2.68b Osmoregulation

Key Points:
1. Osmoregulation: Osmo = Osmosis and Regulation = To control
2. Ideally, the tissue fluid surrounding cells in the body should be isotonic with the cytoplasm of the cells. This means the amount of water going in and out is equal and they will maintain their size.
3. The danger is that the blood going into the tissue may be concentrated causing a hypertonic tissue fluid. Or it could be dilute causing a hypotonic tissue fluid. The aim would be to maintain a isotonic tissue fluid.
4. This is done by controlling the composition of blood.
5. The kidney controls the composition of the blood. Blood flows into the kidney and excess water or salts will be excreted. The tissue fluid will maintain an isotonic behaviour.

2.68a Excretion

1. The role of the kidney in excretion, is the excretion of urea.
2. Urea is poisonous to the human body because it contains nitrogen.
3. The original form of the nitrogen is in our bloodstream as amino acids, which are used for growth, but if there are any in excess they have to be removed.
4. Blood cirulates into the liver, where the amino acids are broken down and converted into urea. This reenters the blood stream into both the kidneys.
5. The kidneys filter the urea from the blood, and add it with water to form urine and this flows down the uretus into the bladder.

2.67b Human Organs of Excretion

Key Points:
1. The major organs of excretion include the lungs, which waste carbon dioxide,the kidneys, which excrete excess water, urea and salts. Urea is the nitrogen waste from amino acids.
2. The third organ of excretion is the skin, which excretes water, salts and to a partial degree, urea but not in large amounts.
3. All of these organs display the loss of metabolic waste

2.67a Excretion in Plants

Key Points:
1. Photosynthesis involves the leaf absorbing light energy and combines CO2 with H2O to make C6H12O6 and O2
2. The release of oxygen is classified as excretion, the release of metabolic waste.
3. The process of respiration is the second excretion example. C6H12O6 -> ATP + CO2 + H20
4. In that process the CO2 is the waste product, so the plant excretes CO2 while respiring and excretes O2 during photosynthesis.

3.34 Causes of mutation

Key Points:
1. Mutation is a change in the base sequence of the gene. New alleles are produced.
2. An example of what causes this is radiation, or ionising radiation like x-rays or sunlight which cause skin cancer.
3. A second example is chemicals, such as tar in tobacco changing the base sequence of the gene. Chemicals which do this are called mutagens. Carcinagens are mutagens which also cause cancer.

3.33 Antibiotic resistance

Key Points:
1. The bacterial population in here is known as staphlococcus aureus.
2. Those who are infected can be treated with methecilline, which is an antibiotic. This chemical will kill the susceptable form of bacteria. There may be a random mutation to the genotype of the bacteria which lets the bacteria survive the chemical. This is known as the resistant form of bacteria.
3. Their mutation has created genes which allow it to break down the antibiotic.
4. The resistant form will survive, and will become more common.

3.32 Types of mutation

Key Points:
1. We begin with the first copy of the gene, and the process of mutation produces new alleles which in turn make new genes. The alleles are responsible for the phenotype and they can be either, beneficial, harmful or neutral.
2. An example of a beneficial mutation might be a boosted efficiency of an enzyme. Or harmfully a enzyme could be rendered useless. A neutral mutation might be an enzyme with no use at the present time, but in time, when the environment changes there could be some beneficial or harmful purpose of this.