TOPIC 6: MICROBIOLOGY AND PATHOGENS

Question 1

Why would we use several nutrient agar plates

Answer 1

To improve reliability

Question 2

Why would we include the same concentration of antibiotic

Answer 2

For validity

Question 3

Is cytoplasm found in both bacteria and viruses

Answer 3

No- Only bacteria contain cytoplasm

Question 4

Explain what is meant by the term bacteriostatic antibiotic

Answer 4

Bacteriostatic antibiotic is used to prevent the reproduction/division of bacteria and it is the immune system that will kill the bacteria

Question 5

Explain what is meant by the term bactericidal

antibiotic

Answer 5

Bactericidal antibiotics destroy and kill the bacteria

Question 6

Where are B and T cells formed

Answer 6

In the Bone marrow

Question 7

How are B cells and T cells able to form clones

Answer 7

Via mitosis

Question 8

State two ways in which the skin flora can help to protect a person from infection by pathogenic bacteria.

Answer 8

1. Skin flora competes with pathogenic bacteria for space and nutrients
2. Skin flora secretes chemicals that affect PH to prevent bacteria from growing

Question 9

Which part of the skin forms a physical barrier against infection by pathogenic bacteria

Answer 9

Epidermis

Question 10

Suggest why antibiotics may be used as part of the treatment for influenza.

Answer 10

1. Influenza may allow development of other infections/diseases so antibiotics will kill/inhibit growth of bacteria

Question 11

Explain why doctors have been advised to limit the prescription of antibiotics.

Answer 11

1. To prevent bacteria from being resistant to the antibiotic as resistant bacteria can survive and pass on this useful gene and it would be harder to contain the infection
2. Some infections cannot be treated with antibiotics

Question 12

Describe how you could investigate the effect of different antibiotics on bacteria

Answer 12

1. Distribute bacteria on the agar in the petri dish evenly using an inoculating loop
2. Apply different antibiotics in the wells of the agar
3. Control the antibiotic concentration
4. Use aseptic technique and incubate at a suitable temperature

Question 13

State one characteristic symptom of TB other than coughing.

Answer 13

Bloody sputum

Question 14

What is the name of the organism that causes TB

Answer 14

Mycobacterium tuberculosis

Question 15

Describe how the organisms that cause TB are taken up by macrophages.

Answer 15

1. Bacterium are recognised as non self cells due to their antigen
2. B lymphocytes detect bacteria and phagocytosis takes place engulfing the bacterium which is then broken down by enzymes in the lymphocytes vacuole

Question 16

Give two differences between the genetic material of bacteria and viruses.

Answer 16

1. Bacteria have DNA, Viruses however can contain RNA or DNA
2. The bacteria have circular genetic material whereas viruses have linear genetic material
3. Bacteria have plasmids whereas viruses do not

Question 17

Suggest why treatment with antibiotics may not be effective against the
dormant bacteria in the tubercles.

Answer 17

1. Bacteria in the tubercules contain a waxy layer which is harder for phagocytosis to occur.
2. Bacteriostatic Antibiotics affect dividing bacteria not dormant ones

Question 18

TB can be prevented by vaccination. Explain how a person can develop artificial active immunity following vaccination.

Answer 18

1. Dead inactivated pathogen is put into the person which stimulates the primary immune response
2. This activates T helper cells and B cells which then go on to produce memory cells

Question 19

Explain why the activity of these bacteria (mycobacterium tubercolosis) and the inhibition of T cells means that
a person may quickly develop severe symptoms leading to death.

Answer 19

1. The mycobacterium can cause lung damage which can cause severe breathing problems.
2. The mycobacterium can also get into the blood which can lead to organ failure.
3. The inhibition of T cells means that the immune system is now weakened which secondary infections may now cause death

Question 20

Distinguish between the structure of bacteria and viruses

Answer 20

1. Bacteria are cells, viruses are not.
2. Bacteria are surrounded by cell wall/slime capusle, viruses however are surrounded by protein capsids
3. The genome of Bacteria are DNA, Viruses can be DNA or RNA

Question 21

Explain how antibodies help a person to recover from an infection.

Answer 21

1. Antibodies bind to bacteria (opsonisation)

2. This causes phagocytosis to be greater

Question 22

Explain what is meant by zone of inhibition

Answer 22

1. Area where no bacteria are replicating

Question 23

Explain why contamination of tissue cultures in investigations has to be avoided.

Answer 23

1. The contaminants compete for nutrients and space

2. The contaminants can cause infection/ disease of tissue

Question 24

Explain why the ambient temperature and the core temperature of the body are used to determine the time of death of a person.

Answer 24

1. The temperature of the body changes with time after death.
2. The core temperature depends on the ambient temperature

Question 25

Describe the differences between a totipotent stem cell and a pluripotent stem cell.

Answer 25

1. Totipotent stem cells can differentiate to become any cell 2. Whereas pluripotent stem cells cannot differentiate to any cell

Question 26

Describe how the bacteria should be added to the Petri dish.

Answer 26

1. Aseptic technique/ use of sterile equipment | 2. Spread bacteria on the agar evenly

Question 27

Why is the petri dish sealed with tape

Answer 27

1. To reduce contamination of culture. | 2. Allow aerobic conditions to reduce growth of harmful bacteria

Question 28

Suggest why an incubation temperature of 37°C should not be used in a school or college laboratory.

Answer 28

encourages growth of bacteria that are harmful to humans

Question 29

Suggest what is meant by the phrase suitably-prepared Petri dish.

Answer 29

1. Contains agar 2. Bacteria are distrubuted evenly 3. Petri dish contains one single bacteria strain

Question 30

Describe how a B cell is activated.

Answer 30

1. Bacteria/virus/pathogen binds to B cell - the antigen of the pathogen binds to the MHC antigens 2. T helper cells bind to B cells 3. Referance to cytokines

Question 31

Describe the role of antigen presentation in the body’s specific immune response to infection by viruses.

Answer 31

1. Macrophages present antigen on their MHC to T helper cells 2. T helper cells bind to macrophages and are activated. 3. B cells also act as APCs and produce plasma that differentiate into antibodies 4. Infected host cells also present antigens to T killer cells which then go onto destroy infected host cells

Question 32

Describe how infection with a bacterium results in the production of plasma cells.

Answer 32

1. Humoral immune response 2. The macrophage engulfs the bacterium via phagocytosis and presets the bacteriums antigens on its surface the macrophage becomes an APC 3. Macrophage APC binds to a T helper cell and activates it. Once the T helper cell is acrivated it divides to form memory T cells and active T helper cells. 4. In the effector stage B cells become APC and present the bacteriums antigens on their MHC 5. T helper cell complementary binds to the APC and produces cytokines that stimulate the B cell. 6. B cells then form clones (B effector and B memory cells). 7. The B effector cells differentiate into plasma cells

Question 33

What type of cell in the human immune system is infected by HIV

Answer 33

T helper cells

Question 34

What is the enzyme used to produce DNA from viral RNA in an infected cell

Answer 34

Reverse transcriptase

Question 35

(i) State two characteristic features of antibodies.

Answer 35

1. They are glycoproteins that have an antigen binding site

Question 36

Explain why an insect bite, which breaks the surface of the skin, may lead to inflammation around the injury.

Answer 36

1. Histamine released as a result of damaged tissue and is released from platelets. 2. The histamine causes vasodilation and an increased blood flow to the area causing redness and swelling

Question 37

Where are B and T cells formed

Answer 37

In the Bone marrow

Question 38

(i) Explain what is meant by the term genetic mutation.

Answer 38

1. Change in the base in DNA | 2. Which leads to change in the sequence of amino acids in the primary structure of the protein

Question 39

What do white blood cells plant cells and prokaryotic cells all contain

Answer 39

1. Ribosomes

Question 40

What can Totipotent stem cells give rise to

Answer 40

Totipotent stem cells and differentiated cells

Question 41

What can Pluripotent stem cells give rise to

Answer 41

Only differntiated cells

Question 42

Suggest how a stem cell in the bone marrow can become a differentiated blood cell.

Answer 42

1. A chemical stimulates some genes to be active in the bone marrow stem cell. 2. So only the active genes are transcribed and mRNA is made which makes the proteins that make the stem cell into a blood cell