Unit 2a: Helpful or Harmful?
A decomposer is an organism (especially a soil bacterium, fungus or invertebrate) that breaks down dead or decaying organisms (e.g. in compost heaps). This process is called decomposition.
Many bacteria & fungi are decomposers. They release chemicals (nutrients) that plants can then absorb, and form an important part of the carbon & nitrogen nutrient cycles.
Decomposers release carbon from the dead matter into the atmosphere, in the form of CO2 gas. Plants then absorb the carbon dioxide gas as they manufacture food.
Decomposers return nitrogen to the atmosphere via their actions. They break down the complex nitrogen compounds in dead organisms & animal wastes, which returns simple nitrogen compounds to the soil. Plants can then use these compounds to make more nitrates. Overall, crop productivity is increased.
Nitrogen fixation is any natural or industrial process that causes free nitrogen (N2 gas in the air) to chemically combine with other compounds, and thus form compounds that are more reactive (e.g. ammonia, nitrates and nitrites).
Plants like clover have nitrogen-fixing bacteria in their roots. These bacteria carry out the above process, converting N2 gas from the air into nitrates. This also increases crop productivity.
Specialized bacteria that live in lumpy nodules on clover roots help the plant fix nitrogen from the air.
Cellulose is the main constituent of plant cell walls, and vegetables fibres such as cotton. It is an insoluble solution, and humans are incapable of digesting it.
Herbivores such as cows & pigs have cellulose-digesting bacteria in their gut. These bacteria help to break down the thick cell walls of plant tissue, thus giving the animal extra nutrition.
Optical microscope images of celluloses.
Humans have found many ways of using micro-organisms to produce foodstuffs, better crops, medical drugs and consumer products. This use of microbes for human ends is called biotechnology.
In its broadest sense, biotechnology is the commercial exploitation of living organisms or their components (e.g. proteins). Basically, it is technology that utilizes biological systems.
Yoghurt bacteria convert lactose sugar in milk to lactic acid. The lactic acid solidifies the milk into yoghurt.
The bacteria used to make yoghurt are Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius supsp. thermophilus. They are classicied as lactic acid bacteria.
Other bacteria are involved in curdling milk for cheese-making.
Pharmaceutical companies use genetically-engineered bacteria to produce chemicals for medical drugs. Special bacteria are used to produce insulin, which diabetics use to control their blood sugar levels.
Yeasts are an important group of fungi. They convert sugar into CO2 and alcohol via fermentation (a form of anaerobic respiration). Yeasts are used to make bread rise, and ferment beer & wine.
Yeast making bread rise via fermentation.
Some fungi are used to produce chemicals called antibiotics.
An antibiotic is a type of antimicrobial substance that inhibits the growth of bacteria, or destroys bacteria. Antibiotics are the most important type of antibacterial agents for fighting bacterial infections.
Some viruses are used to control pest organisms. Calicivirus (RCD) was illegally released in NZ by farmers to control rabbit populations. This use of microbes is called biological control.
Biological control (also called biocontrol) is a method of using other organisms to control pests. It relies upon natural mechanisms (e.g. predation or parasitism), and typically involves an active human management role.
A pathogen is a microbe that causes disease. Pathogens are also called infectious agents, because they cause infections.
Other microbes cause harm by damaging foodstuffs, crops and fabrics. They aren't classified as pathogens because while they do cause harm, they don't cause disease.
All viruses are pathogens. They cause many human diseases, from colds and flus to serious diseases such as polio, hepatitis B and AIDS.
Some bacterial species cause food to rot. You can see colonies of bacteria as shiny spots on meat that has gone off.
Listeria bacteria (sometimes found in shellfish) can cause food poisoning or damage foetuses.
A 3D illustration of Listeria monocytogenes, the species of pathogenic bacteria that causes the infection called listeriosis.
Different fungal species can cause make food rot (e.g. bread mould & potato blight), make fabrics go mouldy, or cause wet rot in timber.
Some species of fungus infect humans (e.g. thrush & athlete's foot).
Antiseptics and Disinfectants
An antiseptic is an antimicrobial substance that kills or inhibits the growth of micro-organisms on intact skin. An antiseptic is applied to living tissue or skin, and will reduce the possibility of infection, sepsis or putrefaction.
A disinfectant is a chemical substance that is used to destroy (or inactivate) micro-organisms on inert surfaces. Disinfectants are generally strong chemicals used around the home.
Source: Science: NCEA Level 1 (New Zealand Pathfinder series).
