AS Biology Unit One AQA

  • Created by: Hannah
  • Created on: 04-04-13 12:42


Any organism (bacteria, fungi and viruses) that cause a disease.

They get in through an organisms surface of contact with the environment (gas exchange system, the skin or the digestive system).

Pathogens cause disease by producing toxins and damaging cells.

Can cause the cells to rupture releasing nutrients, break down nutrients for their own use which then starves and then kills the cell or replicate inside the cell and bursting them when they are released.

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Your lifestyle can affect your risk of developing some diseases.


The risk of developing CHD can be cause by poor diet-a diet high in saturated fat or salt. Smoking, lack of exercise and high alcohol intake can lead to high blood pressure, which then damages the heart and blood vessels increasing the risk of developing CHD.


Cancer is the result of uncontrolled cell division. The risk of developing cancer can be increased by smoking (mouth and lung cancer), excessive exposure to sun light can cause skin cancer (using sunbeds and sunbathing without sun cream can also increase the risk) and excessive alcohol intake can increase the risk of developing many different types of cancer especially liver cancer.

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Long chains of amino acids joined by a peptide bond formed by condensation reactions

Dipeptide-two amino acids

Polypeptide-more than two amiino acids joined together

Carboxyl group (COOH), Amino group (NH ), Carbon atom and an R group.

Amino acids linked togther by condensation reaction, molecule of water is released. A reverse reaction happens during digestion.

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The Structure Of Proteins

A protein's shape determines its function, eg haemoglobin is a compact, soluble molecule so it's easy to transport so its great for transporting oxygen around the body.

Primary structure-the sequence of amino acids in the polypeptide chain

Secondary structure-hydrogen bonds between the amino acids making the amino acids coil into an alpha helix or fold into a beta pleated sheet

Tertiary structure-chain of amino acids coiled or folded further. More bonds formed between the different parts forming their final 3D structure

Quaternary structure-several different polypeptide chains held together by bonds. The way in which the polypeptide chains are assembles together, eg haemoglobin, insulin and collagen

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Carbohydrate Digestion

The polymers in our food are insoluble and therefore cant be directly absorbed our bloodstream and need to be made into new products.The polymers have to be hydrolysed into smaller more soluble molecules by adding water

1.The oesophagus is the tube that takes food from the mouth to the stomach. Amylase is secrected from the salivary glands and begins to hydrolsys starch into maltose

2.The stomach has lots of folds allowing it to expand.The stomach walls produce gastric juice which contains pepsin which hydrolyses proteins into smaller polypeptide chains so they can be absorbed by the body. The food is then turned into an acidic fluid called chyme by the peristalis of the stomach

3.The small intensines (duodenum and ileum). In the duodenum bile and pancreatic juice neutralises the chyme and breaks it down into smaller molecules. In the ileum the small soluble molecules are absorbed through the gut wall via the villi.

4.The large intestines (colon) absorbs water, salts and minerals. Has a folded wall which provides a large surface area. Bacteria that decompose undigested nutrients are found here.

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Inspiration (breathing in)

1. The intercostal muscles and diaphragm contract

2.The causes the rib cage to move up and out and the diaphragm to flatten

3. Therefore this increases the volume inside the lungs. Because the volume of the lungs has increased the pressure within the lungs decreases. This cause air to flow into the lungs because the pressure inside the lungs in lower than the atmospheric pressure and the air moves from higher to lower pressures

Expiration (breathing out)

1. The intercostal muscles and diaphragm relax

2.The causes the rib cage to move down and inwards and the diaphragm becomes curved

3. Therefore the volume inside the lungs decreases causing the pressure within the lungs to decrease. Air is therefore forced out of the lungs because the atmospheric pressure is lower than the pressure inside the lungs

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Lung Function

The lungs contains millions of air sacs called alveoli where gas exchange takes place. Each alveolus is made from a single layer of thin, flat cells called alveolar epithelium. This is so there is a short diffusion pathway.

  • The is a huge number of alveoli in the lungs, so there is a large surface area for the gas exchange of oxygen and carbon dioxide.
  • The alveoli are surrounded by a network of capillaries which are also one cell thick.
  • Oxygen diffuses out from the alveoli across the alveolar epithelium and capillary epithelium and into the haemoglobin in the blood
  • Carbon dioxide diffuses into the alveoli from the haemoglobin in the blood and is then expired.

Alveoli are adapted especially for gas exchange

  • Thin exchange surface which speeds up diffusion
  • Large surface area for gas exchange

There is a steep conc. grad. of oxygen and carbon dioxide increasing the rate of diffusion and is maintained by the flow of blood and ventilation.

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Pulmonary Tuberculosis


  • The bacteria grow and divide in the upper regions of the lungs because there is a good supply of oxygen
  • White blood cells accumulate at the site of infection to ingest the bacteria
  • This causes inflammation and enlargement of the lymph nodes that drain the area of the lungs-primary infection. A healthy peron may show a few symptoms but some bacteria usually remain
  • Years later these bacteria can re-emerge -post-primary tuberculosis
  • The bacteria destroy the tissue in the lungs which results in scar tissue where the lung has repaired itself from the cavities which then further decreases tidal volume

Symptoms- persistent cough, coughing up blood, chest pains, shortness of breath, fatigue, fever and can loss weight due to a loss in appetite

Transmission- when an infected person coughs or sneezes tiny droplets of salvia/mucus containing the bacteria and an uninfected person breathes them in. Crowded conditions:home, work...

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Pulmonary Fibrosis

Fibrosis is the formation of scar tissue in the lungs. This scar tissue is thicker and less elastic than normal lung tissue meaning that the lungs are less able to expand and so cant hold as much air, therefore the tidal volume is reduced.

It's also harder to force air out of the lungs sue to the loss of elasticity. There is therefore a reduction in the rate of gas exchange and diffusion is slower, also because the gases have to cross a ticker scarred membrane.

Symptoms- Shortness of breath, a dry cough, chest pain, fatigue and weakness

Fibrosis suffers have a faster breathing rate than normal because they need to et enough oxygenated air into their lungs to oxygenate the blood

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A localised allergic reaction that can be stimulated by pollen, animal fur and the faeces of house dust mite.

  • The lining of bronchi and bronchioles become inflammed
  • The cells of the epithelial lining secrete large quantities of mucus than normal
  • Fluid leaves the capillaries and enters the airway
  • The muscle surrounding the bronchioles contracts and therefore constricts the airways


  • Difficulty breathing due to the constriction of the bronchi and bronchioles, their imflammed linings and the additional mucus and fluid within them
  • Wheezing sound when breathing caused by air passing through the constricted airways
  • Tight feeling in the chest because you're not able to ventilate the lungs adequately because of the constricted airways
  • Coughing is the reflex response to obstructed airways trying to clear them
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Caused by smoking or long term exposure to air pollution when foreign particles in the smoke become trapped in the alveoli

This cause imflammation which then attracts phagocytes to the are and the phagocytes produce an enzyme that breaks down elastin (a protein found in the walls of the alveoli)

Loss of elastin means the alveoli cant recoil to expel air meaning it gets trapped in the alveoli

Leads to the destruction of the alveoli walls which therefore reduces the surface area of the alveoli meaning the rate of gas exchange decreases.

Symptoms- shortness of breath and wheezing

People with emphysema have an increased breathing rate as they are trying to increase the amount of air containing oxygen reaching their lungs.

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Heart Disease

Atheroma- a fatty deposit that forms within the wall of an artery. Begins as fatty streaks that are accumulations of white blood cells that have taken up low density lipoproteins. These enlarge to form an irregular patch (atheromatous plaque). They bulge into the lumen of ther artery causing it to narrow so that the blood flow is restricted. Atheromas increase the risk of tro other heart conditions: thrombosis and aneurysm.

Thrombosis- If an atheroma breaks through the lining of the blood vessel it forms a rough surface that can result in the formation of a blood clot or thrombus. This can then block the blood vessel, reducing or preventing the supply of blood to the tissues beyond. This region of tissue often dies as a result of the lack of oxygen, glucose and other nutrients that the blood normally provides. Sometimes the thrombus can become unlodged and then block another artery.

Aneurysm- Thrombus can also weaken the artery walls which can then swell to form a balloon-like blood filled structure (aneurysm). These can frequently burst leading to a haemorrhage and therefore a loss of blood to that region of the body.

Myocardinal Infarction- a heart attack, a reduced supply of oxygen to the muscle of the heart. Because of a blockage in the coronary artery and aorta and the heart stops beating.

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The Immune System

 Cellular- T-Cells and other immune system cells that they interact with eg phagocytes  Humoral- B-Cells and the production of antibodies 

Phagocytes engulf pathogens -> phagocytes activate T-Cells -> T-Cells activate B-Cells which divide into plasma cells -> plasma cells make more antibodies to a specific antigen

B-Cells are also a type of white blood cells covered with antibodies, proteins that bind to antigens to form an antigen-antibody complex. Each B-Cell has a different shaped antibody on its membrane so different ones bind to different shaped antigens.

Primary Response- an antigen enters the body for the first time it activates the immune system. Primary response is slow because there aren't many B-Cells with the specific antibody. The body will produce enough of the antibody to overcome the infection. Both B & T-Cells produce memory cells which remain in the body for a long time.

Secondary Response- the same pathogen enters the body again the immune system will produce a quicker & stronger response. Memory B-Cells divide into plasma cells producing the right antigen. Memory T-Cells divide into the correct T-Cells to kill the cell carrying the antigen. Secondary response gets rid of the pathogen before you show symptoms.

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