C1 Cell Structure
Microscopy
Key features:
Comparison between light and electron microscope
(Usually)
- Light microscope has lower resolution and weaker magnification power
- Light microscope can distinguish two points that are close to each other not as
good as electron microscope
- …because wavelength of light is longer than wavelength of electrons beam
- …light = 200nm and electron is 0.5nm
Magnification = number of times an image is enlarged
Resolution = ability to distinguish between 2 point clearly
Light microscope Electron microscope
Advantages ● can observe living tissue ● Higher resolution - because
(so can observe process electron beam has shorter
like mitosis) wavelength (0.5-200 nm)
● portable
● Thinner sections can be
● easy to operate
● can see the actual image obtained
colour ● High magnification power -
● cheap able to see
ribosomes/membranes
detail within organelles
Disadvantages
Light microscope
State the piece of equipment that can be used in the light microscope to work out the
correct proportions of the tissues (1)
- Eyepiece graticule
Why some organelles are not visible using light microscope
- Poor resolution/ Resolving power is not high enough
- … so ability to distinguish between two points not high enough
- Limit of resolution is at 200 nm
- … so organelles smaller than 200 nm are not visible
- …because of organelle
, Electron microscope
How electron microscopes change the shape of cell
- Cell can be fluid and flexible due to change in shape of phospholipids bilayer
- Because high temperature applied in electron microscope
- Preparation (distortion/squashed/artefact)
Differences between electron micrograph and photomicrograph
Photomicrograph Electron Micrograph
● shows, surface / contour / 3-D, views ● showing, 2D / flat, views (of, microvilli /
● shows (only the), the outer / external, mitochondria)
view (of microvilli) ● image in one plane
● idea of good focus with different depths ● showing section through, mitochondria /
microvilli / cell
● shows, internal view of cell / contents of
cell
Organelles
State 3 key features of viruses (3) ****
- Non-cellular / acellular
- Protein coat / capsid
- DNA or RNA // nucleic acid core
Structures and functions of organelle:
Organelles Structure Functions
Nucleus ● Contains chromosomes/ genetic
materials which are information
to coded for synthesis of
polypeptide
○ Sequence of bases code
for different amino acids
● Transcription of mRNA
● Contains nucleolus
● Nucleolus - Manufacture of
ribosomal subunits → makes
ribosome
● DNA is protected from
degradation from intracellular
enzymes
○ E.g. hydrolytic enzymes
● AVP ; e.g. responds to signals
that control, gene expression /
AW post-transcription
, modification / modifies mRNA /
any example repairs DNA
RER ● Ribosome on flattened sac ● Synthesis/transports proteins
● Continuous with nuclear ● Modification of protein
membrane ● Protein transport to Golgi body
● More regular arrangement
than SER
SER ● No ribosome on tubular ● Produces lipids, cholesterol,
structure steroids
● More irregular/ disorganised
arrangement
Golgi ● Single membrane ● Site of synthesis polypeptide
body*** ● Flattened sacs ● processing/modification of
● Stack into layer proteins/polypeptides
● Smooth surface with no
● Packaging molecules into
ribosome
● Swelling ends (Vesicles at the vesicles
ends) ○ Production of golgi
● Close to nucleus (but not vesicles
connected with it) ● Formation of primary lysosomes
Mitochondria ● DNA ● Site of aerobic respiration
● 70S ribosomes for protein ● Production of ATP
synthesis
Vacuole ● Hydrostatic support
● Store water / turgid
● Storage of cell sap (sucrose,
starch, waste)
● Pushes chloroplast to edge of
the cells
Lysosome ● Contain hydrolytic enzymes
● … break down foreign material
(e.g. pathogen)
Plasmodesm ● Allow transport of (named)
ata substances
● Without crossing membrane
● Movement through symplast
pathway
● E.g. companion cells and sieve
tube elements
, ● Allow cell communication
Centrioles ● Assemble microtubules to
produce the mitotic spindle
Features of prokaryotes
- Peptidoglycan cell wall
- DNA free in cytoplasm (Circular loop/naked DNA with no histones)
- 70s ribosome
- AVP: no membrane around flagellum, flagellum is not 9+2 (microtubule pattern)
Cell structure V. cholerae Epithelial cell from the
human intestine
Cell wall
Cell surface membrane
Ribosomes
Large permanent vacuole
Organelles surrounded by a
double membrane
State two ways in which the structure of an animal cell differs from plant cells(2)
- No large/permanent vacuole
- No chloroplast
- No cell wall
- No plasmodesmata
- Centrioles present
Explain why the chloroplasts are seen only around the periphery (edge) of each plant
cell (1)
Chloroplasts at periphery because
- Pushed by vacuole
- Vacuole is turgid
- Vacuole is in the centre of the cell
-
Explain the importance of the division of mitochondria for the cell shown in Fig. 1.1
and for cells in the root tips of thale cress.(2)
- replace, old / worn out / damaged, mitochondria
- require more mitochondria as cells, enlarge / grow
- more mitochondria are needed, for new cells / when cell divides
- so numbers remain the same in the new cells / after cell division
- idea that mitochondria are shared out (between daughter cells) (mitochondria)
provide (most), energy / ATP
Microscopy
Key features:
Comparison between light and electron microscope
(Usually)
- Light microscope has lower resolution and weaker magnification power
- Light microscope can distinguish two points that are close to each other not as
good as electron microscope
- …because wavelength of light is longer than wavelength of electrons beam
- …light = 200nm and electron is 0.5nm
Magnification = number of times an image is enlarged
Resolution = ability to distinguish between 2 point clearly
Light microscope Electron microscope
Advantages ● can observe living tissue ● Higher resolution - because
(so can observe process electron beam has shorter
like mitosis) wavelength (0.5-200 nm)
● portable
● Thinner sections can be
● easy to operate
● can see the actual image obtained
colour ● High magnification power -
● cheap able to see
ribosomes/membranes
detail within organelles
Disadvantages
Light microscope
State the piece of equipment that can be used in the light microscope to work out the
correct proportions of the tissues (1)
- Eyepiece graticule
Why some organelles are not visible using light microscope
- Poor resolution/ Resolving power is not high enough
- … so ability to distinguish between two points not high enough
- Limit of resolution is at 200 nm
- … so organelles smaller than 200 nm are not visible
- …because of organelle
, Electron microscope
How electron microscopes change the shape of cell
- Cell can be fluid and flexible due to change in shape of phospholipids bilayer
- Because high temperature applied in electron microscope
- Preparation (distortion/squashed/artefact)
Differences between electron micrograph and photomicrograph
Photomicrograph Electron Micrograph
● shows, surface / contour / 3-D, views ● showing, 2D / flat, views (of, microvilli /
● shows (only the), the outer / external, mitochondria)
view (of microvilli) ● image in one plane
● idea of good focus with different depths ● showing section through, mitochondria /
microvilli / cell
● shows, internal view of cell / contents of
cell
Organelles
State 3 key features of viruses (3) ****
- Non-cellular / acellular
- Protein coat / capsid
- DNA or RNA // nucleic acid core
Structures and functions of organelle:
Organelles Structure Functions
Nucleus ● Contains chromosomes/ genetic
materials which are information
to coded for synthesis of
polypeptide
○ Sequence of bases code
for different amino acids
● Transcription of mRNA
● Contains nucleolus
● Nucleolus - Manufacture of
ribosomal subunits → makes
ribosome
● DNA is protected from
degradation from intracellular
enzymes
○ E.g. hydrolytic enzymes
● AVP ; e.g. responds to signals
that control, gene expression /
AW post-transcription
, modification / modifies mRNA /
any example repairs DNA
RER ● Ribosome on flattened sac ● Synthesis/transports proteins
● Continuous with nuclear ● Modification of protein
membrane ● Protein transport to Golgi body
● More regular arrangement
than SER
SER ● No ribosome on tubular ● Produces lipids, cholesterol,
structure steroids
● More irregular/ disorganised
arrangement
Golgi ● Single membrane ● Site of synthesis polypeptide
body*** ● Flattened sacs ● processing/modification of
● Stack into layer proteins/polypeptides
● Smooth surface with no
● Packaging molecules into
ribosome
● Swelling ends (Vesicles at the vesicles
ends) ○ Production of golgi
● Close to nucleus (but not vesicles
connected with it) ● Formation of primary lysosomes
Mitochondria ● DNA ● Site of aerobic respiration
● 70S ribosomes for protein ● Production of ATP
synthesis
Vacuole ● Hydrostatic support
● Store water / turgid
● Storage of cell sap (sucrose,
starch, waste)
● Pushes chloroplast to edge of
the cells
Lysosome ● Contain hydrolytic enzymes
● … break down foreign material
(e.g. pathogen)
Plasmodesm ● Allow transport of (named)
ata substances
● Without crossing membrane
● Movement through symplast
pathway
● E.g. companion cells and sieve
tube elements
, ● Allow cell communication
Centrioles ● Assemble microtubules to
produce the mitotic spindle
Features of prokaryotes
- Peptidoglycan cell wall
- DNA free in cytoplasm (Circular loop/naked DNA with no histones)
- 70s ribosome
- AVP: no membrane around flagellum, flagellum is not 9+2 (microtubule pattern)
Cell structure V. cholerae Epithelial cell from the
human intestine
Cell wall
Cell surface membrane
Ribosomes
Large permanent vacuole
Organelles surrounded by a
double membrane
State two ways in which the structure of an animal cell differs from plant cells(2)
- No large/permanent vacuole
- No chloroplast
- No cell wall
- No plasmodesmata
- Centrioles present
Explain why the chloroplasts are seen only around the periphery (edge) of each plant
cell (1)
Chloroplasts at periphery because
- Pushed by vacuole
- Vacuole is turgid
- Vacuole is in the centre of the cell
-
Explain the importance of the division of mitochondria for the cell shown in Fig. 1.1
and for cells in the root tips of thale cress.(2)
- replace, old / worn out / damaged, mitochondria
- require more mitochondria as cells, enlarge / grow
- more mitochondria are needed, for new cells / when cell divides
- so numbers remain the same in the new cells / after cell division
- idea that mitochondria are shared out (between daughter cells) (mitochondria)
provide (most), energy / ATP
