Download Plants as food, selective breeding and microorganisms causing food

Plants as food, selective breeding and microorganisms causing food spoilage
Plants are the basis of all food chains. During photosynthesis, plants use light energy and convert it into a stored,
chemical form. They absorb carbon dioxide and make carbohydrates, mostly stored as starch. They also absorb useful
nitrates from the soil, as well as other minerals, and manufacture other biological molecules. Herbivores make use of all
of these components when they consume and digest plants.
Humans are not herbivores, but are omnivores. This means that as humans, we eat animals and plants. We gain energy
directly from eating plants, and indirectly from eating herbivorous animals. The human food chain is fairly short, but by
increasing the efficiency of the food chain, we can increase food production.
Making food production more efficient in…
plants:
 increase the growth rate of crops
 increase the size of yield from each plant
 reduce losses of plants due to disease and pests
 make harvesting easier by standardising crop sizes
 improve plant responses to fertilisers
animals:
 improve the rate of growth
 increase productivity
 increase resistance to disease
The idea of breeding animals with the most desirable traits to marginalise the undesirable differences is not a new
concept. In fact, even in the time of Darwin, this idea had been implemented. He identified it as artificial selection (the
sister process of natural selection – see 5.5 Natural Selection – except using artificial selection pressures to ‘select’ the
most adapt variations of a species).
Selective breeding involves choosing a pair of animals or plants that display the most desirable characteristics. There
are three main stages in the process. The first is isolation, followed by artificial selection and then inbreeding, or line
breeding. Using selective breeding means that the offspring will have the desired characteristics.
Examples of selective breeding include farmers using cattle that have a high yield for milk or meat. Also some farmed
salmon have been selectively bred so that they grow more quickly and time-to-market has been cut as much as by 30%
A more recent technique, known as marker-assisted selection has been used, which involves using a section of DNA as
a marker to recognise the desired characteristic. Once new offspring have been produced, that marker is checked for in
their DNA, allowing selection to take place from an early age. Examples of marker-assisted selection include tomatoes
being bred with improved disease resistance: the allele for resistance against yellow leaf curl virus was identified in a
wild tomato kind and bred into a domestic variety.
Food production is also improved by the use of certain chemicals. Responses to chemicals can be bred into organisms.
Fertilisers are used to replace minerals in the soil, which may have been used by previous crops, so using fertilisers
containing nitrate, potassium and phosphate is very common in agriculture.
Often, pesticides may be used to kill pests that cause diseases in certain crops, too. Many crops are also sprayed with
fungicides to reduce fungal growth on the roots or leaves. Animals can be treated with antibiotics to treat infectious
diseases, which reduces the spread of disease among animals.
MICROORGANISMS AND FOOD
Many microorganisms obtain nutrition by digesting organic matter around them, and they leave waste behind in doing
so. We consider food to be spoilt when the effects of these actions of microorganisms is on our own food and becomes
noticeable. There are four main ways that microorganisms can spoil food:
1 visible growth of microorganisms on food, most noticeable when fungi colonies grow on our food (e.g. colonies of
the mould Penicillium on bread)
2 microorganisms which use an external digestion process, by releasing enzymes to break down the food molecules
and absorb the nutrients this releases (often causing a sweet, sugary smell as sugars are released)
www.asbiology101.wordpress.com
3 the bacterium Clostridium botulinum produces the botulism-causing toxin botulin which is present on any food
which has a colony of the bacterium living on, and as little as 1μg of the toxin can kill a human adult
4 presence of some microorganisms which cause infection (e.g. Salmonella found in poultry products)
Food spoilage is generally prevented by consuming it whilst it is still fresh. If it is to be kept for longer periods of time, it
must be treated to prevent spoilage. This is done in a wide number of ways, generally which will kill any existing
microbes on the food or stop them from reproducing. Examples include:
 cooking (high temperatures denature enzymes and proteins, killing the microorganisms)
o
o
 pasteurising (heating to 72 C for 15 seconds and then cooling rapidly to 4 C to kill any microorganisms)
 drying, salting and sugar-coating (dehydrates and kills microorganisms as water leaves cells by osmosis)
 pickling (using an acidic pH to denature enzymes and other proteins to kill microorganisms)
 irradiation (ionising radiation disrupts the DNA structure of microorganisms, which kills them)
 cooling and freezing (these actions don’t kill the microorganisms but irregulate enzyme activity, causing problems)
However, microorganisms are not all bad. For many years now they have been used to improve food production.
Examples of the usage of microorganisms to help make food include:
 yoghurt – milk that has been infected by the bacteria Lactobacillus which used lactose in milk to make lactic acid,
which causes the milk to protein and thicken; the bacteria then partially digest the yoghurt making it more easily
digestible by humans
 cheese – made from curdled milk (curd parts of the milk arise from where the Lactobacillus acts), which can have
enhanced flavours using other microorganisms, such as the Penicillium bacteria for blue cheese
 bread – made to rise using yeast, respiring anaerobically releasing bubbles of carbon dioxide which rise the bread
Much more recently is the use of single-cell proteins (proteins maid by microorganisms which are used directly as food)
and more specifically mycoproteins (those made from fungi), such as Quorn, made from the edible fungus Fusarium
venenatum, which has been marketed as a meat substitute for vegetarians and a healthier choice for non-vegetarians,
as it contains no animal fats or cholesterol unlike meat.
www.asbiology101.wordpress.com