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.