communicable diseases

Question 1

what is a pathogen

Answer 1

a pathogen is an organism that causes disease.

Question 2

what are the 4 types of pathogen

Answer 2

bacteria
fungi
viruses
Protoctista

Question 3

how do bacterial pathogens cause damage

Answer 3

their presence can cause damage by releasing waste products and toxins that are toxic to the host.

Question 4

how do fungal pathogens cause damage

Answer 4

Fungus lives in the skin of the animal, and where its hyphae, which forms a mycelium, grow under the skin surface. The fungus can send out specialised reproductive hyphae, which grow to the surface of the skin to release spores. This causes redness and irritation. In plants, the fungus often lives in the vascular tissue, where it can gain nutrients. The hyphae release extracellular enzymes, such as cellulases, to digest the surrounding tissue, which causes decay.

Question 5

How do viruses cause damage

Answer 5

Viruses invade cells and take over the genetic machinery and other organelles of the cell. They then cause the cell to manufacture more copies of the virus. The host cell eventually bursts, releasing many new viruses which will infect healthy cells.

Question 6

How do protocista cause damage

Answer 6

These organisms usually cause harm by entering host cells and feeding on contents as they grow. The malarial parasite plasmodium has immature forms that feed on haemoglobin inside red blood cells.

Question 7

What is the organism that causes tuberculosis

Answer 7

Bacteria- mycobacterium tuberculosis

Question 8

What organism causes the disease- bacterial meningitis

Answer 8

Bacteria- neisseria meningitis or sprepococous pneumonia

Question 9

What organism causes the disease; ring rot

Answer 9

Bacterium- clavibacter mischiganesis subsp.

Question 10

What organism causes the disease HIV/AIDS

Answer 10

Virus- human immunodeficiency virus

Question 11

What type of organism causes influenza

Answer 11

Virus- from family orthomyxoviridae- flu viruses

Question 12

What type of organism causes tobacco mosaic virus

Answer 12

Tobacco mosaic virus- virus

Question 13

What type of organism causes the disease black Sigatoka

Answer 13

Fungus- mycosphaerella fijiensis

Question 14

What organism causes the disease of ringworm in cattle

Answer 14

Fungus- trichophyton verrucosum

Question 15

What type of organism causes the disease of athletes foot in humans

Answer 15

Fungus- trichophyton rubrum

Question 16

What type of organism causes the disease of malaria in humans

Answer 16

Protoctistan- plasmodium falciarum, p.vivax, p.ovale, p.malariae

Question 17

Give 3 forms of direct transport

Answer 17

Direct physical contact, Such as touching a person who is infected or touching contaminated surfaces that harbour pathogens. For example HIV(virus), bacterial meningitis(bacteria), ringworm(fungus) and athletes foot.(fungus)

Facecal- oral transmission, usually by eating food or drinking water contaminated by the pathogen. For example cholera, food poisoning.

Droplet infection- in which the pathogen is carried within tiny. Water droplets in the air. For example, influenza(virus) and tuberculosis( bacteria)

Transmission by spores- which are resistant stage of the pathogen. These can be carried in the air or remain in the soil. For example, anthrax or tetanus.

Question 18

What are the social factors that affect transmission

Answer 18

Overcrowding
Poor ventilation
Poor health
Poor diet
Homelessness
Living or working with people who have migrated from areas where disease is more common

Question 19

What is a mean of indirect transmission in plants

Answer 19

Pathogen often occur as a result of an insect attack, spores or bacteria will become attached to the burrowing insect, such as a beetle, which attacks an infected plant. When that beetle attacks another plant, the pathogen is transmitted to the uninfected plant. The beetle lis acting as a vector. For example, the fungus that causes Dutch elm disease is carried by the beetle scolytus multistriatus

Question 20

Name all the physical passive defences used by plants

Answer 20

Cellulose cell wall - acts as a physical barrier but also in some plant cells cell walls contain a variety of chemical defences that can be activated when the pathogen is detected
Lignin thickening of cell walls- lignin is waterproof and almost completely indigestible.
Waxy cuticles- prevent water collecting on the cell surfaces, since pathogens collect in water and need water to survive, the absence of water is a passive defence.
Bark- most bark organisms contains a variety of chemical defences that work against pathogenic organisms
-stomatal closure - stomata are possible pathogen entry points. When a pathogen is detected the stomata is closed by the guard cells.
-callose- a large polysaccharide that is deposited inside sieve tubes at the end of a growing season. It blocks to flow of phloem sieve tubules meaning that the pathogen cannot travel around the plant.
-tylose formation- a tylose is a balloon like swelling or projection that fills the xylem vessel. When tylose is fully formed, it plugs the vessel and the vessel can no longer carry water. Blocking the xylem vessel prevents the spread of the pathogen. The tylose also contains high concentrations of chemicals such as terpenes that are toxic to pathogens.

Question 21

What are the passive chemical defences in plants

Answer 21

Contain a variety of chemicals that have anti pathogenic properties. These include terpenoids, phenols, alkaloids and hydrolytic enzymes. Some of these chemical such as terpenes and tylose and tannins are found in the bark. But because they take energy gu to produce, most are only released when a pathogen is detected.

Question 22

What is an active defence of a plant

Answer 22

Active defences are the plants defence mechanisms once it has detected the pathogen and the plant is now acting to prevent the spread of it or kill it.

Question 23

What are the physical active defences of plants when exposed to a pathogen

Answer 23

-cell walls become thickened and strengthened with additional cellulose
-deposition of callose between the plant cell and cell membrane near the invading pathogen.
-oxidative bursts that produce highly reactive oxygen molecules capable of damaging the cells of invading organisms
-an increase in population of chemicals

Question 24

Describe the chemical action preformed by terpenoids

Answer 24

A range of essential oils that have antibacterial and anti-fungal properties. They may also create scent, for example, the menthols produced by ,mint plants.

Question 25

Describe the chemical action of phenols

Answer 25

These also have antibiotic and anti-fungal properties. Tannins found in bark inhibit attack of insects. These compounds bind to salivary proteins and digestive enzymes such as trypsin and chymotrypsin, deactivation the enzymes. Insects that injest high amounts of tannins do not grow and will eventually die, helping prevent transmission of pathogens.

Question 26

What chemical action do alkaloids have

Answer 26

Nitrogen containing compounds such as caffeine, nicotine, cocaine, morphine, solanine. These give a bitter to inhibit herbivores feeding.

Question 27

What chemical action do hydrolytic enzymes have

Answer 27

These are found in the spaces between cells. They include chattiness (which breaks down chitin in fungal cell walls), glucanases (which hydrolyse the glycosidic bonds in glucans) and lysosomes( capable of degrading bacterial cell walls.

Question 28

What is necrosis

Answer 28

Deliberate cell suicide. A few cells are sacrificed to save the rest of the plant. By killing cells surrounding the infection, the plant can limit the pathogens accès to water and nutrients and can stop it spreading which later kills it.

Question 29

Describe the primary defence system of the skin

Answer 29

The body is covered by the skin. This is the main primary defence. The outer layer of the skin is called the epidermis, and it consists of layers of cell. Most of these cells are called keratinocytes. These cells are produced by mitosis at the base of the epidermis. They then migrate out to the surface of the skin, they dry out and the cytoplasm it’s replaced by the protein keratin. This process is called keratinisation. It takes about 30 days. By the time that the cells reach the surface, they are no longer alive. The keratinised layer of dead cells acts as an affective barrier to pathogens. Eventually, the dead cells sly off.

Question 30

Describe the process of blood clotting and skin repair as a primary defence against disease

Answer 30

Of course the skin is only protective as long as it is complete. Abrasions and lacerations damage the skin aand open the body to infection. When this occurs, the body must prevent excess blood loss by forming a clot, making a temporary seal to prevent infection, and repairing the skin. Blood clotting involves calcium ions and at least 12 factors- known as clotting factors. Many of these are released by platelets and damaged tissues. These factors activate an enzyme cascade. Once the clot has formed, it begins to dry out and form a scab. The scab shrinks as it dries, drawing the sides of the cut together. This makes a temporary seal, under which the skin is repaired. The first stage is the deposition of the fibrous collagen under the scab. Stem cells in the epidermis then divide by mitosis to form new cells, which then differentiate to form new skin. New blood vessels grow to provide and supply oxygen and nutrients to new tissues. The tisseuse contact to draw the edges together, so that repair can be completed. As new skin is completed the scab will be released.

Question 31

Describe the structure of mucous membranes as a primary defence against pathogens

Answer 31

Certain substances, such as oxygen and the nutrients in our food, must enter our blood. The exchange surfaces where this occurs ,must be thinner and less well protected from pathogens. The air and food that we take in from our environment may harbour microorganisms. Therefore airways, lungs and digestive systems are at risk of infection. So these areas are protected by mucous membranes. The epithelial layer contains mucus secreting cells called goblet cells. There are also extra secreting glands under the epithelium. In airways mucus lines the passage which traps pathogens as you inhale. The ciliated epithelium then beats the band of mucus upwards into the top of the trachea where it can be swallowed and killed by the acidity of the stomach.

Question 32

Describe the passive defence of sneezing and coughing

Answer 32

Areas that are prone to attack are also sensitive. They respond to the irritation that may be caused by the presence of microorganisms or the toxins they release. These reflexes include coughing, sneezing and vomiting. In a cough or sneeze the sudden expulsion of air will carry with it the microorganisms causing irritation.

Question 33

Describe the primary defence against pathogens: inflammation

Answer 33

One of the signs that a tissue is infected is swellings and redness known as inflammation. The tissue may also feel hot and painful. The presence of microorganisms in the tissue is detected by specialised cells called mast cells. These release a cell signalling substance called histamine. Histamine has a range of effects on the surrounding tissue, which act to help combat the infection. The main effect is to cause vasodilation and make the capillary walls more permeable to white blood cells and some proteins. Blood plasma and phagocytic white blood cells leaves the blood and enters the tisssue fluid. This leads to increased production of tissue fluid, which causes the swelling. Excess tissue fluid is drained into the the lymphatic system where lymphocytes are stored. This leads to the pathogens coming into contact with the lymphocytes and initiatiating the specific immune response.

Question 34

Give 3 other primary defences to prevent disease

Answer 34

The eyes are protected by antibodies and enzymes in the tear fluid. The ear canal is lined with wax, which traps pathogens The female reproductive system is protected by mucus plug in the cervix by remaining relatively acidic contions in the vagina

Question 35

What is the first line of the secondary defence

Answer 35

Phagocytes

Question 36

Describe the type of phagocytic white blood cell: neutrophil

Answer 36

The most common phagocytes are neutrophils. You can recognise these by their multi-lobed nucleus. Neutrophils are manifactured in the bone marrow. They travel in the blood and often squeeze out of the blood into tissue fluid. Neutrophils are short lived, but they will be released in large numbers in result of an infection. Neutrophils contain large numbers of lysosomes. They engulf and digest pathogens, but they usually die after digesting a few pathogens. Dead neutrophils may collect in an area of infection, to form pus.

Question 37

Describing the process of phagocytosis

Answer 37

Neutrophils binds to the opsonin attached to the antigen of the pathogen The pathogen is engulfed by endocytosis forming a phagosome vesicle Lysosomes fuse to the phagosome and release lytic enzymes into it After digestion the harmless products can be absorbed into the cell.

Question 38

Describe the type of phagocytic white blood cell: macrophage

Answer 38

Macrophages are larger cells manufactured in bone marrow. They travel in the blood as monocytes before settling in the body tissues. Many are found in lymph nodes where the mature into macrophages. Dendritic cells- a type of macrophage are found in the peripheral tissues. Macrophages play a more important role in initiating the specific responses to pathogens. When a macrophage engulfs a pathogen, it doesn’t fully digest it. The antigen from the surface of the pathogen is saved and moved to a special a protein complex on the surface of the cell. The cell becomes an antigen presenting cell. It exposes the antigen on its surface, so that other cells of the immune system can recognise the antigen. The special protein complex ensures that it is not mistaken for a foreign cell and attacked by other phagocytes.

Question 39

Describe the process of antigen presentation in an active immunity

Answer 39

The antigen presenting cell moves around the body where it can come in to contact with specific cells that can activate the full immune response. These are the T lymphocytes and B lymphocytes. There may be only one B and T cell with the correct recognition site of the antigen. Therefore the role of the antigen presenting cell is to make chances the antigen will come into contact with them more likely.

Question 40

Describe the process of a specific immune response

Answer 40

Activation of the specific B and T cells is called clonal selection. This brings into play a complex series of events that leads to the production of antibodies that can combat the specific pathogen and memory cells that provide long term immunity.

Question 41

What do cytokines do

Answer 41

These stimulate the differentiation and activity of macrophages, B cells and T cells

Question 42

What are the four types of cell T lymphocytes can differentiate into and what is their function

Answer 42

T lymphocytes can differentiate into T helper cells- which release cytokines that stimulate the B cells to develop and stimulante phagocytosis by phagocytes T killer cells- which attack and kill host body cells that display foreign antigens T memory cells- provide long term immunity T regulator cells- which shut down the immune response after the pathogen has been successfully removed. They are also involved in preventing autoimmunity.

Question 43

What do B lymphocytes develop into

Answer 43

Plasma cells- which circulate in the blood, manufacturing and releasing antibodies. B memory cells- which remain in the body for a number of years and act as the immunological memory

Question 44

Why do macrophages and T lymphocytes release interlukins

Answer 44

They stimulate the clonal expansion and differentiation of B and T cells.

Question 45

What is an auto immune disease

Answer 45

An auto immune disease occurs when the immune system attacks a part of the body. Normally, any B or T cells that are specific to our own antigens are destroyed during early development of immune system. An auto immune disease arises when antibodies start to attack our own antigens- possibly because antigens that are not normally exposed become exposed to attack. This could cause arthritis- painful inflammation of the joint.

Question 46

Describe the structure of an antibody

Answer 46

Antibody’s are Y shaped. They have a 2 light poly peptide chains joined to a heavy polypeptide chain by disulphide links. They also have hinge regions to allow flexibility so the molecule can grip more than one antigen. The variable region has a specific shape of the antigen. The constant region which is the same in all antibodies, but it may have a site for binding of phagocytic cells.

Question 47

Describe the function of the antibody type- opsonins

Answer 47

Opsonins are a group of antibodies that bind to the antigens on a pathogen, they act as binding sites for phagocytic cells, so that these can more easily bind and destroy the pathogen. Some opsonins are not very specific and stick to all types of molecules.

Question 48

Describe the function of the antibody type- agglutinins.

Answer 48

Because each antibody molecule has two identical binding sites it is able to crossing pathogens by binding an antigen and one pathogen with its other binding site. When many antibodies preform this cross-linking they clump together pathogens. This has two advantages: agglutinated pathogens are physically impeded for carrying out some functions, such as entering host cells, and the agglutinated pathogens are readily engulfed by phagocytes. This is particularly effective against viruses.

Question 49

What are anti toxins

Answer 49

Some antibodies bind to molecules that are released by pathogenic cells, these molecules may be toxic and the action of anti-toxins renders them harmless