AS Biology - Unit 1 (AQA)

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Unit 1 ­ Biology and disease
Chapter 1 ­ Causes of disease
Microorganisms are single celled organism. Microorganisms which cause disease are called
For a microorganism to be considered a pathogen it must
Gain entry to the host
Colonise the tissues of the host
Resist the defences of the host
Cause damage to the host tissues.
When a pathogen gets into the host and colonises its tissues, it forms an infection.
When an infection leads to recognisable symptoms it is a disease.
When a pathogen is transferred from one individual to another, it is known as a transmission.
Pathogens enter the body through: -
The gas-exchange system
The digestive system ­ Food and water may carry pathogens into the stomach and intestines
via the mouth
Cuts in the skin.
To prevent entry of pathogens: -
A mucous layer that covers exchange surfaces and forms a thick, sticky barrier that is difficult
to penetrate.
The production of enzymes which break down pathogens.
The production of stomach acids which kills microorganisms.
Pathogens affect the body in two main ways: -
By damaging host tissues
By producing toxins
A correlation occurs when a change in one of two variables is reflected by a change in the other
Risk is a measure of the probability that damage to health will occur as a result of a given hazard.
Lifestyle factors that contribute to cancer: -
Diet ­ Low-fat, high-fibre, rich in fruit and vegetables reduces the risk.
Physical activity ­ More exercise reduces risk

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Sunlight ­ The more exposed to sunlight, the greater the risk of skin cancer.
Lifestyle factors that contribute to coronary heart disease (CHD): -
High blood pressure ­ Excessive prolonged stress, certain diets and lack of exercise increase
high blood pressure.
Blood cholesterol levels ­ Can be lowered by eating fewer saturated fatty acids
Diet ­ High levels of salt increases blood pressure while high levels of saturated fatty acids
increases the blood cholesterol concentration.…read more

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Polysaccharides are made up of many monosaccharides joined by glycosidic bonds that were formed
by condensation reactions. They are insoluble so good for storage. Some polysaccharides like starch
are used to give structural support to plant cells.
Starch can be detected as it turns the colour of iodine in potassium iodide solution from yellow to
Amylase is produced in the mouth and pancreas. Amylase hydrolyses the alternate glycosidic bonds
of starch to produce the disaccharide maltose. Maltose is hydrolysed into a monosaccharide by
maltase.…read more

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The molecule which the enzyme works on is called the substrate. It forms an enzyme-substrate
Lock and key model ­ Enzymes are specific in the reactions they catalyse. The shape of the
substrate (key) exactly fits the active site of the enzyme (lock).
Induced fit model ­ The enzyme can change shape slightly to fit the substrate. The enzyme is
As the temperature increases, the molecules move around rapidly and collide with each other more
often.…read more

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The greater the resolving power of an electron microscope compared to a light microscope is due to
the electron beam having a shorter wavelength than light.
Eukaryotic cells have a distinct nucleus and possess membrane-bounded organelles, e.g. epithelial
Epithelial cells absorb and secrete.
Parts of a nucleus: -
Nuclear envelope ­ Double membrane surrounding the nucleus. It controls entry and exit of
materials in and out of the nucleus and contains the reactions taking place within it.…read more

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Once sorted, the
modified proteins and lipids are transported in vesicles.
Functions of Golgi apparatus are to: -
Add carbohydrates to proteins to form glycoproteins.
Produce secretory enzymes.
Secrete carbohydrates.
Transport, modify and store lipids.
Form lysosomes.
Lysosomes are formed when the vesicles produced by the Golgi apparatus contains enzymes such
as proteases and lipases. The lysosomes isolate these potentially harmful enzymes from the rest of
the cell before releasing them, either to the outside or into a phagocytic vesicle within the cell.…read more

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All plasma membranes found around the inside cells have the same phospholipid bilayer structure.
What gives plasma membranes their different properties are the different substances they contain
especially proteins.
Functions of proteins in the membrane: -
Provide structural support
Act as carriers transporting water-soluble substance across the membrane.
Allow active transport across the membrane by forming ion channels.
Form recognition sites by identifying cells.
Help cells adhere together.
Act as receptors.…read more

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Glucose is absorbed through the walls of the small intestine. These are then folded and have villi. Villi
increase the surface area for diffusion. They are thin walled, reducing the distance over which
diffusion takes place. They are well supplied with blood vessels so that blood can carry away
absorbed molecules, and hence maintain a diffusion gradient.
Microvilli are on the cell-surface membrane
Glucose diffuses out of the small intestine and into the blood stream.
Prokaryotic Cells Eukaryotic cells
No true nucleus.…read more

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Damage to the epithelial cells lining the intestine.
Loss of microvilli due to toxins
Excessive secretion of water due to toxins.
To treat diarrhoea you need to rehydrate the patient. This can't be done by simple drinking water as
water is not being absorbed by the small intestine and water won't replace the lost ions.
A rehydration solution needs to contain: -
Water ­ To rehydrate tissues
Sodium ­ To replace lost sodium ions and use sodium-glucose carrier proteins.…read more

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Mycobacterium Bovis
The symptoms of tuberculosis are a persistent cough, tiredness, loss of appetite leading to weight
loss, fever and coughing up of blood may occur.
TB is spread through the air by droplets released into the air when infected individuals cough,
sneeze, laugh and talk. It takes close contact with an infected person over a period of time to
transmit the bacteria.
Once Mycobacterium tuberculosis is inhaled...…read more







well done for making these notes!


I love you, saved my life

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