0. Microbes “Investigate biological ideas relating to interactions between humans and microorganisms”
AS (Sci 1.11) Internal 4 credits Time: 6 weeks (or so)

1. MICROBE TYPES Micro-organisms are also called microbes. little
life forms
There are three main types of microbe:                
Bacteria
Fungi
Viruses
 Check out their comparative sizes...

2. If we were keeping pets….
What would this need? -

3. If we were keeping pets….
What would these need? -

4. GROWING MICROBES
Bacteria and fungi can be cultured (grown on an agar plate).
Agar is a jelly made from seaweed that has nutrients added so the microbes have plenty of food.
Nutrient agar
Petri dish
Swab
Plates can have microbes added very easily. Anything that may have been contacted by microbes can be used to inoculate (add microbes to) the plate. 4 3 1 2
We will do one control for the whole class.
You may like to inoculate your plate from more than one source. Keep track of which is which:

5. BACTERIAL STRUCTURE
Bacteria are single celled organisms, and smaller than most plant and animal cells. The are unique life forms as they have no nucleus.
Like plants, bacteria have a cell wall (lets them keep their shape).
They also have a cell membrane.
Inside is the cytoplasm.
This includes the genetic material, which may be DNA or similar.
The cell may also have plasmids, (extra bits of genetic information).
There is an outer slimy capsule, (stops it drying out).
The flagellum (tail)helps propel the wee fella about.

6. BACTERIAL REPRODUCTION
Bacteria use a process called Binary Fission…
in which they replicate their genetic information and divide into 2 new cells. 
Genetic information is copied
two bits
split
The cell begins to divide
2 bacteria are formed
This makes their growth in ideal conditions incredibly fast.

7. BACTERIAL FEEDING
Bacteria feed using a process called Extra-cellular Digestion.
In this they secrete a digestive enzyme,
which digests the food particles,
and then they absorb the nutrients. Yummy!
secrete
Food (substrate)
absorb
digest

8. COLONY GROWTH They need anything any other pet needs...
 Food (nutrition)
 Warmth (NOT “heat” – heat kills)
 Moisture
 Space to grow   
What difference does Temperature make?
From left to right the incubation temperatures of these three otherwise identically treated samples are:
         4°C, 20°C, and 28°C. 
Obviously bacteria need warmth to reproduce best.

9. FUNGI
Fungi may be single celled, like yeast, or a complex multi-cellular organism, such as a mushroom.
Bread mould is a multi- cellular fungus.
Yeast is a single cellular fungus. It is used in baking and brewing.

10. FUNGI FEEDING AND STRUCTURE
Spores
Structure:
It is made up of a Sporangium, that produces spores (for reproduction), and hyphae, which grow (like roots) into the substrate (food source).
Sporangium
Hyphae
Substrate
Hyphae
Feeding:
Fungi feed by extra-cellular digestion through their hyphae (like bacteria).
secrete
digest
absorb

11. VIRUSES Viruses are tiny, non-cellular microbes.
They are always pathogens (disease causing), because they harm other living things to reproduce.
Like all living things Bacteria and Fungi carry out MRS GREN processes.
Viruses are not really living things at all. They can’t move by themselves, they can't reproduce without other cells, they don't respire, or excrete, or feed.
Structure:
Viruses are very simple. They have genetic material (DNA or RNA) enclosed in a protective protein coat.
They may also have some apparatus to help attach to host cells.

12. VIRUS REPRODUCTION Viruses attach to a host cell,
inject their genetic information,
use host cell processes to make more copies
until the cell bursts.
In doing so they reproduce very rapidly, and destroy many host cells.
This is what causes us disease.
Viruses are so small they can only be seen using a Scanning Electron Microscope.

13. CONTROLLING MICROBES 1
Microbes can also be controlled (in foods) by using:
 Heat (e.g. Pasteurising)
 Drying (e.g. Freeze drying)
 Keeping cold – fridge/freezer
 Acid
 Salt
 Keeping microbes out
Experiment results:
Comparing the antibacterial effect of:
CuSO4 solution
Acid
Base
NaCl solution

14. CONTROLLING MICROBES 2
Pathogens can be chemically controlled by using:
 Disinfectants – strong, used on surfaces
 Antiseptics – weaker, used on skin
 Antibiotics – originally from microbes (e.g. penicillin), used internally
Experiment results:
Comparing the antibacterial effect of (at 50% dilution):
Water
Pams
Pinoclean
Jeyes

15. MICROBE WAY OF LIFE Bacteria and fungi are consumers.
This means that they feed on other things to gain their nutrition.
They are either:
Saprophytes (FEED on dead things/waste) or
Parasites (FEED on living things – a host -)
A symbiotic microbe is one that lives in harmony with its host (mutually beneficial).
Which are these?
E. coli, a bacteria naturally present in your gut, which helps to digest some nutrients.
Fungi and bacteria in a compost heap break down the organic material.
Thrush, a fungus that causes itching and discomfort.

16. RESPIRATION
Bacteria and fungi respire, like us, aerobically (with O2).
Glucose + O2
CO2 +
H2O
Energy
Unlike us, some microbes can also respire anaerobically (without O2). Their toxins (waste products) are usually more poisonous than aerobes.
Instead of making water, they may make acids, or maybe ethanol.
Energy +
H2O
CO2 O2
Glucose
Ethanol (in yeast) or
Lactic acid (in bacteria that make yoghurt) etc

17. HELPFUL MICROBES
Many bacteria and fungi do important jobs, such as breaking down (decomposing) dead matter and waste, and recycling the nutrients.
Bacteria are also important in digestion and food production (yoghurt and cheese etc).
Fungi are used in brewing and fermentation and medicines (penicillin).
Viruses are always harmful.
But they can be used for the biological control of unwanted organisms (e.g. RCD), as well as having potential medical value.

18. HARMFUL MICROBES Many microbes are pathogens (cause disease).
Your body is a great place for microbes as it is warm, moist, and there is plenty to eat.
If they flourish they cause disease. If a disease is contagious the microbe can be transferred between people or other animals such as mosquitoes, flies and rats.
The ways that bacteria and fungi cause disease are:
1.    Feeding directly on your cells, destroying them.
2.    Excreting (waste products) toxins that damage cells.
Microbes also cause harm by spoiling food.

19. DISEASES Viruses are always pathogens. Herpes A tomato virus Diseases
Bacteria
Fungi
Virus
Salmonella
Athletes foot
Chicken Pox
Tetanus
Ringworm
AIDS
Syphilis
Thrush
Colds

20. BODIES DEFENCES Your body is adapted to fight diseases:
Physical barrier – skin. Orifaces are protected by secretions: ear wax, mucous, lysosome (antiseptic) in saliva, urine, tears (also salty).
Phagocytes – White Blood Cells that engulf and destroy foreign bodies. Dead WBCs form pus.
Antibodies are formed to attach to specific antigens on the surface of pathogens. The body can “remember” how to make these so often will not get the same disease twice. This is called immunity.
Artificial immunity can be created by putting a weakened form of the disease into your body (vaccination), or by putting in pre-prepared antibodies from another animal.

21. RESISTANCE
By natural selection, microbes can adapt to be unaffected (resistant) to an antibiotic or antiseptic.
This is caused by microbes coming into contact with an antimicrobial but without being killed by it. E.g. Under-prescribed or under taken doses of antibiotics.
Resistance means that we are constantly having to develop new antibiotics.