C11 - Diseases

Question 1

What’s a disease?

Answer 1

The malfunction of the body or mind, which adversely affects the health of the individual.
The pathogen must first enter and penetrate the host’s first line of defence of the body then colonise the tissues.

Question 2

What’s a communicable disease?

Answer 2

One which can spread from one person to another.

Question 3

What’s virulence?

Answer 3

The ability for a pathogen to cause disease.

Question 4

What’s a pathogen?

Answer 4

A microorganism that can cause disease and must enter the host, colonise and reproduce.

Question 5

What are the 3 main ways in which pathogens cause disease?

Answer 5

1 - By producing toxins which damage the cells and cause symptoms e.g. Rashes and fevers

2 - Secreting enzymes that allow the pathogens to spread through tissues. Some symptoms are allergic reactions to the enzyme e.g. The fungus causing athletes foot.

3 - Entering them and preventing tissue function e.g. Viral replication. Viruses inhibit normal DNA, RNA and protein synthesis of the cell and use the mechanism to produce new viral particles which can cause the cell to rupture and infect new cells.

Question 6

How do bacteria reproduce?

Answer 6

By binary fission (NOT mitosis)

Question 7

How do bacteria differ from viruses?

Answer 7

Bacteria are prokaryotic cells with cytoplasm, circular DNA, plasmids, pilli, flagella etc. and reproduce asexually.

Viruses are small organic particles with no proper cell structure. They have a strand of nucleic acids enclosed within a protein coat and may have an outer envelope from the host cell containing glycoproteins from the virus. They enter cells and infect the host’s metabolic rate.

Question 8

What’s TB?

Answer 8

Caused by Mycobacterium Tuberculosis, it’s a widespread disease that affects the respiratory system.
It’s transmitted through inhalation of infected water droplets e.g. coughs and sneezes.

Question 9

What’s the full name of TB?

Answer 9

Mycobacterium tuberculosis

Question 10

Why is TB so virulent?

Answer 10

It is able to inhibit the action of lysosomes in phagocytic cells that engulf it where it can survive and multiply.

Question 11

What’s secondary TB?

Answer 11

When TB develops and many phagocytic and other cells accumulate round the infected cells to form a tubercle.
Lung tissue is damaged, sputum is bloodstained and it can be fatal.

Question 12

How is TB treated?

Answer 12

By intensive care and extensive antibiotics over 6 months.

Question 13

Why is TB so hard to cure?

Answer 13

It can develop resistance to antibiotics.

Multi-drug resistant TB (MDR TB) describes a strain resistant to 2 antibiotics.

Extensively drug resistant TB (XDR TB) describes a strain resistant to 3+ antibiotics.

Question 14

What’s HIV/AIDS?

Answer 14

An immunodeficiency disease caused by a human immunodeficiency virus.

It’s a retrovirus, meaning it’s genetic information is in the from of RNA not DNA.

It enters and infects T helper cells.

Question 15

How does HIV form?

Answer 15

It’s a retrovirus, meaning it’s genetic information is in the from of RNA not DNA.

It also has the enzyme ‘reverse transcriptase’ which will create the double stranded DNA copy of the viral genome once within the host T helper cell.
The viral DNA copy then becomes part of the DNA of the host cell, forming a provirus.

Once the viral DNA becomes active, viral RNA and proteins are synthesised by the cell and more viruses are produced while T helper cells are destroyed. This prevents resistance from the immune system. (Opportunistic infection)

Question 16

How is HIV controlled?

Answer 16

There’s no cure.

Safe sex encouraged
Reduced needle sharing encouraged
Blood screening before transfusions
Discourage infected mothers from breast feeding
Test 'at risk' groups

Question 17

What type of cell is HIV?

Answer 17

An acellular particle. They’re considered to be specialised parasites.

• It’s can’t reproduce alone, can’t grow and can’t divide
• They don’t transform energy
• They can’t synthesise proteins

Question 18

What’s the structure of a virus?

Answer 18

They have a central core of genetic material, either DNA or RNA, surrounded by a capsid (protein coat).
The capsid is made up of proteins called capsomeres which may be surrounded by a lipid and protein membrane.

Question 19

What is the structure of a HIV virus?

Answer 19

They are spherical and have a central core of two strands of genetic material (RNA) and the enzyme ‘reverse transcriptase’.

The RNA and reverse transcriptase is then surrounded by a capsid (protein coat) which is then surrounded by a spherical lipid and protein membrane.

Question 20

What does reverse transcriptase (found in HIV) do?

Answer 20

It creates the double stranded DNA copy of the viral genome.

Question 21

What’s a capsid?

Answer 21

The protein coat surrounding the genetic material in viruses.

The capsid is cone shaped and surrounded by a lipid and glycoprotein membrane, forming an envelope.
The glycoproteins form peg-like structures which bind to receptors on the cell surface membrane of T helper lymphocytes.

Question 22

Why are aseptic techniques used to culture bacteria?

Answer 22

To prevent contamination.

E.g. Use sterile containers, add sterile agar jelly, inoculate the medium and clean surfaces.

Question 23

What is gram stain?

Answer 23

A stain used for a method of bacteria staining containing the chemical ‘crystal violet’.

This splits bacteria into 2 groups, gram positive bacteria and gram negative bacteria.

Question 24

How is a gram positive bacteria identified?

Answer 24

The crystal violet from the gram stain will stain the bacteria purple/blue which can be seen under a microscope.

Question 25

How is a gram negative bacteria identified?

Answer 25

The crystal violet from the gram stain will stain the bacteria pink which can be seen under a microscope.

Question 26

What is the procedure for gram staining?

Answer 26

1) Prepare bacterial slides, stain with crystal violet for 30 seconds then wash off the stain with water.
2) Flood the slide with Gram’s iodine to bring the crystal violet-iodine complex to the peptidoglycan wall.
3) After 1 minute, rinse the slide with water then alternate between washes of 95% alcohol and water until no further colour loss is identified.
4) Use a colour stain, e.g. safranin, to stain any cells which haven’t retained the crystal violet cells.

5) Blot, dry and observe the slide under a microscope.
If gram-negative, it will appear pink, if gram-positive, it will appear purple/blue.
(The amount of stain retained is due to the thickness of the cell and presence or absence of an outer layer.)

Question 27

What are properties of gram-positive bacteria?

Answer 27

They have a thick peptidoglycan wall that consists of amino acids and sugars outside the cell membrane.
This thick wall takes up and binds to the crystal violet.
When washed with alcohol, the thick layer doesn’t get washed away and the violet stain remains.
The counterstain will also have no effect on the colour, leaving the bacteria stained purple.

Question 28

Hat are the properties of gram-negative bacteria?

Answer 28

The peptidoglycan wall is much thinner and is covered by a lipopolysaccharide layer.
When stained, the crystal violet binds to the layer but is then washed off by the alcohol, removing any crystal violet stain.

When the safranin stain is added, the peptidoglycan layer becomes stained, giving it the pink coloured stain.

Question 29

How do bacterial cells multiply?

Answer 29

By binary fission (NOT mitosis)

Question 30

What’s a bacterial colony?

Answer 30

A small spot growing on a culture medium which is composed of millions of identical bacterial which arose through binary fission.

Question 31

What’s colony morphology?

Answer 31

Characteristics which help to identify different types of bacteria e.g. shape, colour etc.

Question 32

What is the colony morphology of bacteria: cocci, bacilli and spirilla?

Answer 32

Cocci - e.g. Staphylococcus aureus are spherical.

Bacilli - e.g. Mycobacterium tuberculosis are rod shaped with varying lengths.

Spirilla - shaped like a corkscrew / spiral shape.

Question 33

What’s epidemiology?

Answer 33

The study of patterns, distribution and causes of disease.

Question 34

What’s morbidity and mortality data?

Answer 34

Morbidity - people that have the disease

Mortality - people who have the disease

Question 35

What is an endemic, epidemic and pandemic?

Answer 35

Endemic - an infectious disease always present in a population.

Epidemic - a sudden increase in the incidence of an infectious disease within a population.

Pandemic - an increase in incidence of infectious disease across several countries.

Question 36

What are the different methods for controlling a disease?

Answer 36

Vaccination programs
Education 
Improved hygiene
Drugs
Housing
Nutrition

Question 37

What is herd immunity?

Answer 37

When many people in a population are immune so epidemics are less likely to occur.