B5 Communicable diseases Flashcards
What is your health?
a state of physical and mental well-being, not just an absence of disease
What are examples of communicable diseases
tuberculosis, flu, diarrhoeal diseases and malaria
What are communicable diseases caused by?
pathogens such as bacteria and viruses that can be passed from one person to another
What can non-communicable diseases not do?
cannot be transmitted from one person to another
Give examples of non-communicable diseases
Heart disease and arthritis, cancer
What three other factors affect ill health
Diet, stress and life situations
What do life situations include
the part of the world where you live your gender your financial status you ethnic group the level of free health care provided where you live how many children you have local sewage and rubbish disposal
Give an example in which viruses living in cells can trigger changes that lead to cancers
the human papilloma virus can cause cervical cancer
What may be the cause of a defect in the immune system that helps the body to destroy pathogens?
genetic makeup, poor nutrition or infections such as HIV/AIDS; more likely to suffer other communicable diseases
Immune reactions initially caused by a pathogen, even something like the common cold, can trigger allergies to factors in the environment. What can these allergies be called?
skin rashes, hives, or asthma
What can severe physical ill health lead to
depression and other mental illness
What health conditions is malnutrition often linked to
deficiency diseases, a weakened immune system, obesity, cardiovascular diseases, type 2 diabetes, and cancer
What are the microorganisms that cause disease called?
pathogens, infecting animals and plants
What can pathogens be?
bacteria, viruses, protists, or fungi
How are communicable diseases caused?
either directly by a pathogen or by a toxin made by a pathogen
What are pathogens able to do?
can be passed from one infected individual to another individual who does not have the disease
What are known as fairly mild communicable diseases
common cold and tonsillitis
What are known as killer diseases
tetanus, influenza, and HIV/AIDS
Sometimes communicable diseases can be passed between different species of organisms. What is an example.
- infected animals such as dogs or bats can pass rabies onto people
- tuberculosis can be passed from badgers to cows, and from cows to people
What causes the majority of communicable diseases in people?
bacteria and viruses
In pplants, what are the most common pathogens
viruses and fungi
What are bacteria
single-celled living organisms that are much smaller than animal and plant cells
What is bacteria used for?
to make food such as yogurt and cheese, to treat SEWAGE, and to make medicines
Bacteria are important where?
in the environment, as a decomposer, and in the body
How much bacteria do scientists estimate that most people have in their guts?
between 1 and 2 kg of bacteria; having a major effect on our health and well-being
Pathogenic bacteria are the minority
but they are significant because of the major effects they can have on individuals and society
What sort of shape does viruses have?
regular shapes and are even smaller than bacteria
What causes diseases in every type of living organism?
viruses
What happens once bacteria and viruses are inside your body?
they may reproduce rapidly
How may bacteria divide rapidly?
splitting in two (binary fission); may produce toxins (poisons) that affect your body and make you feel ill; sometimes they directly damage your cells
What do viruses do?
take over the cells of your body
What do viruses do once they have taken over the cells of your body?
they live and reproduce inside the cells, damaging and destroying them
What are some common disease symptoms?
high temperature, headaches. and rashes
Why do symptoms happen
by the way your body responds to the cell damage and toxins produced by the pathogens
The more pathogens that get into your body, the more likely..
you will develop an infectious disease
Give three ways in which pathogens spread from one individual to another
by air (including droplet infection)
direct contact
by water
What causes infectious diseases?
microorganisms known as pathogens
How do pathogens make you ill?
as a result of reaction to toxins produced,
or damage caused to cells
By air- droplet infection
droplets full of pathogens expelled in
coughing, sneezing, or talking, droplets breathed in by others,
direct skin contact
pathogens spread from skin of one person to skin of another
direct contact of body fluids
pathogens pass directly from inside
one person’s body into another
by contaminated water
taking in pathogen through digestive
system
by under-cooked or contaminated food-
taking in pathogen through digestive system
By air in plants
fungal spores carried in air from one plant to another
by direct contact-
- pathogens on traces of plant material come into contact with new plants in the soil and infect them
by contaminated water
fungal spores carried in splashes of
water from one plant to another
Describe and explain the main differences between bacteria and viruses and how they cause diease
Bacteria are single-celled organisms much smaller than plant and
animal cells.
Viruses are even smaller than bacteria.
Bacteria divide rapidly by splitting in two (binary fission).
Viruses take over body cells and reproduce inside them.
Bacteria may produce toxins or directly damage body cells.
Viruses damage and destroy cells.
To culture (grow) microogranisms, you must..
provide them with everything they need
what is a culture medium
giving bacteria a liquid or gel containing nutrients
What do culture mediums contain?
carbohydrate as an energy source, various minerals, a nitrogen source so they can make proteins, and sometimes other chemicals
What do most micro-organisms also need to grow?
warmth and oxygen
How does one culture bacteria
Hot agar gel is poured into a Petri dish.
It is then left to cool and set before the micro-organisms are added
Where can you also culture micro-organisms?
in a flask of sterile nutrient broth solution
What sort of cultures of microorganisms do you need to investigate the effects of chemicals such as disinfectants and antibiotics
uncontaminated
Where can contamination come from?
your skin, the air, the soil, or the water around you
Why is it important to avoid any unnecessary contamination?
The bacteria growing may be harmless, however always the risk that a mutation (change in the DNA) will take place and produce a new and dangerous pathogen
Why do scientists culture microorganisms in the labratory
To find out what nutrients they need to grow
and to investigate which chemicals are best at killing them.
Explain why agar gel is important in setting up bacterial cultures
Agar gel is a culture medium
giving microorganisms everything they need to grow
Suggest why bacteria are grown at 25 degrees Celsius or below in the school lab when this is not their optimum temperature for growth
reduces risk of growing dangerous pathogens
Explain why bacteria are often cultured at much higher temperatures in industrial plants and hospital laboratories
Higher temperatures enable microorganisms to grow much more rapidly so that they can be identified sooner (e.g., in hospital labs) or to produce products more quickly in industry (e.g., insulin-producing
GM bacteria).
Explain why petri dishes are not opened before incubation once they have been inoculated and sealed.
To prevent contamination of culture by microorganisms from the environment and to prevent release of potentially harmful microorganisms that might
grow.
Suggest what might limit the growth of bacteria in a culture on a Petri dish because these ideal conditions do not last forever
Petri dish- limited supplies (nothing new added), bacteria use up available food and oxygen (limiting growth).
Petri dish has no mechanism for removal of waste products (build-up of carbon dioxide and other toxins can poison bacteria and stop growth)
What are you surrounded by all the time?
disease causing bacteria
What happens if bacteria have the right conditions, including enough nutrients and a suitable temperature?
They can grow very fast, dividing every 20 minutes
What factors may affect growth rate of a bacteria population
temperature, available nutrients, oxyygen levels, and pH
You can calculate the number of bacteria in a population after a given time as long as you know the mean division time
This varies greatly, from 15-20 minutes to hours, days or even years
What is the formula for calculating bacteria at the end of the growth period?
bacteria at the beginning of the growth period x 2ⁿᵘᵐᵇᵉʳ ᵒᶠ ᵈᶦᵛᶦˢᶦᵒⁿˢ
What are the ways to prevent the growth of bacteria?
- raise/ lower the temperature
- chemicals to stop them growing or kill them
What is a disinfectant?
chemicals used to kill bacteria in the environment around us
What is an antiseptic?
a disinfectant that is safe to use on human skin
What are antibiotics?
chemicals that can be used inside our bodies, which kill bacteria or prevent them from growing
In the mid-1850s, who was Semmelweis?
a doctor at ime where many women in hospital died from childbed fever a few days after giving birth; nobody knew why
What was something important that Semmelweis noticed?
his medical students went straight from dissecting a dead body to delivering a baby without washing their hands
What did Semmelweis wonder?
If they were carrying the cause of disease from the corpses to their patients
What did Semmelweis also notice from another doctor?
another doctor died from symptoms identical to childbed fever after cutting himself while working on a body. This convinced him that the fever was caused by some kind of infectious agent
As a result of Semmelweis’ discovery, what did he insisted to his medical students?
wash their hands before delivering babies; fewer mothers died from the fever. However, other doctors were very resistant to Semmelweis’s ideas
In the mid-to late-19th century, who are two other people who made scientific discoveries in terms of medicine
Louis Pasteur and Joseph Lister
What did Louis Pasteur do?
showed that microorganisms cause disease; developed vaccines against diseases such as anthrax and rabies
What did Joseph Lister do?
started to use antiseptic chemicals to destroy pathogens before they caused infection in operating theatres
As microscopes improved…
it became possible to see pathogens more clearly. This helped convince people that they were really there
What is another way to help us prevent from disease happening?
understanding how communicable diseases are spread from one person to another
What are the four ways to prevent the spread of communicable diseases?
Hygiene
Isolating infected individuals
Destroying or controlling vectors
Vaccination
What are some simple hygiene measures?
Hand washing; using disinfectants on kitchen work surfaces, toilets, etc, to reduce the number of pathogens; keeping raw meat away from food that is eaten uncooked; coughing or sneezing into a tissue; maintaining the hygiene of people and agricultural machinery to help prevent the spread of plant diseases
Explain ‘isolating infected individuals’
The fewer healthy people who come into contact with the infected person, the less likely it is that the pathogens will be passed on
Why may isolating infected individuals may be difficult for plants
only those plants that are small and can be moved and destroyed easily can this be possible
Give a 3 examples of a vectors?
- mosquitoes carry a range of diseases, such as malaria and dengue fever
- Houseflies can carry over 100 human diseases
- rats
What happens when vectors are destroyed?
The spread of disease can be prevented
What happens when the numbers of vectors are controlled?
the spread of disease can be greatly reduced
What happens during vaccination?
doctors introduce a small amount of harmless form of a specific pathogen into your body
How do vaccinations work
If you come into contact with the live pathogen, you will not become ill as your immune system will be prepared
Vaccination is a successful way of…
protecting large numbers of humans and animals against serious diseases
Why can’t vaccinations be used in plants?
they don’t have an immune system
Suggest why other doctors were so resistant to Semmelweis’s ideas?
1.Pathogens are very small, so before development of microscopes- people had no way of seeing bacteria or viruses.
2. Inability to see microorganisms made it very difficult to understand how
diseases spread.
3. Evidence (e.g., improved hygiene reducing the deaths from childbed
fever) was seen as challenging normal practice.
4. Difficult to convince people whose ideas are entrenched.
5. Need people prepared to take a chance (e.g., Pasteur, Lister).
6. Takes time for evidence of effectiveness of new idea to build up
What can viruses do?
can infect and damage all types of cells
Why is it important for viruses to stop them spreading?
Scientists have not developed medicines to cure viral diseases
What are symptoms a result of?
the way the body reacts to the viruses damagining and destroying cells as they reporduce
What are the main symptoms of measles?
fever and red skin rash
How is measles spread?
the inhalation of droplets from coughs and sneezes and is very infectious
Measles is a serious disease; what can it cause?
blindness and brain damage; may be fatal if complications arise
There is no treatment for measles, so what needs to be done to stop the spread of the virus?
isolating infected individuals
How many people died of measles in 2013?
145 700 globally died of measles
Why is measles now rare in the UK?
a result of improved living conditions and a vaccination programme for young children
What disease can eventually lead to aids?
HIV
In 2013, how many people have died of a HIV related disease?
1.5 million people
Why do many people not realise they are infected with HIV
the virus only causes a mild, flu-like illness to begin with
What does HIV do?
attack the immune cells and after the initial mild illness it remains hidden inside the immune system, sometimes for YEARS, until the immune system is so badly damaged that it can no longer deal with infections or certain cancers
How is HIV spread?
direct SEXUAL CONTACTS and the exchange of BODY FLUIDS such as blood, which occurs when drug users share needles or when unscreened blood is used for transfusions
What can be used to prevent the development of AIDS for many years and give HIV positive people an almost normal life expectancy
The regular use of antiretroviral drugs
Why may it be unfortunate for the majority of people infected with HIV who live in areas such as sub-Saharan Africa
It is hard to get antiretroviral drugs
To have the best chance of long-term survival for those with HIV..
antiretroviral drugs must be started as soon as possible after infection
Tobacco mosaic virus was the first…
first virus ever to be isolated
What is TMV?
a widespread plant pathogen that affects around 150 species of plants including tomatoes and tobacco plants
What does TMV cause?
a distinctive ‘mosaic’ pattern of discoloration on the leaves as the virus destroys the cells
How does TMV affect plant growth?
affected areas does not photosynthesise; seriously reducing the yield of crop
How is TMV spread?
contact between diseased plant material and healthy plans; insects can act as vectors
How long can TMV (virus) remain infectious in the soil for?
for about 50 years
There is no treatment for TMV, so what do farmers do?
farmers now grow TMV- resistant strains of many crop plants
What can also help the spread of TMV?
good field hygiene and good pest control
What is salmonella?
bacteria that live in the gut of many different animals
What can antibiotics do?
kill bacteria or stop them growing and cure bacterial
Where can salmonella be found
in raw meat, poultry, eggs and egg products
What happens if salmonella gets into our bodies?
They disrupt the balance of the natural gut bacteria and can cause food poisoning
One common cause for infection of salmonella?
eating undercooked food, when the bacteria have not been killed by heating
What is another cause for salmonella?
eating food prepared in unhygienic conditions where food is contaminated with salmonella bacteria from raw meat
When do the symptoms develop for salmonella?
within 8-72 hours of eating infected food
What are symptoms of salmonella?
fever, abominable cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete
Why may salmonella be very fatal to very young children and the elderly
dehydration
In the UK, poultry are vaccinated vaccinated against salmonella to control the spread of diease
Campylobacter, another bacterium found in chickens, still causes around 280 000 cases of food poisoning each year
To prevent food poisoning…
- keep raw chicken away from food that is eaten uncooked
- avoid washing raw chicken (sprays bacteria)
- wash hands and surfaces well after handling raw chicken
- cook chicken thoroughly
What is a gonorrhoea?
a sexually transmitted disease
How is gonorrhoea spread?
unprotected sexual contact
What are the early symptoms of gonorrhoea?
thick yellow or green discharge or pain in urination
What happens to babies born from infected mothers? (gonorrhoea)
severe eye infections and even become blind
What may untreated gonorrhoea lead to?
long-term pelvic pain, infertility, and ectopic pregnancies
Babies born to infected mothers may have..
severe eye infections and even become blind
What can gonorrhoea be treated with and why?
antibiotics as it is bacterial
Why did gonorrhoea become increasingly difficult to treat?
it used to be cured easily using penicillin but now many antibiotic resistant strains of gonorrhoea have evolved
How can gonorrhoea be prevented?
barrier method of contraception such as a condom and by reducing the number of sexual partners
Where are the relatively few bacterial diseases of plants located?
in tropical and sub-tropical regions
What is Agrobacterium tumefacians?
a bacterium that causes crown galls
What are crown galls?
a mass of unspecialised cells that often grow at the join between the root in infected plants
What do crown galls infect?
many different plant types including fruit trees, vegetables, and garden flowering plants
What do crown galls do?
the bacteria insert plasmids into the plant cells and cause a mass of new undifferentiated genetically modified cells to grow
How may crown galls be beneficial to scientists?
became a key tool for scientists when genetically modifying plant cells. Scientists make use of the way the bacteria naturally infect plant cells and give them new added genes. They manipulate the bacteria so they carry desirable genes into the cells they infect
Name one way that antibiotics work to cure bacteria infections
kill bacteria or prevent growth of bacteria
Describe how people become infected with food poisoning caused by salmonella
Most common causes are eating either under cooked food contaminated
with Salmonella
or food prepared in unhygienic conditions that becomes contaminated
by Salmonella bacteria.
Doctors in the UK rarely treat salmonella food poisoning with antibiotics, why?
doesn’t last long (only a few days)
• unpleasant but not serious for most people
• antibiotics would be lost from system through sickness and
diarrhoea
• risks development of antibiotic resistance
Suggest three ways of preventing the spread of gonorrhoea
- being celibate
- having a single sexual partner,
- limiting number of sexual partners,
- always using barrier method
- of contraception (e.g., condom).
Until recently gonorrhoea was relatively easy to treat, why?
bacterial infection,
so could be treated with antibiotics
Describe the implications of increased antibiotic resistance in the bacteria causing gonorrhoea for the 106 million people who are infected with the disease each year
At this point, lots of people will have the disease
A small number of human fungal diseases can be fatal when..
they attack the lungs or brains of people who are already ill?
What can also develop serious fungal infections?
damaged heart valves
What are usually effective against skin fungi like athlete’s foot but it hard to treat against deep-seated tissue infections?
anti-fungal drugs
What is most common in plants (and most devastating) but not in animals.
fungal diseases
what are some examples of fungal infections?
stem rusts and various rotting diseases
What is Rose Black Spot?
a fungal disease of rose leaves
What does rose black spot do?
causes purple or black spots to develop on the leaves and it is a nuisance in gardens and for commercial flower growers
What happens to the leaves that are affected by rose black spot?
The leaves often turn yellow and drop early.
How does rose black spot weaken the plant?
no green pigment, reduces area of leaves available for photosynthesis
Rose black spot results in the plant not…
flowering well
How are the spores of the fungus spread?
- spread in the environment carried by wind
- spread over the plant after it rains in drips of water that splash from one leaf or plant to another
- spores stay dormant over winter on dead leaves and on the stems of rose plants
How may gardeners or horticulturists try to prevent the spreading of rose black spot?
- removing and burning affected leaves and steps
- chemical fungicides (help treat disease, stops it spreading)
- bred types of roses resistant to black spot (but the disease still cannot be prevented or cured)
What are protists?
a type of single-celled organisms that cause a range of diseases in animals and plants
Protists are relatively ___ pathogens but the _____ they cause are often serious and ____ to those infected
- rare
- diseases
- damaging
Diseases caused by protists usually involve a what?
a vector that transfers the protist to the host
What is one of the best known and globally serious protists disease called?
malaria
What is malaria caused by?
protist pathogens that are parasites
What are parasites?
protist pathogens that live and feed on other living organisms
What does the life cycle of a protist involve?
time in the human body and time in the body of a female Anopheles mosquito
How do protists reproduce?
sexually- in the mosquito
asexually- human body
What do mosquitoes act as to disease?
vectors
Before a female mosquito can lay her eggs…
she needs two meals of human blood
What happens when the protists are passed into the human bloodstream?
the protists travel around the human body in the circulatory system; affecting the LIVER and DAMAGE red blood cells
What are the fatal symptoms of of malaria?
recurrent episodes of fever and shaking when the protists burst out of blood cells; weakening the affected person
If malaria is diagnosed quickly, it can be treated…
using a combination of drugs, but this is not always available in the countries most affected by malaria
What are the ways the spread of malaria can be controlled in a number of ways, most of which target the mosquito vector
- insecticide-impregnated insect nets
- Insecticides
- preventing the vectors from breeding (remove standing water/ spraying water w/ insecticides to kill the larvae)
- antimalarial drugs that kill the parasites in the blood
What gives pathogens a way in in the body?
Every body opening as well as any breaks in the skin
The more pathogens that get into your body, the most likely it is to…
get an infectious disease
What does your skin do?
- covers your body and acts as a barrier.
- prevents bacteria + viruses reaching the tissues beneath
What happens if you damage or cut your skin?
the barrier is broken but your body restores it
-you bleed, and the platelets in your blood set up a chain of events to form a lot that dries into a scab
Your skin produces what to destroy pathogenic bacteria
antimicrobial secretions
What is healthy skin also covered with and why
microorganisms that help keep you healthy and act as an extra barrier to the entry of pathogens
Your respiratory system is a ___ link in your body defences
weak
Every time you breathe in, you…
draw air full of pathogens into the airways of the lungs (same way w/ food and drink)
What features does the nose have to help prevent pathogens constantly causing infections
- full of hairs and produces a sticky liquid
- hairs + mucus: trap particles in the air that may contain pathogens/ irritate lungs
What happens if you spend a long time in an envirnment with lots of pollution
The mucus you produce is blackened
What does the trachea and bronchi do in response to pathogens.
secrete mucus that traps pathogens from the air
What are the lining of the tubes covered in? (trachea and bronchi)
cilia : tiny hair-like projections from the cells
-waft the mucus up to the back of the throat where it is swallowed
What does the stomach do to help prevent pathogensconstantly causing infections
produces acid
-destroys the microorganisms in the mucus you swallow (as well as the majority of pathogens you taken in through your mouth in your food and drink)
In spite of your body’s defence mechanism, some pathogens will get inside your body.
Once there, they will meet your second line of defence- the white blood cells of your immune sustem
What are the three ways WBC’s get rid of pathogens
- ingesting microorganisms
- producing antibodies
- producing antitoxins
What do antibodies do?
target particular bacteria or viruses and destroy them
how are antibodies helpful?
When your WBC’s have produced antibodies once against a particular pathogen, they can be made very quickly if that pathogen gets into the body again.
Some white blood cells produce antitoxins
These counteract (cancel out) the toxins released by pathogens
Why is mucus green?
some WBCs contain green-colored enzymes.
-they destroy the cold viruses and any bacteria trapped in the mucus when you have a cold. The dead wbcs along with the dead bacteria and viruses, are removed in the mucus, making it look green
The global loss of food crops to plant pathogens is what percentage
15-40% a year
Other than viruses, bacteria, and fungi, plants are also vulnerable to?
attacks by pests that cause a lot of damage
Insect pests can..
destroy plants directly and act as vectors of disease
What do aphids have?
sharp mouthparts to penetrate into the phloem vessels of the plant so they can feed on the sugar-rich phloem sap
How do aphids attack?
in huge numbers, depriving the plant cells if the products of photosynthesis; seriously damaging and weakening the plant
Aphids can be destroyed by?
using chemical pesticides or using biological pest control (in enclosed spaces such as greenhouse gases)
What is an example of biological pest control?
releasing aphid-eating insects such as ladybirds and their larvae can control the pathogen population so it does not have an impact on the success of the crop
Why do plants fail to grow and thrive due to pests?
Other plant pests, including tiny nematode worms and many insect larvae that live in the soil, feed in or on plant roots, damaging them so they cannot absorb water and mineral ions effectively
Some plant diseases are the result of mineral deficiencies in the soil where the plants are growing.
They are non-communicable- they are not passed from one plant to another
Why may plants need a good supply of nitrate ions from the soil?
to convert the sugars made in photosynthesis into proteins needed for growth in protein synthesis
What happens in there is a nitrate deficiency in the soil?
protein growth will be limited, the growth of plants will be stunted and they will not produce a crop properly
Why do plants take magnesium ions from the soil?
to make the chlorophyll needed for photosynthesis
What does it mean if the level of magnesium ions in the soil is low?
the plant cannot make enough chlorophyll; the leaves become yellow and growth slows down because the plant cannot photosynthesise fully
What is the yellowing of the leaves due to lack of magnesium ions known as?
chlorosis
What do the symptoms of disease in plants include?
- stunted growth (e.g. nitrate deficiency)
- spots on leaves (black spot fungus in roses)
- areas of decay or rotting (blights on potatoes)
- growths (crown galls)
- malformed stems and leaves (aphids)
- discoloration (chlorosis)
- presence of visible pests
fast detection helps…
reduce the spread of disease between plants, because diseased plants can be treated or removed
What are the four physical barriers that reduce the invasion of pathogens in plants?
- the cellulose cell walls that strengthen plant cells
- tough waxy cuticle on the surface
- bark on trees. and a layer of dead cells on the outside of stems
- leaf fall
Elaborate on ‘the cellulose cell walls that strengthen plant cells’
resist invasions by microorganisms
it is why aphids that pierce cellulose walls are so damaging
elaborate on ‘tough waxy cuticle on the surface’
barrier to entry of pathogens
-it is only at the stomata that pathogens actually have access to the cells within the leaf
elaborate on ‘bark on trees. and a layer of dead cells on the outside of stems’
protective layer hard for pathogens to penetrate
when the dead cells are lost or shed, the pathogens fall off with them
Elaborate on ‘leaf fall’
deciduous trees lose their leaves in autumn. Any pathogens that infect the leaves, such as rose black spot, fall off the tree when the leaves are lost
What are chemical barriers for plants
many plants produce antibacterial chemicals that protect them against invading pathogens
What are mint and witch hazel used for?
as mild antiseptics in cosmetics and over-the-counter medicines
Compounds such as what from plants also have promising antibiotic properties?
pines, cypress, and euphorbias
Plants don’t just defend themselves against microorganisms
they also defend themselves against the large and small animals that want to eat them
What are several defenses against herbivores
- poisons
- thorns
- hairy stems and/or leaves
- drooping or curling when touched
- mimicry
What is mimicry
some plants droop to mimic unhealthy plants and this tricks animals into not eating them
-some mimic butterfly eggs on their surfaces
hairy stems and/or leaves
deter insects and larger animals from feeding on them or laying their eggs on the leaves or stems
drooping or curling when touched
rare but effective- leaves collapse suddenly, dislodging insects and frightening larger animals
why are scientists increasingly investigating plant antibacterial chemicals?
to see if they can be adapted for use as antibiotics against human properties
