AQA BIOLOGY PAPER 3 PRACTICE EXAM 2026
QUESTIONS WITH ACCURATE ANSWERS
◉ Define resolution Answer: The minimum distance apart that two
objects can be in order for them to appear as separate items
◉ In cell fractionation, why is the solution ice cold? Answer: To
reduce enzyme activity that might break down the organelles
◉ In cell fractionation, why is the solution isotonic? Answer: To
prevent organelles bursting or shrinking as a result of osmotic gain
or loss
◉ In cell fractionation, why is the solution buffered? Answer: So that
the pH doesn't fluctuate, this could alter organelle structure or
enzyme function
◉ Describe homogenisation Answer: Organelles are realised from
the cell through homogenisation producing homogenate. This is
then filtered to remove debris and complete cells
◉ Describe ultracentrifugation Answer: Filtrate placed in centrifuge
at low speed
,Heaviest organelles, nuclei go to the bottom forming pellet 1 with
the remaining solution, supernatant 1 on top.
This process is repeated a increasingly higher speeds to remove
other organelles
◉ In what order are organelles collected during ultracentrifugation?
Answer: Nuclei, mitochondria, lysosomes
◉ Outline why an electron is better than an optical microscope.
Answer: Electrons are negetivley charged so can be focused using
electromagnets
An electron beam, with a very short wavelength is used giving it a
high resolving power
◉ What are limitations of a TEM? 4 Answer: Must be in vacuum so
specimens cannot be living
Specimen must be very thin, the cutting process may produce
artefacts
Complex staining process required
Higher electron beam required and this can sometimes damage
specimen
◉ How does a TEM work? Answer: A beam of electrons is passed
through the specimen from below
,Some are absorbed, darker areas
Some pass through, lighter areas
This produces a photomicrograph
◉ What is the resolving power of a TEM? Answer: 0.1nm
◉ How does a SEM work? Answer: A beam of electrons pass back
and forth around the specimen from above
This forms a 3D shape but electrons do not penetrate
◉ Limitations of a SEM? Answer: lower resolving power than TEM
◉ Benefits of a SEM? Answer: Specimen doesn't need to be cut thin,
no risk of artefacts
Colour
◉ What is the resolving power of a SEM? Answer: 20nm
◉ How big is the nucleus? Answer: 10-20um
◉ Function of nuclear envelope Answer: Controls entry and exit of
materials in and out of the nucleus and contains the reactions taking
place within it
, ◉ Function of nuclear pores Answer: Allow passage of large
molecules e.g mRNA out of the nucleus
◉ Function of nucleoplasm Answer: Maintains shape and structure
of nucleus
◉ Function of chromosomes Answer: Contain protein bound linear
DNA
◉ Function of Nucleolus Answer: Makes ribosomal RNA
◉ Structure of the Mitochondria Answer: Double membrane forming
cristae and matrix
◉ Function of cristae Answer: Provides large surface area for the
attachment of enzymes required for respiration
◉ Function of matrix Answer: Contains proteins, lipids, ribosomes,
DNA and enzymes involved in respiration
◉ Structure of chloroplasts? Answer: Double membrane, stroma,
grana made up of thylakoids
QUESTIONS WITH ACCURATE ANSWERS
◉ Define resolution Answer: The minimum distance apart that two
objects can be in order for them to appear as separate items
◉ In cell fractionation, why is the solution ice cold? Answer: To
reduce enzyme activity that might break down the organelles
◉ In cell fractionation, why is the solution isotonic? Answer: To
prevent organelles bursting or shrinking as a result of osmotic gain
or loss
◉ In cell fractionation, why is the solution buffered? Answer: So that
the pH doesn't fluctuate, this could alter organelle structure or
enzyme function
◉ Describe homogenisation Answer: Organelles are realised from
the cell through homogenisation producing homogenate. This is
then filtered to remove debris and complete cells
◉ Describe ultracentrifugation Answer: Filtrate placed in centrifuge
at low speed
,Heaviest organelles, nuclei go to the bottom forming pellet 1 with
the remaining solution, supernatant 1 on top.
This process is repeated a increasingly higher speeds to remove
other organelles
◉ In what order are organelles collected during ultracentrifugation?
Answer: Nuclei, mitochondria, lysosomes
◉ Outline why an electron is better than an optical microscope.
Answer: Electrons are negetivley charged so can be focused using
electromagnets
An electron beam, with a very short wavelength is used giving it a
high resolving power
◉ What are limitations of a TEM? 4 Answer: Must be in vacuum so
specimens cannot be living
Specimen must be very thin, the cutting process may produce
artefacts
Complex staining process required
Higher electron beam required and this can sometimes damage
specimen
◉ How does a TEM work? Answer: A beam of electrons is passed
through the specimen from below
,Some are absorbed, darker areas
Some pass through, lighter areas
This produces a photomicrograph
◉ What is the resolving power of a TEM? Answer: 0.1nm
◉ How does a SEM work? Answer: A beam of electrons pass back
and forth around the specimen from above
This forms a 3D shape but electrons do not penetrate
◉ Limitations of a SEM? Answer: lower resolving power than TEM
◉ Benefits of a SEM? Answer: Specimen doesn't need to be cut thin,
no risk of artefacts
Colour
◉ What is the resolving power of a SEM? Answer: 20nm
◉ How big is the nucleus? Answer: 10-20um
◉ Function of nuclear envelope Answer: Controls entry and exit of
materials in and out of the nucleus and contains the reactions taking
place within it
, ◉ Function of nuclear pores Answer: Allow passage of large
molecules e.g mRNA out of the nucleus
◉ Function of nucleoplasm Answer: Maintains shape and structure
of nucleus
◉ Function of chromosomes Answer: Contain protein bound linear
DNA
◉ Function of Nucleolus Answer: Makes ribosomal RNA
◉ Structure of the Mitochondria Answer: Double membrane forming
cristae and matrix
◉ Function of cristae Answer: Provides large surface area for the
attachment of enzymes required for respiration
◉ Function of matrix Answer: Contains proteins, lipids, ribosomes,
DNA and enzymes involved in respiration
◉ Structure of chloroplasts? Answer: Double membrane, stroma,
grana made up of thylakoids
