November 4, 2011

2.75 Urine

2.75 recall that urine contains water, urea and salts

Urine consists of Salts, Water and Urea.
The Salts and Water are removed as part of the Osmoregulation process to maintain a isotonic tissue fluid with the cells in the body, and the removal of Urea is part of the excretion of metabolic waste.
The composition of Urine varies, depending on the conditions of the person.

2.74 ADH

2.74 Describe the role of AGH in regulating the water content of the blood.

Anti-Diuretic hormone – produced in a region of the brain known as the hypothalamus, like all hormones it flows through the blood stream to its target; the kidney. It’s job is to control and alter the quantity of water in the blood such that the tissue fluid is isotonic with the cells
ADH targets the collecting duct in the kidney nephron; applying the hormone increases the amount of water reabsorbed from the collecting duct. It makes the collecting duct walls more porous.

2.73 Glucose reabsorption

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

Selected reabsorption – a molecule is selected, and then reabsorbed into the blood; we have removed a molecule from the blood, and we want to put it back.
Urine does not normally have glucose in it, but it is found in the Glomerular filtrate. Note: If a positive test for glucose is found in the urine, it could suggest that the individual has Diabetes.
In the first convoluted tubule (the Proximal CT) glucose is removed and reabsorbed into the blood.

2.72 Water re-absorption

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

When ultrafiltration occurs, too much water is displaced from the blood, so it must be returned into the blood stream, this happens in the Collecting duct.
Water is removed from the filtrate as it travels down the duct to the Pelvic region; the water is then recalculated back into the blood through blood vessels. This is known as Selective reabsorption.

2.71 Ultrafiltration

2.71 describe ultrafiltration in the Bowman’s capsule and the composition of the glomerular filtrate.

The filtration of our blood takes place in the Nephron, resulting with two products: the filtered blood and Urine (waste).
The Urine (composed of water, salts and Urea) drains out of the Collecting duct into the pelvic region, and then drains into the bladder.
  1. Blood arrives into the kidney under high pressure through the Afferent Arteriole
  2. The Arteriole begins to branch off and create a twisted knot-like structure called the Glomerulus; the Efferent arteriole has a smaller diameter resulting in a pressure increase in the glomerulus.
  3. The high pressure forces plasma (contains water, salts, amino acids, glucose, urea) out of the blood vessel into the inside of the Bowman’s capsule, The plasma is called Glomerular filtrate

2.70 Nephron Structure

2.70 describe the structure of a nephron, to include Bowman’s capsule and glomerulus convoluted tubules, loop of Henlé and collecting duct.

Nephron = the functioning unit of the kidney, the part that does the filtration and the controlling of the composition of blood

The image below shows the structure of the kidney and the position of the nephrons, NB: There are millions of nephrons in each kidney for simplicity, only one has been drawn in the diagram

The image below outlines all the relevant sections of the nephron, and just below that I have briefly explained what they are/do.

Glomerulus – The knot of blood vessels where the blood is filtered from
Bowman’s Capsule – the “Dead End” to the Nephron, Ultrafiltraion happens here [see 2.71]
Proximal Convoluted tubule – The first twisted section
Loop of Henlé - The Nephron dips into the Medulla
Distal Convoluted tubule – The second twisted section, back in the Cortex
Collecting duct – The final tube where the urine travels to the Pelvic region.

October 28, 2011

2.69 Urinary system

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

  • Kidney (2) – carries out the process of excretion, filtration and osmoregulation.
  • Ureter (2) – tube that carries Urine to the bladder.
  • Bladder – stores Urine.
  • Urethra – Urine is conducted out of the body through this structure.

The Diagram below illustrates the entire Urinary System
1. Urinary system
2. Kidney
3. Renal pelvis
4. Ureter
5. Urinary bladder
6. Urethra (Left side with frontal section)
7. Adrenal gland
8. Renal artery and vein
9. Inferior vena cava
10. Abdominal aorta
11. Common iliac artery and vein
12. Liver
13. Large intestine
14. Pelvis

2.68 Excretion and Osmoroegulation

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


Kidneys excrete Water, Salts, and Urea (contains nitrogen = toxic to the body \ cannot be stored)
  1. Blood circulates to the liver and amino acids are broken down into Urea
  2. Urea re-enters the blood stream and circulates to the kidneys (there are two)
  3. The kidneys filter the Urea from the blood
  4. Urea is diluted with water to form Urine
  5. Drains down the Ureter and collects in the bladder.


Osmo – Osmosis
Regulation – to control
  • The tissue fluid surrounding cells must be isotonic (equal amount of water entering and exiting cells) so that the cells maintain their size and shape and can function.
  • Blood circulating in the tissue may be very concentrated (causing a hypertonic tissue fluid) or too dilute (causing a hypotonic tissue fluid)
  • To keep an isotonic solution the composition of blood must be controlled, this is the job of the kidney.
  • Excess water, and salts can be removed and excreted through the Ureter to control the contents of water and salts in the blood
  • This means that the Tissue fluid can be kept isotonic with the cells cytoplasm.

October 27, 2011

2.67b Human organs of Excretion

2.67b recall that the lungs, kidneys and skin are organs of excretion
  1. Lungs – metabolic waste = Carbon Dioxide.
  2. Kidneys – metabolic waste = Water, Urea (Excess amino acids), Salts.
  3. Skin – metabolic waste = Water + Salts (sweat), Urea (minimal)

2.76a Excretion in Plants

Topic 6: Excretion
2.67a recall the origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of a leaf

  1. Photosynthesis: CO2 + H2O èC6H12O6 + O2
    • The release of Oxygen as a waste product in photosynthesis is an example of excretion
  2. Respiration: C612O6 + O2 è ATP + CO2 + H2O
    • Carbon Dioxide is given off by the plant; it is a metabolic waste, the carbon dioxide is excreted.

October 10, 2011

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)

Mutation – change in base sequence
  1. Radiation
    • Ionising radiation (e.g. gamma rays, X-rays)
    • UV-B rays (sunshine) causes a mutation that causes skin cancer
  2. Chemical – Mutagens
    • Tars in Tobacco – can cause cancer
    • Chemicals which cause mutation are called Mutagens
    • Chemicals that cause mutation and cancer are called Carcinogens

End of Reproduction and Inheritance Topic

3.33 Antibiotic resistance

3.33 understand how resistance to antibiotics can increase in bacterial populations

Staphylococcus aureus (SA) causes Skin infections and Lung infections
It can be treated with methicillin, an antibiotic that can kill SA.
This type of SA, that can be killed by the antibiotic is the susceptible form
MSSA - methicillin-sensitive staphylococcus aureus.

Through random mutation to the genotype, a type of SA is formed that does not die when given methicillin. This is known as the resistant form
MRSA - methicillin-resistant staphylococcus aureus.

This mutation is therefore a beneficial mutation as it aids the species in its survival.

3.32 Types of Mutation

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

Genes   è New alleles [mutation]
Mutation can be:
  • Beneficial e.g. more efficient enzyme
  • Neutral, but could become beneficial/harmful after a change in the environment
  • Harmful, e.g. not working enzyme

3.31 Evolution

3.31 describe the process of evolution by means of natural selection

Evolution     : Change in the form of organisms
 : Change in the frequency of alleles

Natural selection is the mechanism of evolution (first proposed by Charles Darwin)

If we take Staphylococcus aureus (a skin & lung infection) to show this.
  • The original form is susceptible to being killed by the antibiotic methicillin. Known as MSSA (methicillin-sensitive staphylococcus aureus).
  • By Random Mutation a form was formed that was resistant to this antibiotic, because it could break down the antibiotic. Known as MRSA (methicillin-resistant staphylococcus aureus).
  • This positive change in form of the organism caused the change in frequency of the alleles, because the susceptible organisms began to die out and the frequency of the resistant increased.

3.30 Mutation

3.30 recall that mutation is a rare, random change in genetic material that can be inherited

Rare, random changes in the base sequence of a gene that can be inherited.

Mutations change the base sequences in genes to form new alleles (i.e. ACT…  to AAT…)
This is why we have allele variation… because of mutation, new allele
è new protein è new phenotype

3.29 Species Variation

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

Variation = differences in phenotypes Note: these can be measured and shown in a graph

Initially you must understand that a population’s phenotypes are controlled by their Genotype and/or the Environment they live in.

1. Genotype
Some phenotypes are controlled by purely a variation in the individual’s genotype, and their environment has no control in the phenotype whatsoever. An example of this would be blood group. Notice that this creates discontinuous data (i.e. this or this or this etc.)

2. Genotype + Environment
In some cases the variation of a population’s phenotype is controlled by a combination of their genotype and their environment. Height is a good example phenotype for this; if your parents are reasonably tall, your genotype may make you tall, and your changes in your diet (environment) can also have an effect. This produces a continues scale of variation (i.e. between this point and this point)

3. Environment
There can be variations in a population that are purely controlled by the environment, such as your home language; there are no genotypes to control the languages you can speak, simply how you are brought up controls this. This therefore cannot be inherited

October 3, 2011

3.21 Genetic Probabilities

3.21 predict probabilities of outcomes from monohybrid crosses

P1 Cross
Parents                         Red petal      x     White Petal
Genotype                          RR           x             rr       (R>r)
Meiosis                       ½ R or ½ R    x       ½ r or ½ r
Random Fertilisation


Genotype offspring       all Rr
Phenotype F1                all Red
Probability                     100% Red

F1 Cross
Parents            Red petal         x          Red petal
Genotype        Rr        x          Rr        (R>r)
Meiosis            ½ R or ½ r      x          ½ R or ½ r
Random Fertilisation


Genotype offspring       RR:2Rr:rr
Phenotype F2                3 Red : 1 White
Probability                     75% Red, 25% White

3.20 Pedigree

3.20 understand how to interpret family pedigrees

In the diagram below, Squares represent Male phenotypes and Circles represent female phenotypes; if a condition has been inherited the shape is coloured, by condition we generally mean diseases, but not necessarily.

Reading the diagram
Initially the diagram initiates with an “affected” female carrying a condition and a “normal” male. The children of these parents are shown by the vertical line below the parents, a male child has two children with another female... these become the grandchildren, one of the granddaughters has a four children, and two of which can be seen as affected. So two great-grandchildren (a male and a female) are infected in this pedigree diagram

Analysing the diagram
What we now should do is to determine whether the affected condition is caused by a dominant allele or a recessive allele.
If the condition is caused by a dominant allele then the following statement is true: ‘All individuals with genotypes DD and Dd will be affected’. The alternative hypothesis is that ‘All individuals with the genotype dd will be affected’.
If we examine the granddaughter and her infected son we have two unaffected parents and an infected child. If our first hypothesis was correct then the child must contain a “D” allele, which means at least one of the parents must have the “D” allele, but if that where the case then the parent would also be “affected” so we can safely make the assumption that the condition in this case is caused by a the Homozygous recessive genotype.

September 26, 2011

3.19b F1 x F1 Cross

3.19 describe patterns of monohybrid inheritance using genetic diagrams

P1:                    Red petal x White Petal
F1:                    Red (Rr)
F1Cross (F1 x F1)
                    Red Petal x Red Petal
                      Rr x Rr
                          R or r x R or r
Random Fertilisation:



Genotype F2:                    RR : 2Rr : rr
Phenotype:                        Red : 2Red : White
Monohybrid F2 Ratio:

September 25, 2011

3.19a P1 x P1 Cross

3.19 describe patterns of monohybrid inheritance using genetic diagrams

3.18b Codominance

3.18 recall the meaning of the terms; dominant, recessive homozygous, heterozygous, phenotype, genotype and codominance.

3.18 Phenotypes and Genotypes

3.18 recall the meaning of the terms; dominant, recessive homozygous, heterozygous, phenotype, genotype and codominance.

September 17, 2011

3.2 Fertalisation

3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo
  1. The Adult male and female Gametes are formed by Meiosis
  2. These Gametes have half the number of chromosomes as a diploid cell
  3. The two opposite gametes fuse to form a zygote, this is now a diploid cell containing a full set of chromosomes
  4. The Zygote goes the mitosis to divide into a ball of cells, known as a blastula which then grows to form the embryo.

I have created the diagram below to try to visually explain the concept.

3.9 Reproductive Organs

3.9 recall the structure and the function of the male and female reproductive systems

The Male Reproductive Organ System
There are 8 organs that make up the male reproductive system these are:
  1. Bladder – Stores urine
  2. Testis – Carries out meiosis which produces the male gamete; the sperm cell
  3. Epididymis – Store sperm cells
  4. Vas deferens – carries sperm cells to the Penis
  5. Prostate – 20/30% of the volume of the semen, contains sugars. (Alkaline solution, to neutralise the acidic secretions within the vagina)
  6. Seminal Vesicles – Produces 70% of the volume of semen (also sugar based and alkaline)
  7. Urethra – common tube that joins the left and right vas deferens, transports semen and urine down the penis
  8. Penis – carry sperm cells into the vagina during sexual intercourse

Note: Semen = Sperm Cells + Prostate secretions + Seminal Vesicles secretions

The Female Reproductive Organ System
There are 7 organs in the female reproductive system:
  1. Ovary – Meiosis occurs to form the female Gamete; the egg cell
  2. Oviduct – Carry the eggs to the uterus, Fertilisation occurs here. (a.k.a. the fallopian tubes)
  3. Uterus wall – the wall of the uterus, made of muscle, stretches to accommodate a pregnancy
  4. Uterus lining – accepts and develops the egg into a embryo and then to a child, the placenta implants into here.
  5. Uterus Space – where the embryo develops to an unborn child
  6. Cervix – Entrance to the uterus,
  7. Vagina – Collects the sperm cells from the penis and allows them to pass through the cervix into the uterus.

Note: Before pregnancy the entire uterus structure is no larger than an orange

September 10, 2011

3.12 Amniotic Fluid

3.12 Understand how the developing embryo is protected by amniotic fluid.

Surrounding the developing embryo is a fluid, the amniotic fluid.
This fluid can protect the embryo as it acts as a “shock absorber”; the fluid is mainly water and so cannot be compressed so it absorbs all external pressures to the uterus preventing damage to the embryo.
Furthermore thee embryo “floats” in the amniotic fluid so there is no pressure applied onto the developing bones and muscles of the unborn child mean that it can grow and develop much easier.

3.11 Placenta

3.11 describe the role of the placenta in the nutrition of the developing embryo

The developing embryo can’t digest, breathe or excrete so it needs a way to receive nutrients from the mother in order to grow, obviously it gets these nutrients from the mother through what is called the Placenta

The Placental structure consists of the Umbilical Cord containing blood vessels that lead from the embryo to the placenta. It is important to know that the placenta grows out from the embryo not from the mother. Initially the umbilical cord grows up towards the walls of the uterus and upon contact the child’s blood vessels spread out to form the placenta inside the walls of the uterus.
Glucose, amino acids and fats travel through the maternal blood vessel and cross into the embryo’s blood through the placenta. CO2 and Urea from the embryo travel up the umbilical cord and cross into the mother’s blood also at the placenta. To make this process efficient the placenta has a large surface area and the barrier between the mother’s and child’s blood is very thin.

August 29, 2011

3.24 Mitosis

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

What is Mitosis?
Mitosis is a form of cell division that results in the increase in the number of cells.

  1. Begin with a single cell
    • The number of chromosomes in this original cell is referred to as its Diploid number (2n)
    • All animals have a different Diploid number (Humans, 2n = 46)
  2. The cell divides into two daughter cells
    • These cells are identical to the mother cell
    • 1. Each of these cells has a Diploid nucleus (the same number of chromosomes as the mother cell)
    • 2. They have the same set of chromosomes as each other

How are the copies of chromosomes made?

DNA replication
  1. The process takes place inside the nucleus while it is still intact; before any separation has gone underway. This resting stage is known as the interphase stage of the cell cycle
  2. Each chromosome undergoes a copying process to form an identical copy of itself
    • It has all the same Genes and Alleles
  3. These two copies are held together by a structure around the centre by what’s called a centromere.
  4. These two chromosomes held together by a centromere are referred to as a pair of chromatids

How do they separate?

Cell Division
  1. The first sign a cell is entering mitosis is when we see the breakdown of the nuclear membrane (this is known as the Prophase)
    1. The chromosomes then become visible as a pair of Chromatids
  2. A network of Protein molecules (the Spindle and Spindle fibres) extend from one pole of the cell to the other (this is the Late Prophase)
  3. The pair of chromatids work their way towards the middle of the spindle and join onto a spindle fibre by the centromere (the Metaphase)
  4. The Anaphase is where the spindle fibre shortens to pull each chromatid in an opposite direction and ultimately they ultimately separate and each one will rest in the opposing poles.
  5. The final phase is known as the Telophase when the nuclei begin to reform around the chromatids at each pole of the cell. There are now two nuclei
  6. And finally a phase called the Cytokinesis is where the cell splits in two, but this particular stage is not regarded as part of the Mitosis Cycle.
The image below visually explains the process