CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK
Sample answers have been written by the authors.
Coursebook answers
µm magnification, M = size of
Chapter 1 image,
Self-assessment questions =
actual size of specimen I A
1 a Structures that animal and plant cells have in
common:
=
• nucleus with nucleolus and chromatin
therefore magnification = ×2900 b
• cytoplasm containing mitochondria,
Golgi apparatus and other small magnification = ×16 000 (see caption)
structures length on micrograph = 65 mm =
• cell surface membrane. 65 000 µm
size of specimen, A = size of image,
b Structures found only in plant cells:
I
• chloroplasts
=
magnification M
• large, permanent central vacuole
• cell wall with middle lamella and =
plasmodesmata. therefore actual size of chloroplast = 4.1 µm
c Structure found only in animal cells: 4 The resolution of a microscope is limited by the
• centriole. radiation used to view the specimen. Resolution
equals half the wavelength of the radiation used.
2 • Use a sharp pencil. The shortest wavelength of light is 400 nm,
• Do not use shading / do not draw the therefore the resolution of a light microscope is
nucleus as a solid blob. 200 nm. The diameter of a ribosome is much
smaller than this, namely 25 nm.
• Do not cross label lines.
5
• Do not use arrowheads on label lines.
• Use a ruler to draw label lines.
• Make outline of cells less sketchy – lines
should be continuous, not broken.
• Write labels horizontally, not at the same
angle as the label line.
1 Cambridge International AS & A Level Biology © Cambridge University Press 2020
• Interpret what you see. For example, Feature Light Electron
outlines are not very accurate (too microscope microscope
rounded).
source of light electrons
3 a actual diameter = 20 µm (see caption) radiation
diameter on diagram = 58 mm = 58 000
,CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK
wavelength 400–700 nm about 0.005 nm • The nuclear membrane can be seen as a
of radiation double structure (envelope), continuous with
the rough endoplasmic reticulum, and with
used
pores in it.
maximum 200 nm 0.5 nm in
• There is extensive rough and smooth
resolution practice
endoplasmic reticulum throughout the cell.
lenses glass electromagnets
• Free ribosomes are visible in the cytoplasm.
specimen living, non-living or
• Microtubules are visible in the cytoplasm.
nonliving or dead
dead • The mitochondria have a double membrane
(envelope), the inner layer having folds into
stains coloured dyes heavy metals
the matrix.
image coloured black and white • Chloroplasts have a double outer membrane
6 Detail in an animal cell seen with the electron (envelope).
microscope but not apparent using a light • Grana can be seen in the chloroplast, as stacks
microscope: of sacs connected to other grana by longer
• In the nucleus, chromatin can be sacs (thylakoids).
distinguished.
8 a diameter of nucleus (I)
• The nucleus is seen to be surrounded by a = 75 mm = 75 000 µm
double membrane (envelope) with pores in
magnification (M) = ×11 000 therefore
it.
• Mitochondria have a surrounding double actual diameter of nucleus (A) = =
membrane (envelope), the inner layer 6.8 µm
forming finger-like folds pointing inwards.
b The nucleus may not have been
• Endoplasmic reticulum is extensive sectioned at its widest part. If you try
throughout the cell, some with ribosomes cutting a model sausage, the cut surface of a
(rough) and some without (smooth). transverse section will look like a circle. The
• Small structures seen under the light cut surface of a longitudinal section will
microscope can be distinguished by the look like a sausage. Other sections will be
electron microscope as lysosomes and somewhere between circles and
vesicles.
sausages.
• Free ribosomes are seen throughout the
cell. 9 Cilia in the oviduct beat in order to move the
egg from the ovary to the uterus. (It may be
• The centriole is seen to be two separate fertilised along the way.)
centrioles.
• Finger-like extensions of the cell surface 10 Cell surface membrane: essential because it
membrane, known as microvilli, are seen. forms a partially permeable barrier between the
cell and its environment, regulating movement
• Microtubules are visible in the cytoplasm. of materials into and out of the cell. This is
necessary to maintain an environment inside the
7 Detail in a plant cell seen with the electron
cell which is different from that outside the cell.
microscope but not apparent using a light
microscope: Cytoplasm: site of metabolic activity. It contains
• In the nucleus, chromatin can be biochemicals in solution.
distinguished. Ribosomes: sites of protein synthesis, an
essential activity of all cells. (DNA controls cells
by controlling which proteins are made.) Protein
synthesis is a complex process involving the
interaction of many molecules;
the ribosome provides a site where this can
happen in an organised way.
2
Cambridge International AS & A Level Biology © Cambridge University Press 2020
,CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK
DNA: the genetic material. DNA contains the Comparing the success of prokaryotic
information which controls the activities of the
cell. It can replicate itself, enabling new cells to and eukaryotic cells
be formed. Criteria could be:
• complexity of cells
Cell wall (absent in animal cells): prevents the
cell from bursting as a result of osmosis if it is • complexity of the whole organism
exposed to a solution of higher water potential.
• size
Flagellum: needed for locomotion by some cells. • total biomass on the planet
• range of habitats they can live in
Reflection • ability to survive adverse conditions • ability to
What is a cell? regulate their internal environments
A cell is the basic unit of life. All living organisms • number and variety of species.
are made of cells. All cells have a cell surface
membrane, cytoplasm and genetic material in the
form of DNA. All cells have a protein synthesising Is this a meaningless question?
machinery which includes ribosomes. This question probably is a meaningless question,
although it doesn’t stop people discussing it. All living
things have evolved to be adapted to their particular
Why are all living things made of cells? environments (ecological niches) and to this extent are
The biochemistry of life must be separated from the equally successful. Judgements can be made in various
surrounding environment. This separation is ways. Eukaryotes are far more complex than
achieved by the cell surface membrane. The cell prokaryotes. Humans (probably the most intelligent
surface membrane is partially permeable and eukaryotes) have the greatest control over their
controls what enters and leaves the cell. Without it, environments. Bacteria have the greatest biomass and
the chemicals of life would mix with the chemicals are the most versatile of cells. They are probably the
of the environment and a separate chemistry of life most likely cells to survive a catastrophic change in the
would be impossible. Earth’s climate/ environment.
3
Cambridge International AS & A Level Biology © Cambridge University Press 2020
,
Sample answers have been written by the authors.
Coursebook answers
µm magnification, M = size of
Chapter 1 image,
Self-assessment questions =
actual size of specimen I A
1 a Structures that animal and plant cells have in
common:
=
• nucleus with nucleolus and chromatin
therefore magnification = ×2900 b
• cytoplasm containing mitochondria,
Golgi apparatus and other small magnification = ×16 000 (see caption)
structures length on micrograph = 65 mm =
• cell surface membrane. 65 000 µm
size of specimen, A = size of image,
b Structures found only in plant cells:
I
• chloroplasts
=
magnification M
• large, permanent central vacuole
• cell wall with middle lamella and =
plasmodesmata. therefore actual size of chloroplast = 4.1 µm
c Structure found only in animal cells: 4 The resolution of a microscope is limited by the
• centriole. radiation used to view the specimen. Resolution
equals half the wavelength of the radiation used.
2 • Use a sharp pencil. The shortest wavelength of light is 400 nm,
• Do not use shading / do not draw the therefore the resolution of a light microscope is
nucleus as a solid blob. 200 nm. The diameter of a ribosome is much
smaller than this, namely 25 nm.
• Do not cross label lines.
5
• Do not use arrowheads on label lines.
• Use a ruler to draw label lines.
• Make outline of cells less sketchy – lines
should be continuous, not broken.
• Write labels horizontally, not at the same
angle as the label line.
1 Cambridge International AS & A Level Biology © Cambridge University Press 2020
• Interpret what you see. For example, Feature Light Electron
outlines are not very accurate (too microscope microscope
rounded).
source of light electrons
3 a actual diameter = 20 µm (see caption) radiation
diameter on diagram = 58 mm = 58 000
,CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK
wavelength 400–700 nm about 0.005 nm • The nuclear membrane can be seen as a
of radiation double structure (envelope), continuous with
the rough endoplasmic reticulum, and with
used
pores in it.
maximum 200 nm 0.5 nm in
• There is extensive rough and smooth
resolution practice
endoplasmic reticulum throughout the cell.
lenses glass electromagnets
• Free ribosomes are visible in the cytoplasm.
specimen living, non-living or
• Microtubules are visible in the cytoplasm.
nonliving or dead
dead • The mitochondria have a double membrane
(envelope), the inner layer having folds into
stains coloured dyes heavy metals
the matrix.
image coloured black and white • Chloroplasts have a double outer membrane
6 Detail in an animal cell seen with the electron (envelope).
microscope but not apparent using a light • Grana can be seen in the chloroplast, as stacks
microscope: of sacs connected to other grana by longer
• In the nucleus, chromatin can be sacs (thylakoids).
distinguished.
8 a diameter of nucleus (I)
• The nucleus is seen to be surrounded by a = 75 mm = 75 000 µm
double membrane (envelope) with pores in
magnification (M) = ×11 000 therefore
it.
• Mitochondria have a surrounding double actual diameter of nucleus (A) = =
membrane (envelope), the inner layer 6.8 µm
forming finger-like folds pointing inwards.
b The nucleus may not have been
• Endoplasmic reticulum is extensive sectioned at its widest part. If you try
throughout the cell, some with ribosomes cutting a model sausage, the cut surface of a
(rough) and some without (smooth). transverse section will look like a circle. The
• Small structures seen under the light cut surface of a longitudinal section will
microscope can be distinguished by the look like a sausage. Other sections will be
electron microscope as lysosomes and somewhere between circles and
vesicles.
sausages.
• Free ribosomes are seen throughout the
cell. 9 Cilia in the oviduct beat in order to move the
egg from the ovary to the uterus. (It may be
• The centriole is seen to be two separate fertilised along the way.)
centrioles.
• Finger-like extensions of the cell surface 10 Cell surface membrane: essential because it
membrane, known as microvilli, are seen. forms a partially permeable barrier between the
cell and its environment, regulating movement
• Microtubules are visible in the cytoplasm. of materials into and out of the cell. This is
necessary to maintain an environment inside the
7 Detail in a plant cell seen with the electron
cell which is different from that outside the cell.
microscope but not apparent using a light
microscope: Cytoplasm: site of metabolic activity. It contains
• In the nucleus, chromatin can be biochemicals in solution.
distinguished. Ribosomes: sites of protein synthesis, an
essential activity of all cells. (DNA controls cells
by controlling which proteins are made.) Protein
synthesis is a complex process involving the
interaction of many molecules;
the ribosome provides a site where this can
happen in an organised way.
2
Cambridge International AS & A Level Biology © Cambridge University Press 2020
,CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK
DNA: the genetic material. DNA contains the Comparing the success of prokaryotic
information which controls the activities of the
cell. It can replicate itself, enabling new cells to and eukaryotic cells
be formed. Criteria could be:
• complexity of cells
Cell wall (absent in animal cells): prevents the
cell from bursting as a result of osmosis if it is • complexity of the whole organism
exposed to a solution of higher water potential.
• size
Flagellum: needed for locomotion by some cells. • total biomass on the planet
• range of habitats they can live in
Reflection • ability to survive adverse conditions • ability to
What is a cell? regulate their internal environments
A cell is the basic unit of life. All living organisms • number and variety of species.
are made of cells. All cells have a cell surface
membrane, cytoplasm and genetic material in the
form of DNA. All cells have a protein synthesising Is this a meaningless question?
machinery which includes ribosomes. This question probably is a meaningless question,
although it doesn’t stop people discussing it. All living
things have evolved to be adapted to their particular
Why are all living things made of cells? environments (ecological niches) and to this extent are
The biochemistry of life must be separated from the equally successful. Judgements can be made in various
surrounding environment. This separation is ways. Eukaryotes are far more complex than
achieved by the cell surface membrane. The cell prokaryotes. Humans (probably the most intelligent
surface membrane is partially permeable and eukaryotes) have the greatest control over their
controls what enters and leaves the cell. Without it, environments. Bacteria have the greatest biomass and
the chemicals of life would mix with the chemicals are the most versatile of cells. They are probably the
of the environment and a separate chemistry of life most likely cells to survive a catastrophic change in the
would be impossible. Earth’s climate/ environment.
3
Cambridge International AS & A Level Biology © Cambridge University Press 2020
,
