but the excess would just dissolve in the water present, making it impossible to filter.

This problem is solved by doing a titration. Usually, sodium, potassium hydroxide and ammonia solution would be used, but their carbonates can also be used. These solutions are alkaline so the end-point can be determined with an indicator. Usually methyl orange is used. Yellow indicates too little acid and red too much, making orange the endpoint.

The experiment is run twice with indicator to find the correct volumes of each, and then it is performed again without the indicator with the correct volumes.

Finish by evaporating the water until crystals form upon cooling, and then leave the solution to crystallise on its own.

Making other soluble salts

This technique is used with

·       Acid + metal

·       Acid + metal oxide or hydroxide

·       Acid + carbonate

You add the solid to the acid in excess to ensure all the acid is used up, and then filter off the excess solid. The rest is heated until crystals form upon cooling.

You will usually heat the reaction unless it is a carbonate or magnesium.

William Harvey

Born: 1578

University of Padua: 1598 – 1602
History - Medicine through time - 16th/17th Century


Harvey studied at Padua and then left to work in London as a doctor and then as a lecturer in anatomy at the Royal College of surgeons. From 1618 he was physician to James I and then Charles I. He was taught anatomy be Geronimo Fabricius who identified the valves in the veins and wrote about them in De Venarum Ostiolis (1603). He also designed the new anatomy theatre at Padua.

Before Harvey’s discoveries there were others that are important when discussing Harvey. In the 1543 edition of medicorum Pautinae profefforis, de humani corporis fabrica Libri feptum by Andreas Vesalius, Galen’s theory that heart passed through small holes in the Septum was accepted, however in the 1555 edition he went one step further and denied this. Vesalius’ successor at Padua, Realdo Colombo, showed that blood passed from one side of the body to the other via the lungs and wrote about it in De re Anatomica in 1559.

Harvey discovered that Galen’s theory that blood was recreated instant by instant and was not used again was wrong. He discovered this by looking at the hearts of cold blooded animals, and seeing that the blood as circulating far too quickly for it to be remade. He said that blood flowed out in the arteries and back in the veins, which explained his teacher’s findings of the valves. He wrote down his findings in ‘On the Motion of the Heart’ (1628) after first announcing them in public in 1616.

Harvey was helped by technology of his time. Galen was not around in a time where there were pumps such as the ones used to put out fires, whereas Harvey was. This would have meant that the idea of a pump in any situation would be more open to Harvey’s mind in any situation than Galen’s.

Ambroise Paré (1510-1590)

History - Medicine through time - 16th Century
Paré was the the most famous surgeon of his time, having served four successive French kings. He developed and pioneered many new ways to treat war wounds, for example his new treatment of gunshot wounds. His combined works were published in 1575.

Paré was born to a barber-surgeon in 1510, in a small French village. He wanted to be a barber-surgeon too, even though this was considered to be quite a lowly profession.

He went to Paris to train in 1533 and became surgeon to the Hotel-Dieu in 1534, which was the only public hospital in Paris. He didn’t have enough money to take the tests to become a barber-surgeon so he joined the military. France was engaged in much civil and international war, which was advantageous for his practice. He developed a new way of treating gunshot wounds which was much kinder to the victim.

He published his Method of treating wounds in 1545 in French, because he couldn’t speak Latin. In ’52 he was appointed surgeon to Henri II of France and the first edition of his collected works was published in 1575. He was attacked by the Faculty of Physicians but had the king’s support so could go on publishing books. He published The Apology and Treatise of Ambroise Paré in 1585, which criticized those who had done so to him, saying that they hadn’t had any actual experience but merely read books and ‘chatter[ed] in a chair’.

He was the leader of one of the most important developments of the 16^th Century, which was the proper way to test a theory, which he did to eliminate the myth of the bezoar stone in 1575. He wanted the free flow of ideas and made all of his ideas public.

What a legend.

Andreas Vesalius (1514 - 1564)

History - Medicine through time - 16th Century
Vesalius made important discoveries in anatomy and respectfully corrected the mistakes of the famous Roman anatomist Galen. He also established the important link between science and illustration in his book Tabulae Sex and, more famously, the 1543 edition of the Fabric of the Human Body (Humani Corporis Fabrica). 

Vesalius was born into a medical family and grew up around medical books. The fact that the medical profession ran in his family meant that he was more likely to get a job in medicine, and the fact that his family were well educated meant that he was more likely to get a place in a university (which he did, Louvain 1528-1533 and then he moved to Padua, Paris).

Vesalius was a fan of Galen’s ideas and made many ameliorations to his theories without openly challenging him. An example of this would be that in the Tabulae Sex (1538), he showed the human liver to have five lobes (as Galen wrote) instead of two, even though he knew that it had two because he had performed the dissection himself (he also made a drawing of a two lobed liver in a different view). He strongly believed in illustrations to help readers understand exactly which part of the body he was talking about and how exactly it was made up. As such, he personally invigilated every single carving of his illustrations. In 1543 he left Padua to spend months with the printer in Basel. This was while he was planning his book ‘The Fabric of the Human Body’ which was published in 1543. He also wrote a summary of his book, called the Epitome.

He dedicated the Fabric to the Holy Roman Emperor Charles V, and was given a job at Charles’ court. From here he published another edition of the Fabric with more changes on Galen’s theories but he went on as a doctor, not an anatomist.

In the Fabric, he suggested public dissections and led the way with a new way of publishing books by using illustrations. He was helped by the introduction of the printing press by John Gutenberg in 1454 which allowed his diagrams to be accurately reproduced in copies of his books.

In his Letter on Venesection, he argued in favour of the classical doctors, saying that more blood should be taken and that it should be taken from the same side of the body as the illness.

The First Anaestetics

History - Medicine through time - 18th/19th Century
In the 18th Century, surgery was very dangerous and often lethal. Patients very often died of trauma and pain or blood loss during the operation, or of infection shortly afterwards. Blood transfusions usually failed because it was not known that there were blood groups to be matched. There were no anaesthetics except for alcohol and  opium, and operations were carried out in unhygienic conditions. Many doctors in ordinary clothes would gather around an operating table while surgeons performed the operation with unclean instruments and no gloves or face-masks. Surgery in the Middle ages was grim indeed.

The discovery of Anaesthetics - a timeline

1. The first anaesthetic was the result of progress in the field of chemistry when chemist Humphrey David discovered pain could be relieved by inhaling nitrous oxide. He suggested this would be useful in the field of surgery but was ignored by the medical profession.
2. During the 1840s there were several attempts to find an effective anaesthetic and an American doctor, Crawford Long, found out ether was a useful anaesthetic. He did not announce this.
3. In 1845 an American dentist, Horace Wells, made the same connection between nitrous oxide and anaesthesia as Humphrey David. When he tried to demonstrate this he failed as he did not realise nitrous oxide did not have the same affect on everybody, including his volunteer. 
4. In 1846 William Thomas Green Morton convinced the head of surgeon of the Boston Hospital to carry out an operation using ether as an anaesthetic. The patient had a tumor removed from his neck painlessly. News of this spread quickly and use of ether as an anaesthetist soon became common and widely accepted.
5. In 1847, James Young Simpson, a professor of Midwifery at Edinburgh University, wanted to find something to relieve pain during childbirth. He found ether had a pungent smell and irritated the lungs. He discovered the effects of chloroform, which he found was easier to administer than ether. Within a month of his discovery he had used it 50 times with a 100% success rate.

Opposition to anaesthetics

Most people agreed with the use of anaesthetics, however there were certain groups who did oppose it. Some thought that the surgeons could not be trusted to give the correct dose or control the side effects, or that they didn't want to leave themselves unconscious and in the surgeon's power. Lots of Christians thought that women should have to bear pain during childbirth because it is written in the Bible, and the army considered it to be 'soft'.

There were problems that followed the use of anaesthetics which will be covered in another post. An example would be the extra confidence that painless operations gave to surgeons, which led them to delve far too deeply into the human body and expose their patients to disease and infection. As well as the problem of infection, blood loss had also yet to be conquered.

Fall of the Roman Empire and the Dark Ages

A short post on how the fall of the Roman Empire led to a decline in medicine/public health in Europe. 
History - Medicine through time - AD300-500

In AD359 the empire split into East and West (as any RTW player will know).  In AD410 the Goths invaded Italy and sacked Rome.  In AD476 a Germanic chieftain deposed the Roman Emperor.  The last Roman troops left Britain about AD410.

Britain was no longer controlled by the Pax Romana, so it began to fall apart. The Roman infrastructure (e.g. sewage systems and aqueducts) stopped working and some villages became Saxon settlements. Heating systems stopped working and bands of Saxon invaders attacked most towns.

Those with the knowledge of how to build aqueducts or how to treat illness died, and nobody was trained to replace them, therefore the knowledge was lost apart from a very small number of books which made their way into Arabic Libraries via the Nestorians.

For more information on the Nestorians and how knowledge was preserved after the sack of Rome read the 'Islamic Medicine' post.

Reflection of Waves

Physics - Waves - Reflection
When a wave strikes a barrier, it is reflected. For simplicity, we will consider a wave striking a flat barrier. The wave will strike the barrier at a certain angle, and will be reflected at the same angle.

This article is part 1 of the series 'Reflection, Refraction and Diffraction'. Prior knowledge is not required. The link to part 2 of this series is at the foot of this article.

• Whenever we measure a wave being reflected off a barrier, we use an imaginary line Perpendicular (at 90 degrees) to the barrier to measure the angles from. This line is called the Normal. 
• The angle of incidence is the angle from the normal that the wave is incident at. It is abbreviated to i
• Using the rule 'the angle of incidence is always equal to the angle of reflection', we can see that the angle of reflection will be the same. The angle of reflection is abbreviated to r.

We measure from the normal rather than the surface to avoid complications. For example, imagine that a wave was being reflected at the very edge of a mirror - you would have no surface to measure from on one side! Also, as we will go on to explore now, the surface may be uneven.

The angle of reflection is still equal to the angle of incidence. Here is what is happening: each wave strikes a particular point on the surface which will have a particular gradient. We can find this gradient by drawing a tangent to the curve (the red line on the diagram above). This is the gradient at the one point on the surface that the wave hits. Now we can apply the same technique as above to find the angle of reflection. This is what is happening on any non-reflective surface, each wave is reflected off at a different angle to the ones nearby because the surface is so uneven - the waves dont just reflect off in random directions.

Next post in series: Refraction of Light
http://exploringgcses.blogspot.com/2012/01/refraction-of-light.html

Islamic Medicine

History - Medicine through time - 500BC-AD1000
For the first post, I've decided to talk about Islamic Medicine, in particular the century and a half after the collapse of the Roman Empire in 500BC. 


The Muslims lived largely by the guidance of Islam's holy books, mainly the Qur'an which was believed to be the words of Allah, and later the Hadith which contained the prophet Muhammad (Born AD570)'s interpretations of the Qur'an and his 'wise sayings'. By extension, they based much of their medicine on these sacred texts which proved to be beneficial to them.


Their religion encouraged them to embrace learning, which meant that they learned from the Nestorians who were Christians that fled persecution in the West. The Nestorians brought with them medical ideas that had originated in the West from writers such as Hippocrates and Galen. Hippocrates was the author of the idea of Clinical Observation, a medical practice that involved closely watching a patient's symptoms, the Hippocratic Oath that is taken in a modified form by doctors to this day, and many other ideas contained in his collection of books called the Hippocratic Corpus (although it is known that Hippocrates did not write all of the books himself). Galen made anatomical discoveries that were far past his age, and some of his works, such as On Anatomical Procedures were brought back into the West after being translated from Arabic and may not have been preserved had the Muslims not preserved them.

When Muhammad died in AD632, caliphs ruled the Islamic world and they spread their ideas, sometimes by force. They expanded the Muslim Empire and by AD1000 it stretched from Spain to the River Indus. The caliphs became rich and build beautiful cities like Cairo and Baghdad, and built schools and universities because education was important to the society. They also built mosques and public baths because the Qur’an said that hygiene was important. The success of the Muslims is important because they were the ones who had the knowledge of the Greeks and Romans, so they spread their ideas all over their empire.

Now, for some examples of the medicine that they actually used:

• They invented processes like distillation that allowed them to produce the drugs that they wanted. This technique was also carried over into the West by the Muslims.
• Superstitious beliefs were not encouraged because the Qur'an states that Allah did not create pain without a cure.
• The Qur'an insists on cleanliness, and so the authorities organised the construction of public baths and most people followed a regimen of cleanliness and good health.
•       The famous doctor Rhazes wrote over 200 medical books like On Smallpox and Measles and El Hawi which described many diseases and openly embraced Western medicinal ideas.
  ·         Another doctor, Avicenna, also wrote many medical books. His Canon of Medicine also included Greek ideas, and so when it was translated into Latin and brought back to the West it returned the Greek ideas there.
  ·         They invented a way to anaesthetise the patient.
  ·         They used surgery as a last resort because they knew how dangerous it could be. Abulcases wrote about good surgical procedures including preparing everything beforehand and knowing exactly what you are going to do before opening the body.
  ·         They brought their skills in external surgery to the Western world.
  
  
  They were hindered in ways, because:
  ·         Their religion did not allow dissection, and people who set up medical practices without a license from a hospital were not stopped
  
  
  In summary...
  Usually religion is considered a hindering factor in the development of medicine, however in this case the opposite was true. The Islamic empire did make many advances of its own, but was very important in taking in the ideas of the West after its collapse and spreading them throughout their empire, which allowed Western Medicine to advance.