AQA BIOLOGY UNIT 1.1-DISEASE AND PATHOGENS

Pathogens- Gain entry, Colonise tissues, Resist defences, Cause damage Pathogens (organisms that cause disease) include-

Bacteria

Fungi

Viruses’

Pathogens can enter the body via penetration of an organisms interface mainly via-

The gas exchange system (breathe in air containing pathogen)

The digestive system (eat or drink food containing the pathogen)

The skin

Pathogens cause disease by-

Releasing toxins in to the body

Direct damage to the cell (rupturing the cell to release its nutrients, breaking down nutrients

in the cell or replicating inside the cell causing it to burst)

Preventing pathogen entry-

Mucus lining in the lung epithelium

Blood clots at the area of skin damage

Acidic conditions of the stomach

Enzymes which break down pathogens

Lifestyle A risk factor is something that increases your chance of developing a disease.

A disease is a malfunction of part or whole of the body with a characteristic set of symptoms.

CHD (Coronary heart disease) risk factors-

HIGH SATURATED FAT, HIGH SATURATED SALT-poor diet

HIGH BLOOD PRESSURE- due to smoking, lack of exercise or excessive alcohol intake causing

damage to the heart and blood vessels.

Cancer (uncontrolled cell division) risk factors-

Smoking

Carcinogenic chemicals

Ionising radiation

Excessive alcohol intake

A change in lifestyle would result in reduced risk of contracting these conditions.

Data analysis Shows a positive/negative correlation

Correlation does not mean causation

Other named factor

Sample size

Data analysed

AQA BIOLOGY UNIT 1.2- THE DIGESTIVE SYSTEM

Digestion When large insoluble molecules are broken down into smaller more soluble molecules by hydrolysis

from digestive enzymes so they can be absorbed and assimilated.

Oesophagus- takes food from the mouth to the stomach, mouth contains salivary glands

secreting salivary amylase which breaks starch into maltose, mucus on its walls to lubricate

food passage

Stomach- gastric juice to break down food containing HCl, pepsin and mucus, pepsin is an

enzyme which hydrolyses proteins

Small intestine- alkaline bile and pancreatic juices from the pancreas neutralise the acidity of

the HCl from the stomach, small soluble molecules are absorbed in the gut wall by villi

Large intestine- absorbs water, salt and minerals, bacteria that decompose some undigested

nutrients

Rectum- faeces stored here until defecation

Proteins Proteins have a variety of functions such as enzymes, antibodies, transport and structural function.

Primary Structure- sequence of amino acids in a polypeptide chain

Secondary Structure- hydrogen bonds form between amino acids, the chain coils into an

alpha helix or folds into beta pleated sheets

Tertiary Structure- the secondary structure is coiled or folded further, more bonds are

formed, final 3D structure for proteins made from one polypeptide chain

Quaternary Structure- final 3D structure for proteins made of more than one polypeptide

chain

Polypeptides are more than two amino acids are joined.

A dipeptide is when two amino acids join.

A peptide bond is the bond formed between two amino acids.

A condensation reaction, removal of a water molecule, joins two amino acids together, forms a

peptide bond.

A hydrolysis reaction, addition of a water molecule, separates two amino acids, breaks a peptide

bond.

Biuret test

Add NaOH to make the solution alkaline

Add copper(II) sulphate

If protein is present a purple layer forms

If is no protein the solution will remain blue

Enzymes Enzymes are proteins which speed up rate of reaction by acting as catalysts and lowering the

activation energy required for a reaction.

‘Lock and Key’ Model-

Substrate will fit into the enzymes active site

This will form an enzyme substrate complex and break up the substrate

‘Induced Fit’ Model-

Any substrate binds to the active site of the enzyme causing the active site to change shape

The substrate can now form a complimentary enzyme substrate complex and break up the

substrate

Induced Fit model is better as shows how the active site can be specific and only bind to one

substrate.

Factors affecting enzyme activity Temperature

Increase causes an increase in kinetic energy, faster moving molecules, enzymes more likely

to collide with substrates, higher energy collisions which are more likely to result in a

reaction

If it is too high, the enzyme molecule vibrates more, some bonds are broken, the tertiary

structure is altered, active site changes shape, enzyme and substrate no longer fit and the

enzyme is denatured

pH

All enzymes have an optimum pH, most work best at pH 7,

If the pH of an enzyme is not optimum the ionic bonds and hydrogen bonds break, this

changes the shape of the active site and denatures the enzyme

Concentration

Increase causes faster reaction, more substrate molecules means a collision is more likely so

more active sites are filled, levels off when all the active sites are filled so no more enzyme

substrate complexes can be formed

Inhibition of enzymes Competitive Inhibition-

Similar shape to the substrate molecule

Bind to the active site of the enzyme in place of the substrate but no reaction takes place

They block enzyme-substrate complexes forming

Non-competitive Inhibition-

Bind to the enzyme on a place away from the active site

Cause the active site to change shape so the substrate can no longer bind to it

Enzyme-substrate complexes can no longer form

Carbohydrates Starch is made of the polysaccharides amylose and amylopectin which are made of a-glucose.

Amylase released by the salivary glands and the pancreas breaks down starch into

maltose.

Maltose is broken down into a-glucose molecules by maltose which is released by

the epithelium of the small intestine

A-glucose can form glycosidic bonds in a condensation reaction, where a water molecule is lost, to

form maltose. If lots of these join, starch is formed.

Monosaccharides are the monomers of polymers.

Two monosaccharides joined together is a disaccharide.

More than two disaccharides joined together is a polysaccharide.

Disaccharides are formed by condensation reactions of polymers forming glycosidic bonds.

Carbohydrates and proteins are often polymers and are composed of C, H and O.

Disaccharide Hydrolysed by… Into…

Maltose Maltase Glucose + Glucose

Sucrose Sucrase Glucose + Fructose

Lactose Lactase Glucose + Galactose

Tests Reducing sugars

All monosaccharides and some disaccharides

Add Benedict’s reagent to a sample and heat it

If it contains reducing sugars, the sample will turn from blue to brick red

Non-Reducing sugars

Sucrose

Boil the test solution with dilute HCl

Neutralise the solution with sodium hydrogen carbonate

Add Benedict’s reagent to the sample and heat it

If it turns brick red it contains either a reducing sugar or a non-reducing sugar.

Iodine test for starch

Add iodine dissolved in potassium iodide solution

If starch is present, colour change from orange to a dark blue/black

Lactose Intolerance Lactose is a sugar found in milk

Lactase, an enzyme released the epithelium of the intestine, breaks down lactose

Some people don’t have enough lactase so can’t break down the lactose

Can cause stomach cramps, diarrhoea and flatulence

Milk can be purified with lactase to make it suitable for lactose intolerant people

AQA BIOLOGY UNIT 1.3- ORGANISMS AND SURFACE INTERCHANGES

Structure of an epithelial cell

Plasma membrane

Allows substances to move in and out of the cell

Has receptor molecules

Nucleus

Contains DNA which controls the cells activities

Nuclear pore allows substances to move between the nucleus and cytoplasm

Nucleolus makes ribosomes

Ribosomes

Site of protein synthesis

Lysosomes

Contains digestive enzymes which can be used to digest invading cells or break down worn

out components of the cell

Endoplasmic Reticulum

Smooth- synthesises and processes lipids

Rough(has ribosomes on its surface)- folds and processes proteins that have been made at

the ribosomes

Golgi apparatus

Processes and packages new lipids and proteins

Makes lysosomes

Microvilli

Increase the surface area of the plasma membrane for absorption

Mitochondrion

Site of aerobic respiration

Produce ATP for energy

Have a double membrane, the inner one is folded to form cristae, inside is the matrix which

contain enzymes

Microscopes Magnification- How much bigger a sample appears to be under a microscope than it is in real life

Resolution- ability to distinguish between two points on an image

Electron microscopes are better than light microscopes as they have higher resolutions, detailed

images and 3D images. A vacuum is needed however which requires the specimen to be dead, it’s

expensive and skills and training are needed. Light has a longer wavelength than electrons. Electron

microscopes both produce black and white images compared to the colour image produced by light

microscopes. Staining process, thin sample and vacuum needed for electron microscopes. TEM and

SEM may contain artefacts because of the complex staining process.

TEM (Transmission Electron Microscope)

2D image

Highest magnification

Best resolution

Electron beam passes through a thin sample

Magnification Size of object

Size of Image

SEM (Scanning Electron Microscope)

3D image

High resolution

Good resolution

Electron beam bounces off the sample

Cell fractionation and ultracentrifugation 1. Homogenisation- Breaking up the cells

Break open the plasma membrane to release organelles into the solution

2. Filtration- Getting rid of the big bits

Homogenised solution filtered through a gauze to remove any large cell or tissue

debris.

3. Ultracentrifugation- Separating the organelles

Put the solution in a tube un a centrifuge and spin at low speeds

The heaviest organelles will go to the bottom of the centrifuge, the pellet

The supernatant is the suspended fluid above the pellet with the remaining

organelles

The pellet can be removed

The process is repeated at higher speeds to separate all the organelles out until you

are finally left with the lightest organelle.

Plasma membranes The plasma membrane contains proteins, carbohydrates (usually attached to proteins or lipids) and

lipids(mainly phospholipids)

Triglycerides are formed by condensation reactions between glycerol and a fatty acid.

Triglycerides have a glycerol head and three fatty acid tails.

Phospholipids have a glycerol head, two fatty acid tails and a phosphate group attached to

the head.

The phosphate group is hydrophilic and the fatty acid tail is hydrophobic.

A fatty acid may be unsaturated or saturated.

Emulsion test for lipids- Shake the substance with ethanol then pour in water. A lipid will show a

milky emulsion.

Diffusion Diffusion is the passive movement of substances down a concentration gradient from an area with

high concentration to an area with lower concentration.

Factors affecting diffusion-

Surface area

Difference in concentration

Thickness of exchange surface

Particles can diffuse across the plasma membrane as they can move freely through the membrane(if

they are small enough).

Facilitated diffusion-

Still the diffusion of particles down a concentration gradient

Both the carrier proteins and the protein channels are specific to the molecule they are transporting

Carrier proteins- move large molecules in or out of the cell, the molecule attaches to the

carrier protein then the protein changes shape allowing the release of the molecule on the

other side of the membrane

Protein channels- pores in the membrane for charged particles to diffuse through.

Osmosis Diffusion of water molecules across a partially permeable membrane from an area of a high water

potential to an area with low water potential

Water potential is the potential of water molecules to diffuse into or out of a solution, water has the

highest water potential

Isotonic is when two solutions have the same osmotic pressure

Active transport Active transport uses energy to move molecules and ions across plasma membranes, against a

concentration gradient.

Carrier proteins- a molecule attaches to the protein, it changes shape, the molecule is

released on the other side of the membrane, energy is used from ATP to move the solute

against its concentration gradient

Co-transporters- a type of carrier protein, bind two molecules at a time, sodium ions and

glucose, concentration gradient of one molecule used to move the other molecule against its

concentration gradient

Absorption The products of carbohydrate digestion are absorbed in different ways-

Some glucose diffuses across the intestinal epithelium to the blood- there’s a higher

concentration of glucose in the small intestine than the blood when carbohydrates are first

digested so glucose diffuses out.

Some glucose enters the intestinal epithelium by active transport with sodium ions-

1. Sodium ions are actively transported out of the small intestine epithelial cells, into the

blood, by the sodium potassium pump. This causes a concentration gradient of more

sodium ions in the small intestine lumen than in the cell.

2. Sodium ions diffuse into the cell from the small intestine lumen. They do this via sodium-

glucose co-transporter proteins.

3. The co-transporter protein carries glucose into the cell with sodium, glucose

concentration inside the cell increases.

4. Glucose diffuses out of the cell into the blood down its concentration gradient, via a

protein channel by facilitated diffusion.

Cholera Cholera is an example of a prokaryotic organism. Prokaryotic organisms have some different

features than eukaryotic organisms; here is what they consist of-

Flagellum- Long hair like structure that helps the bacterium move

DNA- Free circular DNA in the cytoplasm

Plasma membrane- made mainly of lipids and proteins, controls movement of substances

into and out of the cell

Cell wall- supports the cell

Plasmids- small loops of DNA which contain genes and can be passed between bacteria

Capsule- made of secreted slime, protects the bacteria from attack

Cholera produces a toxin when it infects the body

1. The toxin causes chloride ion protein channels in the plasma membranes of the small

intestine epithelial cells to open

2. Chloride ions move into the small intestine lumen and lower the water potential of the

lumen

3. Water moves out of the blood and into the lumen by osmosis

4. The increase in water in the lumen leads to diarrhoea and dehydration

Oral rehydration solutions are used to treat diarrhoeal disease-

Water for rehydration

Sodium ions to replace those lost from epithelium

Glucose to provide energy and stimulate uptake of sodium ions by co-transport

Potassium ions to replace those lost and stimulate appetite

Other electrolytes to prevent an electrolyte imbalance

AQA BIOLOGY UNIT 1.4- THE LUNGS

The lungs of a mammal act as an interface with the environment

Lung function may be affected by pathogens and lifestyle

As you inhale air enters the trachea

The trachea splits into two bronchi- one leading to each lung

Each bronchus branches off into smaller tubes called bronchioles

The bronchioles end in small air sacs called alveoli where gas exchange occurs

Gas exchange in alveoli

Lots of alveoli for increased surface area for gas exchange of oxygen in and carbon dioxide

out of the body

The alveoli are surrounded by dense capillaries so there is a bigger difference in

concentrations, constantly maintained by blood flow and ventilation

Oxygen diffuses out of the alveoli, across the alveolar epithelium and capillary endothelium

and into haemoglobin in the blood

Carbon dioxide diffuses into the alveoli from the blood and is breathed out

The alveolar epithelium is only one cell think which means there is a short diffusion pathway

to speed up diffusion

Large surface area for gas exchange

Pulmonary Ventilation- Volume of air taken in per minute Don’t get confused with heart equation! All have V’s in!!

Ventilation Rate Tidal Volume

Pulmonary Ventilation

Volume per breath in dm^3 Amount of breaths per minute

Volume of air taken in per minute in

dm^3min-1

Inspiration VS Exhalation Inspiration

Intercostal muscles and diaphragm contract

Ribcage moves upwards and outwards

Volume increases

Lung pressure decreases

Air moves in the lungs

Exhalation

Intercostal and diaphragm muscles relax

Ribcage moves down and inwards

Volume decreases

Lung pressure increases

Air moves out of the lungs

Pulmonary Tuberculosis (TB) Caused by bacteria

Transmitted by droplets in air being breathed in- from mucus/saliva in coughing or sneezing

Phagocytes build a wall around bacteria in the lungs called tubercles

Bacteria destroy tissue of lungs resulting in cavities and scar tissue arises, causing damage to

the gas exchange surface

Bacteria can spread once in blood

The inactive form may stay in the body until your immune system is weakened and then the

active form is stimulated

Coughing mucus or blood, chest pains, fatigue, shortness of breath, fever, weight loss

Emphysema- Smoking/Air pollution Foreign particles are trapped in the alveoli causing inflammation that attracts phagocytes

Phagocytes break down alveoli elastin so the alveoli can’t recoil to expel air

The alveoli walls have a smaller surface area and a lower gas exchange rate

Fibrosis- Infection/Dust/Asbestos Formation of scar tissue

Thicker, less elastic lung tissue, less expansion so lower tidal volume

Slower gas exchange

Faster breathing rate

Asthma- Allergic reaction to pollen/Dust Inflamed and irritated airways

Muscle lining bronchioles contracts and produces mucus

Airways are constricted so tidal volume lower, faster breathing rate

Air flow reduced

Less oxygen enters the alveoli and therefore the blood, slower gas exchange

AQA BIOLOGY UNIT 1.5- THE HEART

The functioning of the heart plays a central role in the circulation of blood and relates to the

level of activity of an individual.

Heart structure

Cardiac cycle 1. Relaxation of the heart- Diastole

Blood enters the atria and ventricles via the pulmonary veins and vena cava

Atria are relaxed and fill with blood

Ventricles are relaxed

Semi lunar valves closed

Left and right Atrioventricular valves open

Relaxed ventricles draws blood from atria

2. Contraction of the atria- Atrial systole

Atria contract to push remaining blood into the ventricles

Semi lunar valves closed

Aorta- carries oxygenated blood to the body

Vena Cava- carries deoxygenated blood to

the heart from the body

Pulmonary Artery- carries deoxygenated

blood to the lungs

Pulmonary Vein- carries oxygenated

blood from the lungs to the heart

Cardiac Output

Heart Rate Stroke Volume

Left and right Atrioventricular valves open

Blood pumped from atria to ventricles

Ventricles remain relaxed

3. Contraction of the ventricles- Ventricular systole

Blood pumped into pulmonary arteries and the aorta

Atria relax

Semi lunar valves open

Left and right atrioventricular valves closed

Ventricles contract

Blood is pushed away from the heart

Myogenic Heart Muscle The atrioventricular node and the sinoatrial node pass electrical activity to each other in order to

make the heart contract.

A wave of electrical activity passes from the SAN causing the atria to contract

Non-conductive tissue stops this electrical activity passing to the ventricles

The electrical activity passes to the AVN which causes a delay so the atria can fully empty

and the atrioventricular valves can fully close so this prevents backflow of blood to the atria

The AVN sends a wave of electrical activity to the bundle of his

It travels down the bundle of his to the purkinje fibres were it makes the ventricles contract

thus forcing blood out of the heart

Heart Problems An atheroma is a build-up of fatty deposits under the epithelium of the artery wall

Causes the lumen to narrow restricting blood flow

Increases chances of aneurysm and thrombosis

Myocardial infarction-

When the lumen is so narrowed that not enough blood can get to the heart muscle

The heart is not supplied with enough oxygen so dies

Thrombosis-

When an atheroma breaks through the lining of the artery

Forms a rough surface

As the body repairs it, a clot may be formed (a thrombus)

Will block the blood vessel further and supply of blood to tissue

Tissue dies due to lack of oxygen and nutrients (glucose)

Clot could detach and block another artery blocking blood flow and thus oxygen flow to the

heart muscle

Aneurysm-

Caused by thrombosis weakening the artery walls

Weakened parts swell to form balloon like structures called aneurysms

These can burst causing haemorrhaging and blood loss- in the brain this is a stroke

Risk factors of CHD A diet high in saturated fats or salts

High blood cholesterol

Smoking

Lack of exercise and excess of alcohol causing high blood pressure

AQA BIOLOGY UNIT 1.6- IMMUNOLOGY

Phagocytosis (Cellular Response) When a pathogen with a foreign antigen enters the body this stimulates the phagocyte

The phagocyte engulfs the pathogen into a vesicle in its cytoplasm

Lysosomes bind to the vesicle and release digestive enzymes to break down the pathogen

The pathogens antigen is then presented on the phagocyte to aid the T cells in the immune

response

T- Cells (Cellular Response) Bind to the antigen presented by the phagocyte

T-Cells bind to the antigen with the complimentary receptor, it is activated and clones

Helper T-Cells stimulate B-Cells

Killer T-Cells locate and destroy the body cells infected by the pathogen/with the antigen

B- Cells (Humoral Response) Helper T-Cells stimulate B-Cells to clone into two types

Plasma cells produce specific antibodies to form antibody antigen complexes with the

pathogen

Memory cells ( of T-Cells and B-Cells ) remain in the body in case of re- infection

An antigen is a molecule which stimulates an immune response and results in producing specific

antibodies

An antibody is a protein made in response to a foreign antigen with binding sites which bind

specifically to the antigen to form an antigen-antibody complex

Antibody shape is complimentary to the antigen

Each antibody will only bind to a specific antigen

Secondary Response Body recognises the foreign antigen

Memory T cells and B cells are stimulated

T cells recognise and bind to the foreign antigen

B cells produce antibodies specific to the antigen and form antigen- antibody complexes to

kill the pathogen

This response is much faster, no symptoms shown

Antigenic variability (Influenza virus) Some pathogens have different strains with different surface antigens

Antigens mutate and change shape

Can’t use secondary response

If your body has suffered from one strain but is re-attacked with another strain the memory

cells do not recognise the antigen

Must go through the cellular and humoral response again

Hard to produce vaccines against

Vaccines (active immunity) Injection of a dead or weakened version of a pathogen

Initiate primary response

No symptoms

Allows for fast secondary response if pathogen invades the body in future

Booster doses increase efficiency

Herd Immunity- When most of the population is vaccinated so it is less likely an individual

will develop a disease even if they are not vaccinated

Monoclonal antibodies- genetically identical B cells/plasma cells Antibodies bind to specific antigens

Can inject mouse with any pathogen to stimulate it to produce an antibody against this

Monoclonal antibodies can be made to bind to tumour markers on cancer cells and we can

attach an anti-cancer drug to the antibody so they bind and target only the cancer cell