Biology- Unit 6

Question 1

What is the lag phase?

Answer 1

Microorganisms are adjusting to the environment before starting to reproduce

Question 2

What is the log phase?

Answer 2

Population size grows exponentially, every round of division doubles population size

Question 3

What is the stationary phase?

Answer 3

When population reaches maximum due to decreasing nutrient levels and build up of toxic substances

Question 4

What is the death phase?

Answer 4

Lack of nutrients and toxic products causes death of organisms

Question 5

How would a cell count be carried out?

Answer 5

Haemocytometer
Sample of broth is diluted 1:1 with trypan blue (stains dead cells blue)
Counted cells have to be fully in boxes
Useful because it only counts living cells and is accurate- but slow an expensive

Question 6

How would turbidimetry be carried out?

Answer 6

Form of colorimetry
As turbidity increases, absorbance increases
Counts dead cells, expensive, assumes density of cells is constant

Question 7

How would dilution plating be carried out?

Answer 7

Colony is grown from a single, viable microorganism
Original culture is serially diluted and streak plating to count individual colonies.
Slow due to incubation period

Question 8

What are endotoxins and which bacteria secrete them?

Answer 8

Lipopolysaccharides in the outer membrane - gram negative

Salmonella

Question 9

What are exotoxins and which bacteria secrete them?

Answer 9

Soluble proteins produced and released by bacteria as they metabolise and reproduce
Staphylococcus

Question 10

What is an example of bacterial disease caused by host tissue invasion?

Answer 10

Tuberculosis

1) First infection is symptomless, infected phagocytes are sealed in tubercles as a result of the inflammatory response
2) Bacteria lie dormant in tubercles and are not destroyed by immune system
3) When immune system weakens, bacteria become active again and destroy lung tissue

Question 11

What is a bactericidal antibiotic?

Answer 11

Destroy bacteria’s cell wall and cause them to burst

Question 12

What is a bacteriostatic antibiotic?

Answer 12

Inhibit growth of bacteria by stopping protein synthesis and production of nucleic acids

Question 13

How can bacterial resistance be combatted?

Answer 13

1) New patients are screened at arrival and isolated if they are infected
2) Antibiotics are only used when needed and courses are completed to minimise selection pressure to prevent resistant strains
3) Strict hygiene, antibiotic gel hand wash, suitable clothing

Question 14

Describe how influenza infects and effects the host

Answer 14

Droplet infection
Infects ciliated epithelial cells- injects viral RNA, host produces new viruses, lysis of cell
Headache, sore throat, coughing, vomiting, fever

Question 15

Describe how stem rust infects and effects the host

Answer 15

Spores via wind/ infected fragments
Spore germinates in water- produces hyphae which enter the plant, grow into mycelium, digest plant and absorb nutrients
Weakened stem, water loss, reduced photosynthesis, pustules on epidermis burst to release more spores

Question 16

Describe how malaria infects and effects the host

Answer 16

Female anopheles mosquito saliva
Parasite travels to liver, infect RBCs, reproduce asexually inside erythrocytes and cause lysis
Sweating, shaking, anaemia, muscle pains, headaches, liver damage

Question 17

How can influenza be treated?

Answer 17

Anti-viral medication
Antibiotics
Painkillers

Question 18

How can malaria be treated?

Answer 18

Mosquito nets
Insect repellent 
Treating still water with pesticides
Proper disposal of sewage 
Antimalarial drugs

Question 19

What are the physical barriers to infection?

Answer 19

Skin- keratin
Stomach acid
Gut and skin flora- competitive

Question 20

What are the non-specific responses to infection?

Answer 20

Inflammation- vasodilation, increase permeability of vessels, more antibodies, WBC
Fever- decreases speed of pathogen reproduction, increases rate of specific immune response
Phagocytosis- WBC engulf pathogens
Lysozyme action- found in tears and mucus, damages bacterial cell walls

Question 21

Where do B cells mature?

Answer 21

Bone marrow

Question 22

Where do T cells mature?

Answer 22

Thymus gland

Question 23

Describe the cell mediated response

Answer 23

Pathogen invades host cell

1) Host cell resents antigen on MHC protein
2) T killer cell with complimentary receptor proteins binds to Antigen-presenting cell
3) Cytokines secreted by T helper cell stimulated T killer cell to divide by mitosis
4) T killer cell divides to form active T killer cells and T memory cells
5) Active T killer cells bind to APCs and secrete chemicals which cause pores to form in cell membrane
6) Infected cell dies

Question 24

Describe the humoral response

Answer 24

1) Bacterium is engulfed by macrophage which presents antigen on MHC protein
2) Macrophage APC binds to complimentary T helper cell
3) The T helper cell is activated and divides by mitosis to form T memory cells and active T helper cells
4) T helper cell presents antigen on MHC protein and activates complimentary B cell with cytokines
5) Cytokines cause B cell to divide rapidly by mitosis to form plasma cells
6) Plasma cells secrete complimentary antibodies

Question 25

What do antibodies do?

Answer 25

They render the pathogens harmless by binding to antigen and group pathogens together so they can be engulfed by macrophages faster

Question 26

What is natural active immunity?

Answer 26

Exposed to antigen/ suffered the disease

Question 27

What is natural passive immunity?

Answer 27

Crossing of a mother’s antibodies through placenta and breast milk

Question 28

What is active artificial immunity?

Answer 28

Vaccinations

Question 29

What is passive artificial immunity?

Answer 29

Injection of antibodies into body