AQA AS Biology Unit 1

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  • Created on: 06-03-13 09:41
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BIOLOGY
1 ­ Causes of disease
Pathogens
Microorganisms = bacteria and viruses Pathogens are BAD microorganisms
Disease ­ a description of certain symptoms, either physical, mental or both.
PATHOGENS:
Gain entry to the host
Colonise the tissues of the host
Resist the defences of the host
Cause damage to the host tissues
Pathogens include bacteria, viruses and fungi. If a pathogen gets into a host and colonises,
it causes an INFECTION. When an infection leads to recognizable symptoms, it becomes a
DISEASE. When a pathogen is transferred to someone else, it is a TRANSMISSION.
Interface: a surface or boundary linking two systems (i.e. linking external to internal
enviro)
The skin is a BARRIER to infection, so invasion only occurs when skin is broken (cuts/bites)
Common points of entry:
Gas-exchange system: pathogens that cause influenza, tuberculosis and bronchitis
infect this way
Digestive system: food and water can carry pathogens such as cholera, typhoid and
dysentery to the stomach and intestines.
The body's natural defences:
Mucous layer that covers exchanges surfaces. The sticky layer is difficult to
penetrate
Enzymes produced break down pathogens
Stomach acid kills microorganisms

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Pathogens affect the body by:
Damaging host tissues ­ the number of pathogens can be damaging by preventing
tissues functioning properly. Viruses inhibit the synthesis of DNA, RNA and proteins
by the host cells. Many proteins break down the membranes of the host cells
By producing toxins ­ most bacterial pathogens produce toxins, such as cholera
which leads to excessive water loss from the lining of the intestines
Some diseases have a single cause, like malaria, other have multiple causes, heart disease.…read more

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CANCER:
Some things are beyond our control however our lifestyle can expose us
to environmental and carcinogenic factors that put us at risk.…read more

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­ Enzymes and the digestive system
Enzymes and digestion
Glands ­ produce enzymes that break down large molecules into small ones ready for
absorption. The digestive system therefore provides an INTERFACE with the environment
because food substances enter the body through it.…read more

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Digestion: physical breakdown (mechanical digestion) and chemical digestion
PHYSICAL BREAKDOWN/ MECHANICAL DIGESTION:-
Large food is broken into smaller pieces by structures like the teeth, making it possible to
INGEST and increasing the SURFACE AREA + for chemical digestion. Food is also
CHURNED BY MUSCLES in the stomach
CHEMICAL DIGESTION:-
Large, insoluble molecules are broken down into smaller soluble ones, done by ENZYMES.…read more

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MONOSACCHARIDES:
Are sweet tasting, soluble with a general
formula of (CH2O)n with n being between
3 and 7
Glucose: C6H12O6
TEST FOR SUGARS:
All monosaccharides and some disaccharides (E.g. maltose) are REDUCING sugars
Reduction (chemical reaction involves gaining electrons)
A reducing sugar can donate electrons to (or reduce) another chemical ­ such as
BENEDICTS REAGENT ­ an alkaline solution of copper (II) sulphate. When a reducing
sugar is heated with this, it forms an insoluble red precipitate of copper (I) oxide.
TEST INSTRUCTIONS:
1.…read more

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TEST FOR NON-REDUCING SUGARS:
Other disaccharides are non-reducing as they do not change the colour of Benedict's
reagent. In order for non-reducing sugars to be detected, the disaccharide must be broken
down into monosaccharides.
TEST INSTRUCTIONS:
1. If sample is not already liquid, it must be first ground up in water
2. Add 2cm3 of the sample to 2cm3 of Benedict's reagent in a test tube
3.…read more

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TEST FOR STARCH:
1. Place 2cm3 of the sample into a test tube (or add two drops of the sample into a
depression on a spotting tile.
2. Add two drops of iodine solu7tion and shake/stir
3. The presence of starch is indicated by it going blue-black
Carbohydrates digestion
STARCH DIGESTION:
An enzyme is SPECIFIC so one type of enzyme may break a long molecule into smaller
section s and then other enzymes break down these sections further into monomers.…read more

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LACTOSE INTOLERANCE
Babies produce lots of LACTASE as milk is their main source of food. As you grow older
and milk is consumed less, the production of lactase DIMINISHES during childhood. BUT
some people end up producing either little or no lactase!!!!
Some people do not produce enough lactase to consume the lactose they have consumed.
When the undigested lactose reaches the small intestine, microorganisms break it down;
meaning a large volume of gas is produced. This may result in BLOATING, NAUSEA,
DIARRHOEA and CRAMPS.…read more

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TEST FOR PROTEINS: Biuret test
1. Place a sample of the test solution in a test tube with an equal volume of sodium
hydroxide solution at room temp.
2. Add a few drops of very dilute (0.05%) copper (II) sulphate solution and mix gently
3.…read more

Comments

Just_Georgia

so so so useful!!

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