Sunday, 1 May 2011

Biology - Genetic Definitions


Are paired structures that are made up of strands of chromatin which contains DNA and proteins. In humans, there are 46 chromosomes (23 pairs) in the cell nucleus of regular cells of the body – called somatic cells – as opposed to the gametes (sperm and egg cells), which contain only 23 unpaired chromosomes. A chromosome has a short arm and a long arm, which are held together by a centromere.

DNA – deoxyribonucleic acid

Is the chemical molecule that serves as genetic material. A strand of DNA is a long chain (a polymer) of nucleotides. Each nucleotide of DNA contains a nitrogenous base, a sugar with five carbon molecules called deoxyribose, and a phosphate group. There are four kinds of nitrogenous bases in DNA; adenine (A), thymine (T), cytosine (C) and guanine (G). The nitrogenous bases (nucleotides) can be and are different throughout the long chain of DNA. DNA exists inside the chromosomes.


Lie along the chain of DNA. They are made up of sections of nucleotides. Some genes can have many nucleotides; others have only a few. Humans have thousands of different genes, which reside on different chromosomes, but on the same chromosomes in all people. For example the gene for cystic fibrosis (CF) is always found in the same location on gene number 7 in all humans. However, not all humans have CF (or any other genetic disorder). Some genes show the effect (they are expressed), whereas other genes do not show an effect (they are repressed).


Are the different forms of a trait. They are alternative forms of a gene or base pair sequence that occur on a chromosome. For example, the gene for hair colour resides in a certain location on a certain gene in all humans. However, humans can have many different shades of hair colour; the different shades are represented by different alleles.

Mendel’s Law

Gregor Mendel was a monk in Austria in the mid 19th century. To pass his quiet time, he watched pea plants grow. As he observed subsequent generations of pea plants growing, he noticed subtle changes and wondered how they occurred. He observed the colour of seeds, flowers, and unripe pods; the shape of the seeds and pods, the length of the stem, and the positions of the flowers. Most importantly, he kept accurate records and an accurate account of what plants showed what traits.

During Mendel’s time, the general thought was that the traits of a father blended with the traits of a mother. So a tall father and a short mother were expected to breed average-sized children. Traits in offspring were expected to be averages of the traits in the parents.

One day Mendel crossed a tall pea plant with a short pea plant, expecting to get average-sized pea plants. However, three tall pea plants and one short pea plant grew. He continued to cross tall with short over and over again, the results were similar every time. What he discovered was that offspring carry all the traits of the parents but each offspring is capable of expressing different ones. He figured that these traits were passed from generation to generation by something that he called factors. What Mendel called factors we now call genes.

After studying 28,000 or so pea plants and reviewing his data, Mendel was fairly confident in his research, to be able to state that heredity followed specific patterns. First, he stated that traits are inherited independently of each other – this is Mendel’s Law of Independent Assortment. This law states that each trait or characteristic is found on separate factors (genes), that each factor (or gene) comes in pairs, and that each pair separates on its own.

Mendel also came up with the Law of segregation, which states that during cell division, each allele of a gene pair will randomly move to different gametes. On one of the number 2 chromosomes you have two H alleles; on the other number 2 chromosome you have two h alleles. You have four alleles for hair colour (H, H and h, h) at the locations of the genes for hair colour. When an egg or sperm cell are produced only half of your genetic material goes into each gamete. So, you produce two gametes containing H alleles and two alleles containing h alleles. But each of those alleles separated randomly into the four gametes.

There a multiple genes and alleles for hair colour. Two of the genes may be next to each other, at a particular position on the chromosome, and they will not separate randomly. Their alleles on their paired chromosome will separate randomly though.

Genetic Crosses

When a geneticist writes a genetic equation, the alleles are represented by letters. The dominant traits are usually capitalized and the recessive traits are usually lowercase. Writing the letters that represent the alleles of a gene is called a genotype. A genotype can be written to represent a phenotype, which is the physical result of the expression of a gene.

Phenotypes are created by crosses between different organisms. For example, if you cross a red rose bush with a white rose bush, you would get a rose bush with red or maybe even pink roses. If you were crossing the rose bushes explicitly to see the result of flower colour, you would be performing a monohybrid cross, which cross examines just one trait. Therefore, the phenotype for the first bush is ‘red flowers’ and so the genotype would be RR. The phenotype for the second bush is ‘white flowers’ and so the genotype would be rr.

Copying your DNA

Your DNA does not copy (replicate) itself – only when you create gametes and mate. Every cell in your body needs to be replaced periodically. Cells never stop working and eventually wear out. Cell turnover, as it is called, happens constantly, on any day your body can be replacing some blood cells, skin cells, hair cells and mucous cells (just to name a few types of cell!). Whatever needs to be replaced, the process of DNA replication is the same.

DNA looks like a twisted ladder, with the nucleotide bases forming the ‘rungs’ of the ladder. During replication the DNA strand must ‘unzip’ so that the rungs are split apart with one nucleotide one each side of the strand. Each side of the original DNA strand becomes a template strand upon which the new complementary strand forms. The ‘unzipping’ of the DNA helix is initiated by the enzyme known as helicase.

The entire DNA strand does not unzip all at one time. Only part of the original DNA strand opens up at one time. When the top of the helix is opened, the original DNA strand looks like a Y. This partly open/partly closed area where replication is going on is called the replication fork.

The nitrogen bases that make up each nucleotide along the strand of DNA include adenine (A), guanine (G), cytosine (C) and thymine (T). In a molecule of DNA, A always pairs with T and C always pairs with G: A – T, C – G.

As the enzyme DNA polymerase moves along the template strand, of a base says A then a T is added to the growing complementary strand. If a base on the template strand says G then a C is added to the growing complementary strand.

The order of the bases is important because the order of bases delineate the genes, and the genes dictate what amino acids are produced, and the amino acids determine which proteins are produced, and proteins are needed in every cell of your body. Proteins make up cell structures themselves, as well as enzymes that initiate cellular processes that keep you alive.

The DNA polymer works continuously on the side known as the leading strand. The other side looks messy because the process does not occur smoothly. On the lagging strand, the DNA polymerase reads the template strand and assembles the new bases in fragments. These fragments are called Okazaki fragments, and they are then joined together by the enzyme DNA ligase to form the new complementary strand.

The replicating DNA strand needs energy to go through the steps of reading the template, producing the complementary base, and joining the base to the growing strand. The molecules of the sugar deoxyribose provide that energy. The phosphate bonds that are broken apart when the original strand of DNA ‘unzips’ provides the chemical energy needed to get the whole process started.

DNA Mistakes

Believe it or not, the newly created DNA strand in cells are proofread before cell division is finalized. If a mistake is detected, it’s back to the template strand. The nucleotide that as inserted in error is removed, and the correct one is put in place. If the proofreading function goes awry, mismatch repair enzymes are available to shore things up. Error recognition and repair mechanisms exist in organisms with eukaryotic cells, the details of how they function are not as well understood.

If a mistake in a new strand of DNA goes undetected or unpaired, the mistake becomes a mutation. A mutation is a deviation from the original DNA strand. The nucleotides are not in the same sequence. Although mutations can and do cause serious defects, not all mutations are bad.

The following list explains how mutations, which are usually caused by certain chemicals or radiation affect humans:


These types of mutations occur when the wrong nucleotide is put in for another nucleotide, for example, if the code for a particular gene read 5’ –A-T-C-G-T-C-A-G-3’, the correct complementary sequence for the code on the new strand of DNA would be 3’ –T-A-G-C-A-G-T-C- 5’.

Genetic code is written in a specific direction, because DNA is a double helix in which two strands intertwine, confusion can easily be created when trying to keep track of the ends of the strands. To avoid confusion, one strand of DNA is labelled 3’ (3 prime) and the other 5’ (5 prime), the strand should be read in the 5’ to 3’ direction.

In the example above, the third base over should be guanine (G) instead of cytosine (C). That base could have been passed over during the ‘reading’ of the strand of DNA, or a new cytosine base could have been put in instead of the guanine base. In either case it is wrong, so it is classed as a mutation. Because the mistake involves only one base it is known as a point mutation. There is a chance that the protein that the gene creates would not be affected by this mutation and is, therefore, called a silent mutation.


If during the creation of a new strand of complementary DNA, a nucleotide is read but the complementary base is not inserted, the complementary strand is missing a nucleotide, this type of mutation is called a deletion. These mutations can cause serious diseases.


If an extra nucleotide is slipped into a newly developing complementary strand, the rest of the strand is read wrong. This type of mutation is called a frameshift mutation because the reading of the frames of genetic code is shifted.

Producing Proteins

Ribonucleic acid (RNA) is very similar to DNA, except for these differences:

RNA is single stranded

It contains the sugar ribose instead of deoxyribose

It uses uracil (U) as a nitrogenous base instead of thymine (T)

The nucleotides in RNA pair up as: A – U and C – G. RNA bases can pair up, even though the RNA molecule is single-stranded, this is because RNA has a secondary structure and can fold up and base pair with itself where complementary. RNA molecules are important for the production of proteins, and, just after DNA has been replicated, the complementary strands produce proteins.

DNA harbours the genes that code for what proteins will be produced in your body. But the code buried in segments of DNA is not what initiates protein production. Firstly, the DNA must be ‘rewritten’ into a strand of RNA, and the mRNA carries the information out of the cell’s nucleus to the ribosomes. At a ribosome, the original message is translated, and then the appropriate protein can be produced. Protein synthesis is initiated on the ribosomes that exist free in the cytoplasm. The ribosomes that are attached to the ER to make proteins to be secreted or transported to other organelles.

Tuesday, 19 April 2011

Atoms and Nuclei

Prior to the results of experiments carried out by Geiger and Marsden, who worked under the guidance of Lord Rutherford in 1911, the atom was thought to have the structure of a “plum pudding”. The negatively – charged electrons were pictured as being evenly distributed within a positively – charged uniform mass.

Geiger and Marsden fired alpha particles (α particles) from radon gas at thin gold foil. They then detected the alpha particles after they had been scattered. They found that:

Most of the alpha particles pass through the foil with no deflection

Some are deflected through a range of angles

A small number are “back scattered”.

Rutherford concluded from these results that:

The atom is mainly empty space, allowing most of the alpha particles to pass through undeflected

There are tiny regions of concentrated charge, which explains the large deflection of a small number of the alpha particles

The charge on these regions must be the same sign as that on the alpha particle – positive – to cause the “back scattering”.

Alpha particle – scattering experiments carried out using other materials show that the amount by which an alpha particle is deflected depends on:

The closeness of its approach to the nucleus – the closer it gets, the bigger the force

The charge on the nucleus – the greater the charge, the greater the force of repulsion

The speed of the alpha particle – the faster it travels, the smaller the deflection.


Biology - Cells - The Fundamental Units of life

Every living thing has cells. Cells are sacs of fluid surrounded by membranes, inside the fluid float chemicals and organelles, which are structures inside the cell, which are used during metabolic processes. Each cell is capable of converting fuel to useable energy, this means that cells not only make up living things, they are living things. Cells are found in all plants, animals and bacteria. Many of the basic structures found inside all types of cells, as well as the way those structures work, are very similar, so the cell is said to be the fundamental unit of life.

The most important characteristic of a cell is that it can reproduce by dividing. If cells did not reproduce living things would not continue to live. Cell division is the process by which cells duplicate and replace themselves.

Viruses are similar to bacteria, but they are not truly living organisms because they lack one crucial characteristic; they cannot grow and divide by themselves. In this respect they are more parasites in that they need to take over the cells of a host to reproduce.

Increasingly more complex organisms are made up of increasingly more complex groups of cells, and the organisms survive based on products that the cells make. As scientists develop new ways of studying cells and groups of cells in more depth, they will certainly discover that there is more to be learned.

Examining eukaryotes

Cells fall into two major categories; eukaryotes and prokaryotes. Prokaryotes are cellular organisms that do not have a ‘true’ nucleus. A nucleus is the control centre of a cell, this nucleus contains the genetic information, which controls the way we develop, and is associated with other organelles that function in the production of amino acids and proteins based on what the genetic information dictates. Prokaryotes have some genetic material, but it is not as well organized as it is in eukaryotes, but still prokaryotes are able to reproduce. Eukaryotes are organisms that contain chromosomes, eukaryotes have the following characteristics:

They have a nucleus that stores their genetic information

Animal cells have an organelle called a mitochondria that effectively combines oxygen and food to convert energy to a useable form

Plant cells have chloroplasts, which use energy from sunlight to create food for the plant

Eukaryotic cells have internal membranes which create compartments inside the cells that have different functions

Plant cells have a cell membrane and a cell wall, which is rigid; animal cells only have a cell membrane, which is soft

The cytoskeleton, which reinforces the cytoplasm of the cell, controls cellular movements.

Cells and Organelles

You have organs that are made up of cells, the organ systems perform certain functions within you, cells have organelles that perform certain functions in the cell. Although it takes many millions of cells to create a human, each cell functions on its own. An organelle in one cell does not do the work for another cell, this means that each cell metabolizes individually.

The Plasma Membrane

The fluid inside a cell (intracellular fluid) is called plasma or cytoplasm (cyto means cell). The membrane holding the fluid in the cell is known as the plasma membrane or sometimes called the cell membrane. The cells themselves are floating in a fluid called a matrix; this matrix is insoluble, which means substances do not dissolve in its fluid. The matrix is just simply supporting the cells. The fluid that squeezes between each cell is called the extracellular fluid. The job of the plasma membrane is to separate the chemical reactions occurring inside the cell, from the chemicals that are floating in the extracellular fluid.

If the plasma membrane did not separate the intracellular fluid from the extracellular fluid, waste products that are excreted from the processes inside the cell, to the outside fluid could flow back inside, causing damage to the cell.

The Fluid Mosaic Model

The plasma membrane has a bilayer of phospholipids (fats with phosphorous attached) which at body temperature are liquid. Each phospholipid has a head that is attached to water (hydrophilic – water loving) and a tail that repels water (hydrophobic – water fearing). Both layers of the plasma membrane have the hydrophilic heads pointing towards the outside, and the hydrophobic tails from the inside of the bilayer. Because cells reside in a watery solution, and they contain a watery solution inside them, the plasma membrane forms a circle around each cell so that the hydrophilic heads are in contact with the fluid, and the hydrophobic tails are protected on the inside.

Proteins and substances, such as cholesterol, become embedded in the bilayer, giving the membrane a mosaic look. Because the plasma membrane has the consistency of vegetable oil at body temperature, the proteins and other substances are able to move across it. That’s why the plasma membrane is described using the fluid mosaic model.

The molecules that are embedded in the membrane also serve a purpose. For example, the cholesterol that is stuck in there makes the membrane more stable and prevents it from solidifying when your body temperature is low. Carbohydrate chains attach to the outer surface of the plasma membrane on each cell. These carbohydrates are specific to every person, and they supply characteristics, such as your blood types.

Transport through the Plasma membrane

Some substances need to move from the extracellular fluid to inside the cell; some substances need to move from inside the cell to the extracellular fluid. The exchanges take place in the plasma membrane.

Some of the proteins that are stuck in the plasma membrane help to form channels in the membrane, through which, some substances, such as hormones or ions, are allowed to pass through. They are recognised by a protein molecule (a receptor) within the cell membrane, or they attach to a carrier molecules, which is allowed through the channels. Because only certain substances can pass through the membrane, it is said to be selectively permeable.

Permeability describes the ease with which substances can pass through a border such as a cell membrane. Permeable means that most substances can easily pass through the membrane. Impermeable means that substances cannot pass through the membrane. Selectively or semi permeable means that only certain substances are able to pass through the membrane.

Transporting substances across the plasma membrane can require the cell to use some of its energy to help move the substance across the border. If energy is used, the transport is called active. If molecules can pass through the plasma membrane without using the cells energy supply, the molecules are using passive transport.

Active Transport

Sometimes the molecules are too big to pass through the plasma membrane, or dissolve in the fluid so that they can be filtered through the membrane. In cases like this, cells have to use active transport to help get molecules in or out of the cell.

Passive Transport

A membrane can allow molecules to be passively transported through it in three ways:

Diffusion ~ sometimes organisms need to move from an area where they are highly concentrated to one area where they are less concentrated. This form of transport is much easier than moving molecules from a low to a high concentration. To go from a high to a low concentration, the molecules need only diffuse across the membrane, separating the areas of concentration.

Osmosis ~ this term is used when talking about water molecules diffusing across a membrane. Osmosis is basically the diffusion of water and works in a similar way to diffusion. However, with osmosis, the concentration of substances in the water is taken into consideration. If a solution is isotonic, that means the concentrations of the solutes and solvent are equal on both sides of the membrane. If one solution is hypotonic, there is a lower concentration of solutes (and more solvents) in it when compared to another solution. If a solution is hypertonic, there is a higher concentration of substances in it (and less solvent) when compared to another solution.

Filtration ~ the last form of passive transport is used most often in the capillaries, which are so thin that diffusion easily takes place through them. The pressure at which blood flows through the capillaries is enough force to push water and small solutes that have dissolved in the water right through the capillary membrane. So basically, the capillary membrane acts as filter paper, allowing fluid to surround the body’s cells keeping large molecules from getting into the tissue fluid.

The Nucleus

Every cell of every living thing has a nucleus, and every nucleus contains genetic material. The genetic material directs the production of proteins that make the entire organism function; the nucleus makes the cell function.

In the nucleus of cells that are not currently dividing, clumps of thread-like genetic material called chromatin appear. However, just before a cell divides the chromatin bunches up into chromosomes, which contain DNA (deoxyribonucleic acid).

The DNA has two strands, each of which has sequences of nitrogenous bases that form the genetic code. The code, which is derived from the nucleotide bases in the genes on strands of DNA, is interpreted by a ribonucleic acid (RNA) molecule called messenger RNA (mRNA). The mRNA uses the information from the genetic code to create amino acids in the cell. The amino acids are then taken by transfer DNA (tRNA) to an organelle called a ribosome, where the final proteins are made.

Every cell of every eukaryote has a nucleus which contains genetic material. In cells that are not currently dividing chromatin can be seen. Chromatin refers to all of the DNA in the cell and its accompanying proteins. Chromatin cannot easily be seen prior to cell division, at which point the chromatin bunches up into chromosomes.

The DNA of eukaryotes is double stranded. Each strand of DNA has sequences of nitrogenous bases that form the genetic code. The code is then interpreted, and then a RNA molecule called mRNA is produced from the DNA template. The mRNA uses information from the genetic code for certain amino acids in the cell, which are then taken by tRNA to a ribosome where the final proteins are made. This code is read and converted to a messenger that is carried to the cytoplasm, where it is translated to produce a protein.

Proteins either contribute to the structure of the cell, or they contribute to the function of the cell, meaning they are used as enzymes in metabolic processes. Either way, it is the genetic material inside the nucleus that ultimately controls the structure and function of each and every cell in all eukaryote organisms.

Each nucleus has a round mass inside it called a nucleolus, which produces the third type of RNA molecule – ribosomal RNA (rRNA). rRNA helps to make ribosomes, which get transferred from the nucleus to the cytoplasm to help in making proteins.

Surrounding each nucleus is a double layer formed from proteins and lipids that separates the nucleus from the cytoplasm. This two-layered structure is called the nuclear envelop or nuclear membrane.

The Endoplasmic Reticulum

The endoplasmic reticulum (ER) looks like folded-up sheets resembling a piece of coral. The ER is a series of canals that connects the nucleus to the cytoplasm of the cell. The part of the ER that is dotted with ribosomes is called rough endoplasmic reticulum; the part of the ER that has no ribosomes is called smooth endoplasmic reticulum. Ribosomes on the rough ER serve as the place for synthesis of proteins that are directed by the genes to be put together in the ER.

The smooth ER contains transport vesicles that shuttle cellular products from cytoplasm to organelle, from organelle to organelle, or from organelle to plasma membrane. In addition to protein synthesis, the ER is involved in the metabolism of lipids.

The main function of ER is to make and transport proteins. The ER is essentially the ‘womb’ for new protein chains. Protein synthesis, or production, begins in the nucleus, with the mRNA molecule carrying the genetic information as to what amino acids should be produced. The tRNA molecules carrying the genetic information as to what amino acids should be produced. The tRNA molecules bring the amino acids from the cytoplasm to the ribosomes, which are produced by rRNA. At the ribosomes, the amino acids are joined together to form a protein, and the protein is stored in the ER until it can be moved to the Golgi apparatus.

The Golgi Apparatus

The Italian scientist, Camillo Golgi, discovered the Golgi apparatus. The Golgi apparatus is very close to the ER, it looks like a maze with water droplets splashing off of it. The ‘water droplets’ are transport vesicles bringing material from the ER to the Golgi apparatus.

Inside the Golgi apparatus, products produced by the cell, such as hormones or enzymes, are packed for export to other organelles or to the outside of the cell. The Golgi apparatus surrounds the product to be secreted with a sac called a vesicle. The vesicle finds its way to the plasma membrane, where certain proteins allow a channel to be produced so that the products inside the vesicle can be secreted to the outside of the cells. Once outside, the products can enter the bloodstream and be transported through the body to where they are needed.


Lysosomes are special vesicles formed by the Golgi apparatus to ‘clean up’ the cell. They contain digestive enzymes, which are used to break down products that may be harmful to the cell and ‘spit’ them back out into the extracellular fluid.

Lysosomes also remove dead organelles by surrounding the dead organelle, breaking down the proteins of the dead organelle, and releasing them to reconstruct a new organelle. Because the Lysosomes acts upon its own cell the process is known as autodigestion.


Peroxisomes are little sacs of enzymes produced by the smooth ER, to help protect the cell from toxic products. The peroxisomes break down hydrogen peroxide, because too much could kill you. Hydrogen peroxide is normally produced in some metabolic reactions, so small amounts are inside you. Hydrogen peroxide becomes harmful to cells if too much accumulates, so the cells peroxisomes are continually breaking down this substance.

The chemical formula for hydrogen peroxide is H 2O 2, very similar to the chemical formula of water (H 2O). Peroxisomes turn hydrogen peroxide into water and an extra oxygen molecule, both of which are always needed in the body, and can be used by any cell.

The Mitochondria

The ER supplies the products, the Golgi apparatus distributes the products, and the mitochondria supply the energy for all processes to take place.

The mitochondria convert fuel to useable energy. When food is digested into its smallest molecules and nutrients, and air is taken in (inspired), the smallest molecules and nutrients cross into the bloodstream. These molecules and nutrients include glucose and oxygen.

If there is more fuel digested than necessary for your body to function, the excess fuel gets stored for when it is needed, as fat.

Inside an organism the amount of energy a cell uses is measured in molecules of adenosine triphosphate (ATP). It is the mitochondria that produce the ATP and to produce it, mitochondria use products of glucose metabolism as fuel.

Mitochondria act like furnaces when they convert glucose into ATP; they use oxygen and give off carbon dioxide, and water. Because the process uses oxygen, it is said to be aerobic. This chemical process of respiration occurs in every cell, so it is called aerobic cellular respiration.

Aerobic cellular respiration can be diagrammed like this, with each step breaking down the products in the step preceding it:

Food + Air

Carbohydrates + oxygen and nitrogen

Glucose + oxygen (final products of digestion and inhalation)

ATP + carbon dioxide and water


Chemistry - A Molecular World - Molecules

Atoms are rarely found on their own, they usually bond together to form molecules or large lattice structures.

A molecule is a group of atoms that are bonded together to form the smallest piece of a substance that normally exists on its own.

A molecule is defined as a stable, electrically neutral group of two or more atoms in a definite arrangement, held together by very strong covalent bonds.

Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds.

Most molecules are far too small to be seen with the naked eye, but there are exceptions; DNA, a macromolecule can reach macroscopic sizes, as can molecules of many polymers.

The first molecules are believed to have been formed in space. Some atoms which came out of a supernova were too light, and so moved too fast, to glue together with ionic bonds.

They travelled out of the star until they were cool enough to attach to a dust grain. There these light atoms met and join together with a new type of bond called a covalent bond.

Molecules are the building blocks of life, made mostly of the atoms hydrogen, oxygen, nitrogen and carbon.

The molecular weight of any molecule is the sum of the atomic weights of all its atoms.

Since the atomic weight of a hydrogen atom is 1.008 amu (relative to carbon-12 as exactly 12 amu), the molecular weight of the H2 molecule is twice this value, or 2.016 amu.

Metals & Alloys

Chemistry - Main Metals & Alloys

There are 65 metals that exist naturally on Earth. Of these, just 20 are used, on their own or as part of an alloy, to produce nearly all manufactured metal-based products.

Here are 25 main metals that are used:

Aluminium – a very light, silvery-white metal that is resistant to corrosion. It is extracted from its ore bauxite by electrolysis. Aluminium is used in overhead electric cables, aircraft, ships, cars, drinks cans, and kitchen foil.

Brass – an alloy of copper and zinc. It is easily shaped and is used for decorative ornaments, musical instruments, screws and tacks.

Bronze – an alloy of copper and tin. It resists corrosion and is easily shaped. Coins made of bronze are used as low-value currency in many countries.

Calcium – a malleable, silvery-white metal found in limestone and chalk. It also occurs in animal bones and teeth. It is used to make cement and high-grade steel.

Chromium – a hard, grey metal used to make stainless steel and for plating other metals to protect them, or give them a shiny, reflective finish.

Copper – a malleable, reddish metal used to make electrical wires, hot water tanks and the alloys, brass, bronze and cupronickel.

Cupronickel – an alloy make from copper and nickel, from which most silver-coloured coins are produced.

Gold – a soft, unreactive, bright yellow element that is used for jewellery and in electronics.

Iron – a malleable, grey-white magnetic metal extracted from its ore haematite by melting it in a blast furnace. It is used in building and engineering, and to make the alloy steel.

Lead – a heavy, malleable, poisonous, blue-white metal extracted from the mineral galena and used in batteries, roofing and as a shield against radiation from X-rays.

Magnesium – a light silvery-white metal that burns with a bright white flame. It is used in rescue flared, fireworks and in lightweight alloys.

Mercury – a heavy, silvery-white, poisonous liquid metal used in thermometers, dental amalgam for filling teeth, and in some explosives.

Platinum – a malleable, silvery-white unreactive metal used for making jewellery, in electronics and as a catalyst.

Plutonium – a radioactive metal produced by bombarding uranium in nuclear reactors and used in nuclear weapons.

Potassium – a light, silvery, highly reactive metal. Potassium compounds are used as fertilizers and to make glass.

Silver – a malleable, grey-white metal that is a very good conductor of heat and electricity. It is used for making jewellery, silverware and photographic film.

Sodium – a very reactive, soft, silvery-white metal that occurs in common salt and is used in street lamps and in the chemical industry.

Solder – an alloy of tin and lead that has a low melting point and is used for joining wires in electronics.

Steel – an alloy of iron and carbon that is one of the most important metals in industry. Stainless steel, and alloy of steel and chromium, resist corrosion and are used in aerospace industries.

Tin – a soft, malleable, silvery-white metal. It is used for tin-plating steel to stop it corroding, and in the alloys bronze, pewter and solder.

Titanium – a strong, white, malleable metal. It is very resistant to corrosion and is used in alloys for spacecraft, aircraft and bicycle frames.

Tungsten – a hard, grey-white. It is used for lamp filaments, in electronics and in steel alloys for making sharp-edged cutting tools.

Uranium – a silvery-white, radioactive metal used as a source of nuclear energy and also in nuclear weapons.

Vanadium – a hard, white, poisonous metal used to increase the strength and hardness of steel alloys. A vanadium compound is used as a catalyst for making sulfuric acid.

Zinc – a blue-white metal extracted from the mineral zinc blende. It is used as a coating on iron to prevent rusting. It is also used in certain electric batteries and in alloys such as brass.


Physics - Volcanoes

In certain places around the world, molten rock from deep in the ground leaks out. These places are volcanoes. Some volcanoes are quiet, some explosive, some in between.

Quiet volcanoes gently ooze hot, runny rock. When it flows out on the surface this rock is called lava. Very runny lava spreads out across the surrounding land. Less runny lava builds a gently sloping cone around the hole or crater that it comes from. Sticky lava builds a tall, steep-sided cone.

Violent Volcanoes

Explosive volcanoes erupt with sudden force. Hot gas trapped underground presses on the rocks above until it hurls them from the mouth of the volcano. Hot ash, cinders and molten rock shoot up into the sky and fall back like mortar shells. Explosive volcanoes build steep cones, mainly made of thick layers of ash.

A third kind of volcano sometimes quietly leaks lava, and sometimes shoots out ash and gas. Such ‘in between’ volcanoes produce cones from sandwiched layers of ash and lava.

Inactive volcanoes

In time volcanoes stop erupting. A volcano may stay quiet for centuries. But it may be merely dormant (sleeping). Hot gas could be building up below a lava plug that blocks its outlet. At last the gas pressure may suddenly blast off the volcano’s lid with an immense explosion.

About 1470 BC the Greek island of Santorini blew up with a force as great as that of hundreds of hydrogen bombs. Some volcanoes stop erupting for good. Edinburgh Castle stands on the remains of one of these extinct, or dead, volcanoes.

Where Volcanoes Grow

Like earthquakes, active volcanoes occur where the Earth’s crustal plates are separating or colliding. At such weak places in the Earth’s crust magma (molten underground rock) can well up and escape.

Electromagnetic Waves

Physics - Electromagnetic Waves

Electromagnetic waves are transverse waves, consisting of oscillating electric and magnetic fields. They have a wide range of frequencies, they can travel through most media, including vacuums, and when they are absorbed, they cause a rise in temperature.

Here are all the products of the Electromagnetic Spectrum in order of increasing photon energy from the highest to the lowest photon energy: Gamma rays, X-rays, Ultraviolet (UV) radiation, Visible light, Infrared radiation, Microwaves and Radio waves.

Gamma rays

Electromagnetic waves emitted by radioactive substances. They have the highest photon energy and have the same properties as X-rays, bur are produced in a different way.


Rays which ionize gases they pass through, they cause phosphorescence and bring about chemical changes on photographic plates.

Ultraviolet (UV) radiation

Ultraviolet radiation is emitted by the Sun, but only in small quantities reach the Earth's surface, These small quantities are vital to life, playing the key part in plant photosynthesis, but larger amounts are dangerous.

Visible light

Visible light waves are the only electromagnetic waves we can see. We see these waves as the colours of the rainbow. Each colour has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light. When white light shines through a prism, the white light is broken apart into the colours of the visible light spectrum. Water vapour in the atmosphere can also break apart wavelengths creating a rainbow.

Infrared radiation

These electromagnetic waves are most commonly produced by hot objects and therefore those which are most frequently the cause of temperature rises. They can be used to form thermal images on special infra-red sensitive film, which is exposed by heat rather than light.


Microwave are very short radio waves used in radar (radio detection and ranging) to determine the position of an object by the time it takes for a reflected wave to return to the source. Microwave ovens use microwaves to cook food rapidly.

Radio Waves

Radio waves are electromagnetic waves which are produced when free electrons in radio antennae are made to oscillate by an electric field. The fact that the frequency of the oscillations is imposed by the field means that the waves occur as a regular stream, rather than randomly.

English Glossary

Learning Resources - English - GCSE English Glossary

Alliteration - the repetition of the same consonant sound, especially at the beginning of several consecutive words in the same line e.g. ‘Five miles meandering in a mazy motion’. (From ‘Kubla Khan’ by Samuel Taylor Coleridge).

Aside – words spoken by a character on stage that are not intended to be heard by the other characters present

Assonance – the repetition of similar vowel sounds e.g. ‘There must be Gods thrown down and trumpets blown’ (From ‘Hyperion’ by John Keats), showing the paired assonance of ‘must’ and ‘trum...’ and ‘thrown’ and ‘blown’

Atmosphere – the pervading feeling created by a description of the setting, or the action e.g foreboding, happiness

Audience – the people being communicated to

Aural imagery – images created through sound, by the use of techniques such as alliteration, assonance and onomatopoeia

Autobiography – an account of a person’s life written by him or herself

Biography – a written account or history of the life of an individual

Blank verse – unrhymed poetry that adheres to a strict pattern in that each line is an iambic pentameter (a ten-syllable line with five stresses). It is close to the rhythm of speech or prose

Characterisation – the variety of techniques that writers use to create and present their characters, including description of their appearance, their actions, their speech and how other characters react to them

Climax – The most important event in the story or play

Connotation – an association attached to a word or phrase in addition to its dictionary definition.

Denouement – near the ending of a play, novel, or drama, where the plot is resolved

Direct speech – the words that are actually spoken

Drama – a composition intended for performance before an audience

Dramatic incitement – the incident which provides the starting point for the main action of the play

Dramatic Irony – a situation in a play, the irony of which is clear to the audience but not to the characters e.g in Twelfth Night, where Olivia and Orsino do not know that ‘Cesario’ (Viola) is really a girl disguised as a boy

Episode – a scene within a narrative that develops or is connected to the main story

Exposition – the opening of the play which introduces characters and sets the scene

Fact – something which has been established as true and correct

Fiction – a story that is invented, not factual, though it may be based on events that actually happened

Form – the way a poem is structured or laid out

Free Verse – a form of poetry not using obvious rhyme patterns or a consistent metre

Iambic Pentameter – a line of verse containing five feet, each foot having an unstressed syllable followed by a stressed syllable

Imagery – the use of words to create a picture or image in the reader’s mind

Imperatives – commands

Interior monologue – similar to a soliloquy, a character talking to him or herself

Interview – a meeting between two people – e.g a journalist and a celebrity using questioning and discussion to ascertain information or for entertainment value

Irony – the conveyance of a meaning that is opposite to the literal meaning of the words, e.g ‘This is a fine time to tell me’, (when it is actually an inappropriate time); a situation or outcome which has a significance unforeseen at the time

Language of Advertising – features and techniques commonly found in advertising, e.g appealing adjectives, exaggeration

Metaphor – figure of speech in which a person or thing is describes as being the thing it resembles, e.g ‘she’s a tiger’ to describe a ferocious person

Mood - the atmosphere created by a piece of writing

Narration, first person – the telling of a story through the voice of a character, in their own words, e.g “I went to the fair, even though I hated it”

Narration, third person – the telling of a story through the voice of the author, describing the actions of the characters, e.g ‘He went to the fair, even though he hated it’

Narrative Structure – the way that a piece of story writing has been put together, for example, in a novel, the development of the plot through the arrangement of chapters and who is telling the story

Narrative techniques – the ways in which an author tells a story

Narrator – the person telling the story

Objective information – factual ideas

Onomatopoeia – when a word sounds like the noise it describes e.g ‘pop’ or ‘the murmuring of innumerable bees’

Opinion – a view held by some but not necessarily by others

Personification – the attribution of human qualities or feelings to inanimate objects; a kind of metaphor where human qualities are given to things or abstract ideas

Plot – the main story or scheme of connected events running through a play or novel

Poetic Voice – the ‘speaker’ of the poem – the ‘voice’ of the poem might be that of the poet but could be that of a character or persona from the poet’s imagination

Preview – a kind of report on a film, programme or book etc, soon to be released

Prose – any kind of writing which is not verse, usually divided into fiction and non-fiction

Purpose – the reason for the communication

Regular metre – a regular succession of groups of long and short, stressed and unstressed syllables in which poetry is often written

Review – usually a kind of report on a film, programme or book etc, already released

Rhetorical Question – question raised in speech that does not require an answer (used for effect)

Rhyme – corresponding sounds in words, often at the end of each line or within lines

Rhyming Couplet – two rhyming lines of verse

Rhythm – the ‘movement’ of a poem, as created by the metre and the way that language is stressed within the poem

Setting – the period of time and the place in which the story is set

Simile – figure of speech in which a person or thing is describes as being like another, usually preceded by ‘as’ or ‘like’, e.g ‘she’s like a tiger’ to describe a ferocious person

Snapshots – separate descriptions of the stages in a sequence

Soliloquy – a speech in which a character in a play, expresses their thoughts and feelings aloud for the benefit of the audience, but not for the other characters, often in a revealing way

Stanza – the blocks of lines into which a poem is divided, forming a definite pattern

Stream of Consciousness – a narrative form where random thoughts give the impression that the words have spilled straight from the narrator’s mind

Structure – the way that a piece of story writing has been put together, for example, in a novel, the development of the plot through the arrangement of chapters

Style – (literary) the particular way in which writers use language to express their ideas

Subjective information – personal opinions and feelings

Sub-Plot – a less important part of a story, that is connected to and develops the main plot

Symbolism – similar to imagery: symbols are things that represent something else e.g red roses are given to loved ones because they symbolise love

Theme – a central idea that the writer explores through a text, e.g love, loss, revenge

Tone – created through the combined effects of the author’s rhythm and diction

Voice – the speaker of the poem or prose, either the poet or author’s own voice or that of an invented character

Biology - Genetics

Genetics is the field of science which examines how traits are passed from one generation to another. Genetics affects everything about every living thing on earth. An organism’s genes control how it looks, behaves and reproduces. It is critical to understand genetics as a foundation for all sciences, including agriculture and medicine.

Genetics is divided into four major subdivisions:

Classical genetics

Describes how traits are passed along from one generation to the next.

Molecular genetics

The study of the chemical and physical structures of DNA, RNA and proteins.

Population genetics

Takes Mendelian genetics and ramps it up to look at the genetic makeup of larger groups.

Quantitive genetics

A highly mathematical field examining the statistical relationships between genes and the traits they encode.

Classical genetics...

Classical genetics is the original form of genetics, and in many ways, it is still the best. Classical genetics is the genetics of individuals and their families, it focuses mostly on studying physical traits as a stand-in for the genes that control appearance, or phenotype.

Classical genetics is sometimes referred to as:

Mendelian genetics

Transmission genetics

Classical genetics includes the study of cells and chromosomes. Cell division is the machine that runs inheritance. Classical genetics provides the framework for many subdisciplines. Genetic counselling depends on understanding patterns of inheritance to interpret people’s medical histories from a genetics perspective. The study of chromosome disorders relies on cell biology and understanding what happens during cells division. Forensics also uses Mendelian genetics to determine paternity and work out who’s who with DNA fingerprinting.

Molecular genetics...

Molecular genetics is the study of actual genes. The area of operations for molecular genetics includes all the machinery that runs cells and manufactures the structures called for by the instructions found in the genes. Molecular genetics focuses on the physical and chemical structures of the DNA, double helix. The messages in your DNA constitute the instructions for your appearance and everything else about you, from how your muscles function and how you eyes blink, to your blood type, and your susceptibility to particular diseases.

Genes are expressed through a complex system of inheritance that begins with copying the DNA into a temporary form known as RNA. RNA carries DNA through the process of translation, which is like taking a blue-print to a factory to guide the manufacturing process. Where genes are concerned, the factory makes the proteins that get folded in complex ways to make living organisms.

The study of gene expression and how the genetic code works at the levels of DNA and RNA is considered part of molecular genetics.

Population genetics...

Population genetics is the study of genetic diversity of a particular species. It is a search for patterns that help describe the genetic signature of a particular group. Population genetics helps scientists understand how the collective genetic diversity of a population influences the health of individuals within the population.

Describing the genetics of populations from a mathematical point is critical to forensics. To pinpoint the uniqueness of one fingerprint, geneticists have to sample the genetic fingerprints of many individuals and decide how common or rare a certain pattern might be.

Medicine also uses population genetics to determine how common mutations are and in an attempt to develop new medicines to treat diseases.

Quantitive genetics...

Quantitive genetics examines traits that vary in very subtle ways and relates those traits to the underlying genetics of organisms.

Quantitive genetics take a rather complex statistical approach to estimate how much variation in a certain trait is due to the environment and how much is genetic.

Scientific Reports - Useful Terms

Learning Resources - Scientific Reports Useful Terms

Factor - Anything that may influence the outcome of an activity.

How carefully you control the factor(s) in your experiment/investigation, will contribute to your results.

Accuracy - The term used to describe how exact your measurements are, for example how close to the real value they are. Equipment you use will affect accuracy.

Weights measured on a balance that records weight to 0.01g will be more accurate than those measured on a balance that records weight to 0.1g.

Taking measurements to the nearest 1mm will be more accurate than taking them to the nearest 1cm.

Precision - Precision depends on how accurate your measurements/observations are and also how careful you are in respect of the detail of your investgiation.

Reliablity - Results that are reliable will be repeatable. In general, measurements of the same quantity, when taken several times, are likely to produce varying results. This could be due to variation in samples and/or limitations in your equipment.

The best estimate of a quantity is the average of several repeat measurements. By repeating the measurements in your experiment/investigation you can improve the reliability of your results.

Range - The range is the difference between the highest and lowest of a set of values and for your scientific report would relate to the range of data you collect and the range of repeated results.

Anomalies/Outliers - Are results that do not fit a clear pattern shown by the other results. A result which has a different value to that which you expected and therefore consider wrong, may have been caused by errors in method(s) or abnormalities in specimens which can cause anomalies/outliers.

Preliminary Work - Work that you carry out as part of your planning to help you clarify what you want to do and how to go about it. By carrying out a trial experiment/investigation, this will help plan for your main experiment/investigation and will show any faults in your method.

Scientific Reports

Learning Resources - Writing Scientific Reports


The title of your investigation/experiment, which should be concise and informative.
Example title: The Investigation of Osmosis in Potato Chips in Varying Concentrations of Salt Solution.

List of Contents

Any report that is more than a few pages long would benefit from having a list of contents. Write it when your report is complete. Use a system of consistent headings and numbers to all sections of your report.


A precise summary of your whole report- a preview of your content which enables the reader to decide whether to read the entire report.

The summary should include a statement of the aim/objective(s) of your investigation/experiment and also:

  • A short description of the method used
  • The main results
  • Conclusions or implications of the results
  • Up to 200 words
  • All content in the summary must be discussed in the main content of your report

Note: Write your introduction after you have written your method and results sections of your report.
  • Provide an explanation of: 
  • Aims of your investigation

 Explain why your report is important and exactly what your report is about.

Note: Your aim in writing your introduction is to help your reader understand the significance of the content within the rest of your report.

Preliminary Work
Describe any preliminary experiment(s) and provide the results.

Explain how you used the results to decide on the method and rang of values in your main experiment.


Describe your method in detail:

Note: Your method should be written precisely and step by step so that your reader could repeat the procedures if required. 

  • Describe the materials used to conduct your experiment and explain your choice of apparatus
  • Draw diagrams if appropriate 
  • Explain how you controlled the factors, other than the one you were investigating
  • Explain how you ensured that your measurements were accurate and reliable
  • Explain/justify why you chose a particular method
  • Provide information and observations, stating changes to your method

Tabulate all of your results clearly.


Present your graph(s) clearly and accurately, using them to visually display the reliability of your data.

State your quantitative conclusion:
  • Explaining the results of your investigation
  • Interpret and describe the pattern of your results and/or correlations.
  • Explore the significance of your findings
  • Review the scatter of any graph(s)


Suggest a plausible scientific explanation of your results.


Review your procedure 
  • Evaluate the reliability and accuracy of your evidence 
  • Discuss + explain any anomalies 
  • Consider + discuss the level of confidence of your evidence
  • Suggest how further data would increase confidence in your conclusion 
  • Describe improvements and modifications to improve the validity and reliability of the data in order to make more confident conclusions.

List any references used.

Reflective Learning

Reflect and learn more.
Take responsibility for your learning and consider what you have learnt.