B5 - Communicable diseases

Question 1

What are pathogens? Name 4 types of pathogens and describe how they might spread:

Answer 1

-microorganisms that can cause infectious disease in plants/animals
-viruses, bacteria, protists, fungi

-can spread by direct contact, water, or air

Question 2

What is the difference between how bacteria cause disease in humans, and how a virus might do so?

Answer 2

-both may reproduce rapidly in the body

-bacteria can produce toxins that damage tissues, making us feel ill
-viruses live and reproduce inside cells, causing cell damage

Question 3

Name 3 viral diseases:

Answer 3

-measles
-HIV
-tobacco mosaic virus (TMV)

Question 4

What is measles? Describe how it is spread, and how it can affect a person:

Answer 4

-viral disease, showing symptoms of fever/red skin rash, can be fatal
-most children are vaccinated against it
-can spread by inhalation of droplets from sneezes/coughs

Question 5

What is HIV? Describe the symptoms, how it can develop further and how it is spread:

Answer 5

-initially causes flu-like illness, and damages the immune system if not controlled early by antiretroviral drugs
-AIDS can develop, meaning it can’t handle other infections/cancer
-virus spread by sexual contact or exchange of bodily fluids (eg sharing needles)

AIDS - acquired immune deficiency syndrome

Question 6

What is TMV? Describe its symptoms and how it is spread:

Answer 6

-tobacco mosaic virus, affects many species of plants including tobacco/tomatoes, producing a mosaic-like discolouration pattern on the leaves
-stunts plant growth, due to lack of PS
-spread through plant contact, or transmission from a gardener’s hands

Question 7

Name 2 bacterial diseases:

Answer 7

-salmonella
-gonorrhoea

Question 8

What is salmonella? How is it controlled, and how does it spread?

Answer 8

-bacteria secretes toxins causing fever, abdominal cramps, vomiting, and diarrhoea
-in UK, poultry are vaccinated to control spread
-spread by bacteria ingested from food prepared in unhygienic conditions

Question 9

What is gonorrhoea? What symptoms arise, and how is it spread/treated/prevented?

Answer 9

-bacteria causes thick yellow/green discharge from vagina/penis and pain during urination
-used to be treated with penicillin but now many resistant strains appeared
-spread by sexual contact (STD)
-prevented with barrier method, treated with antibiotics

Question 10

What is rose black spot? How is it spread and treated?

Answer 10

-fungal disease in plants that causes black/purple spots to appear on leaves, that can turn yellow and drop early
-stunts growth due to reduced PS
-spread by water/through air
-treated with fungicides/removing infected leaves

Question 11

Describe what malaria is caused by, its symptoms and how it can be prevented:

Answer 11

-caused by a protist, which has a life cycle including the mosquito vector
-can cause recurrent episodes of fever + is fatal

-spread is controlled by stopping the vectors from breeding, using mosquito nets, or changing behaviour to avoid being bitten (eg wearing long clothing)

Question 12

Describe 4 physical features that stop the entry of pathogens into the human body:

Answer 12

-skin (physical barrier, secretes antimicrobial fluids, blood clots at wounds)

-nose (mucus traps particles which may contain pathogens)

-trachea/bronchi (mucus too, and cilia waft particles up to be coughed/swallowed)

-stomach acid

Question 13

What are the 3 methods of which a white blood cell can help to fight against infection?

Answer 13

-phagocytosis (engulf + destroy)
-antitoxins (counteracts toxins produced by bacteria)
-antibodies (proteins that target specific antigens on pathogens)

Question 14

What features found on a plant might indicate the presence of a disease? (5)

Answer 14

-discolouration/spots on leaves
-presence of pests (eg aphids)
-growths on malformed stems/leaves
-areas of decay/rotting
-stunted growth

(DP, GAS)

Question 15

Give 3 methods of how to identify the specific pathogen causing a disease found on a plant:

Answer 15

-reference to gardening manual/website
-take infected plant to lab to identify pathogen
-use testing kits that contain MCAs

Question 16

Describe the 2 ion deficiencies that can cause negative effects on a plant:

Answer 16

-nitrate deficiency causes stunted growth (less protein synthesis)

-magnesium deficiency causes chlorosis (less chlorophyll produced, lack of green colour causes yellowing of leaves)

Nitrate ions are combined with glucose to make amino acids, and then protein synthesis

Question 17

Explain how a magnesium deficiency could cause yellow leaves and stunted growth:

Answer 17

-yellow leaves caused by a lack of chlorophyll produced using magnesium ions
-less light absorbed by chlorophyll
-lowers rate of PS
-no glucose produced, so rate of respiration decreases
-less glucose converted into protein using the energy from respiration

Question 18

What do physical defences on plants do? Name 3 of them:

Answer 18

-they all resist the invasion of pathogens or pests

-cellulose cell walls
-tough waxy cuticle on leaves
-layer of dead cells around stems which fall off (eg bark)

Question 19

Give 2 chemical responses that plants use to defend against pathogens:

Answer 19

-antibacterial chemicals
-poisons to deter herbivores

The poison could be from things like poisonous berries

Question 20

Describe 3 mechanical adaptations that protect plants:

Answer 20

-thorns/hairs to deter animals
-drooping/curling leaves
-mimicry to trick animals

Question 21

Why might antibiotic-resistant bacteria populations be on the rise?

Answer 21

-(overuse of) antibiotics kill the non resistant strains
-less competition

Question 22

RP2 - How can you use aseptic techniques to prepare an uncontaminated agar plate?

Answer 22

-sterilise hands + working area (work near roaring BB flame, dip sheet in Virkon disinfectant and work on it)

-hold inoculating loop through flame to sterilise
-scrape loop in container to collect bacteria
-lift one edge of the agar plate’s lid, insert the loop
-swipe the surface of the agar to inoculate the bacteria evenly across the culture medium

The BB flame creates an updraft so no microbes can fall onto the plate

Question 23

RP2 - How would you use an inoculated agar plate to investigate the effect of different antiseptics on bacterial growth?

Answer 23

-cut out equally sized discs of filter paper, and dip one into its own antiseptic
-use forceps to place each disc into the agar plate, noting where each antiseptic is
-store agar plate in incubator
-record mean diameter for each zone of inhibition around the discs, and calculate area

Question 24

RP2 - Describe the conditions needed to store an agar plate safely:

Answer 24

-tape lid on ensuring there are still gaps for oxygen to enter, so harmful anaerobic bacteria don’t grow

-store at 25°C, any higher could grow pathogens that could harm humans

-store upside down to stop condensation falling onto agar’s surface

Question 25

What is a vector?

Answer 25

an organism that transmits an infectious pathogen

Question 26

Give some reasons as to why a plant may have stunted growth or yellow leaves:

Answer 26

-lack of Mg ions (chlorophyll not produced)
-infected by pathogen/pest (aphids, removes sugars from phloem)
-lack of light (chlorophyll breaks down)

Question 27

What factors might be controlled when conducting a large survey on humans?

Answer 27

-age/sex
-smoking/drinking habits
-ethnicity
-fitness levels
-diet + BMI

Make sure the factors you give in a question are relevant to the survey being conducted

Question 28

Why might HIV cases reduce in the future?

Answer 28

-better education on preventing its spread
-condoms more widely available