AQA ALEVEL BIOLOGY ESSAY: THE IMPORTANCE OF THE MOVEMENT OF SUBSTANCES WITHIN LIVING ORGANISMS
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Course
AQA BIOLOGY ESSAY (7402)
Institution
UPPINGHAM SCHOOL
Top Mark AQA A-level biology essay on the importance of the movement of substances within organisms.
topics included are: the cardiac cycle, plant transport, synaptic transmission and cotransport.
Useful for revision for this specific topic and to see a sample structure of a high grade essay.
TIO THE MOVEMENT OF SUBSTANCES WITHIN LIVING ORGANISMS
The movement of blood around the body is important to provide respiring tissues
with the oxygen they require to undergo metabolic reactions such as being the
terminal electron acceptor in respiration to release ATP for energy-requiring
processes such as growth and active transport. The cardiac cycle begins with a
wave of electrical excitation from the medulla sending electrical impulses along
parasympathetic and sympathetic neurons. The impulse spreads from the sinoatrial
node across both atria causing them to contract. The atrioventricular septum is
non-conductive, so it prevents the moment of the impulse directly to the ventricles.
The wave then reaches a second group of cells called the atrioventricular node. Here
after a short delay, the AVN passes the waves of electrical activity onto the bundle of
His down the apex of the heart. The purknye tissue in the bundle of His carries the
waves of electrical activity into the muscular walls of the right and left ventricles,
causing them to contract simultaneously, from the bottom up. Without this
coordinated muscle movement, blood is not able to be pumped out of the aorta at
high pressures so aerobically respiring tissues would not revive oxygen to act as the
terminal electron acceptor in oxidative phosphorylation and will not be able to
produce as much ATP as is needed for muscle contraction via forming and breaking
actin-myosin cross bridges.
The movement of water and mineral ions in plants. Plants absorb mineral salts
needed for healthy growth such as nitrates for producing amino acids which are then
used to form proteins, as well as magnesium which is needed for chlorophyll
production. Xylem tissue transports water and mineral ions in solution, these
substances move up the plant from the roots to the leaves. Water is needed in the
xylem to provide structural integrity to the plant and water is needed in the leaves for
photosynthesis. Phloem tissue transports organic substances like sugars in solution
both up and down the plant. In the xylem, water evaporates from the leaves. This
creates tension as there is now a water potential gradient. Water molecules are
cohesive so can be pulled up the xylem as a continuous column. Water enters the
stem through the root. This movement of water is important to maintain a constant
water potential gradient so that water is an important reactant in photosynthesis. The
photolysis, light splits water into electrons, hydrogen ions and oxygen. The hydrogen
ions and electrons are used to produce ATP and NADPH needed for the Calvin cycle
(GP TO Triose Phosphate) for Triose Phosphate to then make hexose sugars.
reaction can be removed from the leaf via evaporation and water can be absorbed
from the roots. Water also needed to be transported around the plant to keep the
stem stable and upright so it could grow towards the sun and maximise the
absorption of light for the light-dependent reaction of photosynthesis. At the source
end of the phloem, sucrose from photosynthesis is actively transported by
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