GREENHOUSES Flashcards
Why you should not increase temperature in a greenhouse on a dull day
Temperature increases rate of respiration too, therefore the rate of photosynthesis will be too low to replace respiratory losses
Not cost effective
Why yield of crop grown in greenhouse in winter is lower than in summer when enhancing conditions not applied
Lower light intensity limits photosynthesis
Lower light duration limits photosynthesis
Lower temperature limits photosynthesis
How conditions are enhanced
Carbon Dioxide enhanced by burning oil/combustion/manure
Heat enhanced by using heater
Light enhanced by light left on for extra hours
Fertilisers (contain nitrogen) enhanced by regularly application
Farming Practises which increase the productivity of crops
Fertilisers added to soil
Pesticides applied
Selective breeding used
Genetic modification
Ploughing aerates soil and allows nitrification
Crop rotation increases soil nutrients
Irrigation removes the limiting factor of water
Covers and netting protects against birds
Advantages of Inorganic/Artificial fertilisers
Increases yields Replaces ions taken in by crop Ions in readily available form Effects relatively rapid Easy to apply
Disadvantages of Inorganic/Artificial
Quickly leached More likely to cause pollution Relatively expensive Production is energy consuming Fertiliser lowers soil water potential Decreases potential gradient between plant and soil therefore water cannot diffuse from soil into plant via osmosis WHEREAS... Natural fertilisers contain a wide range of elements Natural fertilisers aerate the soil
Why water is needed in soil for plants
To allow stomata to open which then allows CO2 absorption
Advantages of Insecticides (chemical control)
In pests such as weed, removal of weed actually leads to less competition
If it is very low toxicity, it will not affect humans
Acts quickly
Can be applied to specific area
Kills greater variety of pests
Plants with large surface area to volume ratio are easily affected by pesticides as there is a shorter diffusion pathway
disadvantages of Insecticides (chemical control)
Not all plants may be sprayed Some spray may wash of plants Pest may become resistant (grow immune to pesticide) Bioaccumulation Kills beneficial organisms Enters food chain Residue is left on crop
How a pest becomes resistant
There is variation in the pest population
Mutation occurs
This produces the allele giving resistance
There is a selection pressure for this gene
Therefore pests with this gene breed
This leads to an increased frequency of surviving allele
SYSTEMIC INSECTICIDE
Insecticides absorbed by plants allowing plant tissues to kill insects feeding on them
Advantages of Systemic Insecticide
Only affects an insect that eats plant (specific)
Insecticide is not diluted which reduces the amount needed
Insecticide does not cause eutrophication
Advantages of making Genetically Modified Crops against pests
More effective than other methods
Poisons may harm other
Prevent spread of disease
Economic benefit to farmer
Disadvantages of making Genetically Modified Crops against pests
Plasmid may enter another species
May sterilise other species
Disruption of food chain
Why there may be Chemical Pesticides in bodies of other organisms other than the pest
Insect may eat a high number of pests which have been affected by the Chemical Pesticide
The insect cannot break down the chemical, therefore it remains in the insect’s body
Advantages of biological control
If well trained, it will only attack the pests, i.e. specific
Only one application is required and is therefore cheaper
Safer as it does leave chemical residue
Pests do not become resistant
Application linked to life cycle of pest
Maintains low level of pest
Can be used in organic farming
Disadvantages of biological control
You do not completely remove pest Can only be used for glasshouse crops There is a cost of researching It may become a pest itself May attack non-target species It is slower than chemical control It is more subject to environmental factors Difficulty in maintaining population of predator Cost of predator
In Biological Control you must
Study effect of predator on other organisms in laboratory; may outcompete native species or may attack them
Release large number of predators; increases chance of successful introduction so that damage to crops is little
Ensure stable coexistence of predator and pest at low population densities; no further introduction required
Benefits of an Integrated Pest Management Scheme
If one method fails, the other is still partially effective
Reduced amounts of pesticides needed
Increases yield
Less chance of resistance
Less effect on food webs
Chemical controls initial surges in pest numbers whilst biological gives longer term control of pests
