08/02/2025, 17:22 Biology Paper III Essays - Evernote
Importance of Membranes [25 Marker]
Importance of Membranes [25 Marker]
• Function of the membrane in general
• Thylakoid membrane
• Presynaptic and postsynaptic membrane
• Intermembrane space of the mitochondria
• Immune system
• Membranes in digestion – lipids
• Pacinian Corpuscle
Evidence of the importance of membranes can firstly be seen in the
fundamental purpose of the membrane itself which is to provide a separation
between the internal environments of cells and external environments around
the cells. This is vital as the environments are often very different in water, ion,
and organelle concentrations and the internal environment of the cell is
regulated by the cell-surface membrane which is made up of a phospholipid
bilayer which allows lipid-soluble, polar, and small molecules into the cell. It
prevents harmful and unwanted substances from entering and also regulates
the concentration/water potential, so the cell does not undergo lysis or
shrink/shrivel being unable to undergo its metabolic processes without enough
water. In eukaryotes the membrane also is what allows cells to recognise each
other as antigens are present on the cell-surface membrane preventing the
immune system from attacking host cells (which causes diseases such as MS
multiple sclerosis) and allows a functional immune response to occur where
the phagocytes would be chemically attracted to non-self-cells due to the
antigens displayed on the cell-surface membrane. This prevents viruses from
attacking host cells and replicating. Phagocytes also harness their cell surface
membrane as after phagocytosis occurs and they engulf the pathogen
becoming an antigen-presenting-cell allowing T helper cells to bind becoming
activated allowing the humoral response to also be activated as specific B cells
are activated and divide by clonal expansion. Membranes also isolates harmful
components/molecules in the cell (such as lysosomes which contain lysozyme
hydrolytic enzymes involved in the digestion of pathogens), and membranes
also isolate useful components such as chlorophyll in the thylakoid membrane
– another example of the importance of membranes.
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, 08/02/2025, 17:22 Biology Paper III Essays - Evernote
The thylakoid membrane join together lamellae through their thin sheets,
forming grana. The thylakoid membrane is where the light dependant reaction
in photosynthesis occurs as it contains the chlorophyll which absorbs light
energy causing the chlorophyll to become oxidised and lose electrons. The
electrons enter the electron transport chain releasing energy at each carrier
protein through a series of redox reactions. This provides energy for the
movement of protons from the stroma to the thylakoid membrane causing a
concentration gradient to be established where protons then move back into
the stroma driving the synthesis of ATP through the carrier protein ATP
synthase. The protons are also accepted by the coenzyme NADP which is
reduced to NADPH. This shows the importance of the thylakoid membrane as
this process is necessary for photosynthesis to occur and to proceed into the
light independent reaction where the ATP and NADPH is needed for GP to be
reduced to TP and TP converted to glucose or to regenerate RuBP. Therefore,
without the thylakoid membrane glucose would not be produced and plants
would not act as primary producers converting light energy -> chemical energy
in the form of glucose. This would not only effect plants individually where they
would no longer have a respiratory substrate and energy available through
respiration (ATP) for active transport, growth, and repair. It would also affect
ecosystems as a whole. More thylakoid membrane means increased SA for
photosynthesis and increased rate of the light independent reaction therefore
more glucose. This would mean that plants are more competitive and would
grow large and bigger with more leaves providing ecosystems with more food,
habitats, and species. Without the thylakoid membrane biodiversity would
decrease and due to the interconnected nature of the food chains the number
of species present would also decrease. Thylakoid membranes are additionally
important as they contain ribosomes and proteins allowing the plants to
produce any necessary reactants for the light dependant stage. They also have
a large SA and are directly surrounded by the stroma allowing NADPH and ATP
to diffuse into the stroma for further reactions in the Calvin cycle.
The presynaptic and postsynaptic membrane are further examples of the
importance of membranes, specifically in nervous coordination. It ensures that
action potentials are unidirectional and non-overlapping as the presynaptic
membrane can only release neurotransmitters while the post synaptic
membrane only has receptors for the neurotransmitters to bind to. This occurs
as an action potential arrives in the presynaptic membrane causing the voltage
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Importance of Membranes [25 Marker]
Importance of Membranes [25 Marker]
• Function of the membrane in general
• Thylakoid membrane
• Presynaptic and postsynaptic membrane
• Intermembrane space of the mitochondria
• Immune system
• Membranes in digestion – lipids
• Pacinian Corpuscle
Evidence of the importance of membranes can firstly be seen in the
fundamental purpose of the membrane itself which is to provide a separation
between the internal environments of cells and external environments around
the cells. This is vital as the environments are often very different in water, ion,
and organelle concentrations and the internal environment of the cell is
regulated by the cell-surface membrane which is made up of a phospholipid
bilayer which allows lipid-soluble, polar, and small molecules into the cell. It
prevents harmful and unwanted substances from entering and also regulates
the concentration/water potential, so the cell does not undergo lysis or
shrink/shrivel being unable to undergo its metabolic processes without enough
water. In eukaryotes the membrane also is what allows cells to recognise each
other as antigens are present on the cell-surface membrane preventing the
immune system from attacking host cells (which causes diseases such as MS
multiple sclerosis) and allows a functional immune response to occur where
the phagocytes would be chemically attracted to non-self-cells due to the
antigens displayed on the cell-surface membrane. This prevents viruses from
attacking host cells and replicating. Phagocytes also harness their cell surface
membrane as after phagocytosis occurs and they engulf the pathogen
becoming an antigen-presenting-cell allowing T helper cells to bind becoming
activated allowing the humoral response to also be activated as specific B cells
are activated and divide by clonal expansion. Membranes also isolates harmful
components/molecules in the cell (such as lysosomes which contain lysozyme
hydrolytic enzymes involved in the digestion of pathogens), and membranes
also isolate useful components such as chlorophyll in the thylakoid membrane
– another example of the importance of membranes.
https://www.evernote.com/client/web#/notebook/6023ecd6-5695-e5af-51bd-423d67e1dfa4/note/6ba24857-8b48-ba90-166a-825ccc7b6ea4 1/5
, 08/02/2025, 17:22 Biology Paper III Essays - Evernote
The thylakoid membrane join together lamellae through their thin sheets,
forming grana. The thylakoid membrane is where the light dependant reaction
in photosynthesis occurs as it contains the chlorophyll which absorbs light
energy causing the chlorophyll to become oxidised and lose electrons. The
electrons enter the electron transport chain releasing energy at each carrier
protein through a series of redox reactions. This provides energy for the
movement of protons from the stroma to the thylakoid membrane causing a
concentration gradient to be established where protons then move back into
the stroma driving the synthesis of ATP through the carrier protein ATP
synthase. The protons are also accepted by the coenzyme NADP which is
reduced to NADPH. This shows the importance of the thylakoid membrane as
this process is necessary for photosynthesis to occur and to proceed into the
light independent reaction where the ATP and NADPH is needed for GP to be
reduced to TP and TP converted to glucose or to regenerate RuBP. Therefore,
without the thylakoid membrane glucose would not be produced and plants
would not act as primary producers converting light energy -> chemical energy
in the form of glucose. This would not only effect plants individually where they
would no longer have a respiratory substrate and energy available through
respiration (ATP) for active transport, growth, and repair. It would also affect
ecosystems as a whole. More thylakoid membrane means increased SA for
photosynthesis and increased rate of the light independent reaction therefore
more glucose. This would mean that plants are more competitive and would
grow large and bigger with more leaves providing ecosystems with more food,
habitats, and species. Without the thylakoid membrane biodiversity would
decrease and due to the interconnected nature of the food chains the number
of species present would also decrease. Thylakoid membranes are additionally
important as they contain ribosomes and proteins allowing the plants to
produce any necessary reactants for the light dependant stage. They also have
a large SA and are directly surrounded by the stroma allowing NADPH and ATP
to diffuse into the stroma for further reactions in the Calvin cycle.
The presynaptic and postsynaptic membrane are further examples of the
importance of membranes, specifically in nervous coordination. It ensures that
action potentials are unidirectional and non-overlapping as the presynaptic
membrane can only release neurotransmitters while the post synaptic
membrane only has receptors for the neurotransmitters to bind to. This occurs
as an action potential arrives in the presynaptic membrane causing the voltage
https://www.evernote.com/client/web#/notebook/6023ecd6-5695-e5af-51bd-423d67e1dfa4/note/6ba24857-8b48-ba90-166a-825ccc7b6ea4 2/5
