Section 5: Use of biological resources
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a) Food production
5.1: Describe how glasshouses and polythene tunnels can be used to increase the yield of certain crops
Photosynthesis can be helped along by artificially creating the ideal conditions in glasshouses or polytunnels.
Photosynthesis can be helped along by artificially creating the ideal conditions in glasshouses or polytunnels.
- Keeping plants enclosed in a glasshouse makes it easier to keep them free from pests and diseases.
- Commercial farmers often supply artificial light after the sun goes down to give their plants more time to photosynthesize.
- Glasshouses trap the sun's heat to keep the plants warm. In winter, a farmer might also use a heater to keep the temperature at the ideal level.
- Farmers can also increase the level of carbon dioxide in glasshouses, for example, by using a paraffin heater to heat the place. As the paraffin burns, it makes carbon dioxide as a by-product.
- By increasing the temperature and carbon dioxide concentration, as well as the amount of light available, a farmer can increase the rate of photosynthesis for his or her plants. This means the plants will grow faster and bigger - and crop yields will be higher.
5.2: Understand the effects on crop yield of increased carbon dioxide and increased temperature in glasshouses
A plant's rate of photosynthesis can be affected by the amount of carbon dioxide and the temperature. Since plants have to photosynthesize in order to make food for themselves in order to grow, these two factors can be controlled in order to maximize crop yield.
A plant's rate of photosynthesis can be affected by the amount of carbon dioxide and the temperature. Since plants have to photosynthesize in order to make food for themselves in order to grow, these two factors can be controlled in order to maximize crop yield.
5.3: Understand the use of fertilizer to increase crop yield
- Plants need certain elements, e.g. nitrogen, potassium and phosphorus, so they can make important compounds like proteins.
- If plants don't get enough of these elements, their growth and life processes are affected.
- Sometimes these elements are missing from the soil because they've been used up by a previous crop.
- Farmers use fertilizers to replace these missing elements or provide more of them. This helps to increase the crop yield.
5.4: Understand the reasons for pest control and the advantages and disadvantages of using pesticides and biological control with crop plants
- Pests include microorganisms, insects and mammals. Pests that feed on crops are killed using various methods of pest control. This means fewer plants are damaged or destroyed, increasing crop yield.
- Pesticides are a form of chemical pest control. They're often poisonous to humans, so they must be used carefully to keep the amount of pesticide in food below a safe level. Some pesticides also harm other wildlife.
- Biological control is an alternative to using pesticides. It means using other organisms to reduce the numbers of pests, either by encouraging will organisms or adding new ones.
- The helpful organisms could be predators, parasites or disease-causing.
- Biological control can have a longer-lasting effect than spraying pesticides and be less harmful to wildlife. But introducing new organisms can cause problems - e.g. cane toads were introduced to Australia to eat beetles, but they are now a major pest themselves because they poison the native species that eat them.
5.5: Understand the role of yeast in the production of beer
Yeast is a very useful microorganism. When yeast respires aerobically, it turns sugar into carbon dioxide. But when there isn't enough oxygen, yeast respires anaerobically, turning sugar into carbon dioxide and alcohol - we use anaerobically respiring yeast to make beer.
Yeast is a very useful microorganism. When yeast respires aerobically, it turns sugar into carbon dioxide. But when there isn't enough oxygen, yeast respires anaerobically, turning sugar into carbon dioxide and alcohol - we use anaerobically respiring yeast to make beer.
- Firstly, the sugar needs to be extracted from the grain. Beer is made from grain - usually barley. The barley grains are allowed to germinate for a few days, during which the starch in the grains is broken down to sugar by enzymes. Then the grains are dried in a kiln. This is called malting. The malted grain is mashed up and water is added to produce a sugary solution with lots of bits in it. This is then sieved to remove the bits. Hops are added to the mixture of give the beer its bitter flavor.
- Yeast is added and the mixture is incubated. The yeast ferments the sugar into alcohol. The fermenting vessels are designed to stop unwanted microorganisms and air getting in. The rising concentration of alcohol in the fermentation mixture due to anaerobic respiration eventually starts to kill the yeast. As the yeast dies, fermentation slows down. Different species of yeast can tolerate different levels of alcohol. Some species can be used to produce strong beer with a high concentration of alcohol.
- The beer is drawn off through a tap. Sometimes chemicals called clarifying agents are added to remove particles and make it clearer.
- The beer is then pasteurized - heated to kill any yeast left in the beer and completely stop fermentation. Beer tastes better is it's unpasteurized and aged in the right conditions. But big breweries pasteurize it because there's a risk unpasteurized beer will spoil if it's not stored in the right conditions after it's sold. Finally the beer is casked and ready for sale.
5.6: Describe a simple experiment to investigate carbon dioxide production by yeast, in different conditions
You can do experiments to investigate how the rate of carbon dioxide production by yeast changes under different conditions.
The example looks at how the temperature affects the rate, but the basic idea would be the same whatever variable is being investigated. For example, the concentration of sugar could be varied and the temperature of the water bath could be kept the same. The experiment could also be altered to give more accurate results using a gas syringe to measure the volume of carbon dioxide released.
You can do experiments to investigate how the rate of carbon dioxide production by yeast changes under different conditions.
- Mix together some sugar, yeast and distilled water, then add the mixture to a test tube.
- Attach a bung with a tube leading to a second test tube of water.
- Place the tube containing the yeast mixture in a water bath at a certain temperature.
- Leave the tube to warm up a bit and then count how many bubbles are produced in a given period of time. Use this to calculate the rate of carbon dioxide production.
- Repeat the experiment with the water bath set at different temperatures.
- Respiration is controlled by enzymes - so as the temperature increases, the rate of respiration increases, until the optimum temperature is reached.
The example looks at how the temperature affects the rate, but the basic idea would be the same whatever variable is being investigated. For example, the concentration of sugar could be varied and the temperature of the water bath could be kept the same. The experiment could also be altered to give more accurate results using a gas syringe to measure the volume of carbon dioxide released.
At yeast it's an easy experiment!
5.7: Understand the role of bacteria (Lactobacillus) in the production of yogurt
Fermentation is when microorganisms break sugars down to release energy - usually by anaerobic respiration. Yogurt is basically moldy, clotted milk that is made by fermentation:
Fermentation is when microorganisms break sugars down to release energy - usually by anaerobic respiration. Yogurt is basically moldy, clotted milk that is made by fermentation:
- The equipment is sterilized to kill off any unwanted organisms
- The milk is pasteurized (heated up to 72°C for 15 seconds) to kill off any harmful microorganisms. Then the milk is cooled
- Lactobacillus bacteria are added, and the mixture is incubated (heated to about 40°C) in a vessel called a fermenter
- The bacteria ferment the lactose sugar in the milk to form lactic acid
- Lactic acid causes the milk to clot, and solidify into yogurt
- Finally, flavors and colors are sometimes added and the yogurt is packaged
5.8: Interpret and label a diagram of an industrial fermenter and explain the need to provide suitable conditions in the fermenter
- Microorganisms can be used to make really useful stuff like penicillin or insulin
- In industry, microorganisms are grown in large containers called fermenters. The fermenter is full of liquid 'culture medium' in which microorganisms can grow and reproduce
- The conditions inside the fermentation vessels are kept at the optimum levels for growth - this means the yield of products form the microorganisms can be as big as possible
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- If the microorganisms need oxygen for respiration, it's added by pumping in sterile air. This increases the product yield because microorganisms can always respire to provide energy for growth.
- Microorganisms are kept in contact with fresh medium by paddles that agitate the medium around the vessel. This increases the product yield because microorganisms can always access the nutrients needed for growth.
5.9: Explain the methods which are used to farm large numbers of fish to provide a source of protein
Fish can be farmed in cages in the sea:
Fish can be farmed in tanks too. Freshwater fish like carp can be farmed in ponds or indoors in tanks where conditions can be controlled. This is especially useful for controlling the water quality.
Fish can be farmed in cages in the sea:
- The fish are kept in cages in the sea to stop them from using as much energy swimming about
- The cage also protects them from interspecific predation (being eaten by other animals like birds or seals)
- They're fed a diet of food pellets that's carefully controlled to maximize the amount of energy they get. The better the quality the food is, the quicker and bigger the fish will grow.
- Young fish are reared in special tanks to ensure as many survive as possible
- It's important to keep younger fish separate from bigger fish, and to provide regular food - this makes sure that the bigger fish don't eat the little ones. This is intraspecific predation - where organisms eat individuals of the same species.
- Fish kept in cages are more prone to disease and parasites. One pest is sea lice, which can be treated with pesticides which kill them. To avoid pollution from chemical pesticides, biological pest control can be used instead, e.g. a small fish called a wrasse eats the lice off the backs of the fish being farmed
- The fish can be selectively bred to produce less aggressive, faster-growing fish
Fish can be farmed in tanks too. Freshwater fish like carp can be farmed in ponds or indoors in tanks where conditions can be controlled. This is especially useful for controlling the water quality.
- The water can be monitored to check the temperature, pH and oxygen level is okay.
- It's easy to control how much food is supplied and give exactly the right sort of food.
- The water can be removed and filtered to get rid of waste food and fish poo. This keeps the water clean for the fish and avoids pollution wherever the water ends up.
b) Selective breeding
5.10: Understand that plants with desired characteristics can be developed by selective breeding
Plants are selectively bred to develop the best features, which are things like:
Selective breeding can increase crop yield:
Plants are selectively bred to develop the best features, which are things like:
- Maximum yield of grain
- Good health and disease resistance
- Attractive flowers, nice smell, etc.
Selective breeding can increase crop yield:
- Selective breeding can be used to combine two different characteristics
- Tall wheat plants have a good grain yield but are easily damaged by wind and rain. Dwarf wheat plants can resist wind and rain but have a lower grain yield.
- These two types of wheat plant were cross-bred, and the best resulting wheat plants were cross-bred again. This resulted in a new variety of wheat combining the good characteristics - dwarf wheat plants which could resist bad weather and had a high grain yield.
5.11: Understand that animals with desired characteristics can be developed by selective breeding
Animals are selectively bred to develop the best features, which are things like:
Animals are selectively bred to develop the best features, which are things like:
- Good health and disease resistance
- Good qualities like temperament, speed, fertility, good mothering skills, etc.
- Cows can be selectively bred to produce offspring with, e.g. a high meat yield
- First, the animals with characteristics that will increase meat yield (e.g. the larges cows and bulls) are selected and bred together
- Next, the offspring with the best characteristics (e.g. the largest) are selected and bred together
- If this is continued over several generations, cows with very large meat yields can be produced
c) Genetic engineering
5.12: Describe the use of restriction enzymes to cut DNA at specific sites and ligase enzymes to join pieces of DNA together
Enzymes can be used to cut up DNA or join DNA pieces together:
Enzymes can be used to cut up DNA or join DNA pieces together:
- Restriction enzymes recognize specific sequences of DNA and cut the DNA at these points
- Ligase enzymes are used to join two pieces of DNA together
- Two different bits of DNA stuck together are known as recombinant DNA
5.13: Describe how plasmids and viruses can act as vectors, which take up pieces of DNA, then insert this recombinant DNA into other cells
A vector is something that's used to transfer DNA into a cell. There are two sorts - plasmids and viruses:
Here's how genetic engineering works:
A vector is something that's used to transfer DNA into a cell. There are two sorts - plasmids and viruses:
- Plasmids are small, circular molecules of DNA that can be transferred between bacteria
- Viruses insert DNA into the organisms they infect
Here's how genetic engineering works:
- The DNA you want to insert is cut out with a restriction enzyme. The vector DNA is then cut open using the same restriction enzyme
- The vector DNA and the DNA you're inserting are mixed together with ligase enzymes
- The ligases join the two pieces of DNA together to produce recombinant DNA
- The recombinant DNA (i.e. the vector containing new DNA) is inserted into other cells, e.g. bacteria
- These cells can now use the gene you inserted to make the protein you want
5.14: Understand that large amounts of human insulin can be manufactured from genetically modified bacteria that are grown in a fermenter
Genetically modified bacteria containing the gene for human insulin can be grown in huge numbers in a fermenter to produce insulin for people with diabetes.
Genetically modified bacteria containing the gene for human insulin can be grown in huge numbers in a fermenter to produce insulin for people with diabetes.
5.15: Evaluate the potential for using genetically modified plants to improve food production
- Crops can be genetically modified to increase food production in lots of different ways - one is to make them resistant to insects, another is to make them resistant to herbicides (chemicals that kill plants)
- Making crops insect-resistant means farmers don't have to spray as many pesticides so wildlife that doesn't eat the crop isn't harmed. It also increases crop yield, making more food.
- Making crops herbicide-resistant means farmers can spray their crops to kill weeds, without affecting the crop itself. This can also increase crop yield.
- There are concerns about growing genetically modified crops though. One is that transplanted genes may get out into the environment. For example, a herbicide resistance gene may be picked up by weeds, creating a new 'superweed' variety. Another concern is that genetically modified crops could adversely affect food chains - or even human health.
- Some people are against genetic engineering altogether - they worry that changing an organism's genes might create unforeseen problems - which could then get passed on to future generations.
5.16: Recall that the term 'transgenic' means the transfer of genetic material from one species to a different species
Bacteria that contain the gene for human insulin are transgenic - this means that they contain genes transferred from another species. You can get transgenic animals and plants too.
Bacteria that contain the gene for human insulin are transgenic - this means that they contain genes transferred from another species. You can get transgenic animals and plants too.
d) Cloning
5.17: Describe the process of micropropagation (tissue culture) in which small pieces of plants (explants) are grown in vitro using nutrient media
Plants can be cloned form existing plants using a technique called micropropagation (tissue culture):
Plants can be cloned form existing plants using a technique called micropropagation (tissue culture):
- A plant with desirable characteristics (e.g. large fruit or pretty flowers) is selected to be cloned. Small pieces (called explants) are taken from the tips of the stems and the side shoots of this plant.
- The explants are sterilized to kill any microorganisms.
- The explants are then grown in vitro - this means that they're placed in a petri dish containing a nutrient medium. The medium has all the nutrients the explants need to grow. It also contains growth hormones.
5.18: Understand how micropropagation can be used to produce commercial quantities of identical plants (clones) with desirable characteristics
- Cells in the explants divide and grow into a small plant. If large quantities of plants are required (e.g. to sell), further explants can be taken from these small plants, and so on until enough small plants are produced.
- The small plants are taken out of the medium, planted in soil and put into greenhouses - they'll develop into plants that are genetically identical to the original plant - so they share the same characteristics.
5.19: Describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep
The first mammal to be successfully cloned from an adult cell was a sheep called "Dolly" in 1996. This is the method that was used to produce Dolly:
The first mammal to be successfully cloned from an adult cell was a sheep called "Dolly" in 1996. This is the method that was used to produce Dolly:
- The nucleus of a sheep's egg cell was removed, creating an enucleated cell (i.e. a cell without a nucleus).
- A diploid nucleus (with a full set of paired chromosomes) was inserted in its place. This was a nucleus form a mature udder cell of a different sheep.
- The cell was stimulated by an electric shock so that is started dividing by mitosis, as if it was a normal fertilized egg.
- The dividing cell was implanted into the uterus of another sheep to develop until it was ready to be born.
- The result was Dolly, a clone of the sheep that the udder cell came from.
5.20: Evaluate the potential for using cloned transgenic animals, for example to produce commercial quantities of human antibodies or organs for transplantation
There are many possible uses for transgenic animals:
There are many possible uses for transgenic animals:
- Animals that can produce medicines in their milk could be cloned. Researchers have managed to transfer human genes that produce useful proteins into sheep and cows, for example human antibodies used in therapy for illnesses like arthritis, some types of cancer and multiple sclerosis.
- Animals that have organs suitable for organ transplantation into humans could be developed by genetic engineering then cloned in the same way.
- The main benefits of cloning are that the useful genetic characteristics are always passed on - this doesn't always happen with breeding. Farmers also don't have to wait until the breeding season, and infertile animals can be cloned.
- But there are risks too. There's evidence that cloned animals might not be as healthy as normal ones. Embryos formed by cloning from adult cells often don't develop normally.
- Cloning is also a new science and it might have consequences that we're not yet aware of. At the moment it's also difficult, time-consuming and expensive.