A* A level biology essay 'The importance of phosphates in biology.' 6 Paragraphs written to meet the mark scheme criteria, with 957 words.
Written earlier this year so marking is accurate.
One way that phosphates are important in living organisms is their use in making chemical reactions
more likely to occur. Phosphates are a main component of ATP, along with one ribose sugar and one
adenine nitrogenous base. During the hydrolysis of ATP by ATPhydrolase a phosphate molecule and
ADP are produced. The phosphate molecule is important because it can be used to phosphorylate
other molecules which makes them more reactive. This allows molecules to react together as they
have enough energy to overcome the activation energy needed to react. An example of this process
is in aerobic respiration where substrate level phosphorylation occurs and a phosphate molecule
combines with an intermediate compound and then ADP. This converts citrate to oxaloacetate and
produces ATP.
Another way that phosphates are important is in respiration. One Phosphate ion combines with
glucose to form glucose phosphate, another phosphate ion combines with glucose phosphate to
form hexose bisphosphate. This splits into two molecules of triose phosphate. NAD is reduced to
NADH and 2 molecules of pyruvate are formed from triose phosphate producing 4 molecules of ATP.
This process is important as a net amount of 2 ATP molecules are produced. ATP is used in active
transport, an example of this is in cotransport. Where potassium ions are pumped into ileum cells
through sodium-potassium pumps and sodium ions are actively transported out of the ileum using
energy derived from ATP synthesis into the capillary. This creates a sodium ion conncentration
gradient allowing sodium ions and glucose of diffuse into the ileum. The importance of ATP
produced from phosphate molecules is emphasised here as ATP allows a supply of glucose to be
maintained from the ileum to cells in the body. The reduction of two NADH in the process is also
important as NADH is used in oxidative phosphorylation in the mitochondrial matrix to provide
protons for an electrochemical gradient to be produced and ATP to be synthesised from ADP plus Pi.
Another way that phosphates are important is in the phosphorus cycle. Phosphate ions are released
from rocks by weathering into the soil. They are then taken into the plants by roots. Mychorhizzae
greatly increase the rate at which phosphate can be absorbed, phosphates are then assimilated into
nucleotides and DNA. They are then transferred through the food chain as animals eat plants which
are eaten by other animals. Phosphate ions are lost from the animals in waste products, when plants
die saprobiants are involved in the breaking down of organic compounds releasing phosphate ions
into the soil for assimilation of plants. Animals also release phosphate ions from faceces. Weathering
of rocks also releases phosphate ions into seas, lakes and rivers. These are taken up by aquatic
producers e.g algae and are passed along the food chain to birds. Birds produce guano which acts as
a natural fertiliser. Phosphate ions are hence important here for the growth of plants, they increase
biodiversity of plants by acting as a natural fertiliser providing plants with the ions they need to
grow and hence the number of habitats for certain species of animals.
Phosphates also make up the main sugar-phosphate backbone of DNA, as one phosphate molecule is
present in a DNA nucleotide, along with a nitrogenous base, and a deoxyribose sugar. Phosphate
molecules are essential in DNA replication as DNA helicase breaks the hydrogen bonds between
bases guanine and cytosine and adenine and thymine. This causes the polynulectide strands to
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