A-Level Biology: Cells
Compare active and passive immunity - ANSWER✅✅✅1) Active requires exposure to the antigen
while passive does not
2) Active takes a while to develop protection while passive provides immediate protection
3) Active produces memory cells while passive does not
4) Active provides long-term protection while passive provides short-term protection
Compare the cell wall in plants and fungi - ANSWER✅✅✅In plants the cell wall is made of cellulose,
while in fungi it is made of chitin
Define mitosis - ANSWER✅✅✅The part of the cell cycle in which a eukaryotic cell divides to produce
two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA
replication
Describe and explain how HIV replicates inside the host's helper T-cells using cell machinery -
ANSWER✅✅✅1) HIV enters the bloodstream and circulates around the body - eventually an
attachment protein binds to a CD4 protein on a helper T-cell
2) The protein capsid fuses with the cell-surface membrane and uncoats, releasing the RNA and enzymes
of HIV into the cell cytoplasm
3) Reverse transcriptase converts the HIV RNA into DNA
4) The HIV DNA is inserted into the host cell's DNA
5) The HIV DNA hijacks the cell's enzymes to create mRNA which codes for the production of new viral
proteins and RNA
6) The viral proteins and RNA are assembled into new virus particles which break away from the cell
- as they break through the plasma membrane, they remove a chunk of the membrane to from their
lipid envelope
Describe and explain the direct ELISA test - ANSWER✅✅✅Uses a single specific antibody that is
complementary to the antigen being tested for
1) Antigens from a sample are attached to the inside of a well in a well plate
- the well is washed to remove any unattached antigens
2) A detection antibody, which is complementary to a specific antigen, with an attached enzyme is
added
A-Level Biology: Cells
,A-Level Biology: Cells
- if the complementary antigen is present, the detection antibody will bind to it, rendering it immobile
3) The well is washed out to remove any unbound excess antibody
- if not washed out, there could be a false positive result
4) Substrate solution complementary to the enzyme is added to the well
- if the detection antibody (and by extension the complementary antigen) is present, the enzyme will
break down the substrate; therefore there will be a colour change
Describe and explain the process of cell fractionation and ultracentrifugation to separate the organelles
in a cell - ANSWER✅✅✅1) Homogenisation - cells are homogenised to break the plasma membrane
open in order to release the organelles
2) Filter to remove large debris or whole cells
3) Use an isotonic solution to prevent damage to organelles due to osmosis
4) Maintain a cold temperature to prevent organelles from being broken down by enzymes + buffered
solution to prevent enzyme denaturation
5) Centrifuge at a low speed to separate the heavier organelles - will form a pellet
6) Remove the pellet from the supernatant and re-spin the supernatant at a higher speed to obtain the
next densest organelle
Describe and give the function of a vacuole - ANSWER✅✅✅- A membrane-bound organelle
containing cell sap; membrane is called the tonoplast; cell sap contains salts, sugars, amino acids, waste
and pigments (e.g. anthocyanins)
1) Maintains turgor pressure of the cell by pushing against the cel wall; therefore cell remains rigid and
plant does not wilt
2) Involved in isolation of unwanted chemicals in the cell
Describe and give the function of chloroplasts - ANSWER✅✅✅- consists of: the chloroplast envelope
(a double plasma membrane); grana linked by lamellae; stroma
1) Site of photosynthesis
Describe and give the function of the cell-surface membrane - ANSWER✅✅✅- membrane consisting
mainly of lipids and proteins
1) Regulates the passage of substances into and out of the cells
A-Level Biology: Cells
, A-Level Biology: Cells
2) Has receptor molecules which allow it to respond to chemicals
Describe and give the function of the Golgi apparatus - ANSWER✅✅✅- consists of fluid-filled
membrane-bound flattened sacs, called cisternae
1) Process and packages lipids and proteins produced by the endoplasmic reticulum:
- adds carbs to proteins forming glycoproteins
- produces secretory enzymes
- secretes carbs
- transports, modifies and stores lipids
- forms vesicles (e.g. lysosomes)
Describe and give the function of the mitochondria - ANSWER✅✅✅- rod-shaped organelle which
has a double membrane; inner membrane is folded to form cristae which provide a large surface area
for the attachment of enzymes and proteins involved in respiration
- within the double membrane is the matrix, which contains proteins, lipids, ribosomes, DNA and
enzymes involved in respiration
1) Site of aerobic respiration
Describe and give the function of the nucleus - ANSWER✅✅✅- large organelle surrounded by a
nuclear envelope (double membrane) which contains nuclear pores
- within the nuclear envelope are chromosomes and nucleoli
1) Controls the cell's activities via transcription of DNA and stores genetic information
Describe the co-transport of glucose and sodium ions by cells lining the mammalian ileum -
ANSWER✅✅✅- sodium ions are actively transported out of the epithelial cells in the ileum and into
the blood, by the sodium-potassium pump
- there is now a higher concentration of sodium ions in the lumen of the ileum than inside the epithelial
cells
- sodium ions diffuse down a concentration gradient from the lumen of the ileum into the epithelial
cells, via sodium-glucose co-transporter proteins in the cell-surface membrane
- these sodium ions carry the glucose molecules into the epithelial cells with them
A-Level Biology: Cells
Compare active and passive immunity - ANSWER✅✅✅1) Active requires exposure to the antigen
while passive does not
2) Active takes a while to develop protection while passive provides immediate protection
3) Active produces memory cells while passive does not
4) Active provides long-term protection while passive provides short-term protection
Compare the cell wall in plants and fungi - ANSWER✅✅✅In plants the cell wall is made of cellulose,
while in fungi it is made of chitin
Define mitosis - ANSWER✅✅✅The part of the cell cycle in which a eukaryotic cell divides to produce
two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA
replication
Describe and explain how HIV replicates inside the host's helper T-cells using cell machinery -
ANSWER✅✅✅1) HIV enters the bloodstream and circulates around the body - eventually an
attachment protein binds to a CD4 protein on a helper T-cell
2) The protein capsid fuses with the cell-surface membrane and uncoats, releasing the RNA and enzymes
of HIV into the cell cytoplasm
3) Reverse transcriptase converts the HIV RNA into DNA
4) The HIV DNA is inserted into the host cell's DNA
5) The HIV DNA hijacks the cell's enzymes to create mRNA which codes for the production of new viral
proteins and RNA
6) The viral proteins and RNA are assembled into new virus particles which break away from the cell
- as they break through the plasma membrane, they remove a chunk of the membrane to from their
lipid envelope
Describe and explain the direct ELISA test - ANSWER✅✅✅Uses a single specific antibody that is
complementary to the antigen being tested for
1) Antigens from a sample are attached to the inside of a well in a well plate
- the well is washed to remove any unattached antigens
2) A detection antibody, which is complementary to a specific antigen, with an attached enzyme is
added
A-Level Biology: Cells
,A-Level Biology: Cells
- if the complementary antigen is present, the detection antibody will bind to it, rendering it immobile
3) The well is washed out to remove any unbound excess antibody
- if not washed out, there could be a false positive result
4) Substrate solution complementary to the enzyme is added to the well
- if the detection antibody (and by extension the complementary antigen) is present, the enzyme will
break down the substrate; therefore there will be a colour change
Describe and explain the process of cell fractionation and ultracentrifugation to separate the organelles
in a cell - ANSWER✅✅✅1) Homogenisation - cells are homogenised to break the plasma membrane
open in order to release the organelles
2) Filter to remove large debris or whole cells
3) Use an isotonic solution to prevent damage to organelles due to osmosis
4) Maintain a cold temperature to prevent organelles from being broken down by enzymes + buffered
solution to prevent enzyme denaturation
5) Centrifuge at a low speed to separate the heavier organelles - will form a pellet
6) Remove the pellet from the supernatant and re-spin the supernatant at a higher speed to obtain the
next densest organelle
Describe and give the function of a vacuole - ANSWER✅✅✅- A membrane-bound organelle
containing cell sap; membrane is called the tonoplast; cell sap contains salts, sugars, amino acids, waste
and pigments (e.g. anthocyanins)
1) Maintains turgor pressure of the cell by pushing against the cel wall; therefore cell remains rigid and
plant does not wilt
2) Involved in isolation of unwanted chemicals in the cell
Describe and give the function of chloroplasts - ANSWER✅✅✅- consists of: the chloroplast envelope
(a double plasma membrane); grana linked by lamellae; stroma
1) Site of photosynthesis
Describe and give the function of the cell-surface membrane - ANSWER✅✅✅- membrane consisting
mainly of lipids and proteins
1) Regulates the passage of substances into and out of the cells
A-Level Biology: Cells
, A-Level Biology: Cells
2) Has receptor molecules which allow it to respond to chemicals
Describe and give the function of the Golgi apparatus - ANSWER✅✅✅- consists of fluid-filled
membrane-bound flattened sacs, called cisternae
1) Process and packages lipids and proteins produced by the endoplasmic reticulum:
- adds carbs to proteins forming glycoproteins
- produces secretory enzymes
- secretes carbs
- transports, modifies and stores lipids
- forms vesicles (e.g. lysosomes)
Describe and give the function of the mitochondria - ANSWER✅✅✅- rod-shaped organelle which
has a double membrane; inner membrane is folded to form cristae which provide a large surface area
for the attachment of enzymes and proteins involved in respiration
- within the double membrane is the matrix, which contains proteins, lipids, ribosomes, DNA and
enzymes involved in respiration
1) Site of aerobic respiration
Describe and give the function of the nucleus - ANSWER✅✅✅- large organelle surrounded by a
nuclear envelope (double membrane) which contains nuclear pores
- within the nuclear envelope are chromosomes and nucleoli
1) Controls the cell's activities via transcription of DNA and stores genetic information
Describe the co-transport of glucose and sodium ions by cells lining the mammalian ileum -
ANSWER✅✅✅- sodium ions are actively transported out of the epithelial cells in the ileum and into
the blood, by the sodium-potassium pump
- there is now a higher concentration of sodium ions in the lumen of the ileum than inside the epithelial
cells
- sodium ions diffuse down a concentration gradient from the lumen of the ileum into the epithelial
cells, via sodium-glucose co-transporter proteins in the cell-surface membrane
- these sodium ions carry the glucose molecules into the epithelial cells with them
A-Level Biology: Cells
