Disease and the Immune response

Question 1

Define the term communicable disease

Answer 1

Diseases that can be passes from one organism to another of the same or different species

Question 2

Define the term pathogen

Answer 2

Microorganisms that cause disease

Question 3

State the 4 different types of pathogen and give 3 examples of each.

Answer 3

Bacteria- TB, bacterial meningitis, ringrot
Virus- HIV/AIDS, influenza, tobacco mosaic virus
Fungus- Black sigatoka, ringworm, Athlete’s foot
Protoctist- Potato/tomato blight, Malaria

Question 4

Describe the 2 ways of classifying bacteria and state the different types of bacteria in each way.

Answer 4

1. Basic shape- rod shape (bacilli), spherical (cocci)
2. Cell wall- Gram staining- gram positive bacteria are purple/blue under microscope (MRSA), gram negative appear red (E.coli)

Question 5

Draw, label and annotate a diagram of a generalised virus.

Answer 5

1. Genetic material surrounded by protein coat

Question 6

Draw and label a series of diagrams to describe the general reproductive cycle of a virus.

Answer 6

1. Attach to the host cell- requires receptor molecule on virus and molecule on cell surface- complementary shape- specific- infect 1 type of cell
2. Insertion of viral nucleic acid
3. Replication of viral nucleic acid in the cell
4. Synthesis of viral protein- using host cell’s ribosomes
5. Assembly of virus particles
6. lysis of host cells (burst the host cell)

Question 7

Describe 5 general ways in which pathogens can damage host tissue, thereby causing harm.

Answer 7

1. Virus- take over cell metabolism
2. Protoctists- take over cells and break them open- don’t take over genetic material, just digest and use the cell contents as they reproduce
3. Fungi- digest living cells and destroy them
4. Bacteria- produce toxins that poison or damage the host cells causing disease- some break down cell membrane, some damage or inactivate enzymes and some interfere with genetic material so cell can’t divide
5. Fungi- some produce toxins which affect host cells and cause disease

Question 8

Identify the host species of, and the type of pathogen causing, the following disease ring rot

Answer 8

1. Host- potatoes/ tomatoes

2. Pathogen- bacterium

Question 9

Identify the host species of, and the type of pathogen causing, the following disease tobacco mosaic virus

Answer 9

1. Host- plants (tobacco plants especially)

2. Virus

Question 10

Identify the host species of, and the type of pathogen causing, the following disease potato blight

Answer 10

1. Host- potatoes

2. protoctist

Question 11

Identify the host species of, and the type of pathogen causing, the following disease black sigatoka

Answer 11

1. Host- banana plants

2. Fungus

Question 12

Identify the host species of, and the type of pathogen causing, the following disease Tuberculosis

Answer 12

1. Host- animals- humans and cattle

2. Bacteria

Question 13

Identify the host species of, and the type of pathogen causing, the following disease bacterial meningitis

Answer 13

1. Host- humans

2. Bacteria

Question 14

Identify the host species of, and the type of pathogen causing, the following disease HIV/ AIDS

Answer 14

1. Host- humans

2. Virus

Question 15

Identify the host species of, and the type of pathogen causing, the following disease influenza

Answer 15

1. Host- animals including humans

2. Virus

Question 16

Identify the host species of, and the type of pathogen causing, the following disease athlete’s foot

Answer 16

1. Host- humans

2. Fungus

Question 17

Identify the host species of, and the type of pathogen causing, the following disease malaria

Answer 17

1. Host- animals including humans

2. Protoctist

Question 18

Identify the host species of, and the type of pathogen causing, the following disease ring worm

Answer 18

1. Host- cattle

2. Fungus

Question 19

Define the term vector

Answer 19

A living or non-living factor that transmits a pathogen from one organism to another e.g. malaria mosquito

Question 20

Define the term spore

Answer 20

The cells that some organisms use to reproduce asexually, including some protoctists and fungi

Question 21

Describe what is meant by direct transmission of a pathogen, describe 2 clear examples (mode of transmission and pathogen) of each.

Answer 21

Direct transmission:
The pathogen is transferred directly from one individual to another
Examples
1. Kissing or any contact with bodily fluids of another person- bacterial meningitis, STDs
2. direct skin to skin contact- ring worm/ athlete’s foot

Question 22

Describe what is meant by indirect transmission of a pathogen, describe 2 clear examples (mode of transmission and pathogen) of each.

Answer 22

Indirect transmission:
The pathogen travels from one individual to another indirectly
Examples
1. Fomites- inanimate objects like socks can transfer disease- athlete’s foot
2. Vectors- Mosquitoes transmit malaria

Question 23

State the transmission methods for the following plant diseases: ring rot, tobacco mosaic virus, potato blight, black sigatoka.

Answer 23

Direct transmission- ringrot, TMV, tomato and potato blight, black sigatoka
Indirect transmission
1. Soil contamination- balck sigatoka spores and TMV spores
2. Vectors- wind, water, animals, humans all carry the spores of the pathogen

Question 24

State the transmission methods for the following animal diseases: tuberculosis, bacterial meningitis, AIDS, Influenza, Malaria, Ring worm, Athlete’s foot. (F)

Answer 24

AIDS- incoulation, through a break of skin
Athlete’s foot- fomites
TB/ Influenza- droplet infection- saliva and mucus from snezing, talking, coughing etc
Malaria- Vector- mosquito

Question 25

Describe and explain 7 factors that affect the transmission of communicable diseases in animals.

Answer 25

1, Overcrowded living and working conditions 2. Poor nutrition 3. A compromised immune system- have AIDS or immuno-suppressant drugs after transplant surgery 4. Poor disposal of waste- provide breeding sites for vectors 5. climate change- introduces new vectors and new diseases- higher temps promote spread of malaria as the mosquito species is able to survive over a wider area 6. Culture and infrastructure- in some countries traditional medical practises can increase transmission 7. Socioeconomic factors- lack of trained health workers and insufficient public warning can affect transmission rates

Question 26

Describe and explain 6 factors that affect the transmission of communicable diseases in plants.

Answer 26

1. Planting a varieties of crops that are susceptible to disease 2. Over-crowding increases the likelihood of contact 3. poor mineral nutrition reduces resistance of plants 4. damp, warm conditions increase the survival and spread of pathogens and spores 5. climate change- increased rainfall and wind promote the spread of diseases- allow animal vectors to spread to new areas. Drier conditions may reduce the spread of disease

Question 27

Suggest ways to minimise the spread of communicable disease in animals and in plants.

Answer 27

1. Leave plenty of room between plants 2. Rotate crops 3. Clear fields as thoroughly as possible 4. Handwashing

Question 28

State 3 examples of barriers to pathogens in plants

Answer 28

1. Waxy cuticle 2. Bark 3. Cellulose cell wall

Question 29

Describe 2 ways in which a plant cell can detect the presence of a pathogen.

Answer 29

1. Receptors in the cells respond to molecules from the pathogens or to chemicals produced when the plant cell wall is attacked. Or they might detect the breakdown products of the sell wall from digestion from the pathogen 2. This stimulates the release of signalling molecules that appear to switch on genes in the nucleus. 3. This in turn triggers cellular responses which include producing defensive chemicals, sending alarm signals to unaffected cells to trigger their defences and physically strengthening the cell walls.

Question 30

Name two molecules produced by plants to limit the spread of the pathogen.

Answer 30

1. Callose | 2. Lignin- added to callose making the mechanical barrier to invasion even thicker and stronger

Question 31

Describe the structure of callose.

Answer 31

1. Polysaccharide polymer of beta glucose 2. linked by 1,3 and 1,6 glycosidic bonds 3. It is different to cellulose so pathogen requires a different enzyme to break it down

Question 32

Describe 4 ways callose is used to limit the spread of a pathogen.

Answer 32

1. Callose gets deposited between the plant cell wall and plasma membranes after initial attack make it harder for pathogens to enter cells. 2. Large amounts of callose continues to be deposited in cell walls after the initial infection and lignin is added- makes it stronger 3. Callose blocks sieve plates in the phloem, sealing off the infected part and preventing the spread of pathogens 4. Callose deposited in the plasmodesmata between infected cells and their neighbours which may limit the spread of pathogens between cells

Question 33

List 6 different types of plant chemical defences, and for each describe their role and give examples.

Answer 33

1. Insect repellants- pine resin, citronella 2. Insecticides- pyrethrins act as insect neurotoxins, caffeine- toxic to insects 3. Antibacterial compounds including antibodies- phenols- antiseptics made in many different plants 4. Antifungal compounds- phenols, saponins- interfere with fungal cell membranes 5. Anti-oomycetes- glucanases enzymes 6. General toxins- cyanide- toxic to most living things

Question 34

Define the term “non-specific defences”.

Answer 34

They are always present or activated very rapidly | Defends against pathogens in the same way.

Question 35

State 4 barriers the human body has to minimise the entry of pathogens into our cells.

Answer 35

1. Skin- acts as physical barrier, but also produces sebum- an oily substance that inhibits the growth of pathogens 2. Mucous membranes- secrete sticky mucus- traps microorganisms and contains lysozymes which destroy bacterial and fungal cell walls- also contain phagocytes 3. Lysozymes in tears and urine 4. Acid in the stomach denatures proteins and kills pathogens

Question 36

Name 4 expulsive reflexes and explain their value for protection against pathogens.

Answer 36

Coughs and sneezes- eject pathogen-laden mucus from the gas exchange system Vomiting and diarrhoea- expel the contents of the gut along with any infective pathogens.

Question 37

Draw a flow chart to show the process of blood clotting.

Answer 37

1. Tissue is damaged 2. Platelets are activated by damaged tissue 3. Platelets release the enzyme thromboplastin an seratonin (seratonin makes smooth muscle in walls of blood vessels contract- narrows and reduces blood loss) 4. In the presence of calcium ions, thromboplastin catalyses the conversion of prothrombin into thrombin 5. Thrombin, an enzyme, catalyses the conversion of fibrinogen (soluble globular protein) into fibrin (insoluble fibrous protein) 6. Fibrin molecules form a mesh 7. The fibrin mesh traps platelets and red blood cells to form a clot 8. The clot dries out to form a hard tough scab 9. The clot and scab minimise blood loss and minimise the entry of pathogens directly into tissues or the blood through broken skin

Question 38

Describe the processes involved in the inflammatory response and explain their value for protection against pathogens.

Answer 38

1. Mast cells are activated in damaged tissue and release chemicals called histamines and cytokines 2. Histamines make the blood vessels dilate, causing localised heat and redness. The raise temperature helps prevent pathogens reproducing 3. Histamines make the blood vessel walls more leaky so blood plasma is forced out, once forced out of the blood it is know as tissue fluid. Tissue fluid causes swelling and pain 4. Cytokines attract white blood cells to the site which dispose of the pathogens by phagocytosis

Question 39

Describe how fever is initiated in response to invasion by pathogens and explain its value for protection against pathogens.

Answer 39

1. Normal body temp is maintained by thte hypothalamus in your rain 2. When a pathogen invades your body, cytokines stimulate your hypothalamus to reset the thermostat as your temp goes up 3. Most pathogens reproduce est at 37 degrees or lower. So higher temps inhibit pathogen reproduction. 4. The specific immune system works faster at higher temps

Question 40

Define the term “phagocyte” and state two examples of phagocytic cells.

Answer 40

Phagocytes are specialised white cells that engulf and destroy pathogens 1. Neutrophils 2. Macrophages

Question 41

Describe the stages in phagocytosis.

Answer 41

1. Pathogens produce chemicals that attract phagocytes 2. Phagocytes recognise non-human proteins on the pathogen, this is a response not to a specific type of pathogen, but simply a cell or organism that is non-self 3. The phagocyte engulfs the pathogen and encloses it in a vesicle called a phagosome 4. The phagosome combines with a lysosome to form a phagolysosome 5. Enzymes from the lysosome digest and destroy the pathogen 6. Digested pathogen absorbed by the phagocyte-antigens combine with the MHC in the cytoplasm 7. MHC/antigen complex is displayed on phagocyte membrane making an antigen presenting cell

Question 42

Describe the role of major histocompatibility complex glycoproteins in the cytoplasm of macrophages at the end of phagocytosis.

Answer 42

1. When a macrophage has digested a pathogen it combines with antigens from the pathogen surface membrane with special glycoproteins in the cytoplasm called major histocompatability (MHC) 2. The MHC complex moves these pathogen antigens to the macrophage's own surface membrane becoming an antigen presenting cell 3. These antigens now stimulate other cells involved in the specific immune system response

Question 43

Define the term “antigen presenting cell”.

Answer 43

A cell that displays foreign antigens complexed with major histocompatibility complexes on their surfaces

Question 44

Describe the role of cytokines in the non-specific defences.

Answer 44

1. Phagocytes that have engulfed a pathogen produce chemicals called cytokines 2 These act as cell-signalling molecules, informing other phagocytes that the body is under attack and stimulating them to move to the site of infection or inflammation 3. They can also increase the body temp and stimulate the specific immune system

Question 45

Describe the role of opsonins in phagocytosis.

Answer 45

1. They bind to pathogens and tag them so they can be more easily recognised by phagocytes. 2. Phagocytes have receptors on their cell membranes that bud to common opsonins, and the phagocyte then enulfs the pathogen.

Question 46

Explain why blood smears need to be stained for viewing under the light microscope and name a stain used for this procedure.

Answer 46

1. Shows the different nuclei of lymphocytes making them easier to identify 2. Identifying the different numbers of different types of lymphocytes indicates if a non-specific or specific immune response is taking place.

Question 47

Name the different types of cell found in blood and outline how to identify them on blood smear slides.

Answer 47

1. RBC- don't have nucleus 2. Neutrophil- nucleus looks like 3 interconnected blobs - multi-lobed and the cytoplasm is grainy 3. Lymphocyte- smaller than neutrophil and nucleus takes up most of the cell, so little cytoplasm to be seen 4. Monocyte- biggest wbc and is a type of phagocyte, it has a kidney-bean shaped nucleus and a non-grainy cytoplasm