The Ultimate Unit 1 Revision Guide

3.1.1 Disease

Topic Syllabus Statement – What I need to know: Notes

Revised

Exam Q

Pathogens Pathogens include bacteria, viruses and fungi. How pathogens enter the body and cause disease.

Lifestyle Risk factors for cancer and coronary heart disease. Difference between correlations and causal

relationships.

Book Ref Key Term Definition1.1 Pathogen A micro-organism that causes disease

1.1 Transmission Passing a pathogen from one individual to another

1.1 Infection Pathogen colonises host tissues.

1.2 Correlation A change in one variable is reflected by a change in another e.g. incidence of cancer increases as number of

cigarettes increases1.2 Cause There is experimental evidence to prove that one factor

causes another1.3 Risk A measure of the probability that damage to health will

occur as a result of a given hazard1.3 Lifestyle Factors Factors to do with how we live that contribute to

suffering a disease. These are in our power to change.

Microorganisms include: Bacteria and viruses

Pathogens include: Bacteria, fungi and viruses

Pathogens: BacteriumBacteria release toxins as they multiply. These toxins affect and damage cells in the region of infection. Eg, Pulmonary tuberculosisPathogens: VirusViruses enter living cells and disrupt their metabolic systems. The genetic material of the virus incorporates itself into that of the cell and instructs the cell to produce more viruses. Eg. InfluenzaPathogens: FungiFungal hyphae secrete enzymes, which digest subject tissues. The growth of hyphae physically damages tissues. Some fungi also secrete toxins. Eg Athletes foot

For a microorganism to be considered a pathogen, it must: 1) Gain entry to the host, 2) colonise host tissues, 3) resist the host defences, and 4) cause damage to host tissues

How do microorganisms enter the body?

1) Many pathogens enter through the gas exchange system (including ones that cause flu and TB).

2) Food and water can carry pathogens into the stomach and intestines via the mouth and into the digestive system (including ones that cause cholera) (gastrointestinal opening)

3) Broken skin4) Urogenital openings

How are pathogens prevented from entering?

1) Mucous layer that covers the exchange surfaces and forms a thick sticky barrier that is difficult to penetrate

2) Enzymes that break down pathogens3) Stomach acid (low pH) which kills pathogens

How do pathogens cause disease?

1) By damaging host tissues – the sheer number of pathogens causes damage and stops tissues functioning properly – e.g. viruses stop DNA and RNA synthesis.

2) By producing toxins – most bacteria produce toxins which cause damage to the body – e.g. the cholera bacterium produces a toxin which leads to diarrhoea

Correlations and causal relationships:

Correlation: a change in one or two variables is reflected by a change in another variable

Causation: causal relationship one factor is proven to be the direct cause of another by scientific evidence. (Not just correlation or statistical evidence)

Why not causal? Maybe there is another factor involved.

REMEMBER – CORRELATION DOESN’T MEAN CAUSATION

Data that shows there is a correlation between two variables e.g. cancer and smoking can never prove that smoking is the cause of cancer so therefore always look at it critically as it could be that stress is the cause and people smoke to help with stress nothing can be explicitly proved!

Diseases can be caused by two factors: 1) Genetics and 2) Lifestyle

Factors that increase the risk of cancer

1) Smoking – if they smoke the risk is higher2) Diet – low fat and high fibre rich in fruit and vegetables lowers risk3) Obesity – if someone is overweight the risk is higher4) Physical activity – more of this lowers risk5) Sunlight – more someone is exposed to sunbeds or sunlight (without sun cream) the greater

the risk

Factors that increase the risk of CHD

1) If you smoke2) If you have high blood pressure

3) If your blood cholesterol is high4) If you’re obese5) Diet – if you have a high amount of salt this increases blood pressure which increases the

risk and if you have a high amount of saturated fatty acids this increases blood cholesterol which increases risk

6) If you don’t do a lot of physical activity

Therefore you can reduce the risk of CHD and cancer by:

1) Giving up or not taking up smoking2) Avoiding becoming overweight3) Reducing salt intake in the diet4) Reducing saturated fats in the diet5) Doing regular exercise6) Keeping alcohol consumption within the recommended limits7) Increasing intake of fibre and antioxidants in the diet

Section 1.2: Epidemiology

Epidemiology is the study of patterns in diseases and the various factors that affect the spread of disease.

A correlation is different causal link.

Strong, positive correlation

Weak correlation

A positive correlation will occur when an increase in one variable, causes an increase in another. In order for the correlation to be “strong”, there must be little spread in the data.

Negative Correlation

How to prove a link

Wide samples must be used. Data must be analysed over long periods of time. Variables must be controlled.

Demographic Transition

Explains how the population changes over time e.g. from high birth rate.

Section 1.3: Lifestyle and Health

Risk – A measure of probability that damage to health will occur as a result of a given hazard. We need to look at probability that a hazard will occur as a consequence of the hazardous

event. If the consequence of the hazard is high and the probability is low, there is little cause for

concern. A major concern is when both are high.

Measuring risk

0% (no harm will occur) 100% (will definitely occur) A timescale is needed to give the data more weight. Risk must be relative.

A weak correlation occurs when there is a wide spread of data shown in the graph.

A negative correlation will occur when an increase in one variable causes a decrease in another.

Cancer

Cancer – Cell division in an uncontrollable fashion. This continues if there are nutrients. Cancer cells cease to function normally. Carcinogen – Cause the DNA to mutate. They are cancer causing agents. Most mutated cells are destroyed. One mutated cell can cause a mass of mutated cells. Benign – does not move from the point of origin. Usually harmless, however can cause

problems depending on where it grows. Maligment – grow faster and can spread throughout the body. Can have its own blood

supply. The process of moving to another area of the body is called metastasis. Older people = more likely. Genetics can cause approximately 5% of cancers. Tumour producing genes (oncogenes). Lifestyle factors can expose you to more carcinogens. More you smoke, higher the risk. Diet – low fat, high fibre, fruit etc. Radiation, UV light and X-rays are carcinogens. Physical activity – exercise reduces the risk. Alcohol – increases risk. Hormones – high level of sex hormones can increase risk.

Treatments

Prevention is better than cure. Early diagnosis. Surgical removal – Easiest when the tumour is benign. Chemotherapy – using drugs to kill cells in the body. Affects all cells that divide rapidly. Radiotherapy – ionising radiation that destroys tissue. Healthy cells suffer less so there are

little side-effects.

Future treatments

Hyperthermia may destroy cancer because the immune system is better at detecting cancer cells.

It may be possible to create drugs which can locate genes which are responsible for mutating and causing each type of cancer.

Smoking

Heavy smoking over a long period of time will drastically increase the risk of developing lung cancer.

There is a strong correlation, but not a causal link.

Conclusive evidence

Tar in cigarettes contains Benzopyrene (carcinogen) Cancer cells were looked at and scientist found that mutations occurred in 3 places in the

DNA. The gene that mutates is called a tumour suppressor gene.

This is still not a causal link because smoking does not definitely cause cancer, even though it is very likely to be the cause.

It is only a correlation because it is a multi-factorial disease.

Coronary Heart Disease

Largest cause of death in the U.K Occurs when one of the arteries supplying heart tissue with oxygen is blocked. Heart cells respire anaerobically when there is a blood clot. Anaerobic respiration does not release enough energy. Heart attack – myocardial infarction. Blood clot – thrombus Process of a blood clot forming is called thrombosis. If this happens to coronary arteries it is called coronary thrombosis. Smoking narrows blood vessels thus increase blood pressure. High blood pressure increases the rate at which cholesterol is deposited. Exercise can lower blood pressure. Diets high in saturated fats will increase the risk of developing coronary heart disease.

3.1.3 Cells and Transport

Topic Syllabus Statement – What I need to know:

Notes Revised

Exam Q

Cells

The structure of an epithelial cell from the small intestine as seen with an optical microscope.

The appearance, structure and function of plasma membrane, including cell-surface membrane, microvilli, nucleus, mitochondria, lysosomes, ribosomes, endoplasmic reticulum, Golgi apparatus

Transmission v scanning electron microscopes.

The difference between magnification and resolution.

Cell fractionation and ultracentrifugation

Chapter 3 – Cells and Movement in and out of them

Book Ref Key Term Definition

3.1 Resolution The minimum distance apart 2 objects are, so that they look like separate objects under the microscope

3.1 Cell Fractionation The process by which cells are broken up and the organelles separated out

3.1 Prokaryotic Cells Cells that lack a nucleus and any membrane-bound organelles

3.1 Eukaryotic Cells Cells that have a nucleus, chromosomes and other membrane-bound organelles

3.4 Saturated Lipids Fatty acids with only C-C single bonds

3.4 Unsaturated Lipids Fatty acids with one or more C=C double bonds

3.4 Hydrophilic Attracted to water

3.4 Hydrophobic Attracted to fat

3.5 Fluid-mosaic model

The structure of a cell surface membrane and its various molecules

3.5 Extrinsic Proteins Proteins on the surface of the bilayer

3.5 Intrinsic Proteins Proteins spanning the bilayer

3.6 Diffusion The net movement of molecules or ions from a region of high concentration to a region of low concentration

3.7 Osmosis The passage of water from a region of high water potential to a region of low water potential, across a

partially permeable membrane3.8 Active Transport The movement of molecules or ions into or out of a

cell from a region of lower concentration to a region of higher concentration using energy and carrier

molecules

Microscopy

Lenses work more effectively if they are in a compound light microscope.

Light waves a have a relatively long wavelength; therefore, they can only distinguish between objects that are at least 0.2 micrometers apart.

Limitation: cannot distinguish between two organisms less than 0.2 micrometers apart.

Beams of electrons have shorter wavelengths and are therefore able to distinguish between objects as close as 0.1 nm apart. BETTER

Why are electron microscopes better? They have shorter wavelengths!

Magnification

When an object is viewed under a microscope, the object seen under the microscope is called called an image.

Magnification tells you how many times bigger the image is in relation to the actual size of the object. It can be found using the following formula:

Magnification = size of image/size of object

The previous formula can also be rearranged to find the size of an object.

Size of object = size of image/magnification

Increasing magnification DOES NOT always increase the resolution

Resolution

The resolving power of a microscope is the minimum distance two objects can be apart in order for them to appear as separate items.

The greater the resolution, the greater the clarity of the image that is produced.

Cell fractionation: cells are lysed, contents separated

Cell fractionation is the process where cells are broken up and the different organelles they contain are separated out.

Before fractionation begins, the cells are put in a solution that is:

Cold – to reduce enzyme activity that might break down the organelles.

Isotonic – to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water. An isotonic solution is one that has the same water potential as the original tissue.

Buffered – to maintain a constant pH.

To break up the cells a homogeniser/blender is used:

Homogenation

Cells are broken up by a homogeniser that releases the organelles. The fluid is called a homogenate. It is then filtered to remove complete cells and large pieces of debris.

Ultracentrifugation

Ultracentrifugation is the process by which the homogenate is separated in a machine called a centrifuge.

This spins tubes of the homogenate, creating a centrifugal force that makes the mixture separate.

The tube of filtrate is placed in the ultracentrifuge and spun at a slow speed. The heaviest organelles such as the nucleus are forced to the bottom where they form a thin

sediment. The fluid at the top, called the supernatant (e.g ribosomes) is removed, leaving just the

sediment of nuclei at the bottom. The supernatant is then put in another tube where it is spun at an even higher speed than

before. The next heaviest organelles (mitochondria) are forced to the bottom and the process

continues until all the organelles are separated.

Section 3.2 – The electron microscope

Electrons have a shorter wavelength than light and so they have a greater resolving power.

As electrons are negatively charged, the beam can be focused using an electromagnet.

Advantages: Shorter wavelength, focused using an electromagnet

Because electrons are absorbed by molecules in the air, a near vacuum must be created within the chamber of an electron microscope for it to work effectively.

There are two types of electron microscope:

- Transmission electron microscope and scanning electron microscope.

Transmission electron microscope

The TEM consists of a gun that fires electrons which are focused onto the specimen by an electromagnet.

Some of the electrons are absorbed by the specimen and appear dark on the image; other parts allow the electrons through and so appear light. This produces an image of the specimen.

The image that appears on screen is called a photomicrograph.

Because the process takes place in a vacuum, living specimens cannot be observed.

A complex staining process is required and even then the image is only in B&W.

The specimen must be extremely thin.

Artefacts (structure not present in the organism when it was alive) may appear on the image, these appear as a result of the way the specimen is prepared.

Scanning electron microscope

All the limitations of the TEM apply to the SEM but the specimen does not have to be extremely thin as the electrons do not penetrate.

The beam of electrons is directed over the surface of the specimen in a regular pattern.

The electrons bounce on the contours of the specimen and are scattered.

The scattering of the electrons can be analysed and from this an image can be produced using a computer.

***The SEM has a lower resolving power than the TEM (20nm) but is still ten times better than a light microscope.

Classes of cells: Eukaryotic (Distinct nucleus, membrane-bound organelles) or prokaryotic

Epithelial cells are eukaryotic cells. Eukaryotic cells have a distinct nucleus and a membrane that surrounds each organelle.

The function of an epithelial cells is to absorb and secrete.

The nucleus

The nucleus controls the cells activities and contains hereditary material.

The Nuclear envelope is a double membrane that surrounds the nucleus. Its outer membrane is continuous with the endoplasmic reticulum and often has ribosomes on its surface. It can control the substances entering and leaving the nucleus.

Nuclear pores allow the passage of large materials into and out of the nucleus.

Nucleoplasm is granular jelly like material that makes up the bulk of the nucleus.

Chromatin is the DNA found within the nucleoplasm This is the form chromosomes take up when the cells is not dividing.

The nucleolus is small spherical body within the nucleoplasm. It manufactures ribosomal RNA and assembles ribosomes.

Function: control protein synthesis, contain cell’s genetic material, manufacture ribosomes and ribosomal DNA

The mitochondria

A double membrane surrounds the organelle, the outer one controlling the entry and exit of material. The inner membrane inner membrane is folded to form extensions known as cristae.

Cristae are shelf like extensions of the inner membrane. These provide a large surface area for the attachment of enzymes during respiration.

The matrix makes up the remainder of the mitochondria. It is a semi-rigid material that contains proteins, lipids and traces of DNA that allows the mitochondria to control the production of its own proteins. The enzymes involved in respiration are found in the matrix.

Mitochondria are responsible for the production of the energy-carrier molecule ATP. Because of this, high numbers of mitochondria are found in cells where there is a high level of metabolic activity.

Endoplasmic Reticulum

Rough endoplasmic reticulum – has ribosomes present on the outer surface of the membranes. Its functions are to: a) provide a large surface area for the synthesis of

proteins and glycoproteins, b) provide a pathway for the transport of materials, especially proteins throughout the cell.

Smooth endoplasmic reticulum - lacks ribosomes on its surface and is often more tubular in appearance. Its functions are to: a) synthesise, store and transport lipids, b) synthesise store and transport carbohydrates.

Golgi Apparatus

The Golgi apparatus is similar to the SER in structure but is more compact.

It consists of a stack of membranes that form flattened sacks, or cisternae with small rounded hollow structures called vesicles.

The proteins and lipids produced in the ER are passed through the Golgi apparatus in strict sequence.

The Golgi apparatus modifies these proteins often by adding non-protein structures to them such as carbohydrates. It is also labels them so they can be sorted and sent to their correct destination. Once sorted and modified, proteins are transported in vesicles which are regularly removed from the edge of the Golgi cisternae.

These vesicles move to the cell membrane where they fuse and release their contents to the outside (exocytosis).

Lysosomes

Lysosomes are formed when a vesicle contains enzymes.

Lysosomes isolate potentially dangerous enzymes from the rest of the cell before releasing them outside of the cell or into phagocytic vesicles within the cell.

Lysosomes digest worn out organelles so that the useful chemicals they are made of can be reused.

They can completely break down cells after they have died. (Apoptosis)

Ribosomes

Ribosomes occur in either the cytoplasm or the RER. There are two types depending on which cell they are found in:

80S Type – found in eukaryotic cells, is around 25nm in diameter.

70S Type – found in prokaryotic cells, is slightly smaller.

Microvilli

Microvilli are finger like projections of the epithelial cells. Their function is to increase the surface area for diffusion.

Diffusion

Diffusion and effect of surface area, difference in concentration and the thickness of the exchange surface (Fick’s Law).

The role of carrier proteins and protein channels in facilitated diffusion.

Diffusion is defined as the net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower.

All particles are constantly in motion due to the kinetic energy that they possess.

The motion is random and there is no set pattern to the way they move.

Rate of diffusion

The greater the difference in concentration, the greater the rate of diffusion

The larger the area of an exchange surface, the greater the rate of diffusion.

The thinner the exchange surface, the faster the rate of diffusion.

The nature of the plasma membrane; its composition and the number of pores.

The size and nature of the diffusing molecule. For example smaller molecules diffuse faster than big ones.

Diffusion is proportional to: surface area x difference in concentration

Length of diffusion path

Facilitated diffusion

Facilitated is a passive process as it only relies on the kinetic motion of particles.

Facilitated diffusion can only occur at specific point along the plasma membrane where there are special protein molecules.

The proteins for special water filled channels.

The channels only open for specific molecules.

This allows water soluble ions and molecules to pass through. Such molecules such as glucose and amino acids would take much longer to diffuse through the phospholipids bilayer.

When a molecule that is specific to the carrier protein is present, the carrier protein changes shape, causing it to release the molecule on the other side of the plasma membrane.

Osmosis Osmosis and water potential

Osmosis is defined as the passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a partially permeable membrane.

Water potential is measured in Pascal’s.

Under standard conditions of temperature (25oC), pure water is said to have a water potential of 0.

Water with a solute dissolved in it will have a water potential that is less than 0.

Water molecules move from one side where the water potential is higher (less negative) across a partially permeable membrane to another side where the water potential is lower (more negative).

The water moves along a water potential gradient.

At the point where the water potentials on either side of a partially permeable membrane are equal, a dynamic equilibrium is established and there is no net movement of water.

Osmosis in animal cells

If a red blood cell is place in pure water it will absorb water by osmosis because it has a lower water potential.

The cell-surface membrane will eventually burst if too much water enters the cells.

To prevent cells bursting due to too much water entering the cells, cells are often bathed in solutions where the water potential outside the cell is the same as the water potential inside the cell. This is called an isotonic solution.

A hypotonic solution is one where the concentration outside is greater than the concentration inside.

A hypertonic solution is one where the water potential outside the cell is lower than the water potential inside the cell.

Active Transport

The role of carrier proteins and the transfer of energy in the transport of substances against a concentration gradient.

Absorption

Absorption of the products of carbohydrate digestion. The roles of diffusion, active transport and co-transport involving sodium ions.

Cholera

Cholera structure (prokaryotic cell) Causes and symptoms of cholera. Oral rehydration solutions (ORS) and ethical

issues

Section 3.8 – Active transport

Active transport allows cells to exchange molecules against a concentration gradient.

Metabolic energy is required for this process.

Active transport is the movement of molecules or ions into or out of a cell from a region of lower concentration to a region on higher concentration using energy and carrier molecules.

Metabolic energy is needed in the form ATP.

Carrier molecules which act as “pumps” are involved.

Active transport uses ATP in two main ways:

by using ATP to directly move molecules.

By using a concentration gradient that has already been set up by direct active transport. This is known as co-transport.

The carrier molecules accept molecules or ions to be transport on one side of it.

The molecules of the ions bind to the receptors on the channels of the carrier protein.

On the other side of the membrane ATP bind to the carrier protein causing it to split into ADP and a phosphate molecule. This as a result, causes the carrier protein to change shape, releasing the molecule onto the other side.

The phosphate molecule then recombines with the ADP to form ATP again, which causes the carrier protein to revert back to its original shape.

Occasionally, the molecule or ion is moved into the cell at the same time as a different one is being removed from it. One example of this is the sodium-potassium pump

Sodium ions are actively taken in by the cell whilst potassium ones are actively removed from the cell.

Section 3.9 – Absorption in the small intestine

Villi and Microvilli

Villi have walls lined with epithelial cells.

Villi are situated at the interface between the lumen of the intestines and the blood and other tissues inside the body.

Their properties increase the efficiency of absorption because:

They increase the surface area for diffusion

They are very thin walled, thus reducing the distance over which diffusion takes place.

They are able to move and so maintain a concentration gradient

They are well supplied with blood vessels so that the blood can carry away absorbed molecules and hence maintain a diffusion gradient.

The epithelial cells possess Microvilli which further increase the surface area for diffusion. They are situated on the cell surface membrane.

Villi contain muscles which move the food ensuring the glucose is absorbed from the food adjacent to the villi, new glucose rich food replaces it, thus maintains a concentration gradient for diffusion.

Role of active transport in absorption

The way in which most glucose is absorbed from small intestine is an example of co-transport.

1. Sodium ions are actively transported out of the epithelial cells by the sodium potassium pump.

2. There is now a much higher concentration of sodium ions in the lumen than in the cells.

3. The sodium ions diffuse into the cells down a concentration gradient. As they flood back into the cells, they are coupled with glucose molecules which are drawn in with them.

4. The glucose diffuses into the blood through a carrier protein.

It is the sodium ion concentration, rather than the ATP directly, that powers the movement of glucose into the cell.

Section 3.10 – Cholera

Structure of a bacteria cell

The bacterium that causes cholera is called Vibrio Cholerae.

All bacteria possess a cells wall that is made up of peptidoglycan. This is a mixture of polysaccharides and peptides.

Many bacteria also protect themselves by producing a capsule of mucilaginous slime around this wall.

Flagella occur at certain types of bacteria.

Inside the cell-surface membrane is the cytoplasm that contains ribosomes that are smaller than the ones found in eukaryotic cells. (70s type)

Bacteria store food as glycogen granules and oil droplets.

The genetic material of a bacterium is found in the form of a circular strand of DNA.

Separate from this are smaller circular pieces of DNA, called plasmids.

How the cholera bacterium causes disease

Almost all Vibrio cholerae bacteria ingested by humans are killed by the low pH in the stomach but many can still survive, especially if the pH is above 4.5.

When the bacteria enter the lumen of the small intestine they use their flagella to propel themselves through the mucus lining of the intestinal wall.

They then start to produce a toxic protein. The protein has two parts: one part binds to the carbohydrate receptors of the intestinal epithelial cells, whereas the other part enters the epithelial cells. The causes the ion channels of the cell-surface membrane to open, that the chloride ions that are normally contained within the epithelial cells flood into the lumen of the intestine.

The loss of chloride ions from cells increases the water potential in the cell, but lowers the water potential outside the cells. This causes water to move into the small intestine.

The loss of ions from the cells establishes a concentration gradient. Ions move by diffusion into the epithelial cells. This establishes a water potential gradient that causes water to move by osmosis from the blood and other tissues into the small intestine.

Section 3.11- Oral rehydration therapy

What causes diarrhoea?

Damage to the epithelial cells in the lining of the small intestine

Loss of Microvilli due to toxins

Excessive secretion of water due to toxins

What is oral rehydration therapy?

Drinking water to treat diarrhoea is ineffective because:

Water is not being absorbed by the intestine. Indeed, as in the case of cholera, water is actually being lose from cells.

The drinking water does not replace electrolytes that are being lost from cells of the intestine.

As sodium ions are being absorbed, the water potential falls and water enters the cells by osmosis.

A rehydration solution should therefore contain:

Water – to rehydrate tissues

Sodium – to replace the ions lost from the epithelium of the small intestine and to make optimum use of the sodium-glucose carrier proteins.

Glucose – to stimulate the uptake of sodium ions from the intestine and to provide energy

Potassium – to replace lost potassium ions and to stimulate appetite

Other electrolytes – such as chloride and citrate ions, to help prevent electrolyte imbalance

The solution must be given regularly and in large amounts whilst the person has the illness.