CROP PLANTS (5.1 – 5.4)
5.1 – Describe how glasshouses and polythene tunnels can be used to increase the yield
of certain crops.
– Conditions in glasshouses and polythene tunnels can be controlled.
– This means that all the limiting factors for plant growth can be set to the optimum
conditions, thus resulting in higher growth and yield.
5.2 – Understand the effects on crop yield of increased carbon dioxide and increased
temperature in glasshouses.
– Glasshouses and polythene tunnels increase the heat in the environment that crops
are growing in.
– Photosynthesis occur faster when there is more heat and carbon dioxide.
– As a result, more glucose is produced, thus more energy and growth, and increased
crop yield.
5.3 – Understand the use of fertiliser to increase crop yield.
– Fertilisers contain minerals (see 2.21) that plants require to grow (e.g. NPK fertiliser).
5.4 – Understand the reasons for pest control and the advantages and disadvantages of
using pesticides and biological control with crop plants.
– Pesticide: A chemical that kills the pest, but not the crop plant.
• Advantages: Fast and accurate, with almost instant results.
• Disadvantages: Bioaccumulation in food chains; harm other organisms; pest may
become immune; may cause eutrophication.
– Biological control: Introducing a predator into the environment to eat the pest but not
the crop plant.
• Advantages: No need for chemical pesticides; cheap and self-regulating.
• Disadvantages: It may not eat the pest and eat useful species; may increase out of
control.
MICRO-ORGANISMS (5.5 – 5.8)
5.5 – Understand the role of yeast in the production of beer.
C6H12O6 → 2C2H5OH + 2CO2
– Yeast converts glucose to ethanol and carbon dioxide during anaerobic respiration in a
fermenter.
5.6 – Describe a simple experiment to investigate carbon dioxide production by yeast, in
different conditions.
– Have a test tube of yeast in glucose solution.
– Put a layer of oil on top of the test tube to keep conditions anaerobic (i.e. prevent
oxygen from entering the tube).
– Put the test tube in a water bath and heat the water to vary the temperature.
– Collect gas coming off in a tube.
5.7 – Understand the role of bacteria (Lactobacillus) in the production of yoghurt.
MAKING YOGHURT
– Heat the milk to 80℃.
• The milk is heated to 80℃ to pasteurise it and kill pathogenic microorganisms.
– Leave the milk to cool down to 46℃.
• To denature enzymes but avoid killing lactobacillus and allow it to work at the
optimum temperature.
– Add lactobacillus bulgaricus to change the milk into yoghurt.
• The lactobacillus respires anaerobically.
– Leave in a warm place for 8 hours.
• Allows lactobacillus to make lactic acid over time, as well as encourage bacterial
reproduction and enzymes to work at an optimum temperature.
• The pH is lowered and this kills lactobacillus as well as denature the enzymes.
5.8 – Interpret and label a diagram of an industrial fermenter and explain the need
to provide suitable conditions in the fermenter, including aseptic precautions,
nutrients, optimum temperature and pH, oxygenation and agitation, for the growth
of micro-organisms.
– The stirring paddles turns the blades and evenly distributes the mixture.
• Temperature / heat, concentration of substance and oxygen are evenly
distributed by stirring paddles.
– The fermenter is cooled by water flowing within the water jacket.
– The temperature and pH are monitored by temperature and pH probes.
• The fermenter can be adjusted to optimum conditions to allow enzymes to work at
a fastest rate.
– The air inlet allows oxygen to enter the fermenter.
• Oxygen is needed for the micro-organisms to respire aerobically.
– An agitator makes the air into very small bubbles; this means they have a larger
surface area and can dissolve easily, so there is better access to oxygen for
microorganisms.
– Aseptic (disinfected) conditions are needed.
• This prevents the contamination of the wanted product, and prevents other
microorganisms from using up nutrients and oxygen.
– Nutrients are needed in the fermenter so the microorganism can grow.
FISH FARMING (5.9)
5.9 – Explain the methods which are used to farm large numbers of fish to provide a
source of protein, including maintenance of water quality, control of intraspecific and
interspecific predation, control of disease, removal of waste products, quality and
frequency of feeding and the use of selective breeding.
– Water is filtered to maintain water quality (removal of microorganisms, faeces etc).
• Also, if the water is cleaned regularly the spread of disease is minimised and the
oxygen levels can maintain the respiration of the fish.
– Intraspecific predation is competition within a species.
• This can be stopped by separating fish of different ages, separating fish of different
genders, giving fish adequate room.
Interspecific predation is competition between species.
• This can be stopped by fencing the area the fish are in, putting nets around the area
the fish are in, keeping the fish in inside tanks.
– To minimise spread of disease, water should be changed regularly and their
surroundings sterilised often.
• Water is sterilised by adding antibiotics, and the spread of disease minimised by
removing dead or infected fish.
– Waste can be removed by changing the water in a tank or changing the nets.
– Fish need to be fed frequently in small amounts, this is so they don’t starve and
ensures that there is no wasted food (which could cause a decrease in water quality).
• It is important to feed fish food with nutrients (proteins) for growth, as well as add
hormones to increase their growth.
– Selective breeding can ensure that farmers produce fish with desired characteristics
by letting only the fish with the desired characteristics breed and pass on the gene.