5.1 - Food production Flashcards
Why do farmers use Glasshouses and polythene tunnels ?
The knowledge about limiting factors and how they affect the rate of photosynthesis can be used by farmers to improve crop yields
Growing crops outside does not allow farmers to control any of these factors
Glasshouses and polythene tunnels provide an enclosed environment in which farmers can, to some extent, control the climate inside and increase their crop yields
How do glasshouses help to increase the rate of photosynthesis?
Artificial heating (enzymes controlling photosynthesis can work faster at slightly higher temperatures -
Artificial lighting (plants can photosynthesise for longer)
Increasing carbon dioxide content of the air inside (plants can photosynthesise quicker)
Regular watering
What are the problem with glass houses?
farmers need to balance the extra cost of providing heating, lighting and carbon dioxide against the increased income
In tropical countries where temperatures are much hotter, glasshouses may still be used to control other conditions however they may need to be ventilated to release hot air and avoid temperatures rising too high, which could cause the denaturation of the enzymes controlling the photosynthesis reaction
What are the factors limiting photosynthesis
Temperature
As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes
However, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate
of reaction decreases
Light intensity
The more light a plant receives, the faster the rate of photosynthesis
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
Carbon dioxide concentration
Carbon dioxide is one of the raw materials required for photosynthesis
This means the more carbon dioxide that is present, the faster the reaction can occur
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
How can technology increase food supply?
Fertilisers - fertilisers increase the amount of key nutrients in the soil for crop plants, meaning that they can grow larger and are more healthy, which increases yields
Pesticides - these chemicals kill off unwanted insects and weed species, meaning that there is less damage done to crop plants by insects, as well as reducing competition from other plant species, which increases yields
What fertilisers can be used to increase crop yields?
Chemical fertilisers are often applied to the soil as dry granules or can be sprayed on in liquid form
They mainly provide crop plants with nitrogen, phosphorus and potassium:
Nitrogen:
Absorbed in the form of nitrates
Needed to make amino acids which are the building blocks of proteins
Lack of nitrogen causes weak growth and yellowing of the leaves of plants
Phosphorous:
Absorbed in the form of phosphates
Needed to make DNA and cell membranes
Lack of phosphorus can cause poor root growth and discoloured leaves
Potassium:
Absorbed in the form of various compounds of potassium
Allows enzyme reactions to take place to produce ATP in respiration as well as being needed for the enzymes involved in photosynthesis
Lack of potassium can cause poor growth of flowers and fruits, as well as brown spots on leaves
What affects do pests have on crop yields?
Pests such as insects and other animals can damage crops by eating them
Weeds can outcompete crop plants for space, water and soil nutrients
Fungi can infect crop plants and spread disease which can affect growth and yield
All of these can be controlled by using pesticides (chemical control) or by introducing other species (biological control)
What pesticides are used to increase crop yield?
Insecticides kill insect pests
Herbicides kill plant pests
Fungicides kill fungal pests
What are the advantages and disadvantages of pesticides?
What is biological control?
Usually, a species is introduced specifically to prey on the pest species – for example, parasitic wasps can control whitefly in glasshouse tomato crops
As they are based on a predator-prey cycle, they do not completely remove a pest, but keep it at lower levels
What can microorganisms do?
Microorganisms can be used by humans to produce foods and other useful substances
One example of this is the production of bread using yeast
Yeast is a single-celled fungus that can carry out both aerobic and anaerobic respiration
How can yeast produce bread?
When yeast carries out anaerobic respiration, it produces an alcohol (ethanol) and carbon dioxide
Yeast will respire anaerobically if it has access to plenty of sugar, even if oxygen is available
This is taken advantage of in bread making, where the yeast is mixed with flour and water
The yeast produces enzymes that break down the starch in the flour, releasing sugars that can then be used by the yeast for anaerobic respiration
The carbon dioxide produced by the yeast during anaerobic respiration is trapped in small air-pockets in the dough, causing the dough to rise (increase in volume)
The dough is then baked in a hot oven to form bread
During baking, any ethanol produced by the yeast (as a waste product of anaerobic respiration) is evaporated in the heat
This is why bread doesn’t contain any alcohol
The yeast is killed by the high temperatures used during baking
This ensures there is no further respiration by the yeast
How are bacteria useful?
Bacteria are useful because they are capable of producing complex molecules (e.g. certain bacteria added to milk produce enzymes that turn the milk into yoghurt)
They are also useful because they reproduce rapidly, meaning the amount of chemicals they can produce can also rapidly increase
How can bacteria be used to make yoghurt?
Yoghurt is made in a process that relies on the presence of a specific type of bacterium – in this case, Lactobacillus
First, all equipment is sterilised to kill other, unwanted bacteria and to prevent chemical contamination
Milk is then pasteurised (heated) at 85-95°C to kill other, unwanted bacteria
Contamination with other bacteria could slow production of the yoghurt by competing with the Lactobacillus for the lactose in the milk
It could also spoil the taste of the yoghurt
The milk is then cooled to 40-45°C and Lactobacillus bacteria is added
The mixture is incubated at this temperature for several hours, while the Lactobacillus bacteria digest milk proteins and ferment (digest) the sugar (i.e. the lactose) in the milk
The Lactobacillus bacteria convert the lactose into lactic acid and this increased acidity sours and thickens the milk to form yoghurt
This lowering of the pH also helps to prevent the growth of other microorganisms that may be harmful, so acts as a preservative
This means the yoghurt can be kept for a longer time (compared to fresh milk)
The yoghurt is then stirred and cooled to 5°C to halt the action of the Lactobacillus bacteria
Flavourings, colourants and fruit may be added before packaging
What are fermenters?
Fermenters are containers used to grow (‘culture’) microorganisms like bacteria and fungi in large amounts
These can then be used for brewing beer, making yoghurt and mycoprotein and other processes not involving food, like producing genetically modified bacteria and moulds that produce antibiotics (e.g. penicillin)
The advantage of using a fermenter is that conditions can be carefully controlled to produce large quantities of exactly the right type of microorganism
What are the fish farming methods?
