2.70 Nephron Structure

1.68 Urinary System

The urinary system includes

1.       Kidneys : excretion, filtration and osmoregulation

2.       Ureter : (one for each kidney) delivers urine to bladder

3.       Bladder : (One bladder for both ureters) delivers urine to urethra

4.       Urethra

2.68 Excretion

a)      The role of the kidney in the excretion of urea which is made from nitrogen in the form of amino acids, excess amounts can be toxic to the body therefore needs to be excreted.

Amino acids are broken down in to urea in the liver. Urea then circulates with blood into the kidneys which then filters the blood from the urea. Water is then added to urea to create urine and is then transferred to the bladder ready for excretion.

b)      Osmoregulation

Osmo : osmosis

Regulation : to control

Osmoregulation : to control the transfer of liquids

It is the role of the kidney to control the composition of the blood; maintaining control of excess water and salts in the blood by excretion, which in turn keeps the tissue fluid isotonic to the cell cytoplasm maintaining functions of cells.

2.67 Excretion

a) the origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of a leaf

b) major organs of excretion

3.34 Causes of Mutation

The incidence of mutations  can be increased by exposure to ionising radiation (gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (tabbaco)

1.       Radiation – such as the sun (UV-B)   which can cause skin cancer.

2.       Chemicals can also cause mutations such as the effect of tar in tabbaco causing mutations in the base sequence producing new alleles. Chemicals that cause mutations are called mutagens. Chemicals which cause mutations and cancer are called carcinogens.

3.32 Types of mutation

The mutation in a gene creating new alleles can be, beneficial, harmful or nuetral ( neither positive or negative)

An example of a beneficial mutation can be improving the efficiency of an enzyme.

An example of a harmful mutation can be production of a enzyme that doesn’t work.

An example of a nuetral mutation can be production of  that has no particular effect on an idividual, though in the long run it may due to environmental changes.

3.33  Antibiotic Resistance

How resistance to antibiotics can increase in bacterial population.

3.30 Mutation

The base sequence in which the letters are arranged constitutes the gene, the form of the gene is called the allele.

The base sequence of the DNA can be changed as shown in the diagram, producing a new allele which can produce an entirely different protien affecting the phenotype this is called mutation and this is also how the variation in the phenotypes occur.