Saturday, 17 December 2011

2.24a Sources of Food

Recall sources and describe functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, and the mineral ions calcium and iron, water and dietary fibre as components of the diet.

Carbohydrate:
There are a number of different types of grass which having flowered, forms seeds. These seeds are forms of starch provides most of the carbohydrates of our diets, for example, rice and wheat. Another well known source of carbohydrate which are the root tubers of the potatoes. Which is also stored starch and that is a form of carbohydrate. Carbohydrate provides us energy through the process of respiration.

Protein:
Animal  proteins is a well known source of protein and animals such as cows, fishes, pigs, chicken form a large part of the world's protein diet. Plants provide protein through the form of beans or seeds. Protein is associated with growth and repairing cells.

Lipids:
From animals such as cows you would get fat but from animals such as fishes you would get oil and from plants we would get things such as oils, for example, palm oil, sun flower oil. These are associated with stored energy and also insulation.

Wednesday, 7 December 2011

2.5 Elements in biological molecules

Recall the chemical elements present in carbohydrates, proteins and lipids (fats and oils).

Carbohydrate:
The elements present in a carbohydrate is Carbon, Hydrogen and Oxygen (CHO). The simple molecule in carbohydrates are sugars and the larger molecules are the polysaccharites e.g. starch.

Proteins:
The elements present in a protein is Carbon, Hydrogen, Oxygen and Nitrogen (CHON). The simple molecules of proteins are amino acids and the larger molecules are proteins itself.

Lipid:
The elements present in lipids are Carbon, Hydrogen, Oxygen (CHO). Lipids can be split into two categories - the fats and the oils.


Even though lipid and carbohydrates consists of the same elements, the structure is very different from one another. 

2.66 Circulation

Recall the general plan of the circulation system to include the blood vessels to and from the heart, the liver and the kidneys.

Let's start of with some revision:
When blood comes out of the heart it is an artery. When blood comes in the heart its in an vein. The word for lung in biology is pulmonary. The word for liver is hepatic. The word for kidney is renal.


Description: Blood leaves the right ventricle and enters the lungs through the pulmonary artery, then the blood leaves the lungs and enters the left atrium of the heart through the pulmonary vein. Blood then leaves through the major artery - the aorta - through the left ventricle. The Aorta then branches out to the liver and this smaller blood vessels travels through the liver but is still travelling from the heart which is called the hepatic artery. A branch of the aorta travels to the kidney and since this branch is carries blood to the kidney it's called renal artery. Blood returns to the heart through a blood vessel which is called the vena cava. Blood in the liver travels through the capillary and through a vein called hepatic vein. The vein leaving the kidney is called the renal vein.

Tuesday, 6 December 2011

2.65b Blood Vessels

Describe the structure of arteries, veins and capillaries and understand their roles.

The artery is carrying blood in high blood pressure. The walls of the artery is fairly thick, containing muscles. The lumen would be narrow which carries the blood. The muscle contracts and we can see this 'maintains' the blood pressure.

The capillary is the sight of exchange. The capillary walls are very thin (one cell thick) this capillary will have a diameter of a red blood cells.

The vein returns the blood to the heart under low pressure. So although the veins are large, the vein will have a large lumen so the pressure is kept low (low resistance). We can also find that they have valves to stop blood from flowing down.

2.65a Blood vessels

Describe the structure of arteries, vein and caprillaries and understand their roles.

Arteries take blood away from the heart and the high in the arteries are under high pressure. Blood is delivered to another part of the body.

All veins take blood to the heart. Veins take blood which are under low pressure. Blood in veins returns from the organ.

Between the vein and the artery the blood vessel travels through the organ and where the contents of the organ and exchanged with the blood. The blood vessels in the organ are called carpillary. Substance goes into and out of the cell e.g. Oxygen in, Carbon Dioxide out.

264 Heart Output

Understand that the heart rate changes during exercise and under the influence of adrenaline.

Excercising involves muscle contractions and this muscle contract requires energy, this energy is produced by increased levels of muscle cell respiration. So the muscle cell needs more oxygen and the removal of carbon dioxide. By increasing heart rate we can supply more blood and therefore more oxygen and we can remove more carbon dioxide.

 By increasing the output of the heart, more blood is sent to the heart and more carbon dioxide is moved to be excreted by the lungs. The heart can also be influenced by hormones and the particular hormone is adrenaline; this is produced in the adrenal glands which sits on top of the kidney.

This travels to the heart through the blood stream and increases in heart rate. The stimulus for the production includes fear, anxiety, danger. This results in an increase in heart rate. A faster beating heart sends more oxygen and glucose to the body so that they can have more movement or exercise

Friday, 2 December 2011

2.63c Coronary Arteries

Describe the structure of the heart of how it functions.

Heart muscles get its blood supply through the coronary artery. The coronary artery is a branch of the Aorta. So the Aorta leaves the heart and branches to form the coronary artery which takes nutrients such as glucose and oxygen to the heart. The coronary artery is the red blood vessels sweeping across the surface of the heart.
Because of a number of factors including dietary fats, the coronary arteries can become blocked.
If the central part (lumen) becomes blocked the heart would receive less nutrients and less oxygen. This blockage could be a partial blockage which reduces blood flow. A patient suffering from this will suffer from this is experience Angina (heart pain). A serious version of this would be where the coronary artery will completely blocked which is called Myocardial Infarction. If the coronary artery is blocked than all the heart cells supplied by the coronary artery will be deprived or oxygen and nutrients. The cells in that part will begin to die and this is what is better known as a heart attack; when severe this can lead to death. Coronary bypass is where the surgeon re-route the blockage using a extra blood vessel. 

2.63b Heart Function

Describe the structure of the heart and how it functions

Cardiac Cycle = Heart Beat
A normal human heart beat would be around 60 beats per minute (bpm).
Which is one beat per second so the cycle is taking one second.

In the diagram it shows the heart in its Diastole (relaxed) state, all three valves are closed here (semi-lunar valve, bicuspid valve and tricuspid valve)
In this diagram, the heart is still in the state of diastole which means that it is still relaxed, but the atrium is filled with blood this time. This is because the veins (the pulmonary vein and the vena cava) are bringing blood back into the heart. All three valves are still closed.
In the diagram below, the bicuspid and tricuspid valves had opened. The reason for this is because the pressure in the atria is larger than the pressure in the ventricles. So the ventricles fill with blood and a final contraction of the atria and forces blood down the ventricles and stretches the walls of the ventricle and fill up the final volume of the ventricles.
In the fourth diagram, the valves have closed again including the semi-lunar valve. We have contraction of the walls of the ventricle which is also called systole. In which the heart is contracting, which increases the pressure of the blood in the ventricles. Since the ventricle pressure is greater than the atria pressure the valves are now closed. This causes what is known as the first heart sound.'lup'  The semi-lunar valve are still closed, so the blood there are under increasing pressure since it can't escape.
In the fifth stage, the ventricle pressure is larger than the artery pressure so that the semi-lunar valve have both opened. What happens is we eject the pulse of blood into the artery (pulmonary artery and the aorta).
In the last stage, the heart has returned to the state of diastole. The arterry pressure is greater than the ventricle pressure which means the semi-lunar valve both closes together. This causes the second heart sound. 'dup'


Friday, 25 November 2011

2.63a Heart Structure

Describe the structure of the heart and how it functions.

The heart
If blood is going into the heart. The blood vessel is called the vein.
If the blood is comming out of the heart, the vessel is called an artery.
The technical term of the lung is pulmonary and the pulmonary artery takes blood from the heart to the lungs. The pulmonary vein takes blood from the lung to the heart.
The major artery in the body is the aorta. The major vein in the body is called the vena cava.
The heart has two small chambers which is the left and right atrium and two large chambers which is the left ventricle and the right ventricle.  The left side of the heart and the right side of the heart is seperated by a wall called the septum. The aorta takes blood to the body, pulmonary artery takes blood to the lung, and blood returning from the lung from the pulmonary vein and blood returning to the heart through the vena cava.  The valve on the left side of the heart is called the bicuspid valve and valve on the right side of the heart is called the tricuspid valve. The semi lunar valves are located near the end in the right atrium.

Valve Function
When the pressure is high, the blood forces down through the cuspds of the valve open and the blood flows through to a region to a region with low pressure which is the general rule for the valves and blood flow. On the other side of the same valve, if the high pressure area was lower than the low pressure area, such as when the ventricle contracts (the bicuspid/tricuspid valve) high pressure will get behind the cuspds and cause it to close which makes the heart sound - 'Lup' or 'Lub'. This is the first heart sound. The semi lunar valves also works the same way. When the pressure is high in the ventricle, it forces blood through to the artery, but when the heart relaxes blood flows backwards, closing the semi lunar valves making the second heart soun - 'dup'. Which makes the heart sound 'lup' (closure of the atrio ventricular valve) 'dup' (closure of the semi lunar valve) and this is the sound when you hear your heart beating.

2.62 Clottting

Recall that platelets are involved in blood clotting, which prevents blood loss and the entry of microorganism.

Platelets are produced in the bone marrow which are just fragments of cells.
When we have wounds on our body, the exposure of the platelet to the air is that the platelets releases chemicals. In the blood there is a protein called fibrinogen which is soluble and with the chemical from the platelets, this turns into fibre which is solid. What happens is there will be a matrix/network of fibre molecules on the wound and onto this, solidifies the red blood cells and forms a scab. Beneath which, the cells will will be repairing the wounds and stops blood loss. White blood cell will attack any pathogens entering to wound.

Tuesday, 22 November 2011

2.61 Vaccination

Understand that vaccination results in the manufacture of memory cells, which enables future anti-body production to the pathogen to occur sooner, faster and in greater quantity.

In Vaccination, a type of pathogen is introduced into the blood stream (either dead or weakened). The biological word for weakened in attenuated and these pathogens cannot cause diseases. The fragments of the bacteria are introduced to the lymphocytes which produces plasma cells and memory cells. The reason why we vaccinate is because if this happens naturally, it will take time and during this time the organism may be killed or be very severely damaged. If we introduce cells which are attenuated they won't do any harm to the body and still help with the production of memory cells. So if the person actually catches the pathogen which are strong and harmful  the pathogen would be quickly picked up and be eliminated before it harms our body.

2.60b Lymphocytes

Describe how the immune system responds to disease using white blood cells, illustrated by phagocytes ingesting pathogens and lymphocytes releasing antibodies specific to the pathogen.

Unlike Phagocytes, Lymphocytes has a large nucleus.
  • Each type of bacteria has a particular Lymphocyte that can detect it.
  • This is a specific indentification by Lymphocyte of the bacteria. If there was a different bacteria it would require a different Lymphocyte.
  • When they come together, the cell divides to form two different clones and these are called memory cells. The other clones (the Plasma cells) which are produced are the ones that are going to produce the anti-bodies. All genetically identical to the first one.

  • The Plasma cells secrete protein molecules into the bloodstream which are called anti-bodies. One possible action for an anti-body is that it will attach to bacterial cell and act as a label that will attract phagocytes. Second mechanism is that the anti-body attaches and causes bacterial lysis and kills the bacteria. The third more of action, is causing many bacterias to stick together and this is called Aggrototination. This means that the Phagocytes can then engulf the bacterias

  • If after the infection, we meet the same type of bacterial cell The chances of it meeting the memory cell is greater than meeting the original cell and so the consequence of this is is that it reacts faster and more anti-bodies. This is called the seconday response which means the Plasma Cells are the primary response.

2.60a Phagocytosis

Describe how the immune system responds to disease using white blood cells, illustrated by phagocytes ingesting pathogens and lymphocytes releasing antibodies specific to the pathogen.

The process starts with a white blood cell and you can recognise white blood cells through the lobuded nuclues.
  • Phacytosis is the first line of defense of our body, it defends us against bacterias in our blood stream. The white cell can detect the presence of the bacteria because of the chemical the bacteria gives off.
  • The consequence is that the Phagocyte (white blood cell), the chemical stimulus starts the cell to surround the bacteria cells.  The extention is called the Pseudopodia. If we move on to the next stage, the bacteria is closed by the cell membrane of the Phagocyte - this is called the fuse stage.
  • This leads to the next stage which is bacteria enclosed which is called the vescicle. The next step is that the white cell will introduce enzymes which will destroy the bacterial cell. What often happens is that the white cell is excrete and release the fragment of the dead bacteria.




2.57 Composition of Blood

Recall the composition of blood: red blood cells, white blood cells, platelets and plasma.

  • In the blood 45% are cells and 55% are the plasmas.
  • Of the cells the types we have are red blood cells, known as Erythrocytes and the White Blood Cells and in the White blood cells we have phagocytes and Lymphocytes.
  • A plasma is largely composed of water.
  • Also in blood there are fragments of the dead red blood cells known as platelets. These play important role in clotting.

Thursday, 17 November 2011

2.59 Red Blood Cells

Describe the adaptations of red blood cells for the transport of oxygen including shape, structure and the presence of haemaglobin.

If we had a cubic millimeter of blood, there would be 5x10^6 red blood cells, which is 5 million red blood cells per cubic millimeter of blood. Which means 5 trillion cells in a 5 litre circulatory system.

  • The shape is described as a Bioconcave disc. This shape gives you short diffusion distance for oxygen so we get fast diffusion.
  • There is no nucleus in the red blood cell, which means more space for haemaglobin and no mitochondria means that the red blood cells will not use up the oxygen it is transporting.
  • The presence of haemaglobin - haemaglobin is able to carry oxygen and there are millions of haemaglobin molecules (5x10^6) per cell. Each one carrying 4 oxygen molecules.

2.58 Role of Plasma

Understand the role of plasma in the transport of carbon dioxide, digested food, urea, hormones and heat energy.


  • As previously noted, blood is 55% composed of plasma and 45% cells. Plasma is mainly composed of water and the water properties that makes it import is that it is a solvent and a fluid
  • The transportation of carbon dioxide is carried in the plasma dissolved in a form of hydrogen carbonate ions  and some carbon dioxide directly. 
  • Digested food takes the form of soluble sugars and amino acids, which can be transported to the cells through the plasma.
  • Waste molecules such as Urea involved in excretion, are also transported from the liver to the kidney dissolved in the plasma of blood. 
  • In communication terms, blood carries signals from the body through hormones such as ADH, Insulin and Glucagon.
  • Another good property of water is that it is very good at carrying heat so becomes important in maintaining body temperature.

Thursday, 3 November 2011

2.75 Urine

Recall that urine contains water, urea and salts.
  • Urine contains salts, water and urea.
  • Water and salt particularly affects the composition of the tissue fluid which is called osmoregulation.
  • The removal of the urea is part of the excretion of metabolic waste.
  • The salt, water and urea composition in each person varies depending on the condition the person is in.

2.74 ADH

Describe the role of ADH (antidiuretic  hormone) in regulating the water content of the blood.
  • Anti-diuretic hormone is produced in a region of the brain known as the hypothalamus. Like all hormones it flows through the blood stream and the target is the kidney.
  • The effect of ADH is to control and alter the composition of water which is in blood.
  • ADH has the ability to make blood more or less concentrated to keep the tissue fluid isotonic.
  • This is the role of ADH.
  • ADH targets the collecting duct and the effect of ADH is that it allows more water to come out of the collecting duct
  • We know that water selective reabsorption happens in the collecting duct but ADH can increase the amount of water going into the blood.
  • ADH makes the collecting duct walls more porous so that more water can escape from the collecting duct and this water goes back to the blood. 
  • The consequence of ADH secretion is that the urine would be more concentrated and have a lower volume.

2.73 Glucose Reabsorption

Understand that selective reabsorption of glucose occurs at the proximal convoluted tubule.

Selective reabsorption means that it is selected and the reabsorption refers to idea that the glomerulus filtrate will go back to the blood.
  • Filtration happens in the bowman's capsule and the glumerulus filtrate will contain the molecule glucose (and many others e.g. water, salts, amino acids and urea).
  • At the end of the nephron is urine and normally urine does not contain glucose.
  • If you test and find glucose in your urine it is a condition known as diabetes.
  • In the first (proximal) convoluted tubule glucose is removed and taken back to blood.

2.72 Water re-absorption

Understand that water is reabsorbed into the flood from collecting duct

From the previous syllabus statement we learned that Ultrafiltration happens in the bowman's capsule.
  • High pressure blood is forced into the bowman's capsule and the dissolved contents of the blood are forced into the glumerula filtrate and this tube contains glucose, water, salts and urea.
  • When the filtration occurs it will filter out too much water and as the filtrate passes along the tubule here. When it reaches the Collecting duct as the filtrate pass through the collecting duct what happens is that water is removed from the filtrate.
  • The water is then returned to the blood vessel and will go back to the blood stream.
  • Selected reabsorption occurs in the collecting duct.

2.71 Ultrafiltration

Describe ultrafiltration in the Bowman's capsule and the composition of the glomerular filtrate.

In this diagram, we have the same one from 2.70.
  • Nephron's function is to filter blood and ultimately in two things - filtered blood and the waste (urine)
  • The urine is going to emerge at the bottom of the tube and this urine is composed of largely water, salts and also the molecule known as urea (nitrogen waste). The urine goes out into the pelvic region.
  • The first process starts at the bowman's capsule, and the process is called ultrafiltration - the filtration of molecules.
  • The filtration of blood begins with blood comming in through the afferent arteriole and this blood is in high pressure. It is then twisted and branched and becomes much, much smaller (glomerulus) and comes out through the blood vessel efferent arteriole which the diameter of this vessel is smaller than the afferent arteriole.
  • The high pressure forces the liquid (plasma) and plasma contains all the substance contained in blood for example water, salts, amino acids, glucose and urea. These are all forced out from the blood into the space, the inside of the bowman's capsule.
  • When the plasma is forced into bowman's capsule, we call this filtrate and because it is in the glomerulus we call this glomerula filtrate.
  • The blood has been filtered due to high pressure because of the smaller area of the blood vessel.

2.70 Nephron Structure

Describe the structure of a nephron, to cinclude Bowman's capsule and glomerulus, convoluted tubules, loop of Henle and collecting duct.

  • Nephron is the functional unit of the kidney. The part that does the filtration and of the composition of blood.
  • The aorta brings blood and through the renal artery reaches the kidney and waste (urine) then goes through the ureter to the bladder.
  • The filtered blood exits the renal vein and return to the vena cava. If we slice through the kidney we see different colored region, the lighter colored region is called the cotex and the inner, slightly colored region is called the medulla and the lighter colored space is the pelvic region.
  •  In this space it is where the urine collects and drains down the ureter.
  •  The region of the different color is because the kidney is made up of millions of tubes.
  •  The tube starts on the edge of the medulla and moves directly upwards through the medulla and up through the cortex and then will reach a dead-end and is called the bowman's capsule.

If we look at this is more detail we will be looking at the nephron.
  • The tubular structure is called the nephron.
  • Above the dotted line is the cortex and below the dotted line is the medulla.
  • At the end of this tube it will be the pelvic region and its at this place where the urine emerges.
  • The twisted part is called the convoluted tubules and the end tube is called the collecting duct.
  • The dip in the middle is called the loop of henle.
  • The dead end is called the bowman's capsule. The tight knot of blood vessel is called the glomerulus.
  • The first twisted section is called the proximal convoluted tubule (PCT).
  • The second twisted section is called the distal convoluted tubule (DCT).
  • It's the arrangement which gives the different colored region of the kidney. There are millions of nephrons in a kidney.

Thursday, 27 October 2011

2.69 Urinary system

Describe the structure of the urinary system, includin the kidneys, uterus, bladder and urethra.

In the urinary system we have two kidneys the right and the left each with its own blood supply carrying out the process of filtration, osmoregulation, and excretion. From each kidney there is a tube leading to the bladder which is called the ureter. The urine stored in the bladder travels to outside through the urethra and down through the vagina or the penis.

2.68 Excretion

Understand how the kidney carries out its role of excretion and of osmoregulation.

a
To illustrate this we show the excretion of urea (which contains nitrogen which is toxic to the body): The amino acids are used for growth and excess amino acids are excreted as urea. This re-enters into the blood stream and which then enters both kidneys. The kidneys will filter the urea from the blood and the urea will be added to water to form urine and travel down the ureter to collect in the bladder which is stored there as the form of urine. The filtered blood travels back to the blood stream without any urea.

b
Osmo (osmosis) regulation (to control), hypertonic (too concentrated), hypotonic (too dilute)

We want to keep the tissue fluid isotonic (the amount of water into is equal to the output) which is achieved by controlling the composition of blood. The kidney is the organ which controls the composition of blood. Blood circulates through our kidney and excess water or salt is removed and excreted through the ureter here by controlling the content of water and salts in the blood, the kidney can keep the blood and therefore the tissue fluid can be maintained as isotonic which maintains the function of the cells.

2.67b Human organs of Excretion

Recall that the lungs, kidney and skin are organs of excretion.

In the thorax we have lungs, and the metabolic waste the lung excrete is carbon dioxide which is a waste from respiration which we need to release from the body.
The second organ of excretion is the kidneys (we have 2), which excretes excess water, urea (nitrogen waste from amino acids) and salts.
The third organ of excretion is skin and our skin is known to excrete water and salt (sweat) but also a bit of urea.

2.67a Excretion in plants

Recall the origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of the leaves.

Let's start with photosynthesis, which uses light energy to turn CO2+H2O=>C6H12O6+O2 [Excretion]
In respiration in plants with aerobic respiration C6H12O6+O2=enzymes>ATP+CO2[Excretion]+H2O

So in conclusion plants excrete Oxygen and Carbon Dioxide depending upon the process it is doing.

Monday, 10 October 2011

3.10 Menstrual cycle


Understand the roles of oestrogen and progesterone in the menstrual cycle

Oestrogen and progesterone are both hormones, which is produced in the structure called endocrine gland. Hormones will travel through the blood to the target tissue, where the hormone will have effects on.

The ovary is the endocrine gland for (produces) oestrogen that will travel through the blood stream to the lining of the uterus.
The effects of estrogen include:
1. The lining of uterus (wall of endometrium) thickens
2. Flows through the blood stream to out brain and brings the release of sex hormone (LH). It reaches its peak by day 13 of the cycle and causes the ovary to release an egg into the oviduct, where it is possible for fertilization to occur. 

During this first half of menstrual cycle, a circular structure becomes larger and larger. Inside this falloco is the egg. The cells around the fallocal are producing oestogen. It reaches it maximum size by day 13 and causes its wall to rapture and the egg is released. 
LH causes ovulation, the release of the egg.

Now that the fallico is released, the now emptied structure changes its function and develops into the yellow color. This gives us the name corpusinteum that produce progesterone
Progesterone travels through the blood stream to the lining of uterus. 
3. This prevents the lining of uterus from breaking down. This makes it possible that the fertilized egg then can plant into the wall of endometrium and develops into pregnancy. 
4. If no fertilized egg is planted into the wall of endometrium, then it will break down and form what we known as menstrual period/bleeding. 
This mark the end of one menstrual cycle. When the lining is broken down completely, the whole process would repeat

(credits to michelle biology)

3.34 Causes of Mutation

Understand that the incidence of mutations can be increased by exposure to ionizing radiation (for example gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (for example chemicals in tobacco). 


Mutation is the change in base sequence of the genes which creates new alleles. (e.g. ACT => AAT)


Causes:
Radation - Xrays or sunshine (UVB) in this case of UVB this can cause a mutation which leads to skin cancer
Chemicals - effects of tars and tobacco which causes a change in the base sequence which can also lead to cancer.


Chemicals which cause mutation are called mutagens and those that cause cancers are called carcinogen.

3.33 Antibiotic resistance

Understand how resistance to antibiotics can increase in bacterial Population.

An example of this:
Staphlococcus aureus can lead to skin and lung infections.
People with this bacteria can be treated with Methecilline Antibiotics which can kill Staphlococcus aureus.  The Staphlococcus aureus that can be killed by this antibiotic is called the susceptible form. MSSA (Methecilline susceptible Staphlococcus aureus).
What happened was there was a random mutation to the geno of Staphlococcus aureus and when the antibiotics Methecilline is applied it doesn't die and this is called the resistant form. (Methecelline Resistant Staphlococcus aureus)
The mutation has created genes that allowed the bacteria to break down the antibiotics, resisting it so it  can survive. As antibiotics are used across time this type of bacteria increasingly surivives and becomes more common. In time this has become a serious problem in hospitals.

3.32 Types of mutation

Understand that many mutations are harmful but some are neutral and few are beneficial.

Gene=====mutation=======>new alleles

New alleles can be: beneficial, neutral or harmful.
Example of a beneficial mutation might be to improve an efficiency of an enzyme. Example of a harmful mutation might be a production of an enzyme that does not work. If the mutation has no particular effect, we call it a neutral mutation. Although the neutrality may change due to environmental change which can lead to harmful or beneficial mutations.

3.31 Evolution

Describe the process of evolution by means of natural selection.

Evolution can be a change in the form of organisms
Evolution can be a change in the frequency (how many) of alleles.

Natural selections is the mechanism of evolution and was first proposed by Charles Darwin.


Example:
A bacteria staphlococcus aureus which can lead to skin and lung infection is introduced.
The original form of such bacteria is sustained to be kill by methecilline, which is a type of antibiotic. (They are susceptible to the antibiotic.) 
What happens is that a random mutation to the genome of the bacteria allowed us a characteristic of 'breaking down methecilline.' This means that it is no longer killed by the antibiotic. This new form is called the Resistant form, MRSA.
[Refer to definition number 1 of evolution]
Because the MRSA is resistant to the antibiotic, they became increasingly common (increase in frequency of the allele) 
[Refer to definition number 2 of evolution]

Two features of natural selection (process not a thing):
1. Random mutation - produce MRSA form 
2. Non-random selection - due to anti-biotic which is selecting the MRSA to survive and MSSA to be selected and killed

3.30 Mutation

Recall that mutation is a rare, random change in genetic material that can be inherited.

In every DNA there is a base sequence (A,C,T,G,A,A,C,C) which is what constitutes the gene. The form of the gene is called an allele. Certain processes can result in a change of the base sequence which is what we call a mutation. For instance, the base sequence of ACT into AAT. This creates a new version of the allele and it is possible that this process will result in an entirely different protein and therefore creating an entirely different phenotype. The reasons why dominant alleles and recessive alleles exist is because of this process.

3.29 Species Variation

Understand that variation within a species can be genetic, environmental, or a combination of both

Variation = differences in the phenotype
It is often possible to count or to measure these differences and show them in bracket form. Every individual has a phenotype and the appearance for an individual for any of the characteristics is because of their genotype which is be variant to various degrees accordingly to the environment. (Individual Phenotype = Genotype + Environment)
Variation in the population is due to the variation of the genotype and the variation of the environment they occupy and develop in.

Examples of this:



In the first example it shows variation that depends entirely on the genotype with no role of the environment. For example the blood groups.
In the second example it shows where the variation depends on the environment. With one example such as height, one might have been inherited the genotype to be short, however, a good diet may affect his height.
In the third example, it shows a variation in population which depends entirely on the environment. Genes have no roles to play here, for example, languages.

Sunday, 2 October 2011

3.20 Pedigree Diagrams

Understand how to interpret family pedigrees.
If you have inherited a condition, then the square will be filled in if you were male and the circle would be filled in if you were female. Often these are diseases but not necessarily. The circles and squares represent phenotype (characteristics that can be observed)


Pedigree diagrams can also be used to determine whether an affected condition is a dominant allele or a recessive allele:



3.21 Genetic Probabilities

Predict probabilities of outcomes from monohybrid crosses.
(a)
Here we are calculating the chances or probability of offspring from monohybrid cross (crosses involving just the one gene):
[this had already been covered in detail in 3.19]

Parents(phenotype)-        Red Petals          x           White Petals
           (genotype)-               RR                 x             rr                                  R(dominant)>r(recessive)

The next stage involves meiosis in plants, its where they produce the pollen grains.

This shows us:
So there is a 100% chance that the offspring will have red petals (phenotype).

(b)
 Lets breed two heterozygous flowers with red petals together.
   Rr            x               Rr
 
the genotype of the random fertilisation is 25% RR, 25% rr, 50% Rr
the phenotype of the outcome is 25% white petals and 75% red petals.


Tuesday, 27 September 2011

3.22, 3.23 Sex determination

Recall that the sex of a person is controlled by one pair of chromosomes XX in a female and XY in a male.
Describe the determination of sex offspring at fertilisation using a genetic diagram.

In  females they carry a pair of chromosomes X,X (at the same length) and in males they carry XY (X is longer than Y). So when they mate - X x Xy they produce two possibilities XX (female) or XY (male) which is at the ratio of 1:1. So it's the male who determines the sex of their offspring.

3.18 Codominance

Recall the meaning of the terms: dominant, recessive, homozygous, phenotype, genotype and codominance.
Example1
Lets breed a red flower with a white flower.
RR (red flower) x WW (white flower) => Pink (RW)
If you breed Pink (RW) with another Pink (RW) => you will get the following genotypes: RR, RW, RW, WW
This means that there is a 25% chance that the offspring will be red, 25 % chance that the offspring will be white and 50% it will stay pink.
Example2

Wednesday, 21 September 2011

3.19 b F1 x F1 Cross

Describe the patterns of monohybrid inheritance using a genetic diagram
If you want to test for the genotype you always breed with the homozygous recessive. For example, if found a wild black mouse and want to determine the genotype, test it with a white mouse. (in mice white fur is recessive)

3.19 a P1 x P1 Cross

describe patterns of monohybrid inheritance using a genetic diagram
monohybrid: having one gene

Demonstration:
 followed-
 
from the cross we can see all the combination leads to 'Rr' which means that they will all be red because 'R' is the dominant gene and will be all heterozygous 'Rr'.