2.69

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

The right and the left kidneys, each have separate blood supplies. They carry out excretion, filtration and osmoregulation. There is a tube coming out from each kidney (ureter), which carries urine to the bladder. Urine collected in the bladder is excreted through the urethra, down the vagina/ penis.

2.68 Osmoregulation

Osmoregulation

Osmoregulation is the control of osmosis. The tissue fluid (highlighted in yellow) surrounding the cells must be isotonic with the cytoplasm of the cells. Blood going in and out of the fluid must be equal so that the cells maintain their size. If the blood circulating into the tissue is too concentrated, causing a hypertonic fluid, too much water will be removed from the cells. In this case, the kidneys will remove less water and more salts to maintain the balance. Too diluted fluid will cause a hypotonic fluid, where too little water will be removed from the cells. In this case, the kidneys will have to excrete more water adn less salts. Both are undesirable. We want the cytoplasm to be isotonic.

This can be controlled by the kidney controlling the composition of the blood circulating through the kidneys. Excess water and salts can be removed and excreted down through the ureter. By controlling the content of water and salts in the blood, the kidney can keep the tissue fluid isotonic, maintaining the function of the cells. 

2.68 Excretion

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

Excretion

Chemical reactions in your body produce waste like carbon dioxide and urea. Urea contains nitrogen which is toxic and cannot be stored. Originally, urea was amino acids. They are used for growth, but excess amino acids must be removed since they are toxic.

1) Blood circulates to the liver. Amino acids are broken down and converted into urea (process of deamination).

2) Blood re-enters the bloodstream and goes to both of the kidneys. The kidneys will filter the urea from the blood. Water will be added to urea to form urine. Urine will drain down the ureter and will be collected in the bladder.

3) Filtered blood returns to the circulation without urea. 

Amino acids --> LIVER --> Urea --> (less toxic) --> Kidneys

2.67b

2.67 recall that the lungs, kidneys and skin are organs of excretion

Major organs of excretion: lungs, kidneys and skin

1) Lungs: excrete CO₂

2) Kidneys: excrete excess water, urea and salts. This helps the body control the level of water. Urea is the nitrogen waste from amino acids; we can’t store amino acids, so we excrete them as urea.

3) Skin: excretes water & salts (sweating) and a little bit of urea. 

2.67a

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

1) Photosynthesis à O₂ excreted

Leaves absorb light energy, combines with CO₂ and water to form glucose and O₂. O₂ gas is the metabolic waste.

2) Respiration à CO₂ excreted

Plants carry out aerobic respiration where glucose and O₂ are combined together. They go through an enzyme reaction and ATP, water and carbon dioxide are formed. CO₂ is the metabolic waste here. (excretion)

3.34

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).

Causes of mutation: 1) Radiation – Ionising radiation like x-rays and UV rays (à skin cancer)

2) Chemicals – e.g. tars in tobacco à cancerous conditions

Mutagens: chemicals that cause mutations

Carcinogens: chemicals that cause mutations and cancer

3.33

3.33 understand how resistance to antibiotics can increase in bacterial populations

Staphylococcus aureus treated by methicillin (antibiotic)

At first the susceptible form is more common (MSSA), but as the antibiotic is applied, the bacteria that does not die (MRSA) will become more common. The mutation has created genes that break down the antibiotic. As antibiotics are used across time, MRSA increasingly survives and becomes more common. This can be a serious problem in hospitals and treatment. 

3.32

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

First copy of the gene à mutation à new alleles (responsible for phenotype) à results: beneficial, neutral or harmful. Examples:

Beneficial: improve efficiency of enzyme

Harmful: production of non-functional enzyme

Neutral: at first neutral, may become beneficial or harmful after environmental change

3.31

3.31 describe the process of evolution by means of natural selection

Evolution: 1) Change in the form of organisms (new forms rising)

2) Change in the frequency (how many) of alleles

Natural Selection: is the mechanism of evolution first proposed by Charles Darwin (it is a process)

EXAMPLE:

Staphylococcus aureus causes skin infection and lung infection from wounds (e.g. operation wounds).

Methicillin is an antibiotic that kills MSSA (Methicillin Susceptible Staphylococcus Aureus).

A random mutation occurs à develop of breaking down methicillin à no longer killed by this antibiotic à RESISTANT FORM

Now there are two forms of these bacteria (definition of evolution 1).

When antibiotics are applied, the MRSA (Methicillin Resistant Staphylococcus Aureus) survive and become common à increase in frequency of allele for resistance (definition of evolution 2)

2 features of natural selection (process)

- Random mutation à produces MRSA

- Non-random selection due to the antibiotic à selects MRSA à to survive, MSSA selected and killed

3.30

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

Different alleles exist due to mutation, which changes the base sequence – e.g. ACT à AAT

This creates a new version of the allele à production of an entirely different protein à completely different phenotype

3.29

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

Variation: differences in phenotypes of individuals (in how things appear)

It is possible to count or measure these differences and show them in graphic form

Individual’s phenotype = genotype + environment

V_population = V_genotype + V_environment

1)     Purely affected by the genotype – e.g. blood group

2)     Affected by both the genotype and the environment – genetic variation in genotype + modification by the environment to form a smooth curve – e.g. height in humans

3)     Purely affected by the environment, genes have no role to play and this cannot be inherited – e.g. home language

NUMBER 2: GENOTYPE AND ENVIRONMENT

3.20

3.20 understand how to interpret family pedigrees

Inherited condition: filled in squares / circles (OFTEN diseases not always)

Circles and squares are phenotypes (can be observed)

DOMINANT OR RECESSIVE for those affected

Hypothesis 1: Dominant, caused by DD or Dd

That means the son is DD or Dd, which means at least one of the parents need to have a D, but since the parents are not affected, this cannot be true.

Hypothesis 2: Recessive, caused by dd

If both parents were Dd, then, one d from each of the parents might have been inherited to the son, resulting in dd. TRUE

à This inherited condition is caused by HOMOZYGOUS RECESSIVE GENOTYPE of dd 

3.21

3.21 predict probabilities of outcomes from monohybrid crosses

Chances of outcomes of offspring from monohybrid involving just the one gene

Parents (phenotype): Red x White (monohybrids)

Genotype: RR x rr

Meiosis R, R, r, r (homozygous) à Random fertilisation

Genotype offspring: Rr (all) 100%

(F₁) Phenotype offspring: ALL red

F₁ cross F₁ x F₁

Parent Phenotype: Red x Red

Parent Genotype: R, r, R, r (heterozygous)

Meiosis à Random fertilisation

Genotype offspring: RR: 2Rr: rr

Phenotype ratio (F₂): 3:1 (red:white)