AQA Biology Unit 1 Revision Notes

Hello All,

Here is my complete set of AQA Biology Unit 1 revision notes. They have been written against the specification and from variaty of resourse these being: Nelson Thornes AQA Biology AS textbook, CGP AS-Level Biology (AQA), the internet (Wiki, S-cool, etc...) and many teachers notes. 

Feel free to download and check them out. I hope they come in useful to you!

All the best for the exam period.


Ben Bonham

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Causes of Disease
Disease is not a single thing but a description of certain symptoms, physical mental or both. It suggests a
malfunction of body or mind having an adverse effect on good health.
- A pathogen is an organism that causes disease.
- Pathogens include microorganisms and some larger organisms e.g. Tapeworms.
- Pathogenic microorganisms include some bacteria, some fungi and all viruses.
For a microorganism to be considered a pathogen it must:
- Gain entry to a host.
- Colonise the hosts tissues
- Resist the defences of the host
- Cause damage to the host's cells/tissues.
If a pathogen get into a host and colonises its tissues it causes an infection, when/if recognisable
symptoms appear disease has occurred.
Causing Disease
To cause disease a pathogen must first gain access to a host: There are 3 main interfaces
Pathogens get into the body by penetrating one of its interfaces with the environment. An interface is a
surface separating the external environment to the internal environment of an organism.
Skin: When the skin becomes damaged, pathogens on the surface can enter the bloodstream. Blood clots
at the damaged area prevent pathogens entering, but some still get in before one forms.
Gas-Exchange System: When we breathe in pathogens in the air, most of them get trapped in the mucus
lining the lung epithelium which also have tiny projections called cilia that beat and move the mucus up
the trachea to the mouth for removal. However, some still make it to the alveoli, invade cells and cause
Digestive System: Food and water that we consume may carry pathogens. Most of these are killed by the
stomachs acidic conditions. However, some still pass into the intestine, invade cells and cause damage.
Pathogens cause disease in 2 main ways:
- Producing Toxins: Most bacteria produce toxins e.g. the cholera bacteria produces a toxin that
causes excessive water loss from the lining of the intestine.
- Damaging Host Tissues: Pathogens can physically damage a hosts cells preventing the tissues
from functioning properly. They can do this by;
- Rupturing the cells to release nutrients (e.g. Proteins)
- Breaking Down the nutrients inside the cell, starving and killing the host cell.
- Replicating inside the hosts cells and bursting them when they are release (e.g some viruses)

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Some disease like Heart Disease and Cancer have a number of causes like; lifestyle (diet, exercise,
smoking), genetics and pathogens.
Data and Disease
Analysing and interpreting data of disease
Epidemiology is the study of the incidence and pattern of a disease with a view to finding means to
preventing and controlling it. To do this they collect data and look for a pattern or relationship between
the disease and various factors in the lives of suffers of them.…read more

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Enzymes and the Digestive
Major Parts of the Digestive System
The human digestive system is made up of a long muscular tube and its associated glands. These glands
secrete enzymes that break down large molecules into smaller ones for absorption.
Salivary Glands: Pass their secretions
via a duct into the mouth. This
contains mucus, minerals and salivary
amylase which breaks down starch to
Oesophagus: The tube that carries
food from the mouth to the stomach
using waves of muscle contractions call
peristalsis.…read more

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Stages of Digestion
There are 2 main stages of digestion:
1. Physical breakdown,
2. Chemical breakdown.
Physical breakdown: When food is too large it is broken down into smaller pieces by means of structures
such as teeth. This makes it possible to swallow and increases the surface area to help with chemical
digestion. Food is also physically broken up by peristalsis of the stomach.
Chemical breakdown: Breaks down large, insoluble molecules into smaller, soluble ones.…read more

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Structure of amino acids
Amino acids are the basic monomer unit which combine with another amino acid to form a dipeptide
more than this join up together to make a polymer called a polypeptide. Polypeptide combine to form
Every amino acid has a central carbon atom eith 4
different chemical groups attached:
- Amino Group (-NH2): a basic group, deriving the
amino part of amino acid
- Carboxyl Group (-COOH): an acidic group giving
the acid part of the amino acid name.…read more

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This peptide bond under, suitable conditions, can be broken by the addition of water which is
called hydrolysis.
Protein: Primary structure
Many amino acid monomers can be joined together in a process called polymerisation. This chain of
hundreds of amino acids is called a polypeptide. The sequence of amino acids in this chain forms the
primary structure.…read more

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Proteins made from a single polypeptide chain have the tertiary structure as their final 3-D shape.
The 3-D shape makes proteins distinctive and allows it to recognise, and be recognised by, other
Protein: Quaternary Structure
Larger proteins form complex molecules containing multiple polypeptide chains that are linked in various
ways. The way in which these polypeptides are assembled together is the quaternary structure. There
may also be non-protein (prosthetic) groups associated with the molecule e.g. Haem group in
haemoglobin.…read more

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Add an equal volume of Benedict's reagent.
- Heat the mixture in a gentle boiling water bath for 5 minutes.
If a reducing sugar is present an insoluble red precipitate of copper(I) oxides is formed in the blue
The concentration of the reducing sugar will affect the final colour.…read more

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Testing for non-reducing sugars
Some disaccharides are reducing sugars (e.g. maltose) but others are non-reducing sugars that have no
change when mixed with Benedict's solution. To test for what type sugar is in your sample you need to:
1. Test for a reducing sugar: Benedict's Test, no positive result so:
2. Test for a non-reducing sugar:
- Add 2cm3 of sample to 2cm3 of dilute HCL acid in a test tube.
- Place in gently boiling water bath for 5 minutes.…read more

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The epithelial lining also produces sucrase (sucrose Glucose + Fructose) and lactase (Lactose
Glucose + Galactose)
Lactose intolerance
- Milk is the only food for most babies so they have a lot of lactase to hydrolyse the lactose in milk.
- Milk gradually forms less part of the babies diet so lactase production diminishes
- In some case it diminished so much that the individual has little or no lactase.
- This causes all or some the lactose to no be hydrolysed during digestion.…read more


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