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Section F: Crop production (Eutrophication (1) fertilisers enter the water…
Section F: Crop production
Glass Houses and polythene tunnels
In glasshouses and polythene tunnels conditions can be controlled.
This control means that all the limiting factors for plant growth can be set to the optimum conditions; (e.g. it can be set to the optimum temperature, humidity, light and CO2 concentration)
This will result in more growth, so higher yield.
Effects on crop yield
Glass houses and polythene tunnels increase the heat in the environment that crops are growing in.
Reactions happen faster when there is more heat, for example photosynthesis. Given photosynthesis produces energy that the plant needs to grow, if there is more heat there is more growth and so higher yield.
Carbon dioxide is a reactant in photosynthesis. If there is a more than enough carbon dioxide, then every plant will be able to photosynthesise as best as it can.
The more photosynthesis the more glucose, the more glucose the more energy, the more energy the more growth. Hence crop yield is increased.
minerals in plants
As well as water and sunlight, plants require mineral ions to grow.
Different mineral ions do different things:
Nitrates
- contains nitrogen for making
amino acids
and
proteins
. these are needed for cell growth. plants without this have stunted growth and yellow older leaves
Phosphates
- contain phosphorus for making
DNA
and
Cell membranes
and needed for
respiration
and
growth
. Plants without this have poor root growth and purple older leaves
Potassium
to help enzymes needed for
photosynthesis
and
respiration
. Plants without this have poor flowers and fruit and discoloured leaves
Magnesium
is needed for making chlorophyll(needed for photosynthesis). plants without this have yellow leaves
Fertiliser
farmers use fertilisers to replace missing minerals/elements to increase crop yield
Sometimes the elements that a plant needs are missing from he soil because they have been used up by previous plants
Eutrophication
1)
fertilisers
enter the water, adding
extra nutrients
2) the extra nutrients cause
algae
to
grow fast
and
block out the light
3)
plants can't photosynthesise
due to lack of light and
start to die
.
4) With more food available, microorganisms that feed on dead plants
increase in number
and
deplete all the oxygen
in the water
5) Organisms that need oxygen (e.g. fish) die
Pesticides
Pests include microorganisms, insects and mammals. pests that feed on crops are killed using various methods pest control
Pesticides are a form of
chemical pest control
. They're often poisonous to humans so the farmer must be careful to use a small amount. pesticides can also harm other wildlife
Biological control
is an alternative to using pesticides. it means using other organisms to reduce the number of pests either by encouraging wild organisms or adding new ones
the helpful organisms could be
predators
(e.g. ladybirds eat aphids),
parasites
(e.g. some flies lay there eggs on slugs which eventually kills them) or **disease-causing (e.g. bacteria against caterpillars.)
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 where introduced to Australia to eat beetles and are now a major pest