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TOP BAND/A* AQA A Level Biology Synoptic Essay - The importance of the control of movement in cells and living organisms
marked A* syntoptic essay example -Full response for AQA Level Biology essay in paper 3
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The importance of the control of movement in cells and living organismsIn order for lipids to be absorbed from the ileum, micelles must initially move to come into
contact with the epithelial cells lining the villi and subsequently break down into monoglycerides
and fatty acids. Being non-polar, these molecules can freely diffuse through the cell surface
membrane of epithelial cells. Once inside, monoglycerides and fatty acids must move into the
endoplasmic reticulum, where they recombine, forming triglycerides. From here, triglycerides
move into the golgi apparatus to be processed and associated with cholesterol and lipoproteins,
forming chylomicrons. These chylomicrons can now move out of the cell by exocytosis. This
movement within the cell is important as it enables the formation of chylomicrons, which carry
dietary lipids from the small intestine into cells and other tissues where they can be utilised for
energy production.
Translocation refers to the movement of organic molecules (sugars) from one part of the plant
to another. At the source, sucrose is formed from photosynthesising tissue and is actively
transported into the phloem by companion cells, lowering the water potential of the phloem. It is
now important for water in the xylem to move into the phloem down the water potential gradient
by osmosis. This is because, with the increased volume of water in the phloem, the hydrostatic
pressure will also increase. Sucrose will move down the hydrostatic pressure gradient within the
phloem to the sink, where it will be unloaded. At the roots of the plant, unloaded sucrose can be
used in respiration to provide energy or converted into starch to be stored. The movement of
water and sucrose within the phloem is essential, as it supplies cells with the energy formed
during photosynthesis (in the form of sucrose). Without mass flow, this energy will never reach
other parts of the plant and will remain in the leaves where it was produced. In respiring cells,
sucrose will be converted into glucose before it enters the glycolysis pathway and enables the
production of ATP.
During DNA replication, the enzyme DNA helicase breaks the hydrogen bonds between the
complementary base pairs, causing the two strands of DNA to separate. One of these strands
will act as a template. It is important that free DNA nucleotides are able to move in order to line
up along their complementary bases on the template strand, where adenine pairs up with
thymine and cytosine pairs up with guanine. This movement of nucleotides is important as they
will subsequently form the new daughter strand, which lines up against the original parent
strand during DNA’s semi-conservative replication. Without nucleotides lining up alongside one
another, the enzyme DNA polymerase will be unable to join nucleotides in the 5’ to 3’ direction by
phosphodiester bonds in a condensation reaction. As a result, the interphase stage of the cell
cycle will not occur, and the cell will be unable to divide by mitosis to replace damaged or
worn-out tissue.
Mitosis is the process by which cells divide asexually to produce two genetically identical
daughter cells. In order for this division to occur, it is important that the chromosomes within
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