Part 1

Question 1

What is a pathogen?

Answer 1

Patho = disease Gen = Producer

A pathogen is an organism or virus that causes a disease.

Question 2

Characteristics of living things

Answer 2

Properties of life
Cellular Respiration (energy production)
Reproduction
Metabolism (catabolism and anabolism)
Homeostasis
Heredity (DNA and RNA)
Responsiveness (to environment)
Growth and development

Question 3

Why are viruses not living organisms?

Answer 3

Viruses do not
Grow
Demonstrate homeostasis
Metabolize
Viruses do
Infect cells and use cell machinery to make more viruses.
Cause disease in many organisms

Question 4

How do viruses work?

Answer 4

Viruses, though not considered living, are categorized as micro organisms consisting of a strand of DNA or RNA surrounded by a protein coat.
Viruses enter or inject genetic material into cells and hijack the cell machinery to produce more viral particles.
Viruses then burst out of the host cell, destroying or damaging it, and spreading many times more viral particles to infect other cells.

Question 5

Other pathogens

Answer 5

Bacteria
Fungi
Protozoa 
Animals
Prions

Question 6

Antibiotics

Answer 6

Major medical improvement
Produced by fungi and bacteria
Work on bacteria but…
Ineffective on viruses, prions, and protozoa
antibiotics block specific metabolic pathways found in bacteria, but not eukaryotic cells
because viruses reproduce using the host cell (eukaryotic) metabolic pathways, they are unaffected by antibiotics
antibiotics have produced great benefits world-wide in the control of bacterial diseases
Staphylococcus infections controlled
STD’s, such as gonorrhea and syphilis controlled
antibiotic resistance has evolved in bacterial populations

Question 7

Non-specific immunity

Answer 7

The body resists infection with general (non-specific) and specific methods.
Non-specific immunity stops a wide variety of pathogens by preventing their entry into the body.
Non-specific immunity also contests potential infection through the use of antimicrobial chemicals (typically proteins), general phagocytes, and the inflammation response.

Question 8

First line of defence

Answer 8

Skin, mucus membrane, secretion of skin and mucous membrane

Question 9

Second line of defence

Answer 9

Phagocytic white blood cells, antimicrobial proteins, the inflammatory response.

Question 10

Third line of defence

Answer 10

Lymphocytes, antibodies

Question 11

Main immunities

Answer 11

Skin
Mucous membranes
Tears
Sweat
Hair
Sebum
Blood clots
Cilia
Stomach acid

Question 12

Outer Epithelium

Answer 12

Unbroken skin provides a fantastic barrier against pathogens trying to enter the body
Sebum (oil secretions) waterproofing.

Question 13

Mucous Membranes (and other non-specific immunity)

Answer 13

Anywhere on the body that is not protected by skin has its own method of protection.
Lungs – Mucous membranes and cilia
Stomach – Acid
Urethra – mucus membranes + urine is sterile
Eyes – tears contain lysozymes

Vagina – mucous membranes and acidic environment

Anus – mucous membranes

Question 14

Infection!

Answer 14

This occurs if pathogens do get inside the body.

The proteins on the surface of a pathogen are immediately recognized as “foreign”.

Phagocytes (a type of leucocyte) will ingest the pathogen by phagocytosis.

Question 15

Inflammation

Answer 15

Inflammationis an array of complex biological responses ofvasculartissues to harmful stimuli, including pathogens, injury, or irritants.
Inflammation is a protective response involving host cells, blood vessels, proteins, and other mediators intended to eliminate the initial source of cellular injury, as well as the rapid accumulation of necrotic cells and tissues resulting from the original insult, and to stimulate the body’s repair processes.
The conventional signs of acute inflammation include dolor (pain), calor (heat), rubor (flushing redness), turgescenceortumefaction (swelling), and functio laesa (loss of function).

Question 16

Blood Clotting

Answer 16

Clotting is the mechanism that prevents and blood loss from broken blood vessels.

Mechanism
Platelets or damaged cells release a group of proteins
called clotting factors. These clotting factors are released
into the plasma at the wound site.

b) Clotting factors activate the enzyme Thrombin from
its inactive form prothrombin

c) Thrombin turns the soluble plasma protein fibrinogen into its insoluble fibrous form Fibrin.

d) Fibrin binds together platelets and blood cells to form
a solid ‘plug’ for the wound. This plug is called a clot.

Question 17

Phagocytosis

Answer 17

The process employed by cells, particularly various phagocytes, to bind and internalize particulate matter larger than ~0.75µm in diameter, including small-sized dust particles, cell debris, micro-organisms,and potentially apoptoticcells.

This process involves the uptake of solid particles through the invagination of relatively large membrane areas. These membrane invaginations eventually engulf and seal the particle in a specialized vesicle referred to as phagosome.
Phagocytes are found in the blood and in body tissues.
After phagocytes engulf pathogens, they are destroy with digestive enzymes found in lysosomes.
damage to tissues allows invasion across 1st line of defense
microbes successfully invade body fluids or tissues
damaged cells release histamine and other chemicals initiating inflammation

phagocytes attracted to site by chemotaxis toward histamine
phagocytes recognize microbes as foreign by antigen recognition
variety of phagocytic cells: neutrophils (small phagocytic) & macrophages (large phagocytic)

phagocytes endocytotically engulf microbes, that are digested by enzymes held in lysosomes
digested microbe fragments are displayed on cell membrane
phagocytes with microbe fragments displayed = antigen-presenting cells

Question 18

Distinguish between antigens and antibodies

Answer 18

antigen: a molecule recognized as foreign by the immune system; it elicits an immune response
antibody: =immunoglobulin
a globular protein
recognizes an antigen by its complementary shape and charge
thus allowing it to attach to the antigen specifically
marking it for attack by the immune system
Antigens- Anything that elicits an immune response
Usually a foreign proteinMost are proteins or large polysaccharides from a foreign organism.
Microbes: Capsules, cell walls, toxins, viral capsids, flagella, etc.
Nonmicrobes: Pollen, egg white , red blood cell surface molecules, serum proteins, and surface molecules from transplanted tissue.
Lipids and nucleic acids are only antigenic when combined with proteins or polysaccharides.
Challenge and response
Challenge:
antigens:
substances foreign to the host
which stimulate antibody production by B lymphocytes

Response:
antibodies:
immunoglobulins
produced during protein synthesis

Antibodies- Also known as immunoglobulins
Globular glycoproteins
The heavy and light chains are polypeptides
The chains are held together by disulphide bridges
Each antiboby has 2 identical antigen binding sites – variable regions.
The order of amino acids in the variable region determines the shape of the binding site

Question 19

How Antibodies work?

Answer 19

Some act as labels to identify
antigens for phagocytes
Some work as antitoxins i.e. they block toxins for e.g. those causing diphtheria and tetanus
Some attach to bacterial flagella making them less active and easier for phagocytes to engulf
Some cause agglutination (clumping together) of bacteria making them less likely to spread

Question 20

To Vaccinate or not?

Answer 20

Vaccines:
MMR = combined measles/mumps/rubella
DPT = diphtheria, pertussis, typhoid
polio
Benefits:
eradication of some diseases (e.g. small pox)
reduced rate of infection; less illness and death
reduced long-term disability
Dangers:
low percentage of vaccinations produce side effects, including symptoms of disease, sometimes serious or lethal
artificial immunity not as effective at producing immune response as is active immunity
excessive vaccination may reduce the ability of the immune system to respond to new diseases
vaccination possibly implicated in autism

Question 21

Active and passive immunity

Answer 21

Active immunity: immunity acquired through individual immune response
Catching a disease
Passive immunity: immunity acquired through antibodies transferred from one person to another
Mother’s milk
However, it takes time for the body to react to the infection and produce white (B and T) cells. During this time the disease can multiply and spread rapidly.

                 Tetanus is an especially deadly disease that
                  can kill in hours. Antibodies can be     
                  collected from people who have already been vaccinated against it. These can then be injected into people who may have caught the infection. Its only a temporary fix- the spleen and liver break them down. This is Passive Immunity.
            Mothers pass antibodies through the placenta
            during gestation. Colostrum is a liquid made
            in the mammary glands during the first few   
            days after birth- it lines the gut and protects  
           against bacteria and viruses.

Question 22

Where do antibodies come from?= Lymphocytes

Answer 22

Produce antibodies
B-cells mature in bone marrow then concentrate in lymph nodes and spleen
T-cells mature in thymus
B and T cells mature then circulate in the blood and lymph
Circulation ensures they come into contact with pathogens and each other

Question 23

White blood cells

Answer 23

T Lymphocytes
Foreign, mutant or infected cells are
identified as ‘non-self’ by surface antigens.
T helper cell recognises antigens and
alerts the other T cells.
Killer (Cytotoxic) cells attack with perforin
or nitric oxide. T memory cells remember
the antigen for a later attack.
T suppressor cells switch off T and B cells
after attack over.
B Lymphocytes
Plasma ɞ cells have a different shape receptor on its membrane. There are about 10 million kinds in your body at any one time! Each can detect any antigen of a
pathogen. Once activated they divide very fast (clone) and start to secrete specific antibodies. Antibodies slowly removed from blood and lymph. Memory ɞ cells remember antigens and can turn into Plasma ɞ if re-infected.

Question 24

How Do B Cells Produce Antibodies?

Answer 24

B cells develop from stem cells in the bone marrow of adults (liver of fetuses).
After maturation B cells migrate to lymphoid organs (lymph node or spleen).
Clonal Selection: When a B cell encounters an antigen it recognizes, it is stimulated and divides into many clones called plasma cells, which actively secrete antibodies.
Each B cell produces antibodies that will recognize only one antigenic determinant.

Question 25

B -Lymphocytes when challenged

Answer 25

The antibodies travel to the blood, lymph, lining of gut and lungs.
The number of plasma cells goes down after a few weeks
Antibodies stay in the blood longer but eventually their numbers go down too

Question 26

Duality of Immune System

Answer 26

Involves production of antibodies against foreign antigens.
Antibodies are produced by a subset of lymphocytes called B cells.
B cells that are stimulated will actively secrete antibodies and are called plasma cells.
Antibodies are found in extracellular fluids (blood plasma, lymph, mucus, etc.) and the surface of B cells.
Defense against bacteria, bacterial toxins, and viruses that circulate freely in body fluids, before they enter cells.
Also cause certain reactions against transplanted tissue.

Question 27

Production of monoclonal antibodies

Answer 27

Extract B cell that can produce the required antibodies

Hybridise with a tumour cell (capable of endless division)

In culture the hybridoma can produce large quantities of antibodies
Use in diagnosis – (pregnancy diagnostic)
Treatment
Diagnosis: HIV infection can be diagnosed through a blood test
which assays for the presence of anti-HIV antibodies,
antibody produced through monoclonal antibody production is an anti-anti-HIV antibody!
Treatment:
Rabies Virus
monoclonal antibodies can be produced which selectively locate and adhere to cancer cells
anti-cancer drugs can be attached to the monoclonal antibodies
so that they deliver their effects directly to the targeted cancer cells

Question 28

Immune System Abnormalities

Answer 28

Allergies:
Exaggerated immune response to antigens called allergens
Autoimmune diseases:
Body doesn’t recognize “self” and mounts immune response

Question 29

HIV

Answer 29

HIV (Human Immunodeficiency Virus) is a virus that specifically attacks the lymphocytes.
This means the number of lymphocytes decreases.
Less antibodies are made.

Question 30

Transmission of HIV

Answer 30

Infected blood – blood transfusions, sharing needles,
Infected semen and vaginal mucus – unprotected sex
Infected mother’s milk – low risk
Infected saliva – almost zero risk

Question 31

AIDS

Answer 31

Acquired Immuno-Deficiency Syndrome
Caused by the HIV virus that selectively infects the immune system leaving the body open to infection by removing the specific immunity.