Plant Diseases, MC Antibodies and Microorganisms - B3

a microorganism is a very small living thing.

bacteria multiply by a form of cell division called binary fission. it is very simple so it can happen quickly. bacteria can reproduce fastest if:

• it is the optimum temperature
• there is a plentiful supply of nutrients (oxygen, water, mineral ions, glucose etc)

the mean division time is the average time taken for a particular bacterium to reproduce in certain conditions 

to calculate the population using the mean division time:

• first calculate the number of divisions. length of time measured/length of time for one division
• then calculate the number of microbes produced. 1 * 2^number of divisions

example:

the mean division time for a bacterial cell is 20 minutes. calculate the number of bacteria in the population after 2 hours.

number of divisions = 120/20 = 6 divisions

number of bacteria = 1 * 2^6 = 64 bacteria

1) lag phase

• very slow rate of growth
• microbes are adjusting to the conditions in their environment

2) log phase 

• very fast, exponential rate of growth 
• the population doubles each time because it is in the optimum conditions

3) stationary phase

• no increase in the population
• the rate of growth is equal to the rate of death due to a shortage of nutrients that slow down growth

4) death phase

• decrease in the population
• death rate acceeds the rate of reproduction due to a lack of nutrients/space

aseptic technique is a process used by scientists to grow uncontaminated cultures of microorganisms for the following reasons:

• to test new drugs
• to study microbes
• to make useful products (beer, bread, yoghurt, etc)

there are 3 stages to aseptic technique:

• 1) preparing the work area - this is when you wash your hands and disinfect the work surfaces to ensure that no microbes contaminate the culture. cuts are covered by a plaster to ensure that the microbes you are working with do not infect the wound.
• 2) inoculation - this is when you apply the culture to the petri dish filled with agar jelly using an inoculating loop. the loop is sterilised by heating it under a bunsen burner which ensures that microbes on it are killed and prevents contamination. the lid of the dish must always be lifted at an angle to slightly reduce the risk of contamination from the air.
• 3) incubation - this is when you seal the petri dish with gaps to ensure that oxygen can enter and the microbe can respire and grow, and incubate the culture. the maximum temp for incubation in schools is 25°C to ensure that no harmful bacteria is grown, while also being high enough for growth.

• stunted growth
• discolouration
• spots on the leaves  aress of decay (rot)
• abnormal growth (lumps)
• malformed stems/ leaves
• visible pests

the symptoms can be used to identify the disease by:

• referring to a gardening manual or website
• using a laboratory test
• using testing kits that contain monoclonal antibodies

causes:

• pathogens, such as bacteria, viruses, and fungi
• insects 
• ion deficiency diseases

some examples of common diseases and their symptoms:

• tobacco mosaic virus - distinctive mosaic pattern of discolouration on the leaves.
• rose black spot - purple or black spots on the leaves, which turn yellow and drop off.
• aphids - mottled or yellow leaves, wilting snd slow growth rate. visible pests.

nitrate deficiency

• main symptom: stunted growth
• nitrates are needed to make amino acids. amino acids are needed to make protein. protein is needed for growth. so, a lack of nitrates results in stunted growth!!

magnesium deficiency

• the main symptom is chlorosis, a lack of chlorophyll, and can be seen by the plant having yellow leaves.
• magnesium is needed to make chlorophyll. a lack of chlorophyll results in yellow leaves, which can also lead to stunted growth due to less glucose being created in photosynthesis by the chlorophyll.

physical defences (reduce invasion by microorganisms) 

• cellulose cell walls
• tough waxy cuticle on leaves
• layer of dead cells around the stem which falls off (eg bark on trees)

chemical defences

• production of anti-microbial chemicals
• poisons to deter herbivores

mechanical defences

• thorns and hairs to deter animals
• leaves which droop or curl when touched
• mimicry to trick animals

monoclonal antibodies are antibodies that are specific to one binding site on one protein antigen. this means that they can only join together with one specific molecule. they are produced by making an exact copy of one particular cell.

• cells have specific antigens that are unique to that type of cell.
• antibodies have a complementary shape to the antigens so can attach to them

they are useful because they are able to target a specific chemical or specific cells in the body.

problems with monoclonal antibodies

monoclonal antibodies are not as widely used as it was hoped when they were first developed because there are far more side effects than expected. this has limited their development and use.

lymphocyte

• a type of white blood cell that only makes antibodies

myeloma cell

• a type of tumour cell that divides very quickly

hybridoma cell

an artificially produced cell, formed by joining a lymphocyte and a myeloma cell. it can make antibodies and it can divide very quickly.

1) a mouse is injected with the antigen

2) mouse lymphocytes make the specific antibody that can attach to the antigen

3) a lymphocyte is combined with a myeloma cell

4) a hybridoma cell is formed 

5) the hybridoma cell is cloned, producing many identical cells that make the specific antibody

6) large amounts of antibody are collected and purified

1. diagnosis (pregnancy tests)

2. in labs to measure levels of hormones or detect pathogens in the blood

3. in research to locate and identify specific molecules by attaching a fluorescent dye 

4. treat diseases like cancer by targeting particular drugs 

diagnosis - pregnancy testing

• reaction zone -  HCG from the urine binds to the free/ mobile monoclonal antibodies with dye attached to them.
• results window - the HCG attached to the mobile antibody travels up the stick. the HGC also binds to the immobilised antibody in the results window, which results in a coloured line (positive result)
• control zone - some mobile antibodies do not bind to the HGC. instead, they bind to antibodies in the control zone, and this results in a coloured line that shows the test is working.

treating diseases - cancer

• locating and identifying cancer cells - monoclonal antibodies are used to bind fluorescent dyes to the cancer cells so that they can be seen using scans. they bind to the unique antigens on the cancerous cell (named tumour markers) which are not found on healthy cells.
• targeting cancer cells with radioactive or toxic drugs - this helps to reduce side effects as healthy body cells do not have the tumour markers, so are unaffected by the drug
• targeting cancer cells with chemicals that stop growth and division - the drug stops growth factor from working which means the cancerous cells cannot grow as quickly. growth factor can attach to the cancerous cell, but has no effect.