AQA AS BIOLOGY COMPREHENSIVE EXAM SHEET
2025/2026 QUESTIONS AND ANSWERS GRADED A+
✔✔Affect of pH on enzyme activity? - ✔✔if change pH away from optimum, bonds in
tertiary structure break, lose active site shape, no longer form ES complex, enzyme
denatured
✔✔Competitive vs Non-Competitive Inhibitors? - ✔✔Competitive = a substance with a
similar shape to the substrate and a complementary shape to the enzyme's active site,
binds to the active site, blocking it, preventing ES complexes from forming
Non-Competitive = a substance that binds to another site on the enzyme other then the
active site, causes the active site to change shape, so less ES complexes can form
✔✔What are the 3 types of Lipids? - ✔✔Triglycerides (fat for energy store, insulation,
protection of organs)
Phopholipids (to make membranes)
Cholesterol (for membrane stability and make hormones)
✔✔Structure of triglyceride? - ✔✔made of 1 glycerol and 3 fatty acids
joined by condensation reaction, ester bonds
bond is COOC
there are 2 types of triglycerides: saturated fat and unsaturated fat
✔✔Saturated vs Unsaturated Fat? - ✔✔Saturated = has no carbon double bonds in the
R group of the fatty acid
Unsaturated = has carbon double bonds in the R group of the fatty acid
✔✔Structure of phospholipid? - ✔✔made of 1 glycerol, 2 fatty acids and 1 phosphate
phosphate forms a hydrophillic head, fatty acids form hydrophobic tails
forms a phospholipid bilayer, basic structure of membranes
✔✔What are Nucleic Acids? - ✔✔Polymers made from Nucleotides (2 types = DNA and
RNA)
✔✔What is DNA? - ✔✔DeoxyriboNucleic Acid
found in all organisms (animals, plants, microorganisms)
,carries genes
genes = section of DNA that codes for a protein
all organisms are built of proteins
✔✔Building block of DNA? - ✔✔DNA nucleotide (made of phosphate, deoxyribose
sugar, nitrogenous base)
4 types of nucleotides (each has a different base, either
Adenine/Thymine/Cytosine/Guanine)
✔✔DNA structure? - ✔✔DNA Double Helix
join nucleotides by condensation reaction between sugar and phosphate to form a
polynucleotide
join 2 polynucleotides by hydrogen bond between the bases
A joins with T, C joins with G (complementary base pairing)
produces double strand [anti-parallel]
then coil double strand into Double Helix
✔✔Properties of DNA Structure? - ✔✔Double Stranded = makes DNA more stable & 2
strands act as templates in semi-conservative replication
Coil into Helix = more compact
Sugar-phosphate backbone = protects bases (bases code for protein)
Hydrogen bonds between bases = weak, so double strand separates more easily for
semi-conservative replication
Complementary Base Pairing = ensures identical copies of DNA made by semi-
conservative replication
✔✔DNA Replication? - ✔✔occurs in interphase before mitosis & meiosis
occurs by semi-conservative replication
✔✔Describe Semi-Conservative Replication? - ✔✔DNA double strand separate and act
as templates, producing 2 identical copies of the DNA, each has half the original strand
and half the new strand
process:
DNA Helicase breaks hydrogen bonds between the complementary bases
double strand separates, leaves 2 template stands
free complementary nucleotides bind to exposed bases on template strands (A to T, C
to G)
DNA Polymerase joins the sugar-phosphate backbone of the new strand
✔✔Evidence for SCR? - ✔✔Replicating Bacterial DNA in 2 types of Nitrogen Isotopes,
15N and 14N
15N = heavy isotope
14N = light isotope
,Nitrogen found in nitrogenous bases of DNA
Bacterial DNA made from 15N will have a Heavy Density
Bacterial DNA made from 14N will have a Light Density
Experiment = Bacterial DNA made of 15N is replicated in an environment of 14N -
produces DNA molecules with half 15/half 14 (semi-conservative replication, original
strand = 15N & new strand = 14N), therefore, DNA molecule has medium density
✔✔What is RNA? - ✔✔RiboNucleic Acid
2 types (mRNA and tRNA)
mRNA = messenger RNA
tRNA = transfer RNA
both single stranded
both made of RNA Nucleotides (phosphate, ribose sugar, nitrogenous bases - AUCG)
✔✔What is ATP? - ✔✔Adenosine Triphosphate (Energy Carrier Molecule - delivers
energy for life processes)
✔✔Structure of ATP? - ✔✔Adenosine Triphosphate
made from 1 adenosine and 3 phosphates
formation: ADP + Pi (+ energy used) = ATP
condensation reaction using ATP Synthase
carries energy in its bonds
breakdown: ATP = ADP + Pi (+ energy released)
hydrolysis reaction using ATP Hydrolase
releases energy from its bonds
✔✔What makes ATP a good deliverer of energy? - ✔✔immediate source = need to only
break one bond (plus bond is weak)
manageable source = releases small amount of energy
, ✔✔Uses of ATP (releases energy) in organisms? - ✔✔protein synthesis
organelle synthesis
DNA replication
cell division (mitosis)
active transport
metabolic reactions
movement
maintaining body temperature
✔✔Role of Water in Biology? - ✔✔found in living organisms = cytoplasm (all
organisms), xylem/phloem (in plants), tissue fluid and blood (in animals)
also acts as habitats for living organisms
✔✔Properties of Water? - ✔✔Water Molecules (H20) are dipolar
Hydrogen has slightly +ve charge and Oxygen has slightly -ve charge
therefore H20 molecules can form hydrogen bonds with each other
✔✔Role of Water in Living Organisms?
Habitat - ✔✔Habitat (e.g. sea): Water has high specific heat capacity meaning that a lot
of heat needs to be applied before it evaporates due to the presence of the hydrogen
bonds between the water molecules. Also when water freezes it becomes Ice, which is
less dense then liquid water - so it floats on the surface insulating the water beneath it,
preventing it from freezing. In both cases the water remains liquid to provide an habitat
for organisms.
✔✔Role of Water in Living Organisms?
solvent - ✔✔Because H20 molecules are dipolar they can separate out solutes based
on their charge, +ve Hydrogen side mixes with -ve solute and -ve Oxygen side mixes
with +ve solute, so solute mixes with water and becomes dissolved. This is useful in
cytoplasm of all cells and supports the reaction of these solutes, it is also useful in the
processes of diffusion/active transport, and is also useful in transport such as blood and
phloem.
2025/2026 QUESTIONS AND ANSWERS GRADED A+
✔✔Affect of pH on enzyme activity? - ✔✔if change pH away from optimum, bonds in
tertiary structure break, lose active site shape, no longer form ES complex, enzyme
denatured
✔✔Competitive vs Non-Competitive Inhibitors? - ✔✔Competitive = a substance with a
similar shape to the substrate and a complementary shape to the enzyme's active site,
binds to the active site, blocking it, preventing ES complexes from forming
Non-Competitive = a substance that binds to another site on the enzyme other then the
active site, causes the active site to change shape, so less ES complexes can form
✔✔What are the 3 types of Lipids? - ✔✔Triglycerides (fat for energy store, insulation,
protection of organs)
Phopholipids (to make membranes)
Cholesterol (for membrane stability and make hormones)
✔✔Structure of triglyceride? - ✔✔made of 1 glycerol and 3 fatty acids
joined by condensation reaction, ester bonds
bond is COOC
there are 2 types of triglycerides: saturated fat and unsaturated fat
✔✔Saturated vs Unsaturated Fat? - ✔✔Saturated = has no carbon double bonds in the
R group of the fatty acid
Unsaturated = has carbon double bonds in the R group of the fatty acid
✔✔Structure of phospholipid? - ✔✔made of 1 glycerol, 2 fatty acids and 1 phosphate
phosphate forms a hydrophillic head, fatty acids form hydrophobic tails
forms a phospholipid bilayer, basic structure of membranes
✔✔What are Nucleic Acids? - ✔✔Polymers made from Nucleotides (2 types = DNA and
RNA)
✔✔What is DNA? - ✔✔DeoxyriboNucleic Acid
found in all organisms (animals, plants, microorganisms)
,carries genes
genes = section of DNA that codes for a protein
all organisms are built of proteins
✔✔Building block of DNA? - ✔✔DNA nucleotide (made of phosphate, deoxyribose
sugar, nitrogenous base)
4 types of nucleotides (each has a different base, either
Adenine/Thymine/Cytosine/Guanine)
✔✔DNA structure? - ✔✔DNA Double Helix
join nucleotides by condensation reaction between sugar and phosphate to form a
polynucleotide
join 2 polynucleotides by hydrogen bond between the bases
A joins with T, C joins with G (complementary base pairing)
produces double strand [anti-parallel]
then coil double strand into Double Helix
✔✔Properties of DNA Structure? - ✔✔Double Stranded = makes DNA more stable & 2
strands act as templates in semi-conservative replication
Coil into Helix = more compact
Sugar-phosphate backbone = protects bases (bases code for protein)
Hydrogen bonds between bases = weak, so double strand separates more easily for
semi-conservative replication
Complementary Base Pairing = ensures identical copies of DNA made by semi-
conservative replication
✔✔DNA Replication? - ✔✔occurs in interphase before mitosis & meiosis
occurs by semi-conservative replication
✔✔Describe Semi-Conservative Replication? - ✔✔DNA double strand separate and act
as templates, producing 2 identical copies of the DNA, each has half the original strand
and half the new strand
process:
DNA Helicase breaks hydrogen bonds between the complementary bases
double strand separates, leaves 2 template stands
free complementary nucleotides bind to exposed bases on template strands (A to T, C
to G)
DNA Polymerase joins the sugar-phosphate backbone of the new strand
✔✔Evidence for SCR? - ✔✔Replicating Bacterial DNA in 2 types of Nitrogen Isotopes,
15N and 14N
15N = heavy isotope
14N = light isotope
,Nitrogen found in nitrogenous bases of DNA
Bacterial DNA made from 15N will have a Heavy Density
Bacterial DNA made from 14N will have a Light Density
Experiment = Bacterial DNA made of 15N is replicated in an environment of 14N -
produces DNA molecules with half 15/half 14 (semi-conservative replication, original
strand = 15N & new strand = 14N), therefore, DNA molecule has medium density
✔✔What is RNA? - ✔✔RiboNucleic Acid
2 types (mRNA and tRNA)
mRNA = messenger RNA
tRNA = transfer RNA
both single stranded
both made of RNA Nucleotides (phosphate, ribose sugar, nitrogenous bases - AUCG)
✔✔What is ATP? - ✔✔Adenosine Triphosphate (Energy Carrier Molecule - delivers
energy for life processes)
✔✔Structure of ATP? - ✔✔Adenosine Triphosphate
made from 1 adenosine and 3 phosphates
formation: ADP + Pi (+ energy used) = ATP
condensation reaction using ATP Synthase
carries energy in its bonds
breakdown: ATP = ADP + Pi (+ energy released)
hydrolysis reaction using ATP Hydrolase
releases energy from its bonds
✔✔What makes ATP a good deliverer of energy? - ✔✔immediate source = need to only
break one bond (plus bond is weak)
manageable source = releases small amount of energy
, ✔✔Uses of ATP (releases energy) in organisms? - ✔✔protein synthesis
organelle synthesis
DNA replication
cell division (mitosis)
active transport
metabolic reactions
movement
maintaining body temperature
✔✔Role of Water in Biology? - ✔✔found in living organisms = cytoplasm (all
organisms), xylem/phloem (in plants), tissue fluid and blood (in animals)
also acts as habitats for living organisms
✔✔Properties of Water? - ✔✔Water Molecules (H20) are dipolar
Hydrogen has slightly +ve charge and Oxygen has slightly -ve charge
therefore H20 molecules can form hydrogen bonds with each other
✔✔Role of Water in Living Organisms?
Habitat - ✔✔Habitat (e.g. sea): Water has high specific heat capacity meaning that a lot
of heat needs to be applied before it evaporates due to the presence of the hydrogen
bonds between the water molecules. Also when water freezes it becomes Ice, which is
less dense then liquid water - so it floats on the surface insulating the water beneath it,
preventing it from freezing. In both cases the water remains liquid to provide an habitat
for organisms.
✔✔Role of Water in Living Organisms?
solvent - ✔✔Because H20 molecules are dipolar they can separate out solutes based
on their charge, +ve Hydrogen side mixes with -ve solute and -ve Oxygen side mixes
with +ve solute, so solute mixes with water and becomes dissolved. This is useful in
cytoplasm of all cells and supports the reaction of these solutes, it is also useful in the
processes of diffusion/active transport, and is also useful in transport such as blood and
phloem.
