Slides in this set
Fungi develop a symbiotic relationship with plant roots. This is called
micorrhizae. This symbiotic relationship helps the plant, as fungi is
made up of thin strands called hyphae that increase surface area
for more water and nutrients to be absorbed by the plant, and fungi
as it gets organic compounds such as glucose from the plant.…read more
Lets start the nitrogen cycle from a plant. The plant can either die or get eaten by
a consumer. This consumer produces waste or can die. Either way waste is
still going to be made. Decomposers such as saprobionts takes the nitrogen
containing compounds such as amino acids and DNA and changes them
into ammonium ions (NH4+) by ammonification. Two types of nitrifying
bacteria are involved in the next stage called nitrification. This involves one
type changing NH4+ into nitrites and the other to change the nitrites into
nitrates. This is so some of the nitrates can be absorbed by the plant as
nutrients. Denitrifying bacteria changes some of the nitrates into N2 by
denitrification. Nitrogen-fixing bacteria that are free in the soil and in root
nodules of plants convert some of the N2 into NH4+ so that it can be taken to
next stages of the nitrogen cycle.
As part of AQA, the species of each type of bacteria does not need to be known.
However the role of saprobionts needs to be known: Saprobionts secrete
enzymes that digest the food externally and then take up the nutrients. This
is known as extracellular digestion. The nutrients that are taken up are
inorganic ions from organic compounds that have been broken down.…read more
Phosphate ions are released from rocks into the soil by weathering which are
then taken up by plants. The symbiotic relationship known as micorrhizae
increase surface area to increase the rate of the phosphates being
assimilated (phosphate ions being absorbed and then used to make
complex molecules). Phosphate ions are then transferred into consumers
and are lost in waste products. Saprobionts release phosphate ions from
dead organisms and waste products for plants to use for assimilation.
As well as on land, phosphate ions are released by the weathering of rocks into
the oceans and are taken up by aquatic plants such as algae. This is
passed along the food chain to fish and then to birds. Waste produced by
birds (called guano) contains a lot of phosphate ions for soils particularly
near the coastal areas. This is the reason why guano is often used as a
natural fertiliser.…read more
Why are fertilisers used?
Crops being harvested and the removal of livestock reduces the mineral content
of the soil.
Crops that are harvested have taken up phosphate ions and nitrate ions from the
soil. They are not left to die and be decomposed by saprobionts and other
decomposers in the place they were grown. This means that the nutrients
are not returned back to the nitrogen cycle and phosphorus cycle.
Likewise with animals, they eat plants that are on a plot of land and are taken
away to another location to be slaughtered meaning that the ions are not
replaced back into the soil.
Using fertilisers replaces the minerals lost in the soil so more energy from the
ecosystem can be used for growth, increasing the efficiency of energy
Types of fertilisers
Artificial fertilisers are inorganic where they contain chemicals such as
ammonium nitrate in the form of pellets and powders.
Natural fertilisers are organic matter which include manure, composed
vegetables, crop residues (parts of plants left after harvest) and sewage
The use of fertilisers raises issues about the condition that it leaves on the