2.75 Urine

2.75 Recall that urine contains water, urea and salts.

2.74 ADH

2.74 Describe the role of ADH in regulating the water content of blood,

- ADH = Anti-Diuretic Hormone. Is produced in a region of the brain called the Hypothalamus, and its target is the kidney.

- The affect of ADH is to control and alter the composition or quantity of water in blood.

- So ADH has the ability to make the blood more or less concentrated. And we previously established that it is very important for the tissue fluid to be isotonic with the cytoplasm of the cells. This is the role of ADH

- ADH targets the collecting duct. The affect of ADH is that it allows more water to go into the collecting duct increasing the amount of water in the blood. So we have already learned that the collecting duct is where water is selectively reabsorbed into the blood. So applying more of the hormone ADH would make the collecting duct walls more porous so more water can escape from the glomerule filtrate into the collecting duct.

- The consequences of ADH secretion is that the urine coming from the bladder would be more concentrated and have a lower volume. So with ADH secretion more water goes back into the blood, the urine becomes more concentrated, and the volume decreases.

- Our brain releases different amount of the hormone ADH depending on things like the weather - hot or cold day? so that our blood has enough water in it to keep us hydrated.

2.73 Glucose reabsorption

2.73 Understand that selective reabsorbtion of glucose occurs at the proximal convoluted tubule (PCT)

- Selective reabsorbtion means that a molecule is selected to be reabsorbed. This means it will go from the glomerule filtrate and back into the blood. This may seem strange because it has been removed from the blood and now going to be put back into the blood.

- The glucose is removed before the end of the Nephron Tubule because no glucose is found in the Urine (unless you are diabetic). So normally there would be no glucose in the urine. So the glucose has to be returned to the blood stream between the Bowman's capsule (where it is present in the plasma which become the glomerule filtrate) and the pelvic region.

- The answer is that the glucose re-enters the bloodstream at the proximal convuluted tubule which is the section just before the Loop of Henle.

2.72 Water re-absorption

2.72 Understand that water is reabsorbed into the blood from the collecting duct.

- When the plasma is filtered from the blood in the Bowman's capsule, too much water is taken with the plasma from the blood.

- So as the filtrate passes along the Nephron Tube, when it reaches the collecting duct the water is removed from the filtrate and returned back to the blood vessels and back into the blood stream.

- This water has been selected and is reabsorbed by the blood into the blood stream. Because of this is is called Selective Reabsorbtion

- Loop of Henle also collects water but it is the collecting duct that does the controlling of water content of urine and therefore blood.

2.71 Ultrafiltration

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

- The same diagram here is being shown. It is the Nephron which carries out the filtration of our blood, which results in filtered blood with the waste products removed, and the waste known as urine.

Looking at how the urine is actually formed:

- Begins in the Bowman's capsule and is known as ultrafiltration - the filtration of mollecules. Explained using the larger diagram.

- Filtration of blood begins with blood arriving in the Kidney, in the Nephron in the Afferent Arteriole. This blood is under high pressure and as it comes in, and it starts to branch and become much much smaller. This twisted smaller structure is known as the glomerulas.

- The next part to notice is the blood coming out of the Bowman's capsule by the Efferent Arteriole. We should notice that the diameter of this blood vessel in which the blood leaves the Bowman's capsule, is much smaller than the Afferent Arteriole which leads the blood into the Bowman's capsule. Because of the smaller tube, this means the blood pressure increases, and it has a very high pressure. So the glomerulas function is to increase the pressure of the blood. So while the blood is in the glomerulas it is of a very high pressure.

- The consequence of this is that the high pressured blood forces the liquid within blood (plasma - contains components dissolved in blood (salts, water, amino acids, glucose and urea) which forces them out of the blood vessel.

- The high pressure of blood in these twisted tubes, forces the plasma into the space surrounding the glomerulas which is the inside of the Bowman's capsule. When this happens we call this Glomerula filtrate.

- So the blood has been filtered by pressure, due to the restricted space in the blood vessel at the twisted point, which forces the plasma into the Bowman's capsule. The cleaner blood then continues on to do it's job and the plasma travels down the Bowman's capsule and begins it's journey till excretion (See first diagram to understand).

2.70 Nephron Structure

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

- The Nephron is the functional unit of the kidney which does the filtering and the controlling of the composition of blood.

- Blood in the Aorta goes into the kidney via the Renal Artery, and the waste to be excreted is sent down the Ureter and the clean; now filtered blood, goes back to the bloodstream via the Renal Vein which then leads it to the Vena Carva.

- If we slice through the kidney we see different coloured regions. The outer lighter region is the Cortex. The inner darker region is the Medulla. And the very inside lighter coloured space; which is a space, and is known as the pelvic region. This is where the urine collects and drains down the Ureter.

- The reason for the different colours is because the kidney is made up of millions of tubes. This can be seen in the diagram.

- The dead end of the tube which dips in and out of the Cortex and Medulla is called the Bowman's Capsule. This tube is called the Nephron, which we will now look at in more detail.

- The diagram shows the Nephron close up. The part above the dotted line is the Cortex, and below the dotted line is the Medulla

- At the end of the tube in the diagram is in fact the pelvic region, the end of this tube is where the urine emerges.

- The tube is made up of twisted sections, these parts which are in the Cortex are known as the Convoluted Tubules. And the long tube heading towards the pelvic region in the Medulla is called the Collecting Duct (A Duct is a tube).

- The dip inbetween the two Convoluted Tubules which is in the Medulla part of the Kidney is called the Loop of Henle.

- And then the dead end structure is called the Bowman's Capsule. In the diagram you can see the blood vessels tightly noting around it. These are called the Glomerulus.

The Whole structure starts at the Bowman's capsule ---> Proximal Convoluted Tubules (PCT) ---> Loop of Henle --->  Distal Convoluted Tubules (DCT) ---> Collecting Duct ---> Pelvic Region.

- It is the arrangement of this Nephron Structure which gives the Kidney the different colours on the cross section diagram.

2.69 Urinary system

2.69 Understand the structure of the urinary system, including the kidneys, ureters, bladder and urethra.

Most people have two Kidneys – Each with its own separate blood supply, carrying out the process of excretion, filtration and osmoregulation.

From each kidney there is a tube which leads to the bladder. This is called the ureter.

The ureter carries urine from the kidney to the bladder. And then the urine travels through the urethra to exit the body. The urethra is present in both the vagina and the penis so it depends on your sex.

2.68a Excretion & 2.68b Osmoregulation

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

Part A

To illustrate this we will think about excretion of the molecule known as urea.
It is important to remember that urea contains nitrogen which is toxic to our body so it cannot be stored. The original form of nitrogen circulating in our blood stream which is potentially toxic are in the amino acids.

The amino acids are used for growth in our body, but we do have extra amino acids which must be removed because they are toxic. Doing this is the role of both the liver and the kidney.

The first stage of this is when blood circulates into the liver and the amino acids are broken down and converted into urea. This re-enters the blood stream and circulates to the kidneys (both) so it can be removed from the body.

The kidneys will filter the urea from the blood, and it will be added to water to form urine. This is then collected in the bladder, and has been removed from the body.

The filtered blood is then returned to the body from the kidney.

Part B

In the diagram there are some cells in the body surrounded by tissue fluid, which must be isotonic with the cytoplasm of the cells. This means that the amount of water going into and out of these cells is equal so the cells can maintain the same size, shape and function.

However the danger to the tissue is that blood circulating into the tissue will be concentrated causing either a hypertonic or hypotonic tissue fluid. Both of these would be bad because they would either remove, or add too much water to the cell. Maintaining the isotonic relationship between the cells and the tissue fluid is achieved by controlling the composition of blood. It is the role of the kidney to do this. The kidney removes excess water and salts and excretes them. This controls the content of water and salt in the blood, so the kidney can keep the blood isotonic with the cytoplasm of the cells.

2.67b Human organs of Excretion

2.67b Recall that the lungs, kidneys and skin are organs of excretion.

1) Lungs - The lungs excrete carbon dioxide. A waste product from Respiration

2) Kidneys - Excrete excess water, urea and salts.

3) Skin - Excrete water and salts (sweating) and a small bit of Urea.

2.67a Excretion in plants

2.67a Recall the origin of Carbon Dioxide and Oxygen as waste products of metabolism and their loss from the stomata of the leaf.

1) Equation for Photosynthesis: Co2 + H2o -----> C6H12O6 + O2
    The is an example of Excretion because the Oxygen here is a metabolic waste molecule.

2) Equation for Aerobic Respiration: C6H12O6 + O2 ----Enzymes----> ATP + CO2 + H2O
    The is an example of Excretion because the Carbon Dioxide here is a metabolic waste molecule.

So plants excrete oxygen and carbon dioxide depending on whether they are doing Photosynthesis or Respiration.

3.34 Causes of mutation

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

As previously described in 3.30 mutation is changes in the base sequence of the gene. This is where new alleles are produced. The question in 3.34 is what causes these changes to the base sequence of the gene?

1) Ionising Radiation:
      - X-rays
      - UV Rays (Sunlight)

2) Chemicals:
      - Tars
      - Tobacco

Chemicals which cause mutation are called Mutagens
Chemicals which cause mutation and also cause cancer are called Carcinogens

3.32 Types of mutation

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

We start of with the original copy of the gene. Mutation then produces new alleles which are responsible for the phenotype. Their impact could be either beneficial, harmful or neutral and have no positive of negative effect.

Beneficial mutation: To improve the efficiency of an enzyme.

Harmful Mutation: Leads to the production of an enzyme that doesn’t work.

Neutral Mutation: leads to a second or new alleles which has no affect. However this may not last forever, and this new or second alleles could become beneficial or harmful when we have environmental change.

3 31 Evolution & 3.33 Antibiotic resistance

3.31 Describe the process of evolution by means of natural selection.

Evolution is the change in the form of organisms. OR a change in the frequency (how many) of Alleles.

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

In the following example i am going to demonstrate a change in the frequency of alleles by natural selection:


The Eg I am using is Staphlococcus Aureus (SA) which is a Skin Infection and Lung Infection. It can be killed by the antibiotic called Methecilline (M). 


Basically the original form of SA is susceptible to M. However this infection is known to Random Mutation which makes it able to break down M.


Because it can now break down M it is no longer killed by this antibiotic. This is the resistant form of SA


This is an example of evolution because there are now 2 forms of the organism Staphlococcus Aureus (SA)


When antibiotics are applied to the population of SA, the form which is susceptible are decreased, and the form which are resistant increase. This is evolution again because it follows the second definition we have of evolution which is the change in the frequency of Alleles.


There are 2 feature to be noticed here. First the Random Mutation, and the second the Non-Random selection.


Random Mutation produces the form of SA which is resistance to antibiotic M.


Non-Random Selection due to the antibiotic which is selecting the" form of SA which is resistance to antibiotic M" to survive. And for the "form of SA which is susceptible to antibiotic M" to be selected and killed.


These two components here are the classic features of the process of natural selection.

3.33 Understand how resistance to antibiotics can increase in bacterial populations.

Returning to the example of Staphlococcus Aureus (SA) in [3.31], which is a skin or lung infection.  People infected with this can be treated with Methecilline Antibiotic which will kill the SA.

Type which can be killed by antibiotic is the ‘Susceptible SA’.

And a random mutation caused a Resistant form of this infection. ‘Resistant SA’.

The problem here is that the antibiotic is killing the susceptible form of this infection which causes an increase in the resistant form. This is a serious problem because it means the antibiotic no longer works.

3.30 Mutation

3.29 Species Variation

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

Variation = differences that we can see in the phenotype's of individuals. So basically differences in how things appear. It is possible to measure these differences and show them in graphic form.

An individuals have a phenotype, and the appearance of an individual is because of their genotype which will be modified by the environment.

Phenotype = Genotype + Environment

Variation in a population is the variation in all these individuals (talked about above).

V population = V genotype + V environment

So variation in the population; is because of the variation in genotype and because of the variation in the environment in which the species occupy and develop in.

Class 1: Variation in the population/ species is solely down to variation in genotypes. This is discontinuous variation.
- An example of this would be blood groups. Individuals would be typically, A, AB, O or B

Class 2: Variation in the population/ species is down to variation in genotypes and variation in the environment. This is continuous variation.
- An example of this would be an individuals height. One may inherit genes to be very tall, but this will be modified by changes in the environment such as the quality of ones diet.

Class 3: Variation in the population/ species solely down to variation in the environment.This cannot be inherited.
- An example of this would be the home language which you speak. You do not inherit the ability to speak English or French. You speak one of these languages because of your parents or because the place you are born and grow up.

3.25 Mitosis in action

3.25 Understand that mitosis occurs during growth, repair, cloning and asexual reproduction

- Mitosis involves cells dividing to create genetically identical cells.

Growth:

- One of the ways to grow is to add cells, and of course mitosis does this very thing by increasing the cell count.

Repair:

- Helps repair damaged tissue by replacing the dead or damaged cells with new genetically identical cells.

Asexual Reproduction:

- Creates clones by multiplying cells to reproduce.

3.21b Genetic Probabilities

3.21a Genetic Probabilities

3.20A and B Pedigree diagrams

3.18c Codominance

3.18 and 3.19

3.18 Recall the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance.

and...

3.19 Describe the patterns of monohybrid inheritance using a genetic diagram.

3.24 Mitosis

3.24 Understand that the division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes.

- Mitosis is a form of cell division which results in growth which occurs by an increase in the number of cells.

- A normal cell has a nucleus. The number of chromosomes in a nucleus is known as a diploid number which can be abbreviated to the formula 2N. 2N for humans is 46.

- In the process of mitosis this normal cell will divide to form two new cells both with a nucleus. If we take a closer look at the nucleus from each of these cells, we find they both have a diploid nucleus. Meaning they both still have 46 chromosomes meaning they are identical. Sometimes described as daughter cells.

- They are identical because they have the same number of chromosomes and because they have the same set of chromosomes. This means that if we find one chromosome in one of the cells, we will find an identical version of that chromosome in the other cell.

- From this information a number of questions come to mind.
      1) How are the copy of chromosomes made?
      2) How do they separate into the two cells?

These questions are answered in 3.24b



- From 3.24a we have established that a normal cell will copy its chromosomes and divide into two identical cells during mitosis.

- This copy is a process called DNA Replication. In this process each chromosome undergoes a copying process to form an identical copy of itself with all the same genes. These two copies are held together by a central structure called a centromere. These two copies held together by the centromere are called pairs of chromatids.

- This process of DNA Replication takes place in the nucleus while the nucleus is still intact. This means we can't see this process. This is known as the interphase of the cell cycle.

- The process in which the copies of the chromosomes are seperated is dealt with in 3.24c



- Looking at the stages of mitosis:

1) It is during the 'Interphase' of a cell that DNA replication occurs

2) The first sign that a cell is entering mitosis and cell division, is when we see the breakdown of the nuclear membrane. Basically, the nucleus breaks down. This is a phase known as the 'Prophase'. At this point the chromosomes become visible as a pair of chromatids.

3) At this stage the nucleus is gone, and inside the cell a network of protein molecules are present which are known as the spindle, each of which are fibres. They extend from one end (pole) of the cell to the other. During late prophase the chromosome pair will move towards the centre of the spindle and join on to one of the spindle fibres at the centromere.

4) What happens during late phase can be seen in the next stage of mitosis which is known as 'Metaphase.' In the diagram only one pair of chromotids are illustrated. The chromosomes can be seen in the middle attached at the centromere.

5) The next stage is called the 'Anaphase.' Here the fibre (spindle fibre) shortens and pulls one chromotid in one direction towards on of the poles, and one chromatid in the other direction towards the opposite pole. They are moving a part and being separated.

6) The next stage which is the end of mitosis is called 'Telophase.' At thus stage the nucelus begins to reform around the chromosomes at each end of the cell. This will be the new nucleus for the new cell.

7) And finally now the stage called 'Cyto Kinesis' is when the cell splits into two new cells. THIS IS NOT PART OF MITOSIS. The cytoplasm of the original cell splits, and the membrane fuses across the equator to form the new cells. It is important to understand that each of the new cells contain one chromosome.