Infectious Disease

Question 1

Name the two main physical barriers that prevent the invasion of pathogens in the first line of the body’s defence.

Answer 1

Skin and mucus.

Question 2

What are the chemical barriers included in the first line of defence?

Answer 2

Acid from sweat on the skin, enzymes within saliva, mucus and tears - as well as stomach acid.

Question 3

What is mucus?

Answer 3

A thin, clear liquid which consists of water, salts, and immune cells.

Question 4

What is the function of mucus and how does it defend the body?

Answer 4

The viscous and sticky substance traps pathogenic cells and prevents them from entering the body. Immune cells also help to attack pathogens.

Question 5

Where is mucus-secreting tissue located?

Answer 5

Nose, mouth, throat and lungs.

Question 6

What is the complement system and how does it work?

Answer 6

The complement system consists of at least 20 complement proteins that circulate through the blood. They work by binding to bacterial cell membranes and creating pores in its cell wall. This allows water and salts to flood the bacterium and cause it to swell and burst. This is known as lysis. These proteins can also assist other immune functions such as phagocytosis and pathogen flagging.

Question 7

What is another term used for ‘white blood cells?’

Answer 7

Leukocytes.

Question 8

What are the four types of leukocytes?

Answer 8

Macrophage, Natural Killer (NK) cell, Eosinophil, and Neutrophil.

Question 9

Which of the four leukocytes are phagocytic cells?

Answer 9

Macrophages and neutrophil.

Question 10

What do phagocytes do?

Answer 10

Phagocytes remove pathogenic cells through a process known as phagocytosis, where the pathogen is engulfed and digested by the cell.

Question 11

Describe the process of phagocytosis.

Answer 11

Pseudopodia (legs) of a pathogen surround and trap it. The pathogen(s) is then engulfed through endocytosis, where a VACUOLE is formed around it. The vacuole and a lysosome containing enzymes fuse together. This exposes the contained pathogen to the enzymes and other toxic compounds, killing it. Debris from the destroyed pathogen exit the phagocyte through exocytosis.

Question 12

What is the organelle involved in phagocytosis?

Answer 12

Macrophages internalise pathogens through phagocytosis, entrapping them into organelles called phagosomes. Phagosomes then fuse with lysosomes to mature into phagolysosomes, acquiring an acidic and hydrolytic lumen that kills the pathogens.

Answer: Phagosomes or phagolysosomes

Question 13

What is the role of Natural Killer Cells?

Answer 13

Circulating through the blood, the function of NK cells is to locate abnormal cells, which can be infected, cancerous, etc. They then either release cytokine chemicals to cause cell death by lysis, or apoptosis (programmed cell death).

Question 14

What is the role of Eosinophils?

Answer 14

Eosinophils protect your body by assisting inflammation and fighting parasites, allergens, foreign bacteria, and outside organisms that phagocytic cells cannot.

Question 15

What is the role of histamine and how does it help the body fight off pathogens?

Answer 15

In the presence of an injured and/or infected area, white blood cells will release histamine and cytokine proteins to said area. This stimulates the surrounding blood vessels and instigates dilation. This allows more fluid release to the area causing swelling. This allows more immune cells to flood the area and fight off pathogens. This is known as inflammation, which causes redness, pain, swelling, heat, and loss of function in the affected area.

Question 16

What does pus consist of?

Answer 16

Pus, a thick opaque yellowish white substance, is formed usually as a product of inflammation due to invasion of the body by pathogens. It consists of dead/degenerating white blood cells/leukocytes, tissue debris, and living or dead microorganisms.

Question 17

What is fever a result of?

Answer 17

A fever is a part of the nonspecific immune response, where the body instigates a temporary rise (constriction and contraction of vessels and muscles, trapping heat) in body temperature. This occurs when the body is attempting to kill off pathogens with heat.

Question 18

Define an infectious and non-infectious disease.

Answer 18

An infectious disease is a deviation in cell biology and structure in an organism that is not a direct result of physical injury, caused by microorganisms. A non-infectious disease is the same thing, but is congenital and/or caused by genetics.

Question 19

Define:
- Infection
- Host
- Pathogen

Answer 19

• The successful entry of a pathogen into the body. This does not necessarily mean disease will ensue, as the innate and adaptive immune system can still fight it off.
• The organism which allows the pathogen to cause infection within it.
• A microbe which is dangerous and can cause disease.

Question 20

What is the role of the human microbiome?

Answer 20

The human microbiome, a personal bunch of helpful bacteria on and in the human body, helps kill external and potentially dangerous bacteria.

Question 21

What are the 5 main causes of infectious disease?

Answer 21

• Bacteria (prokaryotic cells)
• Viruses (non-living)
• Protozoans (single-celled eukaryotes)
• Fungi (yeasts and moulds)
• Parasites (multicellular eukaryotic animals)

Question 22

Describe how pathogens adhere and enter the cell.

Answer 22

• Exposure to pathogen
• Adherence of pathogen to skin, microbiome can kill it off at this point
• Invasion through openings in the body’s defence (openings in skin like cuts, through the mouth, nose, eyes, etc.)
• Infection in the cells and tissue fluid
• This can lead to toxicity and/or invasion of other tissue
• Which leads to tissue damage, causing disease

Question 23

Describe the process through which bacteria and viruses cause disease.

Answer 23

Once bacteria and viruses successfully adhere and penetrate the host’s cell membrane, they go about similar processes to initiate disease. Bacteria tend to invade the membrane and replicate through asexual binary fission, which then causes tissue damage and disease. Viruses enter cells and hijack their biochemistry by releasing their RNA/DNA within, making host cells replicate the virus.

Question 24

What are the factors that affect disease?

Answer 24

Disease can be influenced by:

• Type of pathogen, (Covid, influenza)
• Microbiome of host
• Age of host
• Season
• Lifestyle (stress, diet, air pollution, sleep, proximity to potential pathogens)
• Genome of host
• State of immune system

Question 25

What is endocytosis?

Answer 25

Endocytosis is a general term describing a process by which cells absorb external material by engulfing it with the cell membrane and forming a vesicle around it within.

Question 26

What is virulence and what affects it?

Answer 26

Virulence is the measure of the ability of a pathogen to cause disease.

It depends on:

• Numerous virulence factors of the pathogen
• The host (pathogens are highly specific for certain organisms)
• Environmental conditions (weather, season, location, etc. Viruses are much more infectious during winter due to less external damage of its RNA/DNA from heat and UV.)

Question 27

Through what ways are diseases transmitted?

Answer 27

Pathogens can be transmitted between hosts through:

• Air (airborne)
• Dust
• Direct contact
• Faeces
• Food
• Animals

Question 28

What is a vector?

Answer 28

A vector is an animal which spreads pathogens from one host to another without suffering any harm itself.

Question 29

Define:
- Disinfectant
- Antiseptic
- Antibiotic
- Antiviral
- Antifungal

Answer 29

A disinfectant is a decontaminant, a liquid chemical which destroys microorganisms on non-living surfaces.

An antiseptic is a liquid chemical that is applied to the skin and/or wounds to reduce the number of microorganisms living there.

An antibiotic is an antibacterial agent which is used to treat bacterial infections and diseases.

An antiviral is a medication which targets specific viruses and prevents them from attaching to and infecting healthy cells, as well as preventing it from multiplying.

An antifungal is a medication which is used to treat fungal infections by directly applying the substance, typically as a cream from a tube, to the infected region.

Question 30

When could a possibly harmless microbe become pathogenic?

Answer 30

If someone’s microbiome and/or immune system is weak, then microbes that wouldn’t usually harm others with adequate microbiomes could harm them

Question 31

What are the factors that affect the survival of a pathogen?

Answer 31

The survival of a pathogen depends on:
1. Ability to enter cells
2. Availability of nutrients and removal of wastes
3. Environmental conditions (Temp, pH & moisture)
4. Ability to replicate and transmit to new hosts

Question 32

If a question is 5 marks in an exam, how many points should you make?

Answer 32

5 or more.

Question 33

Which class of organisms have an adaptive immune response?

Answer 33

Vertebrates only.

Question 34

What are antibodies and what do they do?

Answer 34

Antibodies, created by previous exposure to foreign molecules, recognise antigens, through foreign particles, e.g. a pathogen’s surface proteins. These antibodies neutralise and flag, or mark a pathogen for destruction by phagocytic cells of the innate immune system.

You can acquire antibodies through exposure and birth (i.e. breastfeeding).

Antibodies do not ‘actively search’ for antigens (e.g. surface proteins), they circulate the blood after being secreted by B-cells and have a chance to attach to a pathogen.

Antibodies can sometimes cause clumps of pathogens to stick together (agglutinate) which can increase the efficiency of phagocytosis.

Question 35

What are the types of T-cells?

Answer 35

A T-Helper cell can recognise antigens with its receptor. If it does, it attaches and releases a chemical which stimulates and signals plasma B-cells, which produce antibodies, and cytotoxic T-cells, which possess cytokine receptors to kill the infected cell through released enzymes.

Memory T-cells, much like memory B-cells, will retain a ‘memory’ of a specific pathogen and initiate a faster response when the body is exposed to it again. It does this by dividing into cytotoxic T-cells that instantly know specifically what to target.

Question 36

What are the types of B-cells?

Answer 36

Plasma B-cells secrete specific shaped antibodies which circulate through the blood and potentially bind to the specific complementary surface proteins (antigen) of their respective virus.

Antibodies can attach to B-cells to become Memory B-cells. These attached antibodies allow the B-cell to retain the ‘memory’ of that specific pathogen. If this pathogen infects the body again, memory B-cells can reactivate plasma B-cells to release specific antibodies.