OCR AS Biology
Unit 1: Cells, Exchange and Transport
Cell Structure
Learning objectives
• To understand and discuss the basis of cell theory based
upon milestones in cell biology
• To carry out practical work on cell size and magnifications
using a light microscope
• To be able to draw a plant cell and an animal cell using a
light microscope
• To prepare slides using stains to identify cell structure.
Milestones in Cell Biology
• Read through handout
• Group discussion
– Discuss the impact of the microscope on cell
biology
– List things you think are the most important
Cell theory
• The cell is the fundamental unit of life. All organisms,
whatever their type or size, are composed of cells. The
modern theory of cellular organisation states:– All living things are composed of cells and cell products.
– New cells are formed only by the division of pre-existing cells
– The cell contains inherited information (genes), which is used as
instructions for growth, functioning and development.
– The cell is the functioning unit of life; the metabolic reactions of
life take place within the cells.
Cell Theory - Question
• Before the development of cell theory, it was
commonly believe that living organisms could
arise by spontaneous generation.
• Explain what this term means and why it has
been discredited as a theory.
Plan Diagrams – dicotyledonous leaf
Cell Biology and Microscopy
• When Scientists began to observe cells, they
started with simple microscopes
• There are two different types of microscope
both use a form of radiation to create an
image of the specimen:
– Light microscope – uses light
– Electron microscope – uses electrons
Using a light microscope
• Magnification
– Number of times larger an image is compared
with the real size of the object
• Resolution
– The ability to distinguish between two separate
points
Structure of a generalised animal cell as seen with a very high
power quality light microscope (diameter ~ 20ųm)
Structure of a generalised plant cell as seen with a very high
power quality light microscope (diameter ~ 40ųm)
Light Microscope
• For the microscope in front of you, work out
– The magnification of each lens
– The field of view for each lens
• Using a graticule / stage micrometer
• Collect a prepared slide of Squamous
epithelium, draw what you can see.
– Your diagram should include title, labels,
magnification and a scale bar.
Examination of plant cells
• Strip a pieces of epidermis from the inner lining of one of
the fleshy scales of an onion.
• Mount it in dilute iodine solution
• Observe and draw a cell under low power and high power
• Repeat the above procedure using water instead of iodine.
• what difference does this make to how much you can see?
Examination plant cells - conclusion
• What does this tell you about the value of
staining cells before you look at them under
the microscope?
• Make sure all diagrams have a title, label,
magnification and scale bar.
OCR AS Biology
Microscopy and magnification
Microscopes
• Light microscope
• Long wavelength
• Can only distinguish between two objects if they are
0.2µm apart.
• Electron microscope
• Shorter wavelengths
• Can distinguish between objects 0.1nm apart
Magnification
• How many times bigger the image is
compared to original subject.
size of im age
m agnification 
size of object
• If asked to calculate the size of an object
size of im age
size of object 
m agnification
Magnification
• When calculating magnification make sure the
units of length are the same for both object
and image
unit
Kilometre
Metre
Millimetre
symbol
km
m
mm
Equiv. in m
103
1
10-3
micrometre
nanometre
µm
nm
10-6
10-9
Magnification - example
• Object 100nm in length
• How much is it magnified in a photo?
• Measure object in photo (10mm long)
size of im age 10m m

size of object 100nm
Magnification - example
• The measurements need converting to the
same unit (usually the smallest)
• There are 10 000 000nm in 10mm
• Magnification is:
size of im age 10 000000nm 100000


size of object
100nm
1
100
000 tim es
• 100 
000
times
The effect of progressive
magnification of a portion
of human skin
OCR AS Biology
Structure of plant and animal cells
under an electron microscope
The Electron Microscope
• Two main advantages
– High resolving power (short wavelength of
electrons)
– As electrons negatively are charged the beam can
be focused using electromagnets
• As electrons are absorbed by molecules of air,
a near-vacuum has to be created within the
chamber of an electron microscope.
The Electron Microscope
• Two types
– Transmission Electron Microscope (TEM)
– Scanning Electron Microscope (SEM)
• Activity
– Read through the handout on the electron
microscope
– Answer discussion questions 1 - 4
Comparison of advantages and disadvantages of
the light and electron microscopes
Light Microscope
Advantages
Electron Microscope
Disadvantages
Small and portable
very large
Operated in special rooms
Unaffected by magnetic fields
Affected by magnetic fields
Preparation of material is quick
and simple
Preparation of material is
lengthy
Requires expertise
Material rarely distorted by
preparation
Preparation may distort material
Natural colour of object
observed
Images are in black and white
Cheap to purchase and
operate
Expensive to purchase and
operate
Comparison of advantages and disadvantages of the
light and electron microscopes
Light Microscope
Disadvantages
Electron Microscope
Advantages
Magnifies objects up to Magnifies objects more
1500x only
than 500 000X
Depth of field is
restricted
Possible to investigate
a greater field of
depth
Comparison
of pathways
of the light
and electron
microscopes
Ultrastructure
of an animal
cell as seen
through an
electron
microscope
Ultrastructure of an Animal Cell
Ultrastructure of a plant cell as seen through an
electron microscope
Ultrastructure of a Plant Cell
Pupil Activity
• Cell structure
– Read through the information on each of the
organelles as you colour them in
– Follow the guidance on colouring them in given at
the bottom of the page
– This works on the theory that whilst you are
colouring in, you have time to consider and think
about the structure and function of the organelles
OCR AS Biology
FOUNDATION
Cell Structure Activities
Pupil Activity – Cell Structure
Animal Cell
• In pairs label the diagram of the animal cell
given.
– How many structures can you identify?
– Look at the cells alive animation – how many have
you correctly identified?
• Label the paper copy of the diagram of an
animal cell
Animal Cell
Animal cell - answers
Pupil Activity – Cell Structure
Plant Cell
• In pairs label the diagram of the plant cell
given.
– How many structures can you identify?
– Look at the cells alive animation – how many have
you correctly identified?
• Label the paper copy of a diagram of a plant
cell
Plant cell
Plant cell - answers
Activity:
Introduction to organelle function
• Using the cards, match up organelle, position
and function.
Organelle
Position
Function
Nucleus
Within cytoplasm
Contains genetic code which
controls the activities of the cell
Cytoplasm
Around nucleus
Location of chemical reactions –
does the work of the cell
Cell surface
membrane
Around cytoplasm
Controls exchange of substances
between cytoplasm and
surroundings
Cell wall
around cell membrane
Gives cells rigidity, stops it bursting
if put in water
Cell vacuole
Within cytoplasm
Affects concentration of cytoplasm.
Is a store of inorganic ions.
Tonoplast
Around cell vacuole
Controls exchange of substances in
plant cells between vacuole and
cytoplasm
Large granules
Within cytoplasm
Usually stores food e.g. starch
OCR AS Biology
FOUNDATION
Organelle Structure and function
Nucleus
Structure of nucleus
•
•
•
•
•
Nuclear envelope
Nuclear pores
Nucleoplasm
Chromatin
nuceolus
Function of the nucleus
• Acts as the control centre of the cell through
the production of mRNA and protein synthesis
• Retain genetic material of the cell (DNA /
chromosomes)
• Start the process of cell division
Structure of Nucleus
• Chromatin
– DNA and associated proteins, chromatin
condenses into chromosomes when the cell
divides.
• nucleolus
– Manufactures ribosomal RNA and assembles the
ribosomes
Structure of Nucleus
• Nuclear envelope
– Controls entry and exit of materials
– Outer membrane continuous with endoplasmic
reticulum
• Nuclear pores
– Passage of large molecules (mRNA) out of nucleus
Chloroplasts
Structure and Function of Chloroplasts
• Chloroplast envelope
– Entry and exit of substances
• Stroma
– Enzymes for the light independent stages of
photosynthesis
• Grana (thylakoids/lamellae)
– Light dependent stage of photosynthesis
• Starch grains
– Temporary stores of carbohydrates
Mitochondria
Structure of Mitochondria
• Double membrane
– Inner membrane folded into cristae which provide
a large surface area
• Matrix
– DNA, enzymes and ribosomes
Function of Mitochondria
• Site of Krebs cycle and oxidative
phosphorylation in aerobic respiration
• Production of energy rich ATP molecules from
carbohydrates
Endoplasmic reticulum
Endoplasmic reticulum
• Membranes spreading through the cytoplasm of
cells, continuous with the nuclear membrane
• Enclose flattened sacs called cisternae
• Rough endoplasmic reticulum
– Ribosomes present on outer surface of membrane
• Smooth endoplasmic reticulum
– No ribosomes, tubular in appearance.
Function of endoplasmic reticulum
• RER
– Provide LSA for synthesis of proteins
– Provides a pathway for the transport of materials
(esp. proteins) throughout the cell.
• SER
– Synthesis, stores and transports lipids and
carbohydrates
– Contains lytic enzymes (liver cells)
Ribosomes
Structure and function of ribosomes
• Two types
– 80S – eukaryotic cells
– 70S – prokaryotic cells
• Make up 25% of dry mass of cell
• Important in protein synthesis
Golgi Apparatus
Structure of golgi apparatus
• Stack of membrane bound, flattened sacks
Functions of Golgi Apparatus
• Modifies and packages proteins
– Adds carbohydrates to proteins to form
glycoproteins
– Produces secretory enzymes
• Secretes carbohydrates
• Transports, modifies and stores lipids
• Forms lysosomes
Lysosomes (animal cells only)
Structure of lysosome
• Spherical sac surrounded by a single
membrane
• Contains powerful digestive enzymes
Functions of Lysosomes
• Destroy foreign material inside or outside the
cell.
– Breakdown material ingested by phagocytic cells
– Release enzymes outside the cell
– Digest worn out organelles (autophagy)
– Autolysis break down cells after they have died.
Cilia
Structure and function of cilia
• Structure
– Threads that extend from cell surface
– Made of nine sets of 3 microtubules
• Function
– Move an entire organism
– Move material within an organism
• E.g. cilia lining respiratory tract move mucus towards
the throat.
Flagella / undulipodia
• Structure
– 9 sets of microtubules in a circle
– 2 central microtubules
• Function
– Movement
• Tail of a sperm
• Whole of unicellular organism
Centrioles (animal cells only)
Structure and function of centrioles
• Hollow cylinders of microtubules
• Microtubules form spindle fibres for nuclear
division
• Maybe involved in formation of microtubules
that make up cells cytoskeleton
Plant cell wall
• Structure
– Made of cellulose
• Function
– Supports the cell
• Cell turgor pressure
Homework – in for next lesson
• Similarities between plant and animal cells
– Make a list of the structures plant and animal cells
have in common
– Make a table of the differences between plant and
animal cells
• Include all structures in plant and animal cells
not just the ones observed through a Light
microscope
Movement and Stability in cells
Learning Outcomes
• explain the importance of the cytoskeleton in
providing mechanical strength to cells, aiding
transport within cells and enabling cell
movement;
Cytoskeleton
• Cells contain a network of fibres made of protein, providing
an internal framework.
• Fibres can move organelles round within a cell.
• Microtubules
– Move chromosomes around in cell division
– Move vesicles from endoplasmic reticulum to Golgi apparatus
• ATP is used to drive some of these movements
Division of Labour
Protein synthesis
Learning Outcomes
• outline the interrelationship between the
organelles involved in the production and
secretion of proteins
Protein Production
• Instructions in DNA is nucleus
• Instructions copied onto mRNA
• mRNA moves to ribosome, where protein is
assembled
• Protein transported to Golgi apparatus
• Protein modified and packaged
• Protein moves in a vesicle to the cell surface
membrane
• Protein secreted.
Protein
Production
OCR AS Biology
FOUNDATION
Prokaryotic Cells
Prokaryotic Cells
“pro” – before “karyo“– nucleus
• Prokaryotes were probably the first forms of
life on earth. Their heredity material (DNA) is
not enclosed within a nuclear membrane.
There are no membrane bound organelles
within a prokaryotic cell.
Prokaryotic Cells
• The absence of a true nucleus only occurs in 2
groups.
– Bacteria
– Blue green algae (cyanobacteria)
• Five structures, which are always present in a
prokaryotic cell, are:
– cell wall, plasma membrane, cytoplasm, ribosome,
circular DNA
Structure of a bacterial cell
Activity
• Copy and complete the following table
prokaryotic
Eukaryotic
organisms
Cell size
metabolism
• Include organelles, DNA, RNA and protein synthesis,
ribosome, cell division, cell wall, cellular organisation.
Comparison of prokaryotic and
eukaryotic cells
prokaryotic
Eukaryotic
organisms
Bacteria
cyanobacteria
Protista, fungi, plants,
animals
Cell size
1 – 10 µm
10 –100 µm
metabolism
Anaerobic and
aerobic
Aerobic
organelles
No membrane
bound organelles
Nucleus, mitochondria,
chloroplasts, RER, SER
Comparison of prokaryotic and
eukaryotic cells
prokaryotic
Eukaryotic
DNA
Circular DNA in
cytoplasm
DNA organised into
chromosomes bounded by
nuclear envelope
RNA and
Protein
Synthesis
Synthesised in same
compartment
RNA synthesised and
processed in nucleus
Protein synthesis in
cytoplasm
Ribosomes
70S Type
80S Type
Cell Division
Binary fission
Mitosis or meiosis