infectious disease - responses to pathogens

Question 1

fungal pathogen traits

Answer 1

• Eukaryotic heterotrophic organisms; cells with cell wall
• Some unicellular, most are multicellular
• um to mm

Question 2

what pathogens do to plants

Answer 2

secrete enzymes that are able to digest the plant cell wall matrix and enter via the stomata and ‘steal’ nutrients from the surrounding cells

Question 3

Symptoms of fungal plant infection

Answer 3

• Chlorosis
• Leaf and stem wilting
• Leaf and stem rusting
• Leaf blotching
• Leaf mildew

Question 4

eucalyptus: Phytophthora cinnamomi disease

Answer 4

fungal pathogen

affects both eucalyptus and acacia.

wilted, yellowing foliage, stunted growth and coloured cankers

plants form barrier zones in new tissue and prevents pathogen spread from adjacent tissue.

Question 5

viral pathogen traits

Answer 5

• Non-cellular
• Contains DNA, RNA and protective coat
• Requires a living host cell to replicate
• Less than 500nm
• spread via vectors

Question 6

what does a viral infection cause in plants?

Answer 6

• Chlorosis
• Yellowed leaves
• Mosaic leaf pattern
• Crinkled leaves
• Growth stunting

Question 7

plant physical barriers (1st line of defence)

Answer 7

• Cell walls contain lignin and cellulose
• Waxy epidermal cuticles
• Bark
• Stomata can be closed when signaled

Question 8

gene-for-gene resistance

Answer 8

Plants possess resistance genes (R) which produce proteins that are pathogen-specific. The R protein interacts directly with an Avirulence gene (Avr) protein produced by the pathogen. The pathogen is then unable to infect new cells.

Question 9

basal resistance (Pathogen-associated molecular patterns)

Answer 9

Plants recognise these elicitor molecules as ‘non-self’ and activate basal resistance which results in fortification of plant tissues where cellular junctions are tightened and cell walls become impenetrable to the invading pathogen.

Question 10

hypersensitive response

Answer 10

If basal resistance fails the HR, a localised response, is activated to prevent further spread of the pathogen to other parts of the plant.

The plant cells in the region produce oxidative agents that alter the cell wall chemistry, trapping pathogen inside the host which die with the cell during apoptosis.

The HR is more effective if the R gene-Avr gene complex is present.

Question 11

Systemic acquired resistance (plants)

Answer 11

The SAR is a non-specific, whole plant response that occurs after an earlier localized exposure to a pathogen.

The activation of SAR requires the accumulation of salicylic acid (SA) which initiates a signalling cascade to other parts of the plant ‘prepping’ them for relevant pathogens should they bypass the localised HR. It provides long-lasting protection against a wide variety of pathogens.

Question 12

animal physical barriers (1st line of defence)

Answer 12

• Skin
• Mucous membrane
• Cilia
• Peristalsis
• Urine flow

Question 13

urine

Answer 13

passes through the walls of the ureter and bladder. As urine is acidic, this washing of the walls of the ureter and bladder helps kill and hinder the growth of microbes

Question 14

Acidic & Alkaline Environments

Answer 14

stomach contains hydrochloric acid which is very acidic

This high level of acidic is able to dissolve pathogens or mucus that contains any trapped pathogens.

Similarly, the alkaline environment in our intestines are able to decompose and kill pathogens.

Question 15

animal skin

Answer 15

Since the surface of the skin is waterproof, it is able to be maintained at a dry state which hinders the growth of pathogens.

Sweat glands are also able to produce sweat which naturally occurring bacteria on our skin can breakdown to produce acidic chemicals. This creates an acidic environment that also hinders the growth of pathogens.

Question 16

cilia

Answer 16

tiny-like structures that are located along the respiratory tract.

They vibrate or move at upright direction, resulting mucus (containing trapped pathogens) being propelled to the throat which can be coughed or sneezed out.

Question 17

saliva and tears in protecting the body from pathogens

Answer 17

Saliva contains lysozymes that is capable of decomposing their protective cell wall of bacteria

This therefore prevents infection from the pathogen.

Tears also contain lysozymes that allow us to flush off any pathogens on the surface of our eye (cornea).

Question 18

Mucous membrane

Answer 18

on the surface of the respiratory, digestive, reproductive and urinary tracts.

they produce thick mucus which is able to trap pathogens and antigens.

Saliva that travel across these membranes contain enzymes such as lysozymes that is able to breakdown pathogens.

Question 19

animal chemical barriers

Answer 19

• Stomach acid and enzymes
• Lysozyme (enzymes in tears)
• Alkali pH in the small intestine

Question 20

stomach acid and small intestine as an immune response

Answer 20

Before entering the stomach lysosomes (digestive enzymes) within saliva attack and perforate the cell walls of many bacteria.

The stomach contains hydrochloric acid with a pH between 1-2. The acid is produced by specialised cells called parietal cells.

A mucous membrane protects the stomach from the corrosive acid.

The acid kills most microbes, preventing them from entering your body via food or water.

The release of bile at the duodenum neutralises the contents released from the stomach causing the pH change.

The change in pH is usually enough to kill any microbes that survive the acidic environment of the stomach.

Question 21

animal tears

Answer 21

contain the proteins lysozyme (enzyme) and lactoferrin, both of which inhibit or kill microbes by different mechanisms.

Question 22

antigens

Answer 22

molecules (usually proteins) which the host recognise as being foreign and initiate the adaptive immune response and innate immune response

Question 23

Acidic & Alkaline Environments

Answer 23

stomach contains hydrochloric acid which is very acidic

This high level of acidic is able to dissolve pathogens or mucus that contains any trapped pathogens.

Similarly, the alkaline environment in our intestines are able to decompose and kill pathogens.

Question 24

second line of defence (innate immune response) (P Ly Sy InRe CeDe I&comproteins)

Answer 24

Phagocytosis

Lymphatic System

Inflammation Response

Cell death to seal off pathogens & Antigens

Interferons & complement proteins

Question 25

phagocytosis

Answer 25

the defence mechanism whereby phagocytes modify to their shape to envelope or enclose a non-specific antigen (e.g. a pathogen).

When the phagocyte has ‘engulfed’ the antigen, it will combine with a lysosome, which contains digestive enzymes (e.g. protease) produced by Golgi Apparatus, to breakdown the microbe or antigen.

Question 26

lymphatic system

Answer 26

the lymph nodes in the lymph system facilitate the lymphocytes to bind with antigen and initiate an adaptive immune response.

Question 27

inflammation response

Answer 27

The inflammation response is initiated by infected cells releasing chemicals known as histamines and prostaglandins.

inflammation responses occur at sites of infection.

increased blood flow to the site of infection would increase the temperature of the environment surrounding the infected cells at the infected site.

increase in temperature due to blood flow slows the rate at which pathogens reproduce their enzymes

Question 28

Cell death to seal off pathogens & Antigens

Answer 28

the second line of defence have the mechanism involving neighbouring cells dying to form a wall of dead cells surrounding infected cell(s), forming a capsule structure known as granuloma.

Question 29

interferons & Complement Proteins

Answer 29

induce neighbouring unaffected cells to produce antiviral chemicals which help reduce protein synthesis activity.

amount of viral particles that are reproduced is reduced.

limits the transmission of disease between cells.

Question 30

third line of defence

Answer 30

immune response

T – Lymphocytes (T cells)

B – Lymphocytes (B cells)

Antibodies

Question 31

T - Lymphocytes

Answer 31

type of specialised white blood cells

manufactured in the bone marrow and mature in thymus gland

Question 32

helper T cells

Answer 32

activates other types of T cells via cytokines

start with T helper cells when examining the interaction between T cells and antigens.

Question 33

Cytotoxic T cells (also known as Killer T cells).

Answer 33

will travel towards infected cells and release cytotoxins to eliminate the infected cells which thereby destroys the antigen

Question 34

Memory T cells.

Answer 34

antigen-specific T cells that remain long-term after an infection has been eliminated. The memory T cells are quickly converted into large numbers of effector T cells upon reexposure to the specific invading antigen, thus providing a rapid response to past infection.

Question 35

Suppressor T cells.

Answer 35

A type of immune cell that blocks the actions of some other types of lymphocytes, to keep the immune system from becoming over-active.

Question 36

B - Lymphocytes

Answer 36

also a type of specialised white blood cells

They are manufactured in the bone marrow and also mature there.

have a specific surface antibody protein that can recognise and is specific to a particular antigen.

Question 37

antibodies

Answer 37

Y-shaped, each with two antigen binding sites.

proteins produced by plasma cells.

antibody is able to immobilise the antigen or block their receptors that are used in host cell entry.