3: Infection & Response

Question 1

what are the non-specific defence systems of the human body against pathogens? how do they work?

Answer 1

skin - acts as a physical barrier
nose - internal hairs - physical barrier; also produces mucus to trap pathogens before they enter the lungs
trachea and bronchi - lined w cilia - these move mucus and pathogens upwards towards the throat where it is swallowed into your stomach
stomach - HCl kills pathogens

Question 2

what are the three white blood cells?

Answer 2

phagocytes; ones which produce antibodies (lymphocytes) ; ones which produce antitoxins

Question 3

how do phagocytes work?

Answer 3

engulf and digest pathogens - surrounds pathogen and releases enzymes to digest and break it down to destroy it
can be non-specific

Question 4

how do lymphocytes work?

Answer 4

they produce the antibody that is complementary to the antigens of the pathogen; they make pathogens bind together and cause agglutination (clumping) of pathogens to make them easier for other WBCs to kill
is a specific type of immune response - antibodies produced are specific to each pathogen’s antibodies

Question 5

how does the production of antibodies work?

Answer 5

antitoxins which are complementary to the toxins released by a pathogen are released and bind to them; the antitoxin neutralises the toxin

Question 6

how were drugs traditionally made? give the three examples

Answer 6

extracted from plants and microorganisms

heart drug digitalis originates from foxgloves; painkiller aspirin from willow; penicillin from the penicillium mould

Question 7

how are drugs made now?

Answer 7

they are synthesised by chemists in the pharmaceutical industry - the starting point may still be a chemical extracted from a plant

Question 8

why are drugs testes?

Answer 8

to check toxicity; to work out the correct dosage; to see if they actually work (efficiency)/will treat the disease

Question 9

what is pre-clinical testing?

Answer 9

when a drug is tested on cells/tissue; then if it passes it will be tested on live animals

Question 10

why is pre-clinical testing needed?

Answer 10

to test toxicity; to check if it is safe

Question 11

what is clinical testing? what are the stages?

Answer 11

trials on people
first it is given in v. low doses to healthy volunteers to see if the drug is safe/has any side effects
then further human trials will be carried out to determine the optimum dosage and to see if it is effective

Question 12

why are healthy volunteers used in the initial phase?

Answer 12

there is a higher risk to patients and the dosage would probably be too low to help anyway

Question 13

why are placebo drugs used?

Answer 13

to act as a control, to see the true effects of the real drug; no one knows who is given the placebo drug so responses/reactions are not affected

Question 14

what are monoclonal antibodies?

Answer 14

antibodies made from a single clone of identical cells -so they consist of identical antibodies

Question 15

how are monoclonal antibodies produced?

Answer 15

a mouse is immunised to stimulate antibody production (so injected w a non-self cell); lymphocytes will begin to produce the correct antibody and we can isolate these lymphocytes from the mouse’s spleen; immortal tumour cells are grown in a cell culture in a lab; the lymphocytes are fused w the cultivated tumour cells to form hybridoma cells; these can then divide rapidly (as tumour cells do) to form a clone of identical cells that produce the same antibody; these are then collected and purified = monoclonal antibodies

Question 16

how can monoclonal antibodies be used?

Answer 16

in blood tests to check for pathogens and drugs; in research/treatment to locate and identify part of cells/tissue using a fluorescent dye; in pregnancy tests; to treat diseases such as cancer - can signal an immune response from WBCs against cancer cells; can bind to a receptor on the cancer cell and; stop it from dividing; can deliver drugs/radioactive chemicals to cancer cells to kill the specific cells

Question 17

what are the adv. and dis-adv. of monoclonal antibodies?

Answer 17

adv. : can be produced quickly; can treat cancer - healthy cells aren’t affected; specificity means they could be used to treat a wide range of conditions
dis-adv. : expensive to develop; more side effects than expected; ethical issues concerning mice; also, it may not work on humans despite working on animals

Question 18

what are symptoms of disease in plants?

Answer 18

stunted growth (e.g. nitrate deficiency); spots of leaves (e.g. rose black spot); areas of decay/rotting (e.g. rose black spot); growths (e.g. crown galls caused by bacterial infections); malformed stems/leaves (e.g. aphid infestation) discolouration (e.g. chlorosis, tobacco mosaic virus); presence of visible pests (e.g. aphids)

Question 19

what minerals can plants be deficient of?

Answer 19

nitrate ions; magnesium ions

Question 20

what are nitrate ions need for and what are symptoms when a plant is deficient?

Answer 20

needed to convert the sugars made in photosynthesis into proteins for growth
growth will be stunted; will not properly produce crop

Question 21

what are magnesium ions need for and what are symptoms when a plant is deficient?

Answer 21

to make the chlorophyll needed for photosynthesis

leaves will yellow (known as chlorosis); growth stops

Question 22

what is rose black spot caused by? what are the symptoms?

Answer 22

caused by spores of the fungus spread in the environment, by wind
symptoms: purple/black spots on leaves, leaves will drop early and turn yellow; plant will be weakened and not flower well

Question 23

what is tobacco mosaic disease caused by? what are the symptoms?

Answer 23

caused by virus spread by contact between diseased and healthy; insects can also act as vectors
symptoms: distinctive mosaic pattern of discolouration on leaves as virus destroys cells; affected growth and reduced crop yield

Question 24

what are aphids, what do they do, and how can they be destroyed?

Answer 24

they are insects which feel on the sugar-rich phloem sap by penetrating the phloem vessels w sharp mouthparts; they can also transfer viruses etc. on their mouthparts; they reduce crop yield significantly - deprives plant of products of Ps - and can transfer other diseases which can affect growth too; can be destroyed by chemical pesticides or using a biological control e.g. ladybirds, which eat them and control the pop. so they don’t impact the crop

Question 25

how can plant diseases be identified?

Answer 25

by comparing symptoms to disease descriptions in a gardening manual or online; can send samples to a laboratory; testing kits containing monoclonal antibodies can be used to test for certain pathogens

Question 26

what physical defence responses do plants have? how do they work? (4)

Answer 26

cellulose cell walls -strengthen plant cells to resist invading microorganisms
tough waxy cuticle on leaves - act as a barrier to the entry of pathogens
layers of dead cells around stems (bark on trees) which fall off - form a protective layer which is hard for pathogens to penetrate; when they fall off, so do the pathogens
leaf fall - any pathogens that infect the leaves fall off the tree

Question 27

what chemical defence response do (some) plants have? how does it work?

Answer 27

can produce antibacterial chemicals to protect them; can produce poisons to deter herbivores - animals will avoid them if they know eating them will make them feel unwell

Question 28

how might humans use plant antibacterial chemicals to help us in the future?

Answer 28

could be adapted for use for antibiotics against human pathogens

Question 29

what mechanical adaptations do plants have to deter herbivores? how do they work? (4)

Answer 29

thorns - unpleasant/painful for large herbivores to eat; do not deter insects
hairs - deters insects and larger animals from feeding/laying eggs on the leaves/stems; some plants combine hairs w poisons e.g. nettles
leaves which droop and curl when touched - dislodges insects and frightens large animals
mimicry to trick animals - some plants droop to mimic unhealthy plants to trick animals into not eating them; some mimic butterfly eggs on their surfaces so butterflies don’t lay their eggs to avoid competition w other caterpillars