Biology Essay Importance questions with
complete solutions 2025.
1.3 Phospholipids (and 2.1) - ANSWER: Phosphate heads of phospholipids are charged
--> hydrophilic --> can interact with water. This means that a bilayer is formed with the
hydrophobic fatty acid tails on the inside and the phosphate heads on the outside.
Allows the membrane to be in contact with the contents of the cell and the tissue fluid
around the cell.
Creates a barrier which controls which substances can pass through - allowing there to
be different concentrations of substances either side of the membrane.
1.4.2 Enzymes - ANSWER: Enzymes lowers the activation energy of reaction so that
reactions are able to occur at an organisms' body temperature (which is a lower
temperature than would be the case without an enzyme).
The shape of an active site being complementary to just one substrate means that
specific reactions can be catalysed and controlled.
Inhibitors are important because they allow regulation of rate of enzyme catalysed
reactions, e.g. in end product inhibition the product of the reaction can act as a non-
competitive inhibitor and bind to the enzyme, changing its tertiary structure so the active
site can no longer become complementary to the substrate, so the reaction no longer
takes place. This means that when there is too much product the reaction will be slowed
down, but when there is less product the reaction will take place faster.
1.5.2 DNA replication - ANSWER: The nitrogenous bases are important because there
is complementary base pairing between them. This means it is possible for identical
copies of DNA to be made using the original strands as templates (according to the
semi-conservative model).
So daughter cells can be genetically identical as parent cells (in order for tissue growth
and to replace damaged cells) and it also means that gametes can be formed which
carry the same DNA sequences as the parent, so that offspring inherit alleles from their
parents.
, This allows natural selection to take place because the individuals with the alleles that
make them best adapted to survive are more likely to reproduce and create offspring
with those same alleles, so the allele frequency increases in the population.
It also means that multicellular organisms will not have an immune response to their
own body cells because all cells will be able to make antigens that the body recognise
as 'self' antigens and not foreign antigens
1.5.1 Nucleic acids (structure of RNA and DNA) - ANSWER: The sequence of bases in
DNA controls the sequence of bases in mRNA which controls the sequence of amino
acids
This primary structure of the protein controls the tertiary structure.
The tertiary structure of proteins is very important because it controls the function of the
protein, e.g. enzymes have an active site with a specific tertiary structure, antibodies
have binding sites with a specific tertiary structure, carrier and channel proteins have
specific shapes to control the transport of specific substances through membrane.
Can bond via a phosphodiester bond to the sugar group in the DNA = strong covalent
bonds.
Provides a backbone for the DNA molecule giving it strength and prevent the corruption
of the genetic code.
1.6 ATP - ANSWER: ATP is important as it provides energy is small manageable
amounts so that energy is not wasted
The energy is released in a one-step reaction so it is available quickly.
This means that metabolic reactions and processes such as active transport, protein
synthesis, DNA synthesis, muscle contraction can all take place.
ATP is also important in phosphorylating substances, making them more reactive, e.g.,
glucose is phosphorylated during the first step of glycolysis. This makes reactions
energetically favourable so that they can take place.
The 3 phosphate ions are all negatively charged --> there is repulsion between them
means the energy required to break the bond between the 2nd and 3rd phosphate is not
very high --> ATP hydrolysis results in net release of energy.
Energy released from ATP can be used for processes such as active transport, protein
synthesis, DNA replication, muscle contraction etc.
The phosphate can be used to phosphorylate other molecules to make them more
reactive. This enables reactions to occur more easily. For example, the addition of
phosphate to glucose in glycolysis.
2.2 Mitosis/Cell cycle - ANSWER: Two genetically identical daughter cells are formed.
This makes it possible for multicellular organisms to exist.
Each cell contains all genetic information - this is especially important for stem cells
which therefore have the ability to turn into any type of cell (they are totipotent).
complete solutions 2025.
1.3 Phospholipids (and 2.1) - ANSWER: Phosphate heads of phospholipids are charged
--> hydrophilic --> can interact with water. This means that a bilayer is formed with the
hydrophobic fatty acid tails on the inside and the phosphate heads on the outside.
Allows the membrane to be in contact with the contents of the cell and the tissue fluid
around the cell.
Creates a barrier which controls which substances can pass through - allowing there to
be different concentrations of substances either side of the membrane.
1.4.2 Enzymes - ANSWER: Enzymes lowers the activation energy of reaction so that
reactions are able to occur at an organisms' body temperature (which is a lower
temperature than would be the case without an enzyme).
The shape of an active site being complementary to just one substrate means that
specific reactions can be catalysed and controlled.
Inhibitors are important because they allow regulation of rate of enzyme catalysed
reactions, e.g. in end product inhibition the product of the reaction can act as a non-
competitive inhibitor and bind to the enzyme, changing its tertiary structure so the active
site can no longer become complementary to the substrate, so the reaction no longer
takes place. This means that when there is too much product the reaction will be slowed
down, but when there is less product the reaction will take place faster.
1.5.2 DNA replication - ANSWER: The nitrogenous bases are important because there
is complementary base pairing between them. This means it is possible for identical
copies of DNA to be made using the original strands as templates (according to the
semi-conservative model).
So daughter cells can be genetically identical as parent cells (in order for tissue growth
and to replace damaged cells) and it also means that gametes can be formed which
carry the same DNA sequences as the parent, so that offspring inherit alleles from their
parents.
, This allows natural selection to take place because the individuals with the alleles that
make them best adapted to survive are more likely to reproduce and create offspring
with those same alleles, so the allele frequency increases in the population.
It also means that multicellular organisms will not have an immune response to their
own body cells because all cells will be able to make antigens that the body recognise
as 'self' antigens and not foreign antigens
1.5.1 Nucleic acids (structure of RNA and DNA) - ANSWER: The sequence of bases in
DNA controls the sequence of bases in mRNA which controls the sequence of amino
acids
This primary structure of the protein controls the tertiary structure.
The tertiary structure of proteins is very important because it controls the function of the
protein, e.g. enzymes have an active site with a specific tertiary structure, antibodies
have binding sites with a specific tertiary structure, carrier and channel proteins have
specific shapes to control the transport of specific substances through membrane.
Can bond via a phosphodiester bond to the sugar group in the DNA = strong covalent
bonds.
Provides a backbone for the DNA molecule giving it strength and prevent the corruption
of the genetic code.
1.6 ATP - ANSWER: ATP is important as it provides energy is small manageable
amounts so that energy is not wasted
The energy is released in a one-step reaction so it is available quickly.
This means that metabolic reactions and processes such as active transport, protein
synthesis, DNA synthesis, muscle contraction can all take place.
ATP is also important in phosphorylating substances, making them more reactive, e.g.,
glucose is phosphorylated during the first step of glycolysis. This makes reactions
energetically favourable so that they can take place.
The 3 phosphate ions are all negatively charged --> there is repulsion between them
means the energy required to break the bond between the 2nd and 3rd phosphate is not
very high --> ATP hydrolysis results in net release of energy.
Energy released from ATP can be used for processes such as active transport, protein
synthesis, DNA replication, muscle contraction etc.
The phosphate can be used to phosphorylate other molecules to make them more
reactive. This enables reactions to occur more easily. For example, the addition of
phosphate to glucose in glycolysis.
2.2 Mitosis/Cell cycle - ANSWER: Two genetically identical daughter cells are formed.
This makes it possible for multicellular organisms to exist.
Each cell contains all genetic information - this is especially important for stem cells
which therefore have the ability to turn into any type of cell (they are totipotent).
